Performance information

• Accumulation of Acyl Plastoquinol and Triacylglycerol in Six Cyanobacterial Species with Different Sets of Genes Encoding Type-2 Diacylglycerol Acyltransferase-like Proteins
  Riko Tanikawa; Haruna Sakaguchi; Toshiki Ishikawa; Yukako Hihara
  Plant and Cell Physiology, Nov. 2024, [Reviewed], [Corresponding]
  Abstract
  
  Recently, acyl plastoquinol (APQ) and plastoquinone-B (PQ-B), which are fatty acid esters of plastoquinol and plastoquinone-C respectively, have been identified as the major neutral lipids in cyanobacteria. In Synechocystis sp. PCC 6803, Slr2103 having homology with the eukaryotic enzyme for triacylglycerol (TAG) synthesis, diacylglycerol acyltransferase 2 (DGAT2), was identified as responsible for the synthesis of these plastoquinone-related lipids. On the other hand, TAG synthesis in cyanobacteria remains controversial due to the low accumulation level within cyanobacterial cells together with the high contamination level from the environment. In this study, to quantify more precisely and elucidate the relationship between the accumulation of neutral lipids and the presence or absence of DGAT2-like genes, plastoquinone-related lipids and TAG were analyzed directly from total lipids of six cyanobacterial species with different sets of genes encoding DGAT2-like proteins belonging to two distinct subclades. The results showed that the synthesis of these neutral lipids is highly dependent on clade A DGAT2-like proteins under the culture conditions used in this study, although accumulation level of TAG was quite low. In contrast to APQ highly abundant in saturated fatty acids, the fatty acid composition of TAG was species-specific and partly reflected the total lipid composition. Gloeobacter violaceus PCC 7421, which lacks a DGAT2-like gene, accumulated APQ with a high proportion of C18:0, suggesting APQ synthesis by an unidentified acyltransferase.
  Oxford University Press (OUP), Scientific journal
  DOI：https://doi.org/10.1093/pcp/pcae137
  DOI ID：10.1093/pcp/pcae137, ISSN：0032-0781, eISSN：1471-9053
• Partner-switching components PmgA and Ssr1600 regulate high-light acclimation in Synechocystis sp. PCC 6803
  Riku Nakamura; Yuji Takahashi; Shogo Tachibana; Arisa Terada; Kakeru Suzuki; Kumika Kondo; Yuzuru Tozawa; Yukako Hihara
  Plant Physiology, Volume：196, Number：1, First page：621, Last page：633, Jun. 2024, [Reviewed], [Corresponding]
  Abstract
  
  Photomixotrophic growth A (PmgA) is a pleiotropic regulator essential for growth under photomixotrophic and prolonged high-light (HL) conditions in the cyanobacterium Synechocystis sp. PCC 6803. The overall similarity with the antisigma factor of the bacterial partner-switching system indicates that PmgA exerts a regulatory function via phosphorylation of its target proteins. In this study, we performed an in vitro phosphorylation assay and protein–protein interaction analysis and found that PmgA interacts with 4 antisigma antagonist homologs, Ssr1600, Slr1856, Slr1859, and Slr1912, but specifically phosphorylates Ssr1600. Phenotypic analyses using the set of gene disruption and overexpression strains of pmgA and ssr1600 revealed that phosphorylation by PmgA is essential for the accumulation of Ssr1600 protein in vivo. The ssr1600-disrupted mutant showed similar phenotypes as those previously reported for the pmgA-disrupted mutant, namely, no obvious phenotype just after the shift to HL, but higher chlorophyll content, 5-aminolevulinic acid synthesis activity, and psaAB transcript levels than those in the wild type after 6 h. These findings indicate that the phosphorylated form of Ssr1600 works as the output of the partner-switching system to coordinately repress chlorophyll biosynthesis and accumulation of photosystem I during HL acclimation.
  Oxford University Press (OUP), Scientific journal
  DOI：https://doi.org/10.1093/plphys/kiae323
  DOI ID：10.1093/plphys/kiae323, ISSN：0032-0889, eISSN：1532-2548
• CRISPRi knockdown of the cyabrB1 gene induces the divergently transcribed icfG and sll1783 operons related to carbon metabolism in the cyanobacterium Synechocystis sp. PCC 6803.　　　　　　　　　　　　　　　
  Atsuko Hishida; Ryo Shirai; Akiyoshi Higo; Minenosuke Matsutani; Kaori Nimura-Matsune; Tomoko Takahashi; Satoru Watanabe; Shigeki Ehira; Yukako Hihara
  The Journal of general and applied microbiology, Jan. 2024, [Reviewed], [Corresponding], ［Domestic magazine］
  Most cyanobacterial genomes possess more than two copies of genes encoding cyAbrBs (cyanobacterial AbrB-like proteins) having an AbrB-like DNA-binding domain at their C-terminal region. Accumulating data suggest that a wide variety of metabolic and physiologic processes are regulated by cyAbrBs. In this study, we investigated the function of the essential gene cyabrB1 (sll0359) in Synechocystis sp. PCC 6803 by using CRISPR interference technology. The conditional knockdown of cyabrB1 caused increases of cyAbrB2 transcript and protein levels. However, the effect of cyabrB1 knockdown on global gene expression profile was quite limited compared to the previously reported profound effect of knockout of cyabrB2. Among 24 up-regulated genes, 16 genes were members of the divergently transcribed icfG and sll1783 operons related to carbon metabolism. The results of this and previous studies indicate the different contributions of two cyAbrBs to transcriptional regulation of genes related to carbon, hydrogen and nitrogen metabolism. Possession of a pair of cyAbrBs has been highly conserved during the course of evolution of the cyanobacterial phylum, suggesting physiological significance of transcriptional regulation attained by their interaction.
  English, Scientific journal
  DOI：https://doi.org/10.2323/jgam.2024.01.001
  DOI ID：10.2323/jgam.2024.01.001, PubMed ID：38267064
• Acylated plastoquinone is a novel neutral lipid accumulated in cyanobacteria
  Toshiki Ishikawa; Shunya Takano; Riko Tanikawa; Takashi Fujihara; Kimie Atsuzawa; Yasuko Kaneko; Yukako Hihara
  PNAS Nexus, Mar. 2023, [Reviewed], [Corresponding]
  Abstract
  
  Although cyanobacteria do not possess bacterial triacylglycerol (TAG) synthesizing enzymes, accumulation of TAGs and/or lipid droplets has been repeatedly reported in a wide range of species. In most cases, identification of TAG has been based on the detection of the spot showing the mobility similar to the TAG standard in thin-layer chromatography of neutral lipids. In this study, we identified monoacyl plastoquinol (acyl PQH) as the predominant molecular species in the TAG-like spot from the unicellular Synechocystis sp. PCC 6803 (S.6803) as well as the filamentous Nostocales species, Nostoc punctiforme PCC 73102 and Anabaena sp. PCC 7120. In S.6803, the accumulation level of acyl PQH but not TAG was affected by deletion or overexpression of slr2103, indicating that acyl PQH is the physiological product of Slr2103 having homology with the eukaryotic diacylglycerol acyltransferase-2 (DGAT2). Electron microscopy revealed that cyanobacterial strains used in this study do not accumulate lipid droplet structures such as those observed in oleaginous microorganisms. Instead, they accumulate polyhydroxybutyrate (PHB) granules and/or aggregates of alkane, free C16 and C18 saturated fatty acids and low amounts of TAG in the cytoplasmic area, which can be detected by staining with a fluorescent dye specific to neutral lipids. Unlike these lipophilic materials, acyl PQH is exclusively localized in the membrane fraction. There must be DGAT2-like enzymatic activity esterifying de novo-synthesized C16 and C18 fatty acids to PQH2 in the thylakoid membranes.
  Oxford University Press (OUP), Scientific journal
  DOI：https://doi.org/10.1093/pnasnexus/pgad092
  DOI ID：10.1093/pnasnexus/pgad092, eISSN：2752-6542
• Dual Redox Regulation of the DNA-Binding Activity of the Response Regulator RpaB in the Cyanobacterium Synechocystis sp. PCC 6803　　　　　　　　　　　　　　　
  Naoki Kato; Kazuki Iwata; Taro Kadowaki; Kintake Sonoike; Yukako Hihara
  PLANT AND CELL PHYSIOLOGY, Jun. 2022, [Reviewed], [Corresponding]
  The response regulator RpaB plays a central role in transcriptional regulation of photosynthesis-related genes in cyanobacteria. RpaB is phosphorylated by its cognate histidine kinase Hik33 and functions as both an activator and a repressor under low-light conditions, whereas its phosphorylation level and DNA-binding activity promptly decrease upon the upshift of photon flux density, causing changes in the gene expression profile. In this study, we assessed the possibility of redox regulation of the DNA-binding activity of RpaB in Synechocystis sp. PCC 6803 by the addition of inhibitors of photosynthetic electron transport, 3-(3,4-dichlorophenyl)-1,1-dimethylurea and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, or the reducing agent dithiothreitol under different photon flux densities. Analysis of the phosphorylation level of RpaB revealed that reduction of Q(A) and increase in the availability of reducing equivalents at the acceptor side of photosystem I (PSI) can independently trigger dephosphorylation. The redox-state-dependent regulation by an unidentified thiol other than Cys59 of RpaB is prerequisite for the phosphorylation-dependent regulation of the DNA-binding activity. Environmental signals, recognized by Hik33, and metabolic signals recognized as the availability of reducing equivalents, must be integrated at the master regulator RpaB, in order to attain the flexible regulation of acclimatory responses.
  OXFORD UNIV PRESS, English, Scientific journal
  DOI：https://doi.org/10.1093/pcp/pcac079
  DOI ID：10.1093/pcp/pcac079, ISSN：0032-0781, eISSN：1471-9053, Web of Science ID：WOS:000826597900001
• The NAD Kinase Slr0400 Functions as a Growth Repressor in Synechocystis sp. PCC 6803　　　　　　　　　　　　　　　
  Yuuma Ishikawa; Cedric Cassan; Aikeranmu Kadeer; Koki Yuasa; Nozomu Sato; Kintake  Sonoike; Yasuko Kaneko; Atsuko Miyagi; Hiroko Takahashi; Toshiki Ishikawa; Masatoshi Yamaguchi; Yoshitaka Nishiyama; Yukako Hihara; Yves Gibon; Maki Kawai-Yamada
  Plant and Cell Physiology, Volume：62, Number：4, First page：668, Last page：677, Sep. 2021, [Reviewed]
  
  NADP+, the phosphorylated form of nicotinamide adenine dinucleotide (NAD), plays an essential role in many cellular processes. NAD kinase (NADK), which is conserved in all living organisms, catalyzes the phosphorylation of NAD+ to NADP+. However, the physiological role of phosphorylation of NAD+ to NADP+ in the cyanobacterium Synechocystis remains unclear. In this study, we report that slr0400, an NADK-encoding gene in Synechocystis, functions as a growth repressor under light-activated heterotrophic growth conditions and light and dark cycle conditions in the presence of glucose. We show, via characterization of NAD(P)(H) content and enzyme activity, that NAD+ accumulation in slr0400-deficient mutant results in the unsuppressed activity of glycolysis and tricarboxylic acid (TCA) cycle enzymes. In determining whether Slr0400 functions as a typical NADK, we found that constitutive expression of slr0400 in an Arabidopsis nadk2-mutant background complements the pale-green phenotype. Moreover, to determine the physiological background behind the growth advantage of mutants lacking slr04000, we investigated the photobleaching phenotype of slr0400-deficient mutant under high-light conditions. Photosynthetic analysis found in the slr0400-deficient mutant resulted from malfunctions in the Photosystem II (PSII) photosynthetic machinery. Overall, our results suggest that NADP(H)/NAD(H) maintenance by slr0400 plays a significant role in modulating glycolysis and the TCA cycle to repress the growth rate and maintain the photosynthetic capacity.
  Oxford University Press (OUP), Scientific journal
  DOI：https://doi.org/10.1093/pcp/pcab023
  DOI ID：10.1093/pcp/pcab023, ISSN：0032-0781, eISSN：1471-9053, PubMed ID：33210985, PubMed Central ID：PMC7781788
• シアノバクテリアの転写因子と物質生産　　　　　　　　　　　　　　　
  日原由香子
  Volume：99, Number：8, First page：416, Last page：420, Aug. 2021, [Reviewed], [Invited], [Corresponding]
• The NAD kinase Slr0400 functions as a growth repressor in Synechocystis sp. PCC 6803.　　　　　　　　　　　　　　　
  Yuuma Ishikawa; Cedric Cassan; Aikeranmu Kadeer; Koki Yuasa; Nozomu Sato; Kintake Sonoike; Yasuko Kaneko; Atsuko Miyagi; Hiroko Takahashi; Toshiki Ishikawa; Masatoshi Yamaguchi; Yoshitaka Nishiyama; Yukako Hihara; Yves Gibon; Maki Kawai-Yamada
  Plant & cell physiology, Feb. 2021, [Reviewed], ［Domestic magazine］
  NADP+, the phosphorylated form of nicotinamide adenine dinucleotide (NAD), plays an essential role in many cellular processes. NAD kinase (NADK), which is conserved in all living organisms, catalyzes the phosphorylation of NAD+ to NADP+. However, the physiological role of phosphorylation of NAD+ to NADP+ in the cyanobacterium Synechocystis remains unclear. In this study, we report that slr0400, an NADK-encoding gene in Synechocystis, functions as a growth repressor under light-activated heterotrophic growth conditions and light and dark cycle conditions in the presence of glucose. We show, via characterization of NAD(P)(H) content and enzyme activity, that NAD+ accumulation in slr0400-deficient mutant results in unsuppressed activity of glycolysis and tricarboxylic acid (TCA) cycle enzymes. In determining whether Slr0400 functions as a typical NADK, we found that constitutive expression of slr0400 in an Arabidopsis nadk2-mutant background complements the pale-green phenotype. Moreover, to determine the physiological background behind the growth advantage of mutants lacking slr04000, we investigated the photobleaching phenotype of slr0400-deficient mutant under high-light conditions. Photosynthetic analysis found in the slr0400-deficient mutant resulted from malfunctions in the PSII photosynthetic machinery. Overall, our results suggest that NADP(H)/NAD(H) maintenance by slr0400 plays a significant role in modulating glycolysis and the TCA cycle to repress the growth rate and maintain photosynthetic capacity.
  English, Scientific journal
  DOI：https://doi.org/10.1093/pcp/pcab023
  DOI ID：10.1093/pcp/pcab023, PubMed ID：33560438
• The role of transcriptional repressor activity of LexA in salt-stress responses of the cyanobacterium Synechocystis sp. PCC 6803
  Kosuke Takashima; Syota Nagao; Ayumi Kizawa; Takehiro Suzuki; Naoshi Dohmae; Yukako Hihara
  Scientific Reports, Volume：10, Number：1, Dec. 2020, [Reviewed], [Corresponding]
  
  Different from typical LexA repressors in heterotrophic bacteria exerting SOS response by auto-cleavage, cyanobacterial LexAs, especially that of Synechocystis sp. PCC 6803 (S.6803), have been suggested be involved in regulation of a number of genes related to various cellular processes, rather than the typical SOS regulon. When and how cyanobacterial LexAs are triggered to regulate its target genes have remained unknown. In this study, we found the profound repressing effect of LexA on salt-stress inducible genes in S.6803. The repressing activity of LexA was likely to persist during salt stress and the salt response of these genes was mainly achieved by other regulators than LexA, suggesting that the physiological role of LexA is fine-tuning of gene expression in response to environmental changes. Although the amount and oligomeric state of LexA were unchanged upon salt stress, two-dimensional electrophoresis and liquid chromatography-tandem mass spectrometry analyses detected a change in posttranslational modification in a small fraction of LexA molecules, possibly dephosphorylation of Ser¹⁷³, after 30 min upon the upshift in salt concentration. Activity of LexA in S.6803 may be under gradual control by posttranslational modification to fine-tune gene expression, which is contrasted with the digital switching-off regulation by auto-cleavage in heterotrophic bacteria.
  Springer Science and Business Media LLC, Scientific journal
  DOI：https://doi.org/10.1038/s41598-020-74534-7
  DOI ID：10.1038/s41598-020-74534-7, eISSN：2045-2322
• Quantitative and Qualitative Analyses of Triacylglycerol Production in the Wild-Type Cyanobacterium Synechocystis sp. PCC 6803 and the Strain Expressing AtfA from Acinetobacter baylyi ADP1.　　　　　　　　　　　　　　　
  Motoki Tanaka; Toshiki Ishikawa; So Tamura; Yujiro Saito; Maki Kawai-Yamada; Yukako Hihara
  Plant & cell physiology, Volume：61, Number：9, First page：1537, Last page：1547, Sep. 2020, [Reviewed], [Corresponding], ［Domestic magazine］
  Although cyanobacteria do not possess wax ester synthase/acyl-CoA:diacylglycerol acyltransferase (WS/DGAT), the bacterial enzyme for triacylglycerol (TAG) production, there have been several studies reporting the accumulation of TAG-like compounds in cyanobacteria. In this study, we aimed to evaluate TAG productivity of the ΔrecJ::atfA strain of Synechocystis sp. PCC 6803 generated by inserting atfA encoding WS/DGAT from Acinetobacter baylyi ADP1 into recJ (sll1354), together with the wild type (WT) and the gene-disrupted strain of slr2103 having homology with eukaryotic DGAT2 gene family (Δ2103). Thin-layer chromatography (TLC) of neutral lipids or isolation of the neutral lipid-enriched fraction followed by gas chromatography or liquid chromatography-tandem mass spectrometry was employed for analyses. The ΔrecJ::atfA strain accumulated 0.508 nmol ml-1OD730-1 of TAG after a week of incubation at 100 μmol photons m-2 s-1. The saturated fatty acids C16:0 and C18:0 accounted for about 50% and 20% of the TAG fatty acids, respectively, suggesting that de novo-synthesized fatty acids were preferentially incorporated into TAG molecules. When the neutral lipid profile of the lipid extracts was examined by TLC, a spot located in a slightly lower position compared with the TAG standard was detected in WT but not in the Δ2103 strain. TAG accumulation levels of both strains was only 0.01-0.03 nmol ml-1OD730-1, but the fatty acid composition was substantially different from that of the background. These results suggest that trace amounts of TAG can be produced in Synechocystis cells by enzymes other than Slr2103, and major constituents of the TAG-like spot are unknown lipid species produced by Slr2103.
  English, Scientific journal
  DOI：https://doi.org/10.1093/pcp/pcaa069
  DOI ID：10.1093/pcp/pcaa069, PubMed ID：32433767
• Light-inducible expression of translation factor EF-Tu during acclimation to strong light enhances the repair of photosystem II.　　　　　　　　　　　　　　　
  Jimbo H; Izuhara T; Hihara Y; Hisabori T; Nishiyama Y
  Proceedings of the National Academy of Sciences of the United States of America, Volume：116, Number：42, First page：21268, Last page：21273, Oct. 2019, [Reviewed]
  DOI：https://doi.org/10.1073/pnas.1909520116
  DOI ID：10.1073/pnas.1909520116, ISSN：0027-8424, PubMed ID：31570574
• cyAbrB Transcriptional Regulators as Safety Devices To Inhibit Heterocyst Differentiation in Anabaena sp. Strain PCC 7120.　　　　　　　　　　　　　　　
  Higo A; Nishiyama E; Nakamura K; Hihara Y; Ehira S
  Journal of bacteriology, Volume：201, Number：17, Sep. 2019, [Reviewed]
  DOI：https://doi.org/10.1128/JB.00244-19
  DOI ID：10.1128/JB.00244-19, ISSN：0021-9193, PubMed ID：31085690
• Biocomputational Analyses and Experimental Validation Identify the Regulon Controlled by the Redox-Responsive Transcription Factor RpaB　　　　　　　　　　　　　　　
  Matthias Riediger; Taro Kadowaki; Ryuta Nagayama; Jens Georg; Yukako Hihara; Wolfgang R. Hess
  iScience, Volume：15, First page：316, Last page：331, May 2019, [Reviewed], [Corresponding]
  Elsevier BV, Scientific journal
  DOI：https://doi.org/10.1016/j.isci.2019.04.033
  DOI ID：10.1016/j.isci.2019.04.033, ISSN：2589-0042
• One of the NAD kinases, sll1415, is required for the glucose metabolism of Synechocystis sp. PCC 6803.　　　　　　　　　　　　　　　
  Yuuma Ishikawa; Atsuko Miyagi; Toshiki Ishikawa; Minoru Nagano; Masatoshi Yamaguchi; Yukako Hihara; Yasuko Kaneko; Maki Kawai-Yamada
  the Plant Journal, Volume：98, Number：4, First page：654, Last page：666, May 2019, [Reviewed], ［International magazine］
  Pyridine nucleotides (NAD(P)(H)) are electron carriers that are the driving forces in various metabolic pathways. Phosphorylation of NAD(H) to NADP(H) is performed by the enzyme NAD kinase (NADK). Synechocystis sp. PCC 6803 harbors two genes (sll1415 and slr0400) that encode proteins with NADK homology. When genetic mutants for sll1415 and slr0400 (Δ1415 and Δ0400, respectively) were cultured under photoheterotrophic growth conditions only the Δ1415 cells showed a growth defect. In wild-type cells, the sll1415 transcript accumulated after the cells were transferred to photoheterotrophic conditions. Furthermore, NAD(P)(H) measurements demonstrated that a dynamic metabolic conversion was implemented during the adaptation from photoautotrophic to photoheterotrophic conditions. Electron microscopy observation and biochemistry quantification demonstrated the accumulation of glycogen in the Δ1415 cells under photoheterotrophic conditions at 96 h. Quantitative real-time reverse transcription PCR (qRT-PCR) demonstrated the accumulation of mRNAs that encoded glycogen biosynthesis-related enzymes in photoheterotrophic Δ1415 cells. At 96 h, enzyme activity measurement in the photoheterotrophic Δ1415 cells demonstrated that the activities of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were decreased, but the activities of glucose dehydrogenase were increased. Furthermore, metabolomics analysis demonstrated that the Δ1415 cells showed increased glucose-6-phosphate and 6-phosphogluconate content at 96 h. Therefore, sll1415 has a significant function in the oxidative pentose phosphate (OPP) pathway for catabolism of glucose under photoheterotrophic conditions. Additionally, it is presumed that the slr0400 had a different role in glucose catabolism during growth. These results suggest that the two Synechocystis sp. PCC 6803 NADKs (Sll1415 and Slr0400) have distinct functions in photoheterotrophic cyanobacterial metabolism.
  English, Scientific journal
  DOI：https://doi.org/10.1111/tpj.14262
  DOI ID：10.1111/tpj.14262, PubMed ID：30693583
• Interaction of the GntR-family transcription factor Sll1961 with thioredoxin in the cyanobacterium Synechocystis sp. PCC 6803.　　　　　　　　　　　　　　　
  Junichi Kujirai; Sato Nanba; Taro Kadowaki; Yoshiki Oka; Yoshitaka Nishiyama; Yuuki Hayashi; Munehito Arai; Yukako Hihara
  Scientific reports, Volume：8, Number：1, First page：6666, Last page：6666, Apr. 2018, [Reviewed], [Corresponding], ［International magazine］
  Changes in the redox state of the photosynthetic electron transport chain act as a signal to trigger acclimation responses to environmental cues and thioredoxin has been suggested to work as a key factor connecting the redox change with transcriptional regulation in the cyanobacterium Synechocystis sp. PCC 6803. We screened for redox-dependent transcription factors interacting with thioredoxin M (TrxM) and isolated the GntR-type transcription factor Sll1961 previously reported to be involved in acclimation responses of the photosynthetic machinery. Biochemical analyses using recombinant Sll1961 proteins of wild type and mutants of three cysteine residues, C124, C229 and C307, revealed that an intramolecular disulfide bond is formed between C229 and C307 under oxidizing conditions and TrxM can reduce it by attacking C307. Sll1961 exists in a dimeric form of about 80 kDa both under reducing and oxidizing conditions. C124 can form an intermolecular disulfide bond but it is not essential for dimerization. Based on these observations, tertiary structure models of the Sll1961 homodimer and the Sll1961-TrxM complex were constructed.
  English, Scientific journal
  DOI：https://doi.org/10.1038/s41598-018-25077-5
  DOI ID：10.1038/s41598-018-25077-5, PubMed ID：29703909, PubMed Central ID：PMC5923263
• Oxidation of translation factor EF-Tu inhibits the repair of photosystem II　　　　　　　　　　　　　　　
  Haruhiko Jimbo; Rayakorn Yutthanasirikul; Takanori Nagano; Toru Hisabori; Yukako Hihara; Yoshitaka Nishiyama
  Plant Physiology, Volume：176, Number：4, First page：2691, Last page：2699, Apr. 2018, [Reviewed]
  The repair of photosystem II (PSII) is particularly sensitive to oxidative stress and the inhibition of repair is associated with oxidative damage to the translational elongation system in the cyanobacterium Synechocystis sp. PCC 6803. However, the molecular mechanisms underlying this inhibition are unknown. We previously demonstrated in vitro that EF-Tu, a translation factor that delivers aminoacyl-tRNA to the ribosome, is inactivated by reactive oxygen species via oxidation of the Cys residue Cys-82. In this study, we examined the physiological role of the oxidation of EF-Tu in Synechocystis. Under strong light, EF-Tu was rapidly oxidized to yield oxidized monomers in vivo. We generated a Synechocystis transformant that expressed mutated EF-Tu in which Cys-82 had been replaced with a Ser residue. Under strong light, the de novo synthesis of proteins that are required for PSII repair, such as D1, was enhanced in the transformant and photoinhibition of PSII was alleviated. However, photodamage to PSII, measured in the presence of lincomycin, was similar between the transformant and wild-type cells, suggesting that expression of mutated EF-Tu might enhance the repair of PSII. Alleviating photoinhibition through mutation of EF-Tu did not alter cell growth under strong light, perhaps due to the enhanced production of reactive oxygen species. These observations suggest that the oxidation of EF-Tu under strong light inhibits PSII repair, resulting in the stimulation of photoinhibition.
  American Society of Plant Biologists, English, Scientific journal
  DOI：https://doi.org/10.1104/pp.18.00037
  DOI ID：10.1104/pp.18.00037, ISSN：1532-2548, SCOPUS ID：85045519528
• Effects of inactivation of the cyAbrB2 transcription factor together with glycogen synthesis on cellular metabolism and free fatty acid production in the cyanobacterium Synechocystis sp. PCC 6803　　　　　　　　　　　　　　　
  Kodama Y; Kawahara A; Miyagi A; Ishikawa T; Kawai-Yamada M; Kaneko Y; Takimura Y; Hihara Y
  Biotechnology and Bioengineering, Volume：in press, 2018, [Reviewed], [Corresponding]
  English, Scientific journal
  DOI：https://doi.org/10.1002/bit.26842
  DOI ID：10.1002/bit.26842
• From cyanobacteria and algae to land plants: The RpaB/Ycf27 regulatory network in transition　　　　　　　　　　　　　　　
  Riediger M; Hihara Y; Hess W.R
  Perspectives in Phycology, Volume：2018/0078, 2018, [Reviewed]
  English, Scientific journal
  DOI：https://doi.org/10.1127/pip/2018/0078
  DOI ID：10.1127/pip/2018/0078
• Applying a riboregulator as a new chromosomal gene regulation tool for higher glycogen production in Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  Kinuko Ueno; Yuta Sakai; Chika Shono; Ippei Sakamoto; Kaori Tsukakoshi; Yukako Hihara; Koji Sode; Kazunori Ikebukuro
  APPLIED MICROBIOLOGY AND BIOTECHNOLOGY, Volume：101, Number：23-24, First page：8465, Last page：8474, Dec. 2017, [Reviewed]
  Cyanobacteria are one of the most attractive hosts for biofuel production; however, genetic approaches to regulate specific chromosomal genes in cyanobacteria remain limited. With the aim of developing a novel method to regulate chromosomal gene expression in cyanobacteria, we focused on riboregulatory technology. Riboregulators are composed of two RNA fragments whose interaction leads to target gene regulation with high specificity. In this study, we inserted a riboregulator sequence upstream of the chromosomal gene encoding AbrB-like transcriptional regulator, cyAbrB2, to investigate the utility of this tool. The inserted riboregulator was able to regulate cyabrB2 gene expression, with a high ON-OFF ratio up to approximately 50-fold. The transcription levels of several genes for which cyAbrB2 acts as a transcriptional upregulator were also decreased. Further, the cyAbrB2 expression-repressed mutant showed high glycogen accumulation, equivalent to that in the cyabrB2 deletion mutant (Delta cyabrB2). Phenotypic similarities between the cyabrB2 expression-repressed mutant and the Delta cyabrB2 mutant suggest that the riboregulator can potentially be used as a new chromosomal gene regulation tool in cyanobacteria.
  SPRINGER, English, Scientific journal
  DOI：https://doi.org/10.1007/s00253-017-8570-4
  DOI ID：10.1007/s00253-017-8570-4, ISSN：0175-7598, eISSN：1432-0614, Web of Science ID：WOS:000415906900015
• The LexA transcription factor regulates fatty acid biosynthetic genes in the cyanobacterium Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  Ayumi Kizawa; Akihito Kawahara; Kosuke Takashima; Yasushi Takimura; Yoshitaka Nishiyama; Yukako Hihara
  PLANT JOURNAL, Volume：92, Number：2, First page：189, Last page：198, Oct. 2017, [Reviewed], [Corresponding]
  Specific transcription factors have been identified in various heterotrophic bacterial species that regulate the sets of genes required for fatty acid metabolism. Here, we report that expression of the fab genes, encoding fatty acid biosynthetic enzymes, is regulated by the global regulator LexA in the photoautotrophic cyanobacterium Synechocystis sp. PCC 6803. Sll1626, an ortholog of the well-known LexA repressor involved in the SOS response in heterotrophic bacteria, was isolated from crude extracts of Synechocystis by DNA affinity chromatography, reflecting its binding to the upstream region of the acpP-fabF and fabI genes. An electrophoresis mobility shift assay revealed that the recombinant LexA protein can bind to the upstream region of each fab gene tested (fabD, fabH, fabF, fabG, fabZ and fabI). Quantitative RT-PCR analysis of the wild type and a lexA-disrupted mutant strain suggested that LexA acts as a repressor of the fab genes involved in initiation of fatty acid biosynthesis (fabD, fabH and fabF) and the first reductive step in the subsequent elongation cycle (fabG) under normal growth conditions. Under nitrogen-depleted conditions, downregulation of fab gene expression is partly achieved through an increase in LexA-repressing activity. In contrast, under phosphate-depleted conditions, fab gene expression is upregulated, probably due to the loss of repression by LexA. We further demonstrate that elimination of LexA largely increases the production of fatty acids in strains modified to secrete free fatty acids.
  WILEY, English, Scientific journal
  DOI：https://doi.org/10.1111/tpj.13644
  DOI ID：10.1111/tpj.13644, ISSN：0960-7412, eISSN：1365-313X, Web of Science ID：WOS:000412680200004
• Acclimation of Oxygenic Photosynthesis to Iron Starvation Is Controlled by the sRNA IsaR1　　　　　　　　　　　　　　　
  Jens Georg; Gergana Kostova; Linda Vuorijoki; Verena Schoen; Taro Kadowaki; Tuomas Huokko; Desiree Baumgartner; Maximilian Mueller; Stephan Klaehn; Yagut Allahverdiyeva; Yukako Hihara; Matthias E. Futschik; Eva-Mari Aro; Wolfgang R. Hess
  CURRENT BIOLOGY, Volume：27, Number：10, First page：1425, Last page：+, May 2017, [Reviewed]
  Oxygenic photosynthesis crucially depends on proteins that possess Fe (2+) or Fe/S complexes as co-factors or prosthetic groups. Here, we show that the small regulatory RNA (sRNA) IsaR1 (Iron-Stress-Activated RNA 1) plays a pivotal role in acclimation to low-iron conditions. The IsaR1 regulon consists of more than 15 direct targets, including Fe (2+)-containing proteins involved in photosynthetic electron transfer, detoxification of anion radicals, citrate cycle, and tetrapyrrole biogenesis. IsaR1 is essential for maintaining physiological levels of Fe/S cluster biogenesis proteins during iron deprivation. Consequently, IsaR1 affects the acclimation of the photosynthetic apparatus to iron starvation at three levels: (1) directly, via posttranscriptional repression of gene expression; (2) indirectly, via suppression of pigment; and (3) Fe/S cluster biosynthesis. Homologs of IsaR1 are widely conserved throughout the cyanobacterial phylum. We conclude that IsaR1 is a critically important riboregulator. These findings provide a new perspective for understanding the regulation of iron homeostasis in photosynthetic organisms.
  CELL PRESS, English, Scientific journal
  DOI：https://doi.org/10.1016/j.cub.2017.04.010
  DOI ID：10.1016/j.cub.2017.04.010, ISSN：0960-9822, eISSN：1879-0445, Web of Science ID：WOS:000401696100017
• 多彩な戦略で挑むシアノバクテリア由来の持続可能燃料生産　　　　　　　　　　　　　　　
  日原由香子; 朝山宗彦; 蘆田弘樹; 天尾豊; 新井宗仁; 粟井光一郎; 得平茂樹; 小山内崇; 鞆達也; 成川礼; 蓮沼誠久; 増川一
  Volume：55, First page：88, Last page：97, Jan. 2017, [Reviewed], [Lead]
  Japanese, Scientific journal
  DOI：https://doi.org/10.1271/kagakutoseibutsu.55.88
  DOI ID：10.1271/kagakutoseibutsu.55.88
• Moderate Heat Stress Stimulates Repair of Photosystem II During Photoinhibition in Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  Mamoru Ueno; Penporn Sae-Tang; Yuri Kusama; Yukako Hihara; Mami Matsuda; Tomohisa Hasunuma; Yoshitaka Nishiyama
  PLANT AND CELL PHYSIOLOGY, Volume：57, Number：11, First page：2417, Last page：2426, Nov. 2016, [Reviewed]
  Examination of the effects of high temperature on the photoinhibition of photosystem II (PSII) in the cyanobacterium Synechocystis sp. PCC 6803 revealed that the extent of photoinhibition of PSII was lower at moderately high temperatures (35-42 degrees C) than at 30 degrees C. Photodamage to PSII, as determined in the presence of chloramphenicol, which blocks the repair of PSII, was accelerated at the moderately high temperatures but the effects of repair were greater than those of photodamage. The synthesis de novo of the D1 protein, which is essential for the repair of PSII, was enhanced at 38 degrees C. Electron transport and the synthesis of ATP were also enhanced at 38 degrees C, while levels of reactive oxygen species fell. Inhibition of the Calvin-Benson cycle with glycolaldehyde abolished the enhancement of repair of PSII at 38 degrees C, suggesting that an increase in the activity of the Calvin-Benson cycle might be required for the enhancement of repair at moderately high temperatures. The synthesis de novo of metabolic intermediates of the Calvin-Benson cycle, such as 3-phosphoglycerate, was also enhanced at 38 degrees C. We propose that moderate heat stress might enhance the repair of PSII by stimulating the synthesis of ATP and depressing the production of reactive oxygen species, via the stimulation of electron transport and suppression of the accumulation of excess electrons on the acceptor side of photosystem I, which might be driven by an increase in the activity of the Calvin-Benson cycle.
  OXFORD UNIV PRESS, English, Scientific journal
  DOI：https://doi.org/10.1093/pcp/pcw153
  DOI ID：10.1093/pcp/pcw153, ISSN：0032-0781, eISSN：1471-9053, Web of Science ID：WOS:000393158000016
• Metabolomic analysis of NAD kinase-deficient mutants of the cyanobacterium Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  Yuuma Ishikawa; Atsuko Miyagi; Yuto Haishima; Toshiki Ishikawa; Minoru Nagano; Masatoshi Yamaguchi; Yukako Hihara; Maki Kawai-Yamada
  JOURNAL OF PLANT PHYSIOLOGY, Volume：205, First page：105, Last page：112, Oct. 2016, [Reviewed]
  NAD kinase (NADK) phosphorylates NAD(H) to NADP(H). The enzyme has a crucial role in the regulation of the NADP(H)/NAD(H) ratio in various organisms. The unicellular cyanobacterium Synechocystis sp. PCC 6803 possesses two NADK-encoding genes, sll1415 and slr0400. To elucidate the metabolic change in NADK-deficient mutants growing under photoautotrophic conditions, we conducted metabolomic analysis using capillary electrophoresis mass spectrometry (CE-MS). The growth curves of the wild type parent (WT) and NADK-deficient mutants (Delta 1415 and Delta 0400) did not show any differences under photoautotrophic conditions. The NAD(P)(H) balance showed abnormality in both mutants. However, only the metabolite pattern of Delta 0400 showed differences compared to WT. These results indicated that the two NADK isoforms have distinct functions in cyanobacterial metabolism. (C) 2016 Elsevier GmbH. All rights reserved.
  ELSEVIER GMBH, URBAN & FISCHER VERLAG, English, Scientific journal
  DOI：https://doi.org/10.1016/j.jplph.2016.09.002
  DOI ID：10.1016/j.jplph.2016.09.002, ISSN：0176-1617, eISSN：1618-1328, Web of Science ID：WOS:000385858600014
• Overexpressed Superoxide Dismutase and Catalase Act Synergistically to Protect the Repair of PSII during Photoinhibition in Synechococcus elongatus PCC 7942　　　　　　　　　　　　　　　
  Penporn Sae-Tang; Yukako Hihara; Isao Yumoto; Yoshitake Orikasa; Hidetoshi Okuyama; Yoshitaka Nishiyama
  PLANT AND CELL PHYSIOLOGY, Volume：57, Number：9, First page：1899, Last page：1907, Sep. 2016, [Reviewed]
  The repair of PSII under strong light is particularly sensitive to reactive oxygen species (ROS), such as the superoxide radical and hydrogen peroxide, and these ROS are efficiently scavenged by superoxide dismutase (SOD) and catalase. In the present study, we generated transformants of the cyanobacterium Synechococcus elongatus PCC 7942 that overexpressed an iron superoxide dismutase (Fe-SOD) from Synechocystis sp. PCC 6803; a highly active catalase (VktA) from Vibrio rumoiensis; and both enzymes together. Then we examined the sensitivity of PSII to photoinhibition in the three strains. In cells that overexpressed either Fe-SOD or VktA, PSII was more tolerant to strong light than it was in wild-type cells. Moreover, in cells that overexpressed both Fe-SOD and VktA, PSII was even more tolerant to strong light. However, the rate of photodamage to PSII, as monitored in the presence of chloramphenicol, was similar in all three transformant strains and in wild-type cells, suggesting that the overexpression of these ROS-scavenging enzymes might not protect PSII from photodamage but might protect the repair of PSII. Under strong light, intracellular levels of ROS fell significantly, and the synthesis de novo of proteins that are required for the repair of PSII, such as the D1 protein, was enhanced. Our observations suggest that overexpressed Fe-SOD and VktA might act synergistically to alleviate the photoinhibition of PSII by reducing intracellular levels of ROS, with resultant protection of the repair of PSII from oxidative inhibition.
  OXFORD UNIV PRESS, English, Scientific journal
  DOI：https://doi.org/10.1093/pcp/pcw110
  DOI ID：10.1093/pcp/pcw110, ISSN：0032-0781, eISSN：1471-9053, Web of Science ID：WOS:000384717400009
• Intracellular Imaging of Qdots-Labeled DNA in Cyanobacteria　　　　　　　　　　　　　　　
  Alexandre Loukanov; Veselin Zhelyazkov; Yukako Hihara; Seiichiro Nakabayashi
  MICROSCOPY RESEARCH AND TECHNIQUE, Volume：79, Number：5, First page：447, Last page：452, May 2016, [Reviewed]
  In this contribution, they have attempted to develop a labeling technique for in vivo imaging of functionally active plasmid DNA in cyanobacterial cells through its decoration with semiconductor quantum dots (Qdots) as fluorescent nanoprobes. For that purpose biotinylated plasmid slr2060 DNA was conjugated with Qdots-streptavidine. The intact DNA was visualized in a single green color by light microscopy. These Qdots-DNA conjugates were capable of expressing the acyltransferase enzyme. Qdots-DNA conjugates and confocal microscope imaging technique were adopted to visualize the gene transport across the membrane of the live cyanobacteria cell in real time. Long-term kinetic study enabled to reveal the steps of extracellular and intracellular microenvironment for plasmid transportation into the live cell. To confirm these processes a confocal microscope and indicator plate assay test were applied in tandem. In this contribution, Qdots-labeled plasmid DNA was utilized for the first time for long-term intracellular imaging studies in cyanobacteria species PCC6803. The results showed that the Qdots-labeled plasmid DNA detection could be used as a powerful labeling technique for visualization of exogenous DNA entry and tracking into living cells by confocal microscopy. (C) 2016 Wiley Periodicals, Inc.
  WILEY-BLACKWELL, English, Scientific journal
  DOI：https://doi.org/10.1002/jemt.22651
  DOI ID：10.1002/jemt.22651, ISSN：1059-910X, eISSN：1097-0029, Web of Science ID：WOS:000374551100013
• A Feed-Forward Loop Consisting of the Response Regulator RpaB and the Small RNA PsrR1 Controls Light Acclimation of Photosystem I Gene Expression in the Cyanobacterium Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  Taro Kadowaki; Ryuta Nagayama; Jens Georg; Yoshitaka Nishiyama; Annegret Wilde; Wolfgang R. Hess; Yukako Hihara
  PLANT AND CELL PHYSIOLOGY, Volume：57, Number：4, First page：813, Last page：823, Apr. 2016, [Reviewed], [Corresponding]
  Since cyanobacteria need to decrease PSI content to avoid absorption of excess light energy, down-regulation of PSI gene expression is one of the key characteristics of the high-light (HL) acclimation response. The transcriptional regulator RpaB and the small RNA PsrR1 (photosynthesis regulatory RNA1) have been suggested to be the two most critical factors for this response in Synechocystis sp. PCC 6803. In this study, we found that the HLR1 DNA-binding motif, the recognition sequence for RpaB, is highly conserved in the core promoter region of the psrR1 gene among cyanobacterial species. Gel mobility shift assay revealed that RpaB binds to the HLR1 sequence of psrR1 in vitro. RNA gel blot analysis together with chromatin affinity purification (ChAP) analysis suggested that PSI genes are activated and the psrR1 gene is repressed by the binding of RpaB under low-light (LL) conditions. A decrease in DNA binding affinity of RpaB occurs within 5 min after the shift from LL to HL conditions, leading to the prompt decrease in PSI promoter activity together with derepression of psrR1 gene expression. Accumulating PsrR1 molecules then prevent translation from pre-existing PSI transcripts. By this dual repression at transcriptional and post-transcriptional levels, rapid and strict down-regulation of PSI expression under HL is secured. Our findings suggest that RpaB and PsrR1 constitute a feed-forward loop for the regulation of PSI gene expression to achieve a rapid acclimation response to the damaging HL conditions.
  OXFORD UNIV PRESS, English, Scientific journal
  DOI：https://doi.org/10.1093/pcp/pcw028
  DOI ID：10.1093/pcp/pcw028, ISSN：0032-0781, eISSN：1471-9053, Web of Science ID：WOS:000376654100015
• Oxidation of a Cysteine Residue in Elongation Factor EF-Tu Reversibly Inhibits Translation in the Cyanobacterium Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  Rayakorn Yutthanasirikul; Takanori Nagano; Haruhiko Jimbo; Yukako Hihara; Takashi Kanamori; Takuya Ueda; Takamitsu Haruyama; Hiroki Konno; Keisuke Yoshida; Toru Hisabori; Yoshitaka Nishiyama
  JOURNAL OF BIOLOGICAL CHEMISTRY, Volume：291, Number：11, First page：5860, Last page：5870, Mar. 2016, [Reviewed]
  Translational elongation is susceptible to inactivation by reactive oxygen species (ROS) in the cyanobacterium Synechocystis sp. PCC 6803, and elongation factor G has been identified as a target of oxidation by ROS. In the present study we examined the sensitivity to oxidation by ROS of another elongation factor, EF-Tu. The structure of EF-Tu changes dramatically depending on the bound nucleotide. Therefore, we investigated the sensitivity to oxidation in vitro of GTP- and GDP-bound EF-Tu as well as that of nucleotide-free EF-Tu. Assays of translational activity with a reconstituted translation system from Escherichia coli revealed that GTP-bound and nucleotide-free EF-Tu were sensitive to oxidation by H2O2, whereas GDP-bound EF-Tu was resistant to H2O2. The inactivation of EF-Tu was the result of oxidation of Cys-82, a single cysteine residue, and subsequent formation of both an intermolecular disulfide bond and sulfenic acid. Replacement of Cys-82 with serine rendered EF-Tu resistant to inactivation by H2O2, confirming that Cys-82 was a target of oxidation. Furthermore, oxidized EF-Tu was reduced and reactivated by thioredoxin. Gel-filtration chromatography revealed that some of the oxidized nucleotide-free EF-Tu formed large complexes of >30 molecules. Atomic force microscopy revealed that such large complexes dissociated into several smaller aggregates upon the addition of dithiothreitol. Immunological analysis of the redox state of EF-Tu in vivo showed that levels of oxidized EF-Tu increased under strong light. Thus, resembling elongation factor G, EF-Tu appears to be sensitive to ROS via oxidation of a cysteine residue, and its inactivation might be reversed in a redox-dependent manner.
  AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC, English, Scientific journal
  DOI：https://doi.org/10.1074/jbc.M115.706424
  DOI ID：10.1074/jbc.M115.706424, ISSN：0021-9258, eISSN：1083-351X, Web of Science ID：WOS:000372551800032
• Transcriptional and posttranscriptional regulation of cyanobacterial photosynthesis　　　　　　　　　　　　　　　
  Annegret Wilde; Yukako Hihara
  BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS, Volume：1857, Number：3, First page：296, Last page：308, Mar. 2016, [Reviewed], [Invited]
  Cyanobacteria are well established model organisms for the study of oxygenic photosynthesis, nitrogen metabolism, toxin biosynthesis, and salt acclimation. However, in comparison to other model bacteria little is known about regulatory networks, which allow cyanobacteria to acclimate to changing environmental conditions. The current work has begun to illuminate how transcription factors modulate expression of different photosynthetic regulons. During the past few years, the research on other regulatory principles like RNA-based regulation showed the importance of non-protein regulators for bacterial lifestyle. Investigations on modulation of photosynthetic components should elucidate the contributions of all factors within the context of a larger regulatory network.
  Here, we focus on regulation of photosynthetic processes including transcriptional and posttranscriptional mechanisms, citing examples from a limited number of cyanobacterial species. Though, the general idea holds true for most species, important differences exist between various organisms, illustrating diversity of acclimation strategies in the very heterogeneous cyanobacterial Glade. This article is part of a Special Issue entitled Organization and dynamics of bioenergetic systems in bacteria, edited by Prof Conrad Mullineaux (C) 2015 Elsevier B.V. All rights reserved.
  ELSEVIER SCIENCE BV, English, Scientific journal
  DOI：https://doi.org/10.1016/j.bbabio.2015.11.002
  DOI ID：10.1016/j.bbabio.2015.11.002, ISSN：0005-2728, eISSN：0006-3002, Web of Science ID：WOS:000370895500012
• Free fatty acid production in the cyanobacterium Synechocystis sp PCC 6803 is enhanced by deletion of the cyAbrB2 transcriptional regulator　　　　　　　　　　　　　　　
  Akihito Kawahara; Yusuke Sato; Yujiro Saito; Yasuko Kaneko; Yasushi Takimura; Hiroshi Hagihara; Yukako Hihara
  JOURNAL OF BIOTECHNOLOGY, Volume：220, First page：1, Last page：11, Feb. 2016, [Reviewed], [Corresponding]
  The cyAbrB2 (Sll0822) transcriptional regulator in Synechocystis sp. PCC 6803 is involved in coordination of carbon and nitrogen metabolism and its deletion causes distinct phenotypes such as decreased expression levels of nitrogen-regulated genes and high accumulation of glycogen granules. From the viewpoint of metabolic engineering, the highly accumulated glycogen granules in the Delta cyabrB2 mutant could be a valuable source for the production of biofuels. Here, by disruption of the aas gene (sir] 609) encoding acyl-acyl carrier protein synthetase and introduction of a gene encoding thioesterase from Umbellularia californica (UcTE), we conferred the ability of production and secretion of free fatty acids on the Delta cyabrB2 mutant. Notable features of the resulting Delta cyabrB2 Delta aas::UcTE strain compared with Delta cyabrB2 by RNA-seq analysis were decrease in expression levels of genes related to uptake and subsequent metabolism of nitrogen and carbon and increase in the expression level of sigE encoding a group 2 sigma factor. These changes in gene expression profile were not observed when the same genetic modification was introduced in the wild-type background. The Delta cyabrB2 Delta aas::UcTE strain showed two-folds higher free fatty acid productivity on a per OD730 basis compared with the Delta aas::UcTE strain, without expense of the accumulated glycogen granules. This shows the potential of the Delta cyabrB2 mutant as the platform of biofuel production. The effective utilization of the accumulated glycogen must be the next task to be pursued. (C) 2015 Elsevier B.V. All rights reserved.
  ELSEVIER SCIENCE BV, English, Scientific journal
  DOI：https://doi.org/10.1016/j.jbiotec.2015.12.035
  DOI ID：10.1016/j.jbiotec.2015.12.035, ISSN：0168-1656, eISSN：1873-4863, Web of Science ID：WOS:000369371400001
• RNA-seq Profiling Reveals Novel Target Genes of LexA in the Cyanobacterium Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  Ayumi Kizawa; Akihito Kawahara; Yasushi Takimura; Yoshitaka Nishiyama; Yukako Hihara
  FRONTIERS IN MICROBIOLOGY, Volume：7, First page：193, Feb. 2016, [Reviewed], [Corresponding]
  LexA is a well-established transcriptional repressor of SOS genes induced by DNA damage in Escherichia coil and other bacterial species. However, LexA in the cyanobacterium Synechocystis sp. PCC 6803 has been suggested not to be involved in SOS response. In this study, we performed RNA-seq analysis of the wild-type strain and the lexA-disrupted mutant to obtain the comprehensive view of LexA-regulated genes in Synechocystis. Disruption of lexA positively or negatively affected expression of genes related to various cellular functions such as phototactic motility, accumulation of the major compatible solute glucosylglycerol and subunits of bidirectional hydrogenase, photosystem I, and phycobilisome complexes. We also observed increase in the expression level of genes related to iron and manganese uptake in the mutant at the later stage of cultivation. However, none of the genes related to DNA metabolism were affected by disruption of lexA. DNA gel mobility shift assay using the recombinant LexA protein suggested that LexA binds to the upstream region of pilA7, pilA9, ggpS. and slr1670 to directly regulate their expression, but changes in the expression level of photosystem I genes by disruption of lexA is likely a secondary effect.
  FRONTIERS MEDIA SA, English, Scientific journal
  DOI：https://doi.org/10.3389/fmicb.2016.00193
  DOI ID：10.3389/fmicb.2016.00193, ISSN：1664-302X, Web of Science ID：WOS:000370563900001
• Analysis of spontaneous suppressor mutants from the photomixotrophically grown pmgA-disrupted mutant in the cyanobacterium Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  Yoshiki Nishijima; Yu Kanesaki; Hirofumi Yoshikawa; Takako Ogawa; Kintake Sonoike; Yoshitaka Nishiyama; Yukako Hihara
  PHOTOSYNTHESIS RESEARCH, Volume：126, Number：2-3, First page：465, Last page：475, Dec. 2015, [Reviewed], [Corresponding]
  The pmgA-disrupted (Delta pmgA) mutant in the cyanobacterium Synechocystis sp. PCC 6803 suffers severe growth inhibition under photomixotrophic conditions. In order to elucidate the key factors enabling the cells to grow under photomixotrophic conditions, we isolated spontaneous suppressor mutants from the Delta pmgA mutant derived from a single colony. When the Delta pmgA mutant was spread on a BG11 agar plate supplemented with glucose, colonies of suppressor mutants appeared after the bleaching of the background cells. We identified the mutation site of these suppressor mutants and found that 11 mutants out of 13 had a mutation in genes related to the type 1 NAD(P)H dehydrogenase (NDH-1) complex. Among them, eight mutants had mutations within the ndhF3 (sll1732) gene: R32stop, W62stop, V147I, G266V, G354W, G586C, and deletion of 7 bp within the coding region. One mutant had one base insertion in the putative -10 box of the ndhC (slr1279) gene, leading to the decrease in the transcripts of the ndhCKJ operon. Two mutants had one base insertion and deletion in the coding region of cupA (sll1734), which is co-transcribed with ndhF3 and ndhD3 and comprises together a form of NDH-1 complex (NDH-1MS complex) involved in inducible high-affinity CO2 uptake. The results indicate that the loss of the activity of this complex effectively rescues the Delta pmgA mutant under photomixotrophic condition with 1 % CO2. However, little difference among WT and mutants was observed in the activities ascribed to the NDH-1MS complex, i.e., CO2 uptake and cyclic electron transport. This may suggest that the NDH-1MS complex has the third, currently unknown function under photomixotrophic conditions.
  SPRINGER, English, Scientific journal
  DOI：https://doi.org/10.1007/s11120-015-0143-8
  DOI ID：10.1007/s11120-015-0143-8, ISSN：0166-8595, eISSN：1573-5079, Web of Science ID：WOS:000362006900025
• Zeaxanthin and Echinenone Protect the Repair of Photosystem II from Inhibition by Singlet Oxygen in Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  Yuri Kusama; Shuhei Inoue; Haruhiko Jimbo; Shinichi Takaichi; Kintake Sonoike; Yukako Hihara; Yoshitaka Nishiyama
  PLANT AND CELL PHYSIOLOGY, Volume：56, Number：5, First page：906, Last page：916, May 2015, [Reviewed]
  Carotenoids are important components of antioxidative systems in photosynthetic organisms. We investigated the roles of zeaxanthin and echinenone in the protection of PSII from photoinhibition in Synechocystis sp. PCC 6803, using mutants of the cyanobacterium that lack these carotenoids. The activity of PSII in mutant cells deficient in either zeaxanthin or echinenone was more sensitive to strong light than the activity in wild-type cells, and the activity in mutant cells deficient in both carotenoids was hypersensitive to strong light, indicating that the absence of these carotenoids increased the extent of photoinhibition. Nonetheless, the rate of photodamage to PSII, as measured in the presence of chloramphenicol, which blocks the repair of PSII, was unaffected by the absence of either carotenoid, suggesting that these carotenoids might act by protecting the repair of PSII. Knockout of the gene for the so-called orange carotenoid protein (OCP), in which the 3'-hydroxyechinenone cofactor, a derivative of echinenone, is responsible for the thermal dissipation of excitation energy, increased the extent of photoinhibition but did not affect photodamage, suggesting that thermal dissipation also protects the repair of PSII. In mutant cells lacking OCP, as well as those lacking zeaxanthin and echinenone, the production of singlet oxygen was stimulated and the synthesis de novo of various proteins, including the D1 protein, was markedly suppressed under strong light. These observations suggest that the carotenoids and thermal dissipation might protect the repair of photodamaged PSII by depressing the levels of singlet oxygen that inhibits protein synthesis.
  OXFORD UNIV PRESS, English, Scientific journal
  DOI：https://doi.org/10.1093/pcp/pcv018
  DOI ID：10.1093/pcp/pcv018, ISSN：0032-0781, eISSN：1471-9053, Web of Science ID：WOS:000355313900009
• Identification of OmpR-Family Response Regulators Interacting with Thioredoxin in the Cyanobacterium Synechocystis sp. PCC 6803 (vol 19, e0119107, 2015)　　　　　　　　　　　　　　　
  Taro Kadowaki; Yoshitaka Nishiyama; Toru Hisabori; Yukako Hihara
  PLOS ONE, Volume：10, Number：4, First page：e0119107, Apr. 2015, [Reviewed], [Corresponding]
  PUBLIC LIBRARY SCIENCE, English, Scientific journal
  DOI：https://doi.org/10.1371/journal.pone.0124571
  DOI ID：10.1371/journal.pone.0124571, ISSN：1932-6203, Web of Science ID：WOS:000352845100265
• Oxidation of translation factor EF-G transiently retards the translational elongation cycle in Escherichia coli　　　　　　　　　　　　　　　
  Nagano T; Yutthanasirikul R; Hihara Y; Hisabori T; Kanamori T; Takeuchi N; Ueda T; Nishiyama Y
  Journal of Biochemistry, Volume：158, Number：2, First page：165, Last page：172, 2015, [Reviewed]
  Japanese Biochemical Society, English
  DOI ID：10.1093/jb/mvv026, ISSN：0021-924X, CiNii Articles ID：40020554133, CiNii Books ID：AA00694073, ORCID：25618254, Web of Science ID：WOS:000359684400008
• The effects of dark incubation on cellular metabolism of the wild type cyanobacterium Synechocystis sp. PCC 6803 and a mutant lacking the transcriptional regulator cyAbrB2　　　　　　　　　　　　　　　
  Masamitsu Hanai; Yusuke Sato; Atsuko Miyagi; Maki Kawai-Yamada; Kyoko Tanaka; Yasuko Kaneko; Yoshitaka Nishiyama; Yukako Hihara
  Life, Volume：4, Number：4, First page：770, Last page：787, Nov. 2014, [Reviewed], [Corresponding]
  The cyAbrB2 transcriptional regulator is essential for active sugar catabolism in Synechocystis sp. PCC 6 803 grown under light conditions. In the light-growncyabrB2-disrupted mutant, glycogen granules and sugar phosphates corresponding to early steps in the glycolytic pathway accumulated to higher levels than those in the wild-type (WT) strain, whereas the amounts of 3-phosphoglycerate, phosphoenolpyruvate and ribulose 1,5-bisphosphate were significantly lower. We further determined that accumulated glycogen granules in the mutant could be actively catabolized under dark conditions. Differences in metabolite levels between WT and the mutant became less substantial during dark incubation due to a general quantitative decrease in metabolite levels. Notable exceptions, however, were increases in 2-oxoglutarate, histidine, ornithine and citrulline in the WT but not in the mutant. The amounts of cyAbrBs were highly responsive to the availability of light both in transcript and protein levels. When grown under light-dark cycle conditions, diurnal oscillatory pattern of glycogen content of the mutant was lost after the second dark period. These observations indicate that cyAbrB2 is dispensable for activation of sugar catabolism under dark conditions but involved in the proper switching between day and night metabolisms.
  MDPI AG, English, Scientific journal
  DOI：https://doi.org/10.3390/life4040770
  DOI ID：10.3390/life4040770, ISSN：2075-1729, SCOPUS ID：84938900212
• Deletion of the Transcriptional Regulator cyAbrB2 Deregulates Primary Carbon Metabolism in Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  Yuki Kaniya; Ayumi Kizawa; Atsuko Miyagi; Maki Kawai-Yamada; Hirofumi Uchimiya; Yasuko Kaneko; Yoshikata Nishiyama; Yukako Hihara
  PLANT PHYSIOLOGY, Volume：162, Number：2, First page：1153, Last page：1163, Jun. 2013, [Reviewed], [Corresponding]
  cyAbrB is a transcriptional regulator unique to and highly conserved among cyanobacterial species. A gene-disrupted mutant of cyabrB2 (sll0822) in Synechocystis sp. PCC 6803 exhibited severe growth inhibition and abnormal accumulation of glycogen granules within cells under photomixotrophic conditions. Within 6 h after the shift to photomixotrophic conditions, sodium bicarbonate-dependent oxygen evolution activity markedly declined in the Delta cyabrB2 mutant, but the decrease in methyl viologen-dependent electron transport activity was much smaller, indicating inhibition in carbon dioxide fixation. Decreases in the transcript levels of several genes related to sugar catabolism, carbon dioxide fixation, and nitrogen metabolism were also observed within 6 h. Metabolome analysis by capillary electrophoresis mass spectrometry revealed that several metabolites accumulated differently in the wild-type and mutant strains. For example, the amounts of pyruvate and 2-oxoglutarate (2OG) were significantly lower in the mutant than in the wild type, irrespective of trophic conditions. The growth rate of the Delta cyabrB2 mutant was restored to a level comparable to that under photoautotrophic conditions by addition of 2OG to the growth medium under photomixotrophic conditions. Activities of various metabolic processes, including carbon dioxide fixation, respiration, and nitrogen assimilation, seemed to be enhanced by 2OG addition. These observations suggest that cyAbrB2 is essential for the active transcription of genes related to carbon and nitrogen metabolism upon a shift to photomixotrophic conditions. Deletion of cyAbrB2 is likely to deregulate the partition of carbon between storage forms and soluble forms used for biosynthetic purposes. This disorder may cause inactivation of cellular metabolism, excess accumulation of reducing equivalents, and subsequent loss of viability under photomixotrophic conditions.
  AMER SOC PLANT BIOLOGISTS, English, Scientific journal
  DOI：https://doi.org/10.1104/pp.113.218784
  DOI ID：10.1104/pp.113.218784, ISSN：0032-0889, Web of Science ID：WOS:000319819900047
• Acclimation to high-light conditions in cyanobacteria: from gene expression to physiological responses　　　　　　　　　　　　　　　
  Masayuki Muramatsu; Yukako Hihara
  JOURNAL OF PLANT RESEARCH, Volume：125, Number：1, First page：11, Last page：39, Jan. 2012, [Reviewed], [Invited], [Corresponding]
  Photosynthetic organisms have evolved various acclimatory responses to high-light (HL) conditions to maintain a balance between energy supply (light harvesting and electron transport) and consumption (cellular metabolism) and to protect the photosynthetic apparatus from photodamage. The molecular mechanism of HL acclimation has been extensively studied in the unicellular cyanobacterium Synechocystis sp. PCC 6803. Whole genome DNA microarray analyses have revealed that the change in gene expression profile under HL is closely correlated with subsequent acclimatory responses such as (1) acceleration in the rate of photosystem II turnover, (2) downregulation of light harvesting capacity, (3) development of a protection mechanism for the photosystems against excess light energy, (4) upregulation of general protection mechanism components, and (5) regulation of carbon and nitrogen assimilation. In this review article, we survey recent progress in the understanding of the molecular mechanisms of these acclimatory responses in Synechocystis sp. PCC 6803. We also briefly describe attempts to understand HL acclimation in various cyanobacterial species in their natural environments.
  SPRINGER JAPAN KK, English, Scientific journal
  DOI：https://doi.org/10.1007/s10265-011-0454-6
  DOI ID：10.1007/s10265-011-0454-6, ISSN：0918-9440, Web of Science ID：WOS:000298056000002
• Physiological Roles of the cyAbrB Transcriptional Regulator Pair Sll0822 and Sll0359 in Synechocystis sp strain PCC 6803　　　　　　　　　　　　　　　
  Yuki Yamauchi; Yuki Kaniya; Yasuko Kaneko; Yukako Hihara
  JOURNAL OF BACTERIOLOGY, Volume：193, Number：15, First page：3702, Last page：3709, Aug. 2011, [Reviewed], [Corresponding]
  All known cyanobacterial genomes possess multiple copies of genes encoding AbrB-like transcriptional regulators, known as cyAbrBs, which are distinct from those conserved among other bacterial species. In this study, we addressed the physiological roles of Sll0822 and Sll0359, the two cyAbrBs in Synechocystis sp. strain PCC 6803, under nonstress conditions (20 mu mol of photons m(-2) s(-1) in ambient CO2). When the sll0822 gene was disrupted, the expression levels of nitrogen-related genes such as urtA, amt1, and glnB significantly decreased compared with those in the wild-type cells. Possibly due to the increase of the cellular carbon/nitrogen ratio in the sll0822-disrupted cells, a decrease in pigment contents, downregulation of carbon-uptake related genes, and aberrant accumulation of glycogen took place. Moreover, the mutant exhibited the decrease in the expression level of cytokinesis-related genes such as ftsZ and ftsQ, resulting in the defect in cell division and significant increase in cell size. The pleiotrophic phenotype of the mutant was efficiently suppressed by the introduction of Sll0822 and also partially suppressed by the introduction of Sll0359. When His-tagged cyAbrBs were purified from overexpression strains, Sll0359 and Sll0822 were copurified with each other. The cyAbrBs in Synechocystis sp. strain PCC 6803 seem to interact with each other and regulate carbon and nitrogen metabolism as well as the cell division process under nonstress conditions.
  AMER SOC MICROBIOLOGY, English, Scientific journal
  DOI：https://doi.org/10.1128/JB.00284-11
  DOI ID：10.1128/JB.00284-11, ISSN：0021-9193, Web of Science ID：WOS:000292698100002
• Cross-talk between photomixotrophic growth and CO2-concentrating mechanism in Synechocystis sp strain PCC 6803　　　　　　　　　　　　　　　
  Maya Haimovich-Dayan; Shira Kahlon; Yukako Hihara; Martin Hagemann; Teruo Ogawa; Itzhak Ohad; Judy Lieman-Hurwitz; Aaron Kaplan
  ENVIRONMENTAL MICROBIOLOGY, Volume：13, Number：7, First page：1767, Last page：1777, Jul. 2011, [Reviewed]
  Simultaneous catabolic and anabolic glucose metabolism occurs in the same compartment during photomixotrophic growth of the model cyanobacterium Synechocystis sp. PCC 6803. The presence of glucose is stressful to the cells; it is reflected in the high frequency of suppression mutations in glucose-sensitive mutants. We show that glucose affects many cellular processes. It stimulates respiration and the rate of photosynthesis and quantum yield in low-but not high-CO2-grown cells. Fluorescence and thermoluminescence parameters of photosystem II are also affected but the results did not lend support to sustained glucose driven over reduction in the light. Glucose-sensitive mutants such as Delta pmgA (impaired in photomixotrophic growth) and Delta hik31 (lacking histidine kinase 31) are far more susceptible under high than low air level of CO2. A glycine to tryptophan mutation in position 354 in NdhF3, involved in the high-affinity CO2 uptake, rescued Delta pmgA. A rise in the apparent photosynthetic affinity to external inorganic carbon is observed in high-CO2-grown wild-type cells after the addition of glucose, but not in mutant Delta pmgA. This is attributed to upregulation of certain low-CO2-induced genes, involved in inorganic carbon uptake, in the wild type but not in Delta pmgA. These data uncovered a new level of interaction between CO2 fixation (and the CO2-concentrating mechanism) and photomixotrophic growth in cyanobacteria.
  WILEY-BLACKWELL, English, Scientific journal
  DOI：https://doi.org/10.1111/j.1462-2920.2011.02481.x
  DOI ID：10.1111/j.1462-2920.2011.02481.x, ISSN：1462-2912, Web of Science ID：WOS:000292308500008
• The PedR transcriptional regulator interacts with thioredoxin to connect photosynthesis with gene expression in cyanobacteria　　　　　　　　　　　　　　　
  Mayumi Horiuchi; Kinu Nakamura; Kouji Kojima; Yoshitaka Nishiyama; Wakako Hatakeyama; Toru Hisabori; Yukako Hihara
  BIOCHEMICAL JOURNAL, Volume：431, First page：135, Last page：140, Oct. 2010, [Reviewed], [Corresponding]
  The redox state of the photosynthetic electron transport chain acts as a critical sensing mechanism by regulating the transcription of key genes involved in the acclimation response to a change in the environment. In the present study we show that the small LuxR-type regulator PedR interacts with Trx (thioredoxin) to achieve photosynthetic electron-transport-dependent transcriptional regulation in the cyanobacterium Synechocystis sp. PCC 6803. TrxM, an isoform of Trx, was isolated as an interacting factor of PedR by pull-down assays. In vitro analysis revealed that the intermolecular disulfide bond formed between Cys(80) residues of the PedR homodimer was reduced by both TrxM and TrxX. It has been shown previously that, although PedR is active under low-light conditions, it becomes transiently inactivated following a shift to high-light conditions, with a concomitant conformational change [Nakamura and Hihara (2006) J. Biol. Chem. 281, 36758-36766]. In the present study, we found that the conformational change of PedR and the change in the transcript level of its target gene were minimal when mutants of Synechocystis that lack ferredoxin-Trx reductase or NADPH-Trx reductase were exposed to high levels of light. These results indicate that the reduction of PedR by Trx causes transient inactivation of PedR upon the shift of cyanobacterial cells to high-light conditions.
  PORTLAND PRESS LTD, English, Scientific journal
  DOI：https://doi.org/10.1042/BJ20100789
  DOI ID：10.1042/BJ20100789, ISSN：0264-6021, Web of Science ID：WOS:000282852800014
• Role of Multiple HLR1 Sequences in the Regulation of the Dual Promoters of the psaAB Genes in Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  Tomoko Takahashi; Nanako Nakai; Masayuki Muramatsu; Yukako Hihara
  JOURNAL OF BACTERIOLOGY, Volume：192, Number：15, First page：4031, Last page：4036, Aug. 2010, [Reviewed], [Corresponding]
  Previously, we analyzed the promoter architecture of the psaAB genes encoding reaction center subunits of photosystem I (PSI) in the cyanobacterium Synechocystis sp. PCC 6803. There exist two promoters, P1 and P2, both of which show typical high-light (HL) response of PSI genes; their activities are high under low-light (LL) conditions but rapidly downregulated upon the shift to HL conditions. In this study, it was suggested that a response regulator RpaB binds to multiple high-light regulatory 1 (HLR1) sequences in the upstream region of the psaAB genes. We explored the regulatory role of cis-elements, including these HLR1 sequences on the individual activity of P1 and P2. Under LL conditions, the most influential cis-element is HLR1C (-62 to -45, relative to the transcriptional starting point of P1) working for positive regulation of P1. The other HLR1 sequences also affect the promoter activity under LL conditions; HLR1A (-255 to -238) is involved in repression of P1, whereas HLR1B (-153 to -126) works for activation of P2. Upon the shift to HL conditions, regulation via HNE2 located within the region from -271 to -177 becomes active in order to downregulate both P1 and P2 activities. A positive effect of HLR1B on P2 may persist under HL. These results suggest that cis-elements, including multiple HLR1 sequences, differently regulate the activities of dual promoters of the psaAB genes to achieve the fine-tuning of the gene expression.
  AMER SOC MICROBIOLOGY, English, Scientific journal
  DOI：https://doi.org/10.1128/JB.00444-10
  DOI ID：10.1128/JB.00444-10, ISSN：0021-9193, Web of Science ID：WOS:000279782000021
• A cyanobacterial AbrB-like protein affects the apparent photosynthetic affinity for CO2 by modulating low-CO2-induced gene expression　　　　　　　　　　　　　　　
  Judy Lieman-Hurwitz; Maya Haimovich; Gali Shalev-Malul; Ai Ishii; Yukako Hihara; Ariel Gaathon; Mario Lebendiker; Aaron Kaplan
  ENVIRONMENTAL MICROBIOLOGY, Volume：11, Number：4, First page：927, Last page：936, Apr. 2009, [Reviewed]
  In Synechocystis sp. strain PCC 6803, over 450 genes are upregulated following transfer of the cells from a high (1-5% CO2 in air, HC) to a low level of CO2 (as in air or lower, LC). This includes sbtA, ndhF3 and cmpA involved in inorganic carbon (Ci) uptake. Earlier studies implicated NdhR in the regulation of LC-induced genes but there are indications that additional components are involved. Following extraction of proteins from cells grown under HC and (NH4)(2)SO4 fractionation, we have identified LexA and two AbrB-like proteins, Sll0359 and Sll0822, which bind to a fragment of the sbtA promoter. Using extracts prepared from LC-grown cells, Sll0822 did not bind to the sbtA promoter despite its presence in the cells, suggesting that it may serve as a repressor of LC-induced genes. This is supported by the fact that sbtA, ndhF3 and cmpA normally expressed only under LC in the wild-type are transcribed under both HC and LC in a Delta sll0822 mutant. When grown under HC this mutant exhibits an elevated apparent photosynthetic affinity to Ci, typically observed in the wild-type only under LC. Clearly, expression of genes essential for Ci uptake was sufficient to raise the apparent photosynthetic affinity for external Ci.
  WILEY-BLACKWELL, English, Scientific journal
  DOI：https://doi.org/10.1111/j.1462-2920.2008.01818.x
  DOI ID：10.1111/j.1462-2920.2008.01818.x, ISSN：1462-2912, Web of Science ID：WOS:000264881300018
• Mechanism of downregulation of photosystem I content under high-light conditions in the cyanobacterium Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  Masayuki Muramatsu; Kintake Sonoike; Yukako Hihara
  MICROBIOLOGY-SGM, Volume：155, First page：989, Last page：996, Mar. 2009, [Reviewed], [Corresponding]
  Downregulation of photosystem I (PSI) content is an essential process for cyanobacteria to grow under high-light (HL) conditions. In a pmgA (sll 968) mutant of Synechocystis sp. PCC 6803, the levels of PSI content, chlorophyll and transcripts of the psaAB genes encoding reaction-centre subunits of PSI could not be maintained low during HL incubation, although the causal relationship among these phenotypes remains unknown. In this study, we modulated the activity of psaAB transcription or that of chlorophyll synthesis to estimate their contribution to the regulation of PSI content under HL conditions. Analysis of the psaAB-OX strain, in which the psaAB genes were overexpressed under HL conditions, revealed that the amount of psaAB transcript could not affect PSI content by itself. Suppression of chlorophyll synthesis by an inhibitor, laevulinic acid, in the pmgA mutant revealed that chlorophyll availability could be a determinant of PSI content under HL. It was also suggested that chlorophyll content under HL conditions is mainly regulated at the level of 5-aminolaevulinic acid synthesis. We conclude that, upon the shift to HL conditions, activities of psaAB transcription and of 5-aminolaevulinic acid synthesis are strictly downregulated by regulatory mechanism(s) independent of PmgA during the first 6 h, and then a PmgA-mediated regulatory mechanism becomes active after 6 h onward of HL incubation to maintain these activities at a low level.
  SOC GENERAL MICROBIOLOGY, English, Scientific journal
  DOI：https://doi.org/10.1099/mic.0.024018-0
  DOI ID：10.1099/mic.0.024018-0, ISSN：1350-0872, Web of Science ID：WOS:000264515100034
• The Response Regulator RpaB Binds to the Upstream Element of Photosystem I Genes To Work for Positive Regulation under Low-Light Conditions in Synechocystis sp Strain PCC 6803　　　　　　　　　　　　　　　
  Yurie Seino; Tomoko Takahashi; Yukako Hihara
  JOURNAL OF BACTERIOLOGY, Volume：191, Number：5, First page：1581, Last page：1586, Mar. 2009, [Reviewed], [Corresponding]
  The coordinated high-light response of genes encoding subunits of photosystem I (PSI) is achieved by the AT-rich region located just upstream of the core promoter in Synechocystis sp. strain PCC 6803. The upstream element enhances the basal promoter activity under low-light conditions, whereas this positive regulation is lost immediately after the shift to high-light conditions. In this study, we focused on a high-light regulatory 1 (HLR1) sequence included in the upstream element of every PSI gene examined. A gel mobility shift assay revealed that a response regulator RpaB binds to the HLR1 sequence in PSI promoters. Base substitution in the HLR1 sequence or decrease in copy number of the rpaB gene resulted in decrease in the promoter activity of PSI genes under low-light conditions. These observations suggest that RpaB acts as a transcriptional activator for PSI genes. It is likely that RpaB binds to the HLR1 sequence under low-light conditions and works for positive regulation of PSI genes and for negative regulation of high-light-inducible genes depending on the location of the HLR1 sequence within target promoters.
  AMER SOC MICROBIOLOGY, English, Scientific journal
  DOI：https://doi.org/10.1128/JB.01588-08
  DOI ID：10.1128/JB.01588-08, ISSN：0021-9193, Web of Science ID：WOS:000263503600024
• An AbrB-like transcriptional regulator, Sll0822, is essential for the activation of nitrogen-regulated genes in Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  Ai Ishii; Yukako Hihara
  PLANT PHYSIOLOGY, Volume：148, Number：1, First page：660, Last page：670, Sep. 2008, [Reviewed], [Corresponding]
  Every cyanobacterial species possesses multiple genes encoding AbrB-like transcriptional regulators (cyAbrBs) distinct from those conserved among other bacterial species. In this study, two genes encoding cyAbrBs in Synechocystis sp. PCC 6803, sll0359 and sll0822, were insertionally disrupted in order to examine their physiological roles. A fully segregated disrupted mutant of sll0822 (Delta sll0822 mutant) but not of sll0359 was obtained, although both mutants exhibited similar phenotypes (i.e. decreases in growth rate and pigment content). The growth rate of the Delta sll0822 mutant was low under any condition, but the low pigment content could be partially recovered by nitrate supplementation of the medium. DNA microarray and RNA-blot analyses revealed that the level of expression of a part of the NtcA regulon, such as urtA, amt1, glnB, sigE, and the nrt operon, was significantly decreased in the Delta sll0822 mutant, although the induction of these genes upon nitrogen depletion was still observed to some extent. Sll0822 seems to work in parallel with NtcA to achieve flexible regulation of the nitrogen uptake system. The Sll0822 protein exists mainly in a dimeric form in vivo, and the amount of the protein was not affected by nitrogen availability. This observation, together with the low binding specificity of the purified histidine-tagged Sll0822 protein, implies that the activity of Sll0822 may be posttranslationally modulated in Synechocystis cells.
  AMER SOC PLANT BIOLOGISTS, English, Scientific journal
  DOI：https://doi.org/10.1104/pp.108.123505
  DOI ID：10.1104/pp.108.123505, ISSN：0032-0889, eISSN：1532-2548, Web of Science ID：WOS:000258947600055
• Difference in metabolite levels between photoautotrophic and photomixotrophic cultures of Synechocystis sp PCC 6803 examined by capillary electrophoresis electrospray ionization mass spectrometry　　　　　　　　　　　　　　　
  Hideyuki Takahashi; Hirofumi Uchimiya; Yukako Hihara
  JOURNAL OF EXPERIMENTAL BOTANY, Volume：59, Number：11, First page：3009, Last page：3018, Aug. 2008, [Reviewed], [Corresponding]
  Capillary electrophoresis mass spectrometry (CE/MS) was applied for the comprehensive survey of changes in the amounts of metabolites upon the shift from photoautotrophic to photomixotrophic conditions in Synechocystis sp. PCC 6803. When glucose was added to the photoautotrophically grown culture, the increase in the metabolites for the oxidative pentose phosphate (OPP) pathway and glycolysis, together with the decrease in those for the Calvin cycle, was observed. Concomitantly, the increase in respiratory activity and the decrease in photosynthetic activity took place in the wild-type cells. In the pmgA-disrupted mutant that shows growth inhibition under photomixotrophic conditions, lower enzymatic activities of the OPP pathway and higher photosynthetic activity were observed, irrespective of trophic conditions. These defects brought about metabolic disorders such as a decrease in ATP and NADPH contents, a failure in the activation of respiratory activity, and the aberrant accumulation of isocitrate under photomixotrophic but not under photoautotrophic conditions. A delicate balancing of the carbon flow between the Calvin cycle and the OPP pathway seems indispensable for growth specifically under photomixotrophic conditions and PmgA is likely to be involved in the regulation.
  OXFORD UNIV PRESS, English, Scientific journal
  DOI：https://doi.org/10.1093/jxb/ern157
  DOI ID：10.1093/jxb/ern157, ISSN：0022-0957, Web of Science ID：WOS:000258330200009
• Coordinated high-light response of genes encoding subunits of photosystem I is achieved by AT-rich upstream sequences in the cyanobacterium Synechocystis sp strain PCC 6803　　　　　　　　　　　　　　　
  Masayuki Muramatsu; Yukako Hihara
  JOURNAL OF BACTERIOLOGY, Volume：189, Number：7, First page：2750, Last page：2758, Apr. 2007, [Reviewed], [Corresponding]
  Genes encoding subunits of photosystem I (PSI genes) in the cyanobacterium Synechocystis sp. strain PCC 6803 are actively transcribed under low-light conditions, whereas their transcription is coordinately and rapidly down-regulated upon the shift to high-light conditions. In order to identify the molecular mechanism of the coordinated high-light response, we searched for common light-responsive elements in the promoter region of PSI genes. First, the precise architecture of the psaD promoter was determined and compared with the previously identified structure of the psaAB promoter. One of two promoters of the psaAB genes (P1) and of the psaD gene (P2) possessed an AT-rich light-responsive element located just upstream of the basal promoter region. These sequences enhanced the basal promoter activity under low-light conditions, and their activity was transiently suppressed upon the shift to high-light conditions. Subsequent analysis of psaC, psaE, psaK1, and psaL1 promoters revealed that their light response was also achieved by AT-rich sequences located at the -70 to -46 region. These results clearly show that AT-rich upstream elements are responsible for the coordinated high-light response of PSI genes dispersed throughout Synechocystis genome.
  AMER SOC MICROBIOLOGY, English, Scientific journal
  DOI：https://doi.org/10.1128/JB.01903-06
  DOI ID：10.1128/JB.01903-06, ISSN：0021-9193, Web of Science ID：WOS:000245842000020
• A network of genes regulated by light in cyanobacteria　　　　　　　　　　　　　　　
  Rajeev Aurora; Yukako Hihara; Abhay K. Singh; Himadri B. Pakrasi
  OMICS A Journal of Integrative Biology, Volume：11, Number：2, First page：166, Last page：185, 2007, [Reviewed]
  Oxygenic photosynthetic organisms require light for their growth and development. However, exposure to high light is detrimental to them. Using time series microarray data from a model cyanobacterium, Synechocystis 6803 transferred from low to high light, we generated a gene co-expression network. The network has twelve sub-networks connected hierarchically, each consisting of an interconnected hub-and-spoke architecture. Within each sub-network, edges formed between genes that recapitulate known pathways. Analysis of the expression profiles shows that the cells undergo a phase transition 6-hours post-shift to high light, characterized by core sub-network. The core sub-network is enriched in proteins that (putatively) bind Fe-S clusters and proteins that mediate iron and sulfate homeostasis. At the center of this core is a sulfate permease, suggesting sulfate is rate limiting for cells grown in high light. To validate this novel finding, we demonstrate the limited ability of cell growth in sulfate-depleted medium in high light. This study highlights how understanding the organization of the networks can provide insights into the coordination of physiologic responses. © Mary Ann Liebert, Inc.
  English, Scientific journal
  DOI：https://doi.org/10.1089/omi.2007.4323
  DOI ID：10.1089/omi.2007.4323, ISSN：1536-2310, PubMed ID：17594236, SCOPUS ID：34347352108
• Photon flux density-dependent gene expression in Synechocystis sp PCC 6803 is regulated by a small, redox-responsive, LuxR-type regulator　　　　　　　　　　　　　　　
  Kinu Nakamura; Yukako Hihara
  JOURNAL OF BIOLOGICAL CHEMISTRY, Volume：281, Number：48, First page：36758, Last page：36766, Dec. 2006, [Reviewed], [Corresponding]
  The expression of many cyanobacterial genes is regulated by the redox state of the photosynthetic electron transport chain. However, factors involved in this regulation have not been identified. In this study, we demonstrate that a small LuxR-type regulator in Synechocystis sp. PCC 6803, PedR (Ss10564), senses the activity of photosynthetic electron transport to achieve the photon flux density-dependent transcriptional regulation. PedR is constitutively expressed in Synechocystis cells and exists as a dimer bridged by intermolecular disulfide bond(s). It activates the expression of chlL, chlN, chlB, and slr1957 and represses that of ndhD2, rpe, and the pedR (ssl0564)-sll0296 operon under conditions where the activity of photosynthetic electron transport is low. When the supply of reducing equivalents from photosynthetic electron transport chain increases upon the elevation of photon flux density, PedR is inactivated through its conformational change within 5 min. This mechanism enables transient induction or repression of the target genes in response to sudden changes in light environment. The fact that orthologs of PedR are conserved among all the cyanobacterial genomes sequenced so far indicates that this type of transcriptional regulation is essential for cyanobacteria to acclimate to changing environments.
  AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC, English, Scientific journal
  DOI：https://doi.org/10.1074/jbc.M606797200
  DOI ID：10.1074/jbc.M606797200, ISSN：0021-9258, Web of Science ID：WOS:000242220800033
• Characterization of high-light-responsive promoters of the psaAB genes in Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  Masayuki Muramatsu; Yukako Hihara
  PLANT AND CELL PHYSIOLOGY, Volume：47, Number：7, First page：878, Last page：890, Jul. 2006, [Reviewed], [Corresponding]
  In cyanobacteria, transcription of genes encoding subunits of PS1 is tightly repressed under high-light conditions. To elucidate the molecular mechanism, we examined the promoter architecture of the psaAB genes encoding reaction center subunits of PS1 in a cyanobacterium Synechocystis sp. PCC 6803. Primer extension analysis showed the existence of two promoters, P1 and P2, both of which are responsible for the light intensity-dependent transcription of the psaAB genes. Deletion analysis of the upstream region of psaAB fused to bacterial luciferase reporter genes (luxAB) indicated that the light response of these promoters is achieved in a totally different manner. The cis-element required for the fight response of P1, designated as PE1, was located just upstream of the -35 element of P1 and was comprised of AT-rich sequence showing significant homology to the upstream promoter (UP)-element often found in strong bacterial promoters. PE1 activated P1 under low-light conditions, and the down-regulation of P1 was achieved by rapid inactivation of PE1 upon the shift to high-light conditions. On the other hand, the cis-element required for the light response of P2, designated as HNE2, was located upstream of the P1 region, far from the basal promoter of P2. The down-regulation of P2 seemed to be attained through the negative regulation by HNE2 activated only under high-light conditions. DNA gel mobility shift assays showed that at least five regions in psaAB promoters were responsible for the binding of putative regulatory protein factors.
  OXFORD UNIV PRESS, English, Scientific journal
  DOI：https://doi.org/10.1093/pcp/pcj060
  DOI ID：10.1093/pcp/pcj060, ISSN：0032-0781, Web of Science ID：WOS:000239430500007
• A putative sensor kinase, Hik31, is involved in the response of Synechocystis sp strain PCC 6803 to the presence of glucose　　　　　　　　　　　　　　　
  S Kahlon; K Beeri; H Ohkawa; Y Hihara; O Murik; Suzuki, I; T Ogawa; A Kaplan
  MICROBIOLOGY-SGM, Volume：152, First page：647, Last page：655, Mar. 2006, [Reviewed]
  The reason(s) for glucose sensitivity in certain cyanobacterial strains is poorly understood. Inactivation of genes encoding the putative sensor kinase Hik31 in Synechocystis sp. strain PCC 6803 resulted in a mutant unable to grow in the presence of D-glucose. Sensitivities to D-glucose, its analogue 2-deoxy-D-glucose, and fructose, were alleviated in mutants in which glcP, encoding the glucose transporter, was inactivated. These data indicate that permeation of these substrates is required to inflict cell death, The mutant Delta hik31, and the glucose-sensitive strain of Synechocystis, do not possess glucokinase activity, although a transcript originating from glk, encoding glucokinase, is present. Inactivation of glk led to severe sensitivity to glucose, indicating that the presence of glucose itself, within the cells, inflicted this sensitivity. On the other hand, sensitivity to 2-deoxy-D-glucose was lower in Delta glk, thus distinguishing between the effect of glucose itself and that of its analogue, which, in the absence of glucokinase activity, may not be phosphorylated. Addition of glucose led to a small rise in glucose-6-phosphate dehydrogenase activity in the wild type, but constitutive activity was observed in the Delta hik31 mutant regardless of the presence of glucose. Microarray analyses showed only small changes in the abundance of global transcripts in Synechocystis following glucose addition, but the transcription levels of several genes, including icfG, but not glk, were strongly affected by inactivation of hik31. The mechanism(s) whereby Hik31 is involved in glucose sensing and response is discussed.
  SOC GENERAL MICROBIOLOGY, English, Scientific journal
  DOI：https://doi.org/10.1099/mic.0.28510-0
  DOI ID：10.1099/mic.0.28510-0, ISSN：1350-0872, Web of Science ID：WOS:000236321700008
• The mutant of sll1961, which encodes a putative transcriptional regulator, has a defect in regulation of photosystem stoichiometry in the cyanobacterium Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  T Fujimori; M Higuchi; H Sato; H Aiba; M Muramatsu; Y Hihara; K Sonoike
  PLANT PHYSIOLOGY, Volume：139, Number：1, First page：408, Last page：416, Sep. 2005, [Reviewed]
  In acclimation to changing light environments, photosynthetic organisms modulate the ratio of two photosynthetic reaction centers ( photosystem IIPSI] and photosystem II). One mutant, which could not modulate photosystem stoichiometry upon the shift to high light, was isolated from mutants created by random transposon mutagenesis. Measurements of chlorophyll fluorescence and analysis of the reaction center subunits of PSI through western blotting in this mutant revealed that the content of PSI could not be suppressed under high-light condition. In the mutant, transposon was inserted to the sll1961 gene encoding a putative transcriptional regulator. DNA microarray analysis revealed that the expression of sll1773 was drastically induced in the sll1961 mutant upon exposure to high light for 3 h. Our results demonstrate that a transcriptional regulator, Sll1961, and its possible target proteins, including Sll1773, may be responsible for the regulation of photosystem stoichiometry in response to high light.
  AMER SOC PLANT BIOLOGISTS, English, Scientific journal
  DOI：https://doi.org/10.1104/pp.105.064782
  DOI ID：10.1104/pp.105.064782, ISSN：0032-0889, Web of Science ID：WOS:000231765300038
• PsaK2 subunit in photosystem I is involved in state transition under high light condition in the cyanobacterium Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  T Fujimori; Y Hihara; K Sonoike
  JOURNAL OF BIOLOGICAL CHEMISTRY, Volume：280, Number：23, First page：22191, Last page：22197, Jun. 2005, [Reviewed]
  To avoid the photodamage, cyanobacteria regulate the distribution of light energy absorbed by phycobilisome antenna either to photosystem II or to photosystem I ( PSI) upon high light acclimation by the process so-called state transition. We found that an alternative PSI subunit, PsaK2 (sll0629 gene product), is involved in this process in the cyanobacterium Synechocystis sp. PCC 6803. An examination of the subunit composition of the purified PSI reaction center complexes revealed that PsaK2 subunit was absent in the PSI complexes under low light condition, but was incorporated into the complexes during acclimation to high light. The growth of the psaK2 mutant on solid medium was inhibited under high light condition. We determined the photosynthetic characteristics of the wild type strain and the two mutants, the psaK1 ( ssr0390) mutant and the psaK2 mutant, using pulse amplitude modulation fluorometer. Non-photochemical quenching, which reflects the energy transfer from phycobilisome to PSI in cyanobacteria, was higher in high light grown cells than in low light grown cells, both in the wild type and the psaK1 mutant. However, this change of non-photochemical quenching during acclimation to high light was not observed in the psaK2 mutant. Thus, PsaK2 subunit is involved in the energy transfer from phycobilisome to PSI under high light condition. The role of PsaK2 in state transition under high light condition was also confirmed by chlorophyll fluorescence emission spectra determined at 77 K. The results suggest that PsaK2-dependent state transition is essential for the growth of this cyanobacterium under high light condition.
  AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC, English, Scientific journal
  DOI：https://doi.org/10.1074/jbc.M500369200
  DOI ID：10.1074/jbc.M500369200, ISSN：0021-9258, Web of Science ID：WOS:000229557900064
• A cyanobacterial gene encoding an ortholog of Pirin is induced under stress conditions　　　　　　　　　　　　　　　
  Y Hihara; M Muramatsu; K Nakamura; K Sonoike
  FEBS LETTERS, Volume：574, Number：1-3, First page：101, Last page：105, Sep. 2004, [Reviewed]
  Pirin is a recently identified protein in eukaryotes as a transcription cofactor or as an apoptosis-related protein. Although Pirin is highly conserved from bacteria to human, there have been no reports on prokaryotic Pirin orthologs. We show here that pirA (sll1773) encoding an ortholog of Pirin together with an adjacent gene, pirB (ssl3389), was upregulated under high salinity and some other stress conditions in a cyanobacterium Synechocystis sp. PCC 6803. Induction of the pirAB genes was not related to cell death and disruption of pirA did not affect the gene expression profile. Expression of the pirAB genes was negatively regulated by a LysR family transcriptional regulator encoded by pirR (slr1871) located immediately upstream of pirAB in the divergent direction. DNA microarray analysis indicated that PirR repressed expression of closely located ORFs, slr1870 and mutS (sll1772), in addition to pirAB and pirR itself. (C) 2004 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.
  ELSEVIER SCIENCE BV, English, Scientific journal
  DOI：https://doi.org/10.1016/j.febslet.2004.06.102
  DOI ID：10.1016/j.febslet.2004.06.102, ISSN：0014-5793, Web of Science ID：WOS:000224041600018
• DNA microarray analysis of redox-responsive genes in the genome of the cyanobacterium Synechocystis sp strain PCC 6803　　　　　　　　　　　　　　　
  Y Hihara; K Sonoike; M Kanehisa; M Ikeuchi
  JOURNAL OF BACTERIOLOGY, Volume：185, Number：5, First page：1719, Last page：1725, Mar. 2003, [Reviewed], [Corresponding]
  Whole-genome DNA microarrays were used to evaluate the effect of the redox state of the photosynthetic electron transport chain on gene expression in Synechocystis sp. strain PCC 6803. Two specific inhibitors of electron transport, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), were added to the cultures, and changes in accumulation of transcripts were examined. About 140 genes were highlighted as reproducibly affected by the change in the redox state of the photosynthetic electron transport chain. It was shown that some stress-responsive genes but not photosynthetic genes were under the control of the redox state of the plastoquinone pool in Synechocystis sp. strain PCC 6803.
  AMER SOC MICROBIOLOGY, English, Scientific journal
  DOI：https://doi.org/10.1128/JB.158.5.1719-1725.2003
  DOI ID：10.1128/JB.158.5.1719-1725.2003, ISSN：0021-9193, Web of Science ID：WOS:000181151200029
• Transcriptional regulation of genes encoding subunits of photosystem I during acclimation to high-light conditions in Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  M Muramatsu; Y Hihara
  PLANTA, Volume：216, Number：3, First page：446, Last page：453, Jan. 2003, [Reviewed], [Corresponding]
  Cyanobacteria, algae and plants reduce photosystem contents and modulate photosystem stoichiometry upon acclimation to high-light (HL) conditions to avoid the damage due to excess light energy. In order to elucidate the molecular mechanism of HL acclimation, mRNA levels of genes encoding subunits of photosystems were examined in response to change of photon flux density in the wild-type strain of Synechocystis sp. PCC 6803. Transcript levels and promoter activities of photosystem I (PSI) genes rapidly decreased upon the shift to HL to less than 10% of the initial level within I h, whereas responses of photosystem 11 (PSII) transcript levels were not coordinated. The prompt change in promoter activities of PSI genes, but not PSII genes, seems important for Synechocystis cells to regulate their photosystem contents in response to changes in photon flux density. The mRNA stabilities of PSI genes also decreased during HL incubation. The down-regulation of PSI transcripts under HL did not depend on de novo protein synthesis, contrasting with the requirement of newly synthesized protein factor(s) for the accumulation of PSI transcripts under low light. When gene expression profiles of wild-type cells and a pmgA-disrupted mutant that cannot modulate photosystem stoichiometry under HL were compared, a large increase in the psaAB and psaA transcript levels was observed in the mutant under prolonged exposure to HL for 6 h. Repression of the promoter activity of the psaA gene by a pmgA-dependent mechanism was shown to be essential for the adjustment of photosystem stoichiometry under HL conditions.
  SPRINGER-VERLAG, English, Scientific journal
  DOI：https://doi.org/10.1007/s00425-002-0859-5
  DOI ID：10.1007/s00425-002-0859-5, ISSN：0032-0935, Web of Science ID：WOS:000180820800011
• Physiological significance of the regulation of photosystem stoichiometry upon high light acclimation of Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  K Sonoike; Y Hihara; M Ikeuchi
  PLANT AND CELL PHYSIOLOGY, Volume：42, Number：4, First page：379, Last page：384, Apr. 2001, [Reviewed]
  We characterized the photosynthetic properties of the pmgA mutant of Synechocystis PCC 6803, which cannot change its photosystem stoichiometry under a high-light condition (200 mu mol m(-2) s(-1)), in order to clarify the physiological significance of the regulation of photosystem stoichiometry. We found that (1) PSII activity was inhibited more in wild-type cells on the first day under the high-light conditions than in mutant cells. (2) The growth of the mutants following the initial imposition of high light was faster than that of wild-type cells. (3) However, growth was severely inhibited in the mutants after the third day of exposure to high light, (4) The growth inhibition in the mutants under the extended high-light conditions was reversed by the addition of sublethal concentrations of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), which seemed to mimic photoinhibition of PSII, These results suggest that the main role of adjusting the photosystem stoichiometry with respect to light intensity is not to maintain efficient photosynthesis, but to down regulate electron transfer. Failure to down regulate electron flow leads to cell death under prolonged exposure to high light in this cyanobacterium.
  OXFORD UNIV PRESS, English, Scientific journal
  DOI：https://doi.org/10.1093/pcp/pce046
  DOI ID：10.1093/pcp/pce046, ISSN：0032-0781, Web of Science ID：WOS:000168210000005
• DNA microarray analysis of cyanobacterial gene expression during acclimation to high light　　　　　　　　　　　　　　　
  Y Hihara; A Kamei; M Kanehisa; A Kaplan; M Ikeuchi
  PLANT CELL, Volume：13, Number：4, First page：793, Last page：806, Apr. 2001, [Reviewed], [Corresponding]
  DNA microarrays bearing nearly all of the genes of the unicellular cyanobacterium Synechocystis sp PCC 6803 were used to examine the temporal program of gene expression during acclimation from low to high light intensity. A complete pattern is provided of gene expression during acclimation of a photosynthetic organism to changing light intensity, More than 160 responsive genes were identified and classified into distinct sets. Genes involved in light absorption and photochemical reactions were downregulated within 15 min of exposure to high light intensity, whereas those associated with CO2 fixation and protection from photoinhibition were upregulated. Changes in the expression of genes involved in replication, transcription, and translation, which were induced to support cellular proliferation, occurred later. Several unidentified open reading frames were induced or repressed, The possible involvement of these genes in the acclimation to high light conditions is discussed.
  AMER SOC PLANT PHYSIOLOGISTS, English, Scientific journal
  DOI：https://doi.org/10.1105/tpc.13.4.793
  DOI ID：10.1105/tpc.13.4.793, ISSN：1040-4651, Web of Science ID：WOS:000168219000007
• A novel gene, pmgA, specifically regulates photosystem stoichiometry in the cyanobacterium Synechocystis species PCC 6803 in response to high light　　　　　　　　　　　　　　　
  Y Hihara; K Sonoike; M Ikeuchi
  PLANT PHYSIOLOGY, Volume：117, Number：4, First page：1205, Last page：1216, Aug. 1998, [Reviewed], [Lead]
  Previously, we identified a novel gene, pmgA, as an essential factor to support photomixotrophic growth of Synechocystis species PCC 6803 and reported that a strain in which pmgA was deleted grew better than the wild type under photoautotrophic conditions. To gain insight into the role of pmgA, we investigated the mutant phenotype of pmgA in detail. When low-light-grown (20 mu E m(-2) s(-1)) cells were transferred to high light (HL [200 mu E m(-2) s(-1)]), pmgA mutants failed to respond in the manner typically associated with Synechocystis. Specifically, mutants lost their ability to suppress accumulation of chlorophyll and photosystem I and, consequently, could not modulate photosystem stoichiometry. These phenotypes seem to result in enhanced rates of photosynthesis and growth during short-term exposure to HL. Moreover, mixed-culture experiments clearly demonstrated that loss of pmgA function was selected against during longer-term exposure to HL, suggesting that pmgA is involved in acquisition of resistance to HL stress. Finally, early induction of pmgA expression detected by reverse transcriptase-PCR upon the shift to HL led us to conclude that pmgA is the first gene identified, to our knowledge, as a specific regulatory factor for HL acclimation.
  AMER SOC PLANT PHYSIOLOGISTS, English, Scientific journal
  DOI：https://doi.org/10.1104/pp.117.4.1205
  DOI ID：10.1104/pp.117.4.1205, ISSN：0032-0889, Web of Science ID：WOS:000075485800010
• Toward the elucidation of physiological significance of pmgA-mediated high-light acclimation to adjust photosystem stoichiometry: Effects of the prolonged high-light treatment on pmgA mutants　　　　　　　　　　　　　　　
  Y Hihara; M Ikeuchi
  PHOTOSYNTHESIS: MECHANISMS AND EFFECTS, VOLS I-V, First page：2929, Last page：2932, 1998, [Reviewed], [Lead]
  SPRINGER, English, International conference proceedings
  Web of Science ID：WOS:000085848500687
• Mutation in a novel gene required for photomixotrophic growth leads to enhanced photoautotrophic growth of Synechocystis sp. PCC 6803　　　　　　　　　　　　　　　
  Y Hihara; M Ikeuchi
  PHOTOSYNTHESIS RESEARCH, Volume：53, Number：2-3, First page：243, Last page：252, Sep. 1997, [Reviewed], [Lead]
  In the glucose-tolerant strain of Synechocystis sp. PCC 6803, we found two types of cells with distinct growth properties. Under photoautotrophic conditions at any light intensity, one type gave larger colonies (designated WL) than the other (designated WS). Notably, the WL cells produced much larger colonies than the WS cells at higher light intensity. In contrast, growth of the WL cells was severely suppressed under mixotrophic conditions with glucose and light, while the WS cells grew normally. A gene which could complement the WL phenotype was obtained from a wild-type genomic library. The gene, designated pmgA, coded for a 23 kDa polypeptide of 204 amino acid residues with no apparent homology to known genes. In the WL genome, the base substitution of T for C at position 193 of pmgA caused replacement of Leu with Phe at position 65 of the product. The phenotype of pmgA disruption mutants was similar to that of the WL cells, indicating that the WS cells expressed a functional pmgA product. By direct sequencing of polymerase chain reaction-amplified pmgA from genomic DNA, it was revealed as an example of microevolution that WL had expelled WS from the photoautotrophic culture of wild-type in our laboratory for a year or so. Mixed culture in liquid also demonstrated that the WL cells increased gradually under photoautotrophic conditions, while they decreased rapidly under photomixotrophic conditions. These results suggest that pmgA product is essential for photomixotrophic growth, whereas it represses photoautotrophic growth. To our knowledge, the WL cells and pmgA-disrupted mutants are the first in cyanobacteria, which shows much improved photosynthetic growth than wild-type especially at high light intensity.
  KLUWER ACADEMIC PUBL, English, Scientific journal
  DOI：https://doi.org/10.1023/A:1005879905365
  DOI ID：10.1023/A:1005879905365, ISSN：0166-8595, Web of Science ID：WOS:000070979000016
• The mechanism of the degradation of psaB gene product, one of the photosynthetic reaction center subunits of Photosystem I, upon photoinhibition　　　　　　　　　　　　　　　
  K Sonoike; M Kamo; Y Hihara; T Hiyama; Enami, I
  PHOTOSYNTHESIS RESEARCH, Volume：53, Number：1, First page：55, Last page：63, Jul. 1997, [Reviewed]
  The psaB gene product (PsaB protein), one of the reaction center subunits of Photosystem I (PS I), was specifically degraded by light illumination of spinach thylakoid membranes. The degradation of the protein yielded N-terminal fragments of molecular mass 51 kDa and 45 kDa. The formation of the 51 kDa fragment was i) partially suppressed by the addition of phenylmethylsulfonyl fluoride or 3,4-dichloroisocoumarin, which are inhibitors of serine proteases, and ii) enhanced in the presence of hydrogen peroxide during photoinhibitory treatment, but iii) not detected following hydrogen peroxide treatment in the dark. These results suggest that the hydroxyl radical produced at the reduced iron-sulfur centers in PS I triggers the conformational change of the PS I complex, which allows access of a serine-type protease to PsaB. This results in the formation of the 51 kDa N-terminal fragment, presumably by cleavage on the loop exposed to the stromal side, between putative helices 8 and 9. On the other hand, the formation of the 45 kDa fragment, which was enhanced in the presence of methyl viologen but did not accompany the photoinhibition of PS I, was not affected by the addition of hydrogen peroxide or protease inhibitors. Another fragment of 18 kDa was identified as a C-terminal counterpart of the 45 kDa fragment. N-terminal sequence analysis of the 18 kDa fragment revealed that the cleavage occurred between Ala(500) and Val(501) on the loop exposed to the lumenal side, between putative helices 7 and 8 of the PsaB protein.
  KLUWER ACADEMIC PUBL, English, Scientific journal
  DOI：https://doi.org/10.1023/A:1005852330671
  DOI ID：10.1023/A:1005852330671, ISSN：0166-8595, Web of Science ID：WOS:A1997YD40800007
• Expressed sequence tags in developing anthers of rice (oryza sativa L.)　　　　　　　　　　　　　　　
  Yukako Hihara; Keiko Shoda; Qiang Liu; Chikage Hara; Masaaki Umeda; Kinya Toriyama; Hirofumi Uchimiya
  Plant Biotechnology, Volume：14, Number：1, First page：71, Last page：75, 1997, [Reviewed], [Lead]
  Japanese Society for Plant Cell and Molecular Biology, English, Scientific journal
  DOI：https://doi.org/10.5511/plantbiotechnology.14.71
  DOI ID：10.5511/plantbiotechnology.14.71, ISSN：1347-6114, SCOPUS ID：0009785626
• Isolation and characterization of two cDNA clones for mRNAs that are abundantly expressed in immature anthers of rice (Oryza sativa L.)　　　　　　　　　　　　　　　
  Y Hihara; C Hara; H Uchimiya
  PLANT MOLECULAR BIOLOGY, Volume：30, Number：6, First page：1181, Last page：1193, Mar. 1996, [Reviewed], [Lead]
  The relationship between the length of anthers and the stage of development of microspores was examined in rice (Oryza sativa L. cv. Hayayuki). Anthers of less than or equal to 2 mm and 2.1-2.2 mm in length and those ready to dehiscence were determined to be at the uninucleate, binucleate and trinucleate microspore stage, respectively.
  Two cDNAs (YY1 and YY2), representing genes that are specifically expressed in anthers at the uninucleate microspore stage, were isolated and characterized. YYI cDNA encoded an open reading frame of 95 amino acids. Eight cysteine residues with the potential to form disulfide bridges were present in the amino acid sequence. There was a hydrophobic region at the N-terminus of the putative protein, suggesting that the YY1 protein might be secreted. This cysteine motif and the hydrophobic N-terminus are conserved among products of several anther-specific genes or cDNAs isolated from various plant species. These proteins are thought to form a superfamily of proteins that are confined to anthers. The YY1 transcript was localized in the tapetal cells and the peripheral cells of the vascular bundle. YY2 cDNA encoded an open reading frame of 389 amino acids and the deduced amino acid sequence exhibited substantial homology to that of chalcone synthase. Expression of YY2 mRNA was confined to the tapetal cells. The genes correspond to YY1 and YY2 cDNAs were shown to exist as single copies in the rice genome.
  KLUWER ACADEMIC PUBL, English, Scientific journal
  DOI：https://doi.org/10.1007/BF00019551
  DOI ID：10.1007/BF00019551, ISSN：0167-4412, Web of Science ID：WOS:A1996UX50400009
• NUCLEOTIDE-SEQUENCE OF A RICE ACIDIC RIBOSOMAL PHOSPHOPROTEIN P0 CDNA　　　　　　　　　　　　　　　
  Y HIHARA; M UMEDA; C HARA; K TORIYAMA; H UCHIMIYA
  PLANT PHYSIOLOGY, Volume：105, Number：2, First page：753, Last page：754, Jun. 1994, [Reviewed], [Lead]
  AMER SOC PLANT PHYSIOLOGISTS, English, Scientific journal
  DOI：https://doi.org/10.1104/pp.105.2.753
  DOI ID：10.1104/pp.105.2.753, ISSN：0032-0889, Web of Science ID：WOS:A1994NR44300038

• Analysis of cyAbrB1 Transcription Factors in the Cyanobacterium Synechocystis sp. PCC 6803 using CRISPRi Technology　　　　　　　　　　　　　　　
  菱田温子; 肥後明佳; 松谷峰之介; 荷村(松根)かおり; 渡辺智; 得平茂樹; 日原由香子
  日本植物生理学会年会(Web), Volume：62nd, 2021
  J-Global ID：202102224598369645
• リボレギュレーターを用いたcyabrB2遺伝子の発現制御によるグリコーゲン高生産シアノバクテリアの構築　　　　　　　　　　　　　　　
  上野絹子; 酒井雄大; 生野千佳; 坂本一平; 上野絹子; 酒井雄大; 生野千佳; 坂本一平; 塚越かおり; 日原由香子; 早出広司; 池袋一典; 日原由香子; 早出広司; 池袋一典
  Volume：69th, 2017
  J-Global ID：201702257403107900
• Transcriptional regulation by Sll1961 that modulates photosystem stoichiometry in Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  Mio Tamori; Tamaki Fujimori; Hiroshi Ozaki; Hanayo Sato; Yukako Hihara; Kintake Sonoike
  PLANT AND CELL PHYSIOLOGY, Volume：48, First page：S96, Last page：S96, 2007
  OXFORD UNIV PRESS, English, Summary international conference
  ISSN：0032-0781, Web of Science ID：WOS:000245922700380
• The coordinated high-light response of genes encoding subunits of photosystem I is achieved by AT-rich upstream sequences in the cyanobacterium Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  Yukako Hihara; Masayuki Muramatsu
  PLANT AND CELL PHYSIOLOGY, Volume：48, First page：S127, Last page：S127, 2007
  OXFORD UNIV PRESS, English, Summary international conference
  ISSN：0032-0781, Web of Science ID：WOS:000245922700502
• Functional Analysis of PmgA involved in high-light acclimation in Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  MasMki Muramatsu; Kintake Sonoike; Yukako Hihara
  PLANT AND CELL PHYSIOLOGY, Volume：48, First page：S177, Last page：S177, 2007
  OXFORD UNIV PRESS, English, Summary international conference
  ISSN：0032-0781, Web of Science ID：WOS:000245922701186
• Characterization of putative transcriptional regulators having an AbrB-type DNA binding domain in Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  A Ishii; Y Hihara
  PLANT AND CELL PHYSIOLOGY, Volume：47, First page：S87, Last page：S87, 2006
  OXFORD UNIV PRESS, English, Summary international conference
  ISSN：0032-0781, Web of Science ID：WOS:000236401400348
• The activity of chlorophyll a biosynthesis determines the amount of photosystem I complex under high-light conditions in a cyanobacterium Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  M Muramatsu; K Sonoike; Y Hihara
  PLANT AND CELL PHYSIOLOGY, Volume：47, First page：S87, Last page：S87, 2006
  OXFORD UNIV PRESS, English, Summary international conference
  ISSN：0032-0781, Web of Science ID：WOS:000236401400346
• The sensing mechanism of the redox state of photosynthetic electron transport chain by a small LuxR-type regulator, Ss10564, in Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  K Nakamura; Y Hihara
  PLANT AND CELL PHYSIOLOGY, Volume：47, First page：S87, Last page：S87, 2006
  OXFORD UNIV PRESS, English, Summary international conference
  ISSN：0032-0781, Web of Science ID：WOS:000236401400347
• The redox sensing mechanism of a small LuxR-type regulator, Ss10564, in a cyanobacterium Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  K Nakamura; Y Hihara
  PLANT AND CELL PHYSIOLOGY, Volume：46, First page：S42, Last page：S42, 2005
  OXFORD UNIV PRESS, English, Summary international conference
  ISSN：0032-0781, Web of Science ID：WOS:000228104100167
• Promoter analysis of genes encoding subunits of photosystem I in Synechocystis sp PCC 6803　　　　　　　　　　　　　　　
  M Muramatsu; Y Hihara
  PLANT AND CELL PHYSIOLOGY, Volume：46, First page：S41, Last page：S41, 2005
  OXFORD UNIV PRESS, English, Summary international conference
  ISSN：0032-0781, Web of Science ID：WOS:000228104100164
• Transcriptional regulation of a novel stress-induced operon, pirAB, in a cyanobacterium Synechocystis sp PCC 6803.　　　　　　　　　　　　　　　
  Y Hihara; M Muramatsu; K Nakamura; K Sonoike
  PLANT AND CELL PHYSIOLOGY, Volume：45, First page：S129, Last page：S129, 2004
  OXFORD UNIV PRESS, English, Summary international conference
  ISSN：0032-0781, Web of Science ID：WOS:000220592700508
• PsaK2 subunit of Synechocystissp. PCC6803 is involved in the energy transfer from the phycobilisome to the photosystem I under high light condition　　　　　　　　　　　　　　　
  T Fujimori; K Sonoike; Y Hihara
  PLANT AND CELL PHYSIOLOGY, Volume：43, First page：S170, Last page：S170, 2002
  OXFORD UNIV PRESS, English, Summary international conference
  ISSN：0032-0781, Web of Science ID：WOS:000174726400607
• Search for redox responsive genes in Synechocystis sp. PCC 6803 by using DNA microarrays　　　　　　　　　　　　　　　
  Y Hihara; K Sonoike; M Kanehisa; M Ikeuchi
  PLANT AND CELL PHYSIOLOGY, Volume：43, First page：S178, Last page：S178, 2002
  OXFORD UNIV PRESS, English, Summary international conference
  ISSN：0032-0781, Web of Science ID：WOS:000174726400632
• Regulation mechanism of the photosystem? Content during the acclimation to high light in Synechocystis sp. PCC 6803　　　　　　　　　　　　　　　
  M Muramatsu; Y Hihara
  PLANT AND CELL PHYSIOLOGY, Volume：43, First page：S178, Last page：S178, 2002
  OXFORD UNIV PRESS, English, Summary international conference
  ISSN：0032-0781, Web of Science ID：WOS:000174726400633
• DNA MICROARRAY ANALYSIS OF Symechocystis sp. PCC 6803 UNDER CONDITIONS OF PSII AND PSI LIGHT :　　　　　　　　　　　　　　　
  HIHARA Yukako; IKEUCHI Masahiko
  Plant and cell physiology, Volume：42, First page：s165, 2001
  Japanese Society of Plant Physiologists, English
  ISSN：0032-0781, CiNii Articles ID：110003715790, CiNii Books ID：AA0077511X
• FUNCTIONAL ANALYSIS OF LEXA-LIKE GENE, sll 1626 IN Synechocystis sp. PCC 6803 USING DNA MICROARRAY :　　　　　　　　　　　　　　　
  KAMEI Ayako; HIHARA Yukako; GENG Xiao Xing; IKEUCHI Masahiko
  Plant and cell physiology, Volume：42, First page：s95, 2001
  Japanese Society of Plant Physiologists, English
  ISSN：0032-0781, CiNii Articles ID：110003715513, CiNii Books ID：AA0077511X
• ANALYSIS OF HIGH LIGHT-INDUCED GENES IN CYANOBACTERIUM Synechocystis sp. PCC 6803 USING DNA MICROARRAY :　　　　　　　　　　　　　　　
  HIHARA Yukako; KAMEI Ayako; IKEUCHI Masahiko
  Plant and cell physiology, Volume：41, First page：s74, 2000
  Japanese Society of Plant Physiologists, English
  ISSN：0032-0781, CiNii Articles ID：110003722207, CiNii Books ID：AA0077511X
• SCREENING OF GENES WHICH INTERACT WITH pmgA BY COMPLEMENTATION OF LIGHT/GLUCOSE SENSITIVITY　　　　　　　　　　　　　　　
  HIHARA Yukako; IKEUCHI Masahiko
  Volume：40, First page：s43, Last page：s43, Mar. 1999
  English
  ISSN：0032-0781, CiNii Articles ID：10003757879, CiNii Books ID：AA0077511X
• PHYSIOLOGICAL SIGNIFICANCE OF PHOTOSYSTEM STOICHIOMETRY IN A CYANOBACTERIUM UPON LIGHT ACCLIMATION　　　　　　　　　　　　　　　
  SONOIKE Kintake; HIHARA Yukako; IKEUCHI Masahiko
  Volume：40, First page：s43, Last page：s43, Mar. 1999
  English
  ISSN：0032-0781, CiNii Articles ID：10003757878, CiNii Books ID：AA0077511X
• PHYSIOLOGICAL ROLE AND GENE EXPRESSION OF A NOVEL GENE, pmgA, WHICH IS INVOLVED IN ACCLIMATION TO HIGH LIGHT IN A CYANOBACTERIUM Synechocystis sp. PCC 6803　　　　　　　　　　　　　　　
  HIHARA Yukako; SONOIKE Kintake; IKEUCHI Masahiko
  Volume：39, First page：S27, Last page：S27, May 1998
  English
  ISSN：0032-0781, CiNii Articles ID：10003751571, CiNii Books ID：AA0077511X
• A novel mutant phenotype of pmgA and its involvement in adaptation to high light by changing photosystem II photosystem I stoichiometry in Synechocystis sp. PCC 6803.　　　　　　　　　　　　　　　
  Y Hihara; M Ikeuchi
  PLANT PHYSIOLOGY, Volume：114, Number：3, First page：1035, Last page：1035, Jul. 1997
  AMER SOC PLANT PHYSIOLOGISTS, English, Summary international conference
  ISSN：0032-0889, Web of Science ID：WOS:A1997XL11901067
• The mechanism of degradation of PsaB protein, a reaction center subunit of photosystem I, upon photoinhibition.　　　　　　　　　　　　　　　
  K Sonoike; M Kamo; Y Hihara; T Hiyama; Enami, I
  PLANT PHYSIOLOGY, Volume：114, Number：3, First page：159, Last page：159, Jul. 1997
  AMER SOC PLANT PHYSIOLOGISTS, English, Summary international conference
  ISSN：0032-0889, Web of Science ID：WOS:A1997XL11900203

• Cyanobacteria biotechnology　　　　　　　　　　　　　　　
  Akihito Kawahara; Yukako Hihara, [Contributor], Chapter 11: Biosynthesis of fatty acid derivatives by cyanobacteria: from basics to biofuel production
  Wiley-VCH, Jul. 2021
  English, Total pages：xviii, 542 p.
  ISBN：9783527347148

• 制御系の進化から解き明かす始原的光合成超分子の環境適応原理　　　　　　　　　　　　　　　
  01 Apr. 2023 - 31 Mar. 2028
  Grant amount(Total)：169780000, Direct funding：130600000, Indirect funding：39180000
  Grant number：23H04962
• Photosynthesis ubiquity: Supramolecular complexes and their regulations to enable ph otosynthesis all around the globe　　　　　　　　　　　　　　　
  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Transformative Research Areas (A), 01 Apr. 2023 - 31 Mar. 2028
  Osaka University
  Grant amount(Total)：111280000, Direct funding：85600000, Indirect funding：25680000
  Grant number：23H04957
• シアノバクテリアのパートナースイッチング制御系による環境応答機構の解明　　　　　　　　　　　　　　　
  01 Apr. 2019 - 31 Mar. 2023
  Grant amount(Total)：4290000, Direct funding：3300000, Indirect funding：990000
  Grant number：19K06717
• Elucidation of the mechanism of photosynthetic electron transport-dependent transcriptional regulation mediated by thioredoxin　　　　　　　　　　　　　　　
  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (C), 01 Apr. 2015 - 31 Mar. 2019
  Hihara Yukako, Saitama University
  Grant amount(Total)：4940000, Direct funding：3800000, Indirect funding：1140000
  We performed biochemical and physiological characterization of two transcription factors in Synechocystis sp. PCC 6803, RpaB and Sll1961, which were previously identified as interacting partners of thioredoxin. As for RpaB, we performed genome-wide search of its target genes and analysis of regulatory mechanism of its DNA binding activity dependent on redox state of photosynthetic electron transport chain. As for Sll1961, we identified changes in its thiol-redox state upon interaction with thioredoxin. Moreover, we successfully identified target genes of Sll1961 from the results of RNA-seq analysis.
  Grant number：15K07096
• Elucidation of the mechanism of photosynthetic electron transport-dependent transcriptional regulation　　　　　　　　　　　　　　　
  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (C), 2011 - 2013
  HIHARA Yukako, Saitama University
  Grant amount(Total)：5330000, Direct funding：4100000, Indirect funding：1230000
  Photosynthetic organisms are known to perceive environmental changes as changes in redox state of photosynthetic electron transport chain to start transcriptional regulation. However, information on transcriptional regulators working on the process has been very limited. In this study, we established the new screening system to detect interaction between a transcriptional regulator and the redox-dependent regulatory protein, thioredoxin. We successfully identified five transcriptional regulators as new targets of thioredoxin using this screening system. By characterizing these regulators, the mechanism of photosynthetic electron transport-dependent transcriptional regulation will be elucidated.
  Grant number：23570047
• Mechanism of transcriptional regulation in cyanobacteria upon acclimation to high-light conditions　　　　　　　　　　　　　　　
  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Young Scientists (B), 2008 - 2010
  HIHARA Yukako, Saitama University
  Grant amount(Total)：4160000, Direct funding：3200000, Indirect funding：960000
  Previously, we analyzed the promoter architecture of the psaAB genes encoding reaction center subunits of photosystem I (PSI) in the cyanobacterium Synechocystis sp. PCC 6803. There exist two promoters, P1 and P2, both of which show typical high-light (HL) response of PSI genes ; their activities are high under low-light (LL) conditions but rapidly downregulated upon the shift to HL conditions. In this study, it was shown that a response regulator RpaB binds to multiple high-light regulatory 1 (HLR1) sequences in the upstream region of the psaAB genes. We explored the regulatory role of cis-elements, including these HLR1 sequences on the individual activity of P1 and P2. Our results suggest that cis-elements, including multiple HLR1 sequences, differently regulate the activities of dual promoters of the psaAB genes to achieve the fine-tuning of the gene expression.
  Grant number：20770026
• シアノバクテリアにおける光合成電子伝達鎖のレドックス検知機構の解明　　　　　　　　　　　　　　　
  2005 - 2007
  Grant amount(Total)：3500000, Direct funding：3500000
  Grant number：17770029
• シアノバクテリアの順化応答における光化学系I遺伝子群の転写調節機構の解析　　　　　　　　　　　　　　　
  2002 - 2004
  Grant amount(Total)：3400000, Direct funding：3400000
  Grant number：14740433
• -　　　　　　　　　　　　　　　
  Competitive research funding