title: 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.
abstract: 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.
authors.affiliation: Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan.
authors.forename: Taro
authors.initials: T
authors.lastname: Kadowaki
authors.affiliation: Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan.
authors.forename: Ryuta
authors.initials: R
authors.lastname: Nagayama
authors.affiliation: University of Freiburg, Institute of Biology III, Schänzlestr. 1, D-79104 Freiburg, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Georg
authors.affiliation: Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan.
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Nishiyama
authors.affiliation: University of Freiburg, Institute of Biology III, Schänzlestr. 1, D-79104 Freiburg, Germany.
authors.forename: Annegret
authors.initials: A
authors.lastname: Wilde
authors.affiliation: University of Freiburg, Institute of Biology III, Schänzlestr. 1, D-79104 Freiburg, Germany.
authors.forename: Wolfgang R
authors.initials: WR
authors.lastname: Hess
authors.affiliation: Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan hihara@molbiol.saitama-u.ac.jp.
authors.forename: Yukako
authors.initials: Y
authors.lastname: Hihara
mesh_terms: D000064:Acclimatization / Q000235:genetics; D001665:Binding Sites; D025461:Feedback, Physiological; D015964:Gene Expression Regulation, Bacterial; D008027:Light; D045331:Photosystem I Protein Complex / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012329:RNA, Bacterial / Q000235:genetics / Q000378:metabolism; D046939:Synechocystis / Q000235:genetics / Q000502:physiology*
chemical_list: D045331:Photosystem I Protein Complex; D012329:RNA, Bacterial
keywords: Cyanobacteria; High-light acclimation; Photosystem I; Post-transcriptional regulation; Small RNA; Transcriptional regulation