期刊名称:Proceedings of the National Academy of Sciences
印刷版ISSN:0027-8424
电子版ISSN:1091-6490
出版年度:2015
卷号:112
期号:26
页码:8082-8087
DOI:10.1073/pnas.1504228112
语种:English
出版社:The National Academy of Sciences of the United States of America
摘要:SignificanceCyanobacteria have sophisticated photosensory systems to adapt to ambient-light conditions to improve oxygenic photosynthesis efficiency. Their genomes contain many genes encoding cyanobacteriochromes (CBCRs), which are the photoreceptors of light-signaling pathways. Although the photochemical properties of many CBCRs have been characterized, whether and how multiple photoreceptors work together are unknown. Herein we describe how three CBCRs work together in a light color-sensitive manner to regulate cyanobacterial cell aggregation. The three CBCRs have distinguishable, but congruent, light color-dependent c-di-GMP synthetic and/or degrading activities. Ours is the first report, to our knowledge, concerning synchronization of distinctive CBCR activities, which emphasizes the underlying need for CBCR photoreceptors with diverse activities. Cyanobacteriochromes (CBCRs) are cyanobacterial photoreceptors that have diverse spectral properties and domain compositions. Although large numbers of CBCR genes exist in cyanobacterial genomes, no studies have assessed whether multiple CBCRs work together. We recently showed that the diguanylate cyclase (DGC) activity of the CBCR SesA from Thermosynechococcus elongatus is activated by blue-light irradiation and that, when irradiated, SesA, via its product cyclic dimeric GMP (c-di-GMP), induces aggregation of Thermosynechococcus vulcanus cells at a temperature that is suboptimum for single-cell viability. For this report, we first characterize the photobiochemical properties of two additional CBCRs, SesB and SesC. Blue/teal light-responsive SesB has only c-di-GMP phosphodiesterase (PDE) activity, which is up-regulated by teal light and GTP. Blue/green light-responsive SesC has DGC and PDE activities. Its DGC activity is enhanced by blue light, whereas its PDE activity is enhanced by green light. A {Delta}sesB mutant cannot suppress cell aggregation under teal-green light. A {Delta}sesC mutant shows a less sensitive cell-aggregation response to ambient light. {Delta}sesA/{Delta}sesB/{Delta}sesC shows partial cell aggregation, which is accompanied by the loss of color dependency, implying that a nonphotoresponsive DGC(s) producing c-di-GMP can also induce the aggregation. The results suggest that SesB enhances the light color dependency of cell aggregation by degrading c-di-GMP, is particularly effective under teal light, and, therefore, seems to counteract the induction of cell aggregation by SesA. In addition, SesC seems to improve signaling specificity as an auxiliary backup to SesA/SesB activities. The coordinated action of these three CBCRs highlights why so many different CBCRs exist.
关键词:photoreceptors ; signal transduction ; light sensing ; second messenger ; sessility