Faculty of Biology, Institute of Biology III, University of Freiburg, 79104, Freiburg, Germany.
BIOSS Centre of Biological Signalling Studies, University of Freiburg, 79106, Freiburg, Germany.
Mol Microbiol. 2018 Dec;110(5):847-861. doi: 10.1111/mmi.14129. Epub 2018 Oct 23.
Cyanobacteria exhibit rhythmic gene expression with a period length of 24 hours to adapt to daily environmental changes. In the model organism Synechococcuselongatus PCC 7942, the central oscillator consists of the three proteins KaiA, KaiB and KaiC and utilizes the histidine kinase SasA and its response regulator RpaA as output-signaling pathway. Synechocystis sp. PCC 6803 contains in addition to the canonical kaiAB1C1 gene cluster two further homologs of the kaiB and kaiC genes. Here, we demonstrate that the SasA-RpaA system interacts with the KaiAB1C1 core oscillator only. Interaction with KaiC2 and KaiC3 proteins was not detected, suggesting different signal transduction components for the clock homologs. Inactivation of rpaA in Synechocystis sp. PCC 6803 leads to reduced viability of the mutant in light-dark cycles, especially under mixotrophic growth conditions. Chemoheterotrophic growth of the ∆rpaA strain in the dark was abolished completely. Transcriptomic data revealed that RpaA is mainly involved in the regulation of genes related to CO - acclimation in the light and to carbon metabolism in the dark. Further, our results indicate a link between the circadian clock and phototaxis.
蓝藻表现出 24 小时的节律性基因表达，以适应日常环境变化。在模式生物集胞藻 PCC 7942 中，中央振荡器由三种蛋白质 KaiA、KaiB 和 KaiC 组成，并利用组氨酸激酶 SasA 和其反应调节剂 RpaA 作为输出信号通路。集胞藻 PCC 6803 除了包含规范的 kaiAB1C1 基因簇外，还含有两个 kaiB 和 kaiC 基因的进一步同源物。在这里，我们证明 SasA-RpaA 系统仅与 KaiAB1C1 核心振荡器相互作用。未检测到与 KaiC2 和 KaiC3 蛋白的相互作用，表明时钟同源物具有不同的信号转导成分。在集胞藻 PCC 6803 中敲除 rpaA 会导致突变体在光暗循环中的生存能力降低，特别是在混合营养生长条件下。∆rpaA 菌株在黑暗中的异养生长完全被废除。转录组数据显示，RpaA 主要参与与光照下 CO 适应和黑暗中碳代谢相关基因的调控。此外，我们的结果表明生物钟与趋光性之间存在联系。
