(419e) Synechocystis Sp. PCC 6803: Light Plus Endogenous Regulation Governing Gene Expression Patterns in the Diurnal Cycle

Cyanobacteria are the only photosynthetic prokaryotes with circadian behavior. Based on global transcriptomic data, several cyanobacteria including the strain Synechocystis sp. PCC 6803 have been analyzed thus revealing their oscillatory temporal expression. Synechocystis cells tune the transcriptional level of genes in response to the oscillation of daily diurnal cycle. However, it is still unclear how changes in cellular physiology are coordinated by this cyclic light exposure. In this study, we measured and subsequently analyzed expression patterns of nearly 3,500 genes in Synechocystis 6803 over two consecutive diurnal periods. Based on this analysis, at least 39% of genes with many from major cellular processes including central carbon metabolism, transport, and regulation were found to exhibit oscillating expression profiles. The pattern of gene expression also led to the development of two distinct transcriptional networks of co-regulated oscillatory genes. These networks described how Synechocystis regulated its cellular processes at the end of the dark period so as to make efficient use of light at the early light period. Interestingly, the light peaking genes showed damping patterns even in the middle of the light period which led to the inference not only the presence/absence of light but also endogenous regulation controlled the oscillatory gene expression patterns. We then measured important physiological parameters including glycogen concentration, ATP level, and NADPH/NADP⁺ ratio in two consecutive light/dark cycles and, thereby, analyzed the physiological changes and their correlations with temporal expression patterns. This global transcriptional analysis of Synechocystis sheds light on the global coordination of cellular processes as evidenced in the transcriptional levels of genes.