| Abstract : |
Circadian rhythms are of major biological importance to most organisms and are important for proper timing of cellular events in coordination with daily light-dark changes. The photosynthetic cyanobacterium Synechococcus elongatus is a model organism for the circadian clock. Currently, there is interest in photosynthetic organisms to produce biofuel, pharmaceutical products, and industrial chemicals. On an industrial scale, photosynthetic organisms are grown outdoors, which are subject to light-dark cycles that impact product yields through alterations in metabolism. Experiments have not been conducted on how the clock regulates glycogen − an energy storage molecule − in these organisms and how environmental cycles integrate with clock control. Glycogen degradation is important for night-time survival and glycogen content is regulated by the circadian clock. The transcriptional regulator RpaA is the primary output from the S. elongatus circadian clock and has over 170 gene targets. Mutants in rpaA display poor glycogen degradation at night and are sensitive to light-dark cycles. We hypothesize that these phenotypes are due to the rpaA mutant?s mis-regulation of glycogen metabolic genes, rather than a direct effect of the lack of RpaA protein. To test this hypothesis we have cloned genes that are known RpaA transcriptional targets, have decreased expression in an rpaA mutant, and are important in glycogen metabolism. We expressed these genes in an rpaA mutant background using the highly expressed psbAI promoter. Elucidating how the circadian clock controls glycogen metabolism in environmentally relevant light-dark cycles is important if we are to optimize biomolecule production on a mass scale. |