Sugar catabolism regulated by light- and nitrogen-status in the cyanobacterium Synechocystis sp. PCC 6803.

In photosynthetic organisms, sugar catabolic pathways, such as glycolysis and the oxidative pentose phosphate pathway, are indispensable for survival in the absence of light. In this review, we will focus on the regulation of sugar catabolic gene expression in cyanobacteria, especially that of Synechocystis sp. PCC 6803 (Synechocystis). In Synechocystis, the expression of sugar catabolic genes is activated by the shift from light-to-dark and diurnally during the evening, and positively regulated by a histidine kinase, Hik8, and a RNA polymerase sigma factor, SigE. Mutants for these regulators are defective for survival in the dark and unable to carry out light-activated heterotrophic growth. It has also been shown that transcripts of sugar catabolic genes are increased by nitrogen depletion and a global nitrogen regulator NtcA is essential for the induction. These results indicate a regulatory connection between nitrogen status and sugar catabolism in cyanobacteria.