Abstract
In oxygen-evolving photosynthetic organisms, photosystem stoichiometry (PSI/PSII) is modulated in order to optimize electron transport in acclimation to various environmental changes. Under high light condition, PSI/PSII is reduced by decreasing PSI amount to avoid excess electron transport. In the cyanobacterium Synechocystis sp. PCC 6803, pmgA was characterized as a factor responsible for this regulation. This mutant lost the ability to decrease PSI amount and consequently could not modulate PSI/PSII. In the present study, we identified sll1961 and glnA as novel factors for moderate PSI/PSII. These mutants showed impaired regulation of PSI/PSII under high light. The growth of Δsll1961, ΔglnA and ΔpmgA under medium light condition were severely suppressed by addition of glucose to growth medium, which no phenotype was observed under low light. glnA encodes glutamate-ammonia ligase related to the metabolism of nitrogen. These data suggest that PSI/PSII may be regulated by the balance between carbon and nitrogen (C/N ratio).
