Genetic manipulation to overexpress rpaA altered photosynthetic electron transport in Synechocystis sp. PCC 6803.

Cyanobacteria are a group of prokaryotic organisms that perform oxygenic photosynthesis using a similar photosynthetic apparatus as is used in higher plants and eukaryotic algae. Cyanobacteria are also known to have a circadian rhythm. Here, we evaluated the effects on photosynthesis caused by the genetic manipulation of RpaA, which is a response regulator of a two-component regulatory system responsible for the signal output from circadian clocks. Using the unicellular cyanobacterium Synechocystis sp. PCC 6803, photosynthetic activities and transcript levels of photosystem I and photosystems II in the rpaA-overexpressing strain were measured, and it was found that the parameters, such as F/F, F'/F', qP, and ϕII, obtained from chlorophyll fluorescence analysis were decreased by rpaA overexpression. These results suggest that rpaA overexpression modified photosynthetic electron transport under normal light conditions. Thus, we demonstrated that RpaA regulates photosynthesis in cyanobacteria and can be a potential target of photosynthetic engineering in this cyanobacterium.