ABSTRACT
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 Fv/Fm, Fv'/Fm', qP, and ÏII, 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.
Subject(s)
Bacterial Proteins/genetics , Gene Transfer Techniques , Photosynthesis/genetics , Synechocystis/genetics , Bacterial Proteins/metabolism , Chlorophyll/metabolism , Electron Transport/genetics , Gene Expression Regulation, Bacterial , Light , Organisms, Genetically Modified , Photosystem I Protein Complex , Photosystem II Protein Complex/metabolism , Synechocystis/metabolism , Transformation, BacterialABSTRACT
Cyanobacteria perform oxygenic photosynthesis, and the maintenance of photosynthetic electron transport chains is indispensable to their survival in various environmental conditions. Photosynthetic electron transport in cyanobacteria can be studied through genetic analysis because of the natural competence of cyanobacteria. We here show that a strain overexpressing hik8, a histidine kinase gene related to the circadian clock, exhibits an altered photosynthetic electron transport chain in the unicellular cyanobacterium Synechocystis sp. PCC 6803. Respiratory activity was down-regulated under nitrogen-replete conditions. Photosynthetic activity was slightly lower in the hik8-overexpressing strain than in the wild-type after nitrogen depletion, and the values of photosynthetic parameters were altered by hik8 overexpression under nitrogen-replete and nitrogen-depleted conditions. Transcripts of genes encoding Photosystem I and II were increased by hik8 overexpression under nitrogen-replete conditions. Nitrogen starvation triggers increase in amino acids but the magnitude of the increase in several amino acids was diminished by hik8 overexpression. These genetic data indicate that Hik8 regulates the photosynthetic electron transport, which in turn alters primary metabolism during nitrogen starvation in this cyanobacterium.
