Regulation of psbA and psaE Expression by Light Quality in Synechocystis Species PCC 6803. A Redox Control Mechanism

Abstract

Abstract We investigated the influence of light of different wavelengths on the expression of the psbA gene, which encodes the D1 protein of the photosystem II and the psaE gene, which encodes the subunit Psa-E of the photosystem I, inSynechocystis sp PCC 6803. In an attempt to differentiate between a light-sensory and a redox-sensory signaling processes, the effect of orange, blue, and far-red light was studied in the wild-type and in a phycobilisome-less mutant. Transferring wild-type cells from one type of illumination to another induced changes in the redox state of the electron transport chain and inpsbA and psaE expression. Blue and far-red lights (which are preferentially absorbed by the photosystem I) induced an accumulation of psbA transcripts and a decrease of the psaE mRNA level. In contrast, orange light (which is preferentially absorbed by the photosystem II) induced a large accumulation of psaE transcripts and a decrease of psbA mRNA level. Transferring mutant cells from blue to orange light (or vice versa) had no effect either on the redox state of the electron transport chain or on the levels of psbAand psaE mRNAs. Thus, light quality seems to regulate expression of these genes via a redox sensory mechanism inSynechocystis sp PCC 6803 cells. Our data suggest that the redox state of one of the electron carriers between the plastoquinone pool and the photosystem I has opposite influences onpsbA and psaE expression. Its reduction induces accumulation of psaE transcripts, and its oxidation induces accumulation of psbA mRNAs.