Photosynthetic electron flow regulates transcription of the psaB gene in pea (Pisum sativum L.) chloroplasts through the redox state of the plastoquinone pool.

Plants respond to changing light conditions by altering the stoichiometry between components of the photosynthetic electron transport chain of chloroplast thylakoids. We measured specific run-on transcription of the chloroplast genes psaB, psbA and rbcL in pea (Pisum sativum L.) seedlings grown under three different conditions of illumination: light selective for photosystem I (PSI-light); light selective for photosystem II (PSII-light); and a combination of PSI- and PSII-light (mixed light, ML). The transcriptional rate of the psaB gene increased under PSII-light and decreased under PSI-light, while the transcriptional rates of the psbA and rbcL genes were affected only in a non-specific way. Similar effects also occurred in plants grown under ML and switched to either PSI- or PSII-light for 4 h. Addition of the inhibitors of photosynthetic electron transport 3-(3,4 dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) influenced psaB transcription in isolated, illuminated chloroplasts: DCMU addition resulted in oxidation of the plastoquinone pool and decreased transcription of psaB; DBMIB addition resulted in reduction of the plastoquinone pool and increased transcription of psaB. The experimental results obtained in vivo and in vitro provide evidence for coupling between the redox state of plastoquinone and the rate of transcription of the psaB gene in pea.