Redox regulation of PSI nuclear genes through photosynthetic electron flow

Abstract

Light is one of the most important environmental cues that regulate photosynthesis genes. Recently, significance of the redox regulatory system has been suggested in the light regulation of photosynthesis genes, in cyanobacteria, eukaryotic algae, and also in higher plants. In this study, we examined how PSI nuclear genes of Chlamydomonas reinhardtii are regulated in response to light. When Chlamydomonas cells were transferred from the darkness to the light, psaE mRNA level was drastically increased. This light induction was inhibited by the photosynthetic electron transport inhibitors, DCMU and DBMIB, but not by an uncoupler, CCCP. These demonstrate that, in this induction, photosynthetic electron flow plays a pivotal role but photophosphorylation is not necessary. Subsequently, we examined whether redox state of intersystem electron carrier is responsible for this induction. For this sake, we irradiated the Chlamydomonas cells with PSI-light (695nm) or PSII-light (644nm), which makes plastoquinone pool oxidative and reductive, respectively. However, both monochromes induced the psaE mRNA to similar extent, indicating that the redox state of intersystem electron carriers, e.g. plastoquinone pool, is not responsible for this light induction. We are currently examining how the photosynthesis-derived signal causes this response, and several hints obtained by our recent experiments will be discussed.