Regulation of petB mRNA stability in pea chloroplasts by redox poise

The intensity and quality of light affect the expression of many genes which code for proteins of the photosynthetic apparatus. A number of proteins in pea (Pisum sativum L. cv. Sockerärt de grace) chloroplasts undergo changes in in organello protein synthesis under different redox conditions: different subsets of plastid proteins are synthesised in response to changes in the redox poise. Under equal redox conditions, the photosynthesis‐related psbA and petB mRNAs behave differently. In the presence of various chemical redox reagents the amounts of petB mRNA, which codes for cytochrome b6 of the b6/f complex of photosynthetic membranes, change: they drastically decrease under oxidising conditions, whilst reducing conditions do not cause any significant change. In contrast, psbA mRNA levels are not altered by changes in redox poise. Slot‐blot hybridisation assays show that the decay rate of petB mRNA is affected by different redox potentials. Northern blot analysis indicates that the observed effects are not due to processing events but rather to differential degradation of petB containing sequences. We therefore conclude that the level of petB mRNA in pea chloroplasts is post‐transcriptionally regulated through the redox potential. We hypothesize that redox‐regulated RNA‐binding protein(s) is involved in the selective and regulatable degradation of chloroplast mRNA.