REGULATION OF PETB MESSENGER-RNA 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. Sockerart de grace) chloroplasts undergo changes in in organello protein synthesis under different red ox conditions: different subsets of plastid proteins are synthesised i n response to changes in the redox poise. Under equal redox conditions , the photosynthesis-related psbA and petB mRNAs behave differently. I n the presence of various chemical redox reagents the amounts of petB mRNA, which codes for cytochrome b(6) Of the b(6)/f complex of photosy nthetic membranes, change: they drastically decrease under oxidising c onditions, whilst reducing conditions do not cause any significant cha nge. In contrast, psbA mRNA levels are not altered by changes in redox poise. Slot-blot hybridisation assays show that the decay rate of pet B mRNA is affected by different redox potentials. Northern blot analys is indicates that the observed effects are not due to processing event s 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 h ypothesize that redox-regulated RNA-binding protein(s) is involved in the selective and regulatable degradation of chloroplast mRNA.