Increased mRNA accumulation in a psaB frame-shift mutant of Chlamydomonas reinhardtii suggests a role for translation in psaB mRNA stability.

Regulation of mRNA stability is an important control in the differential accumulation of chloroplast mRNAs that occurs in response to developmental and environmental signals. The mechanism by which differential mRNA accumulation is achieved is unknown. We have examined mRNA accumulation in a chloroplast mutant of Chlamydomonas reinhardtii previously shown to contain a single AT base-pair deletion in the psaB gene. In this mutant, steady-state levels of mRNA from psaB accumulate to a level more than twice that found in cells that have had the mutation repaired by chloroplast transformation. In vivo pulse labeling of RNA shows that increased mRNA accumulation is due to a more stable transcript. We show that inhibitors of chloroplast protein synthesis also increase mRNA accumulation from the psaB gene. The results are consistent with a link between polysome association, active synthesis and stability of psaB transcripts.