Mutations at three different nuclear loci of Chlamydomonas suppress a defect in chloroplast psbD mRNA accumulation.

In the photosynthetic chloroplast mutant PRB2A of Chlamydomonas reinhardtii the psbD mRNA is unstable. Three strains were isolated, in which the underlying site-directed mutation within the psbD 5' UTR (untranslated region) is suppressed. In all three suppressors, psbD RNA levels and RNA 5' maturation are restored to a varying extent, suggesting a tight coupling of RNA stabilization and 5' processing. Expression of the psbA gene is not compromised in these strains. Genetic crosses revealed that the suppressor mutations affect three unlinked nuclear loci, which may encode new factors involved in psbD gene expression.