HCF5, A NUCLEAR PHOTOSYNTHETIC ELECTRON-TRANSPORT MUTANT OF ARABIDOPSIS-THALIANA WITH A PLEIOTROPIC EFFECT ON CHLOROPLAST GENE-EXPRESSION

A photosynthetic mutant of Arabidopsis thaliana, hcf5, was isolated by screening M-2 seedlings for high chlorophyll fluorescence. Thylakoid morphology was strikingly abnormal, with large grana stacks and almost no stroma lamellae. Fluorescence induction kinetics, activity assays, and immunoblotting showed that photosystem II was absent. Polypeptide s of the photosystem I complex, the Cyt b(6)/complex, coupling factor, and the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygen ase were also severely depleted. However, the nuclear-encoded chloroph yll a/b light-harvesting complex polypeptides were unaffected. The rbc L transcript was present at very low levels, the pattern of transcript s from the polycistronic psbB-psbH-petB-petD operon was abnormal, and the mature psbH message was almost completely lacking. This suggests t hat the hcf5 locus may encode a product required for the correct expre ssion of several chloroplast genes.