A nuclear mutation affects the synthesis of the chloroplast psbA gene production Chlamydomonas reinhardtii.

The effect of the nuclear mutation F34 on the synthesis of chloroplast-encoded photosystem II (PSII) polypeptides has been controversial. While we had concluded that the synthesis of the psbC gene product (P6) was specifically deficient in this mutant, another laboratory has found that the synthesis of the psbA gene product, the herbicide-binding protein D1, was primarily affected. These conflicting results were re-analyzed through genetic and biochemical characterization of the different strains used by the two laboratories in question. While the strain used in our laboratory carries the single F34 mutation responsible for the deficiency of P6, the other strain contains three nuclear mutations: the original F34 mutation, a suppressor mutation of F34 and a second PSII mutation, F35. Mutation F35 does not affect P6 synthesis but is responsible for the deficiency in the synthesis of the herbicide-binding protein D1. Furthermore, since both F34 and F35 mutant strains accumulate wild-type levels of psbC and psbA transcripts, we show that these nuclear mutations affect nuclear genes whose products are involved in the expression of psbC or psbA at a post-transcriptional level.