A pentatricopeptide repeat gene of rice is required for splicing of chloroplast transcripts and RNA editing of ndhA

The pentatricopeptide repeat (PPR) family has been reported to be involved in many post-transcriptional processes, including RNA editing and RNA splicing in both chloroplasts and mitochondria. There are a large number of PPR proteins in plant genome, however, the biological functions of most PPR proteins have not yet been determined. We describe the involvement of a new PPR member (OsPPR4) for the splicing and RNA editing of chloroplast transcripts. The rice P-class PPR protein, OsPPR4, possesses an RNA recognition motif (RRM) and 15 PPR motifs. A retrotransposon (Tos17)-insertion mutant, osppr4, showed an albino phenotype with early seedling lethality. The same results were obtained from plants transformed with an OsPPR4 RNA interference (RNAi) construct. Disruption of OsPPR4 expression led to a strong defect in the splicing of atpF, ndhA, rpl2, and rps12-2 introns and influences the splicing of petB and rps16 introns. In addition, RNA editing of unspliced ndhA transcripts was decreased in the osppr4 line, whereas both spliced and unspliced ndhA were completely edited in WT plants. These results suggest that OsPPR4 is an essential factor for greening in plants and plays a non-redundant role in post-transcriptional regulation of chloroplast genes.