Diverged molecular function of pentatricopeptide repeat proteins with the DYW motif in chloroplasts

Abstract

In RNA editing, specific cytidine nucleotides are frequently altered to uridine in RNA in plant organelles. The plant-specific PPR proteins with the DYW motif (DYW subclass) have been postulated to be involved in RNA editing of organelle transcripts. We discovered that the DYW proteins CRR22 and CRR28 are required for RNA editing of several specific sites in plastids, but their DYW motifs are dispensable for editing activity in vivo. Replacement of the DYW motifs of CRR22 and CRR28 by that of CRR2, shown to be capable of endonucleolytic cleavage, blocks the editing activity of both proteins. In return, the DYW motifs of neither CRR22 nor CRR28 can be functionally replaced by that of CRR2. Based on these results, we discuss the evolution of the DYW subclass and RNA editing in plant organelles.