Pentatricopeptide Repeat Proteins with the DYW Motif Have Distinct Molecular Functions in RNA Editing and RNA Cleavage in Arabidopsis Chloroplasts

The plant-specific DYW subclass of pentatricopeptide repeat proteins has been postulated to be involved in RNA editing oforganelle transcripts. We discovered that the DYW proteins CHLORORESPIRATORY REDUCTION22 (CRR22) and CRR28 arerequired for editing of multiple plastid transcripts but that their DYW motifs are dispensable for editing activity in vivo.Replacement of the DYW motifs of CRR22 and CRR28 by that of CRR2, which has been shown to be capable ofendonucleolytic cleavage, blocks the editing activity of both proteins. In return, the DYW motifs of neither CRR22 nor CRR28can functionally replace that of CRR2. We propose that different DYW family members have acquired distinct functions inthe divergent processes of RNA maturation, including RNA cleavage and RNA editing.