Required for specific RNA editing events in chloroplasts and stabilizes specific chloroplast mRNAs (PubMed:19297624). ADP-ribosylated by the Pseudomonas syringae type III effector HopU1. ADP-ribosylation reduces the ability of the protein to bind RNA. No visible phenotype under normal growth conditions, but mutant plants exhibit multiple specific editing defects in chloroplast transcripts.