RNA Editing to Rescue Plants from Organelle Genome Mutations

Plant organelle genomes cope with T to C mutations by post-transcriptional correction of Cs to Us by RNA editing.  The proper C must be selected for editing so as not to disrupt expression of correctly encoded codons. Individual members of the large nuclear-encoded pentatricopeptide repeat (PPR)-motif containing family are responsible for site-specific recognition of cis-elements 5’ to C targets of editing.  Some members of this family contain C-terminal extensions termed the DYW domain that carry putative cytidine deaminase motifs which, when mutated, disrupt RNA editing. The plant RNA editosome is a small RNA/protein complex less than 400 kD in size. Affinity purification followed by mass spectrometric analysis of protein content has led to the identification of three additional nuclear-encoded proteins required for editing in either chloroplasts or mitochondria: the RIP, ORRM, and OZ families.  Mutations of genes encoding individual members of these families affect efficiency of editing of some, often many, but not all C targets.  Thus, editosomes are diverse in composition, not only between different organelles, but within the same organelle.  This flexibility in editosome constitution may have evolved in order to deal with new T to C mutations as they arose.