C-to-U and U-to-C: RNA editing in plant organelles and beyond


 The genomes in the two energy-converting organelles of plant cells, chloroplasts and mitochondria, contain numerous “errors” that are corrected at the level of RNA transcript copies. The genes encoded in the two endosymbiotic organelles would not function properly if their transcripts would not be altered by site-specific cytidine-to-uridine exchanges and by additional reverse U-to-C exchanges in hornworts, lycophytes and ferns. These peculiar processes of plant RNA editing, re-establishing genetic information that could alternatively be present at the organelle genome level, has spurred much research over more than 30 years. Lately this has revealed numerous interesting insights, notably on the biochemical machinery identifying specific pyrimidine nucleobases for conversion from C to U and vice versa. Here, I will summarize prominent research findings that have lately contributed to our better understanding of these phenomena introducing an added layer of information processing in plant cells. Some of this recent progress is based on the successful functional expression of plant RNA editing factors in bacteria and mammalian cells. These research approaches have recapitulated natural processes of horizontal gene transfer through which some protist lineages seem to have acquired plant RNA editing factors and adapted them functionally for their own purposes.