RNA editing has been lost in the mitochondrial cox3 and rps13 mRNAs in Asparagales

RNA editing in plant mitochondria alters the RNA sequence by converting C-to-U or U-to-C at a specific site. We investigated the requirement for RNA editing in the complete genomic sequences of the gene encoding the cytochrome oxidase subunit III (cox3) and the ribosomal protein S13 (rps13) in 59 closely related species within the Asparagales and Liliales (monocots). To obtain a comprehensive picture of the degree of variation in editing we explored the non-synonymous RNA editing sites within the newly sequenced cox3 and rps13 genes by a comparative phylogenetic approach. RNA editing is predicted to occur in all the surveyed species, but to different extents. Zero to one non-synonymous editing site is inferred in the cox3 mRNA in species from Amaryllidaceae and Iridaceae. No RNA editing of rps13 mRNAs is required in Amaryllidaceae, because all respective genomic sequences resemble the edited version of the mRNAs of other analysed land plants. The observed absence of cox3 and rps13 RNA editing in Iridaceae and Amaryllidaceae and the striking RNA editing reduction of ccb2 in the latter family is likely generated by recombination and reverse transcription mediated events involving edited mitochondrial transcripts.