Contiguous RNA editing sites in the mitochondrial nad1 transcript of Arabidopsis thaliana are recognized by different proteins

Pentatricopeptide repeat (PPR) proteins have been identified as site-specific factors for RNA editing in plant organelles. These proteins recognize cis-elements near the editing site. It is unclear how contiguous sites are addressed, and whether one or two factors are required. We here show the PPR MEF25 to be essential for RNA editing at the nad1-308 site in Arabidopsis mitochondria. Another editing site just one nucleotide upstream, nad1-307, is edited normally in mef25 mutant lines. This finding shows that two independent factors recognizing similar cis-elements are involved at these contiguous sites without competing with each other in vivo.