Identification of new pentatricopeptide repeat proteins, MREF1 and 2, involved in mitochondrial RNA editing, using computational target RNA prediction

C-to-U RNA editing has been widely observed in mitochondrial and plastid RNAs in plants. The editing sites are known to be recognized by pentatricopeptide repeat (PPR) proteins, which belong to one of the largest protein families in vascular plants. PPR proteins are sequence-specific RNA-binding proteins that participate in various steps of organelle RNA metabolism, such as cleavage, stabilization, splicing, translation, and editing. Elucidating the underlying mechanisms of sequence-specific RNA recognition by PPR proteins expanded our understanding of the role of PPR proteins in plant organellar RNA editing and enabled the computational prediction of target RNA-editing sites for PPR proteins of interest. Combining computational prediction and experimental verification, we identified three new PPR proteins involved in mitochondrial RNA editing: At1g56570, known as PGN for RNA editing of nad6_leader_-73 and cox2_742, At4g04370 for RNA editing of nad5_242, and At2g41080 for atp1_1292. Therefore, At4g04370 and At2g41080 were designated as mitochondrial RNA-editing factor 1 (MREF1) and MREF2, respectively. This study supports the use of computational prediction in establishing connections between PPR proteins and specific RNA-editing sites, which are important for maintaining various physiological processes, such as plant development, embryogenesis, and biotic-and abiotic-stress responses.