Role of editing in plant mitochondrial transfer RNAs

Abstract Editing in plant mitochondria consists in C to U changes and mainly affects messenger RNAs, thus providing the correct genetic information for the biosynthesis of mitochondrial (mt) proteins. But editing can also affect some of the plant mt tRNAs encoded by the mt genome. In dicots, a C to U editing event corrects a C:A mismatch into a U:A base pair in the acceptor stem of mt tRNA Phe (GAA). In larch mitochondria, three C to U editing events restore U:A base pairs in the acceptor stem, D stem and anticodon stem, respectively, of mt tRNA His (GUG). For both these mt RNA Phe and tRNA His , editing of the precursors is a prerequisite for their processing into mature tRNAs. In potato mt tRNA Cys (GCA), editing converts a C 28 :U 42 mismatch in the anticodon stem into a U 28 :U 42 non-canonical base pair, and reverse transcriptase minisequencing has shown that the mature mt tRNA Cys is fully edited. In the bryophyte Marchantia polymorpha this U residue is encoded in the mt genome and evolutionary studies suggest that restoration of a U 28 residue is necessary when it is not encoded in the gene. However, in vitro studies have shown that neither processing of the precursor, nor aminoacylation of tRNA Cys , requires C to U editing at this position. But sequencing of the purified mt tRNA Cys has shown that Ψ is present at position 28, indicating that C to U editing is a prerequisite for the subsequent isomerization of U into Ψ at position 28.