RNA Editing in Plant Organelles

RNA editing is a post-transcriptional process that occurs in the organelles of vascular plants and changes the coding information in mRNAs. In higher plants, specific cytidine residues are converted to uridine residues in chloroplasts or in mitochondrial transcripts, and this process frequently re-specifies the codon to direct the incorporation of a non-synonymous amino acid residue. The amino acid incorporated by the edited codon is typically the evolutionarily conserved amino acid at that position, and the unedited codon would direct the incorporation of a radical amino acid substitution. In several instances, expression of an unedited version of a transcript that requires editing results in a mutant phenotype; thus, demonstrating a genetic requirement for RNA editing in gene expression. Analysis of RNA editing in transgenic chloroplasts and development of in vitro editing systems suggest that RNA editing site recognition may occur by specific trans-acting protein factors. In addition, recent results demonstrate that a single trans-acting factor may recognize several editing sites with sequence similarity and editing site “clusters” may exist.