Plant organelle gene expression: Altered by RNA editing

Transcripts of the higher plant plastid and mitochondrial genomes undergo cytosine-to-uracil RNA editing. Although only about 0.13% of the codons in the entire maize chloroplast genome are altered, plant mitochondrial protein coding genes typically have 3–15% of the codons affected by editing. Incompletely edited transcripts of certain genes are abundant, indicating that plant organelle-transcript editing is a post-transcriptional process. Partially edited transcripts can enter the translation apparatus, resulting in more than one protein product encoded by the same gene. How are cytosine residues selected for editing? Recent data from chloroplast transformants and abnormal mitochondrial genes provide some clues.