RNA Editing by Base Conversion in Plant Organellar RNAs

Awareness of the RNA editing process in plants grew gradually. The first discrepancies in nucleotide identities between mRNA and DNA were noted as the appearance of thymidylates in the sequence ladders of cDNAs at positions of cytidylates in the genomic sequence. The existence of RNA editing in plant mitochondria resolved initial problems with nonconserved amino acid codons found in the plant gene sequences. A schematic view of RNA editing in plant organelles is discussed in this chapter. In analogy to the analysis of RNA editing in other systems, the chapter also presents a separate discussion of the process in plant organelles, that is, the biochemistry of the modification of nucleotide identity and the specificity determinants, which decide where editing should occur. Evolutionary selection and streamlining should have eliminated RNA editing, unless there is some advantage to be gained for the genetic system. RNA editing significantly increases the efforts required to analyze gene expression in plant organelles. RNA editing in plastids and mitochondria also complicates in vitro manipulation of organellar genes and expression. The similarity of the RNA editing processes in plastids and mitochondria of a given plant cell suggests a common evolution of the respective editing processes and very similar mechanistic features.