RNA editing mutants as surrogates for mitochondrial SNP mutants

In terrestrial plants, RNA editing converts specific cytidines to uridines in mitochondrial and plastidic transcripts. Most of these events appear to be important for proper function of organellar encoded genes, since translated proteins from edited mRNAs show higher similarity with evolutionary conserved polypeptide sequences. So far about 100 nuclear encoded proteins have been characterized as RNA editing factors in plant organelles. Respective RNA editing mutants reduce or lose editing activity at different sites and display various macroscopic phenotypes from pale or albino in the case of chloroplasts to growth retardation or even embryonic lethality. Therefore, RNA editing mutants can be a useful resource of surrogate mutants for organellar encoded genes, especially for mitochondrially encoded genes that it is so far unfeasible to manipulate. However, connections between RNA editing defects and observed phenotypes in the mutants are often hard to elucidate, since RNA editing factors often target multiple RNA sites in different genes simultaneously. In this review article, we summarize the physiological aspects of respective RNA editing mutants and discuss them as surrogate mutants for functional analysis of mitochondrially encoded genes.