The molecular basis of cytoplasmic male sterility and fertility restoration

Cytoplasmic male sterility (CMS) is a maternally inherited condition in which a plant is unable to produce functional pollen. It occurs in many plant species and is often associated with chimeric mitochondrial open reading frames. In a number of cases, transcripts originating from these altered open reading frames are translated into unique proteins that appear to interfere with mitochondrial function and pollen development. Nuclear restorer (Rf or Fr) genes function to suppress the deleterious effects of CMS-associated mitochondrial abnormalities by diverse mechanisms. There are now several well-characterized CMS systems, for which the mitochondrial sequences thought to be responsible have been described. Possible mechanisms by which nuclear restoration occurs in these systems can now be postulated.