THE MOLECULAR-BASIS OF CYTOPLASMIC MALE-STERILITY AND FERTILITY RESTORATION

Cytoplasmic male sterility (CMS) is a maternally inherited condition i n which a plant is unable to produce functional pollen. It occurs in m any plant species and is often associated with chimeric mitochondrial open reading frames. In a number of cases, transcripts originating fro m these altered open reading frames are translated into unique protein s that appear to interfere with mitochondrial function and pollen deve lopment. Nuclear restorer (Rf or Fr) genes function to suppress the de leterious effects of CMS-associated mitochondrial abnormalities by div erse 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 occur s in these systems can now be postulated.