POLLEN FERTILITY RESTORATION BY NUCLEAR GENE FR IN CMS COMMON BEAN - AN FR LINKAGE MAP AND THE MODE OF FR ACTION

The Fr gene in common bean, Phaseolus vulgaris L., is a unique gene fo r the study of plant nuclear-mitochondrial interactions because it app ears to directly influence plant mitochondrial genome structure, resul ting in the restoration of pollen fertility in cytoplasmic male steril e plants. This gene action is distinct from other pollen fertility res toration systems characterized to date. As a first step towards the ma p-based cloning of this unusual nuclear gene, we identified RAPD marke rs linked to Fr using bulked segregant analysis of near-isogenic lines . Using DNA gel blot hybridization, we localized the identified RAPD m arkers to a linkage group on the common bean RFLP map and constructed a linkage map of the Fr region using both RAPD markers and RFLP marker s. Analysis of the mode of Fr action with the aid of identified Fr-lin ked DNA markers indicated that Fr functions in a semidominant fashion, showing dosage effect in controlling the dynamics of a heteroplasmic mitochondrial population. We also present our observations on the deve lopmental distinctions, crucial in the accurate mapping of the Fr gene , between spontaneous cytoplasmic reversion and Fr-driven fertility re storation, two phenomena that are phenotypically indistinguishable.