Mitochondrial DNA rearrangement associated with fertility restoration and cytoplasmic reversion to fertility in cytoplasmic male sterile Phaseolus vulgaris L.

Restoration of pollen fertility to cytoplasmic male sterile (CMS) Phaseolus vulgaris by a nuclear restorer gene provides a system for studying nuclear-cytoplasmic interactions. Introduction of a nuclear restorer gene to this CMS line of P. vulgaris (CMS-Sprite) results in a mitochondrial genome rearrangement similar to that observed upon spontaneous cytoplasmic reversion to fertility. Three spontaneous heritable cytoplasmic revertants were derived from CMS-Sprite. Five fully fertile restored lines were also produced by using restorer line R-351 (BC(3)F(3) populations). Comparison of the mitochondrial DNA restriction patterns of CMS-Sprite, the three fertile revertants, and the five restored lines revealed loss of a 6.0-kilobase (kb) Pst I fragment in all restored and revertant lines. Southern hybridizations with a 1.3-kb BamHI clone, internal to the 6.0-kb Pst I fragment, as a probe revealed two configurations of 6.0-kb homologous sequences in the sterile cytoplasm; one of the configurations was lost upon reversion or restoration. Mitochondrial DNA rearrangement has thus been observed upon restoration by a nuclear restorer gene in this CMS system.