Plant Genome III Conference

IDENTIFYING NUCLEAR FACTORS THAT INFLUENCE MITOCHONDRIAL GENE EXPRESSION AND GENOME STRUCTURE.

Cytoplasmic male sterility in common bean (Phaseolus vulgaris L) is associated with a 3.7kb unique mitochondrial DNA sequence designated pvs. The pvs sequence contains an open reading frame of 239 amino acids (pvs-orf239) that is transcribed in all plant tissues tested. The ORF239 gene product is only detected in developing pollen and ovule tissues of the male sterile plant, and localizes to the callose layer of developing pollen prior to abortion. Introduction of nuclear gene Fr2 by sexual crossing results in loss of pvs-orf239 expression and restoration of normal pollen development. Introduction of nuclear gene Fr results in irreversible loss of the mitochondrial genome segment encompassing pvs and, again, restoration of normal pollen development. Genetic analyses demonstrate that expression of the pvs sequence is necessary for Fr effect, and PCR-based analyses suggest that the pvs loss goes to completion during gametogenesis. These unusual nuclear-mitochondrial genetic interactions provide a valuable opportunity to investigate the molecular basis of mitochondrial regulation in a higher eukaryote. Efforts to localize the Fr gene are now in progress.