ORGAN-SPECIFIC REDUCTION IN THE ABUNDANCE OF A MITOCHONDRIAL PROTEIN ACCOMPANIES FERTILITY RESTORATION IN CYTOPLASMIC MALE-STERILE RADISH

The mitochondrial DNA of plants containing the male sterility-causing Ogura cytoplasm of radish contain a novel gene, orf138, that is transc ribed as part of a bicistronic mRNA. Genetic studies have previously l inked male sterility with the orf138 locus. To determine if orf138 is expressed at the protein level, and investigate the effect of fertilit y restoration on ORF138 levels, we have raised antibodies to an ORF138 -glutathione S-transferase fusion protein. Anti-ORF138 antibodies dete ct a 20 kDa protein that is associated with the mitochondrial membrane of sterile Ogura radish plants. Nuclear restoration is accompanied by a dramatic reduction in the amount of this protein in mitochondria of flowers and leaves, but not roots of fertile Ogura radish plants. The presence or absence of fertility restoration genes has no detectable effect on the size, abundance, or RNA editing patterns of orf138 trans cripts. These results support genetic studies that have implicated orf 138 in Ogura cytoplasmic male sterility and suggest that the restorer genes may be affecting either the translation or stability of ORF138.