Nuclear and cytoplasmic genes controlling synthesis of variant mitochondrial polypeptides in male-sterile maize

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Abstract
The polypeptides synthesized in vitro by mitochondria isolated from etiolated maize shoots of a number of different nuclear and cytoplasmic genotypes were compared by using polyacrylamide gel electrophoresis. It was previously shown that mitochondria from maize plants carrying the T or C forms of cytoplasmically inherited male sterility (cms-T and cms-C mitochondria) can be distinguished from each other and from the mitochondria of normal (N) plants by the synthesis of a single additional or variant polypeptide species. Using lines that carry the T cytoplasm, and that differ principally in the presence or absence of nuclear restorer alleles that suppress the male-sterile phenotype, it was found that these nuclear genes specifically suppress synthesis of the 13,000 Mr variant polypeptide. A 21,000 Mr polypeptide that is synthesized by N mitochondria is not detectable among the translation products of cms-T mitochondria from either restored or nonrestored lines. Results obtained with a number of lines possessing dominant restorer alleles from different sources indicate that it is the restorer gene at the Rf1 locus that is primarily responsible for regulating synthesis of the 13,000 Mr polypeptide. Mitochondria from lines with the S form of cytoplasmic male sterility (cms-S) were found to synthesize a group of minor polypeptides, ranging in MW from 42,000-88,000, which were not detected in N, cms-T, or cms-C mitochondria. In the case of the S and C forms of male sterility no differences were found between the translation products of mitochondria from restored and nonrestored lines.