The role of coxI-associated repeated sequences in plant mitochondrial DNA rearrangements and radish cytoplasmic male sterility.

The gene coxI, encoding subunit I of mitochondrial cytochrome c oxidase, has been characterized from the normal (fertile) and Ogura (male-sterile) cytoplasms of radish to determine if a previously identified mitochondrial DNA rearrangement, and its associated transcriptional differences, could play a role in Ogura cytoplasmic male sterility (CMS). The normal and Ogura loci are virtually identical for 2.8 kb, including a 527-codon open reading frame whose product is approximately 95% identical to other plant COXI polypeptides. A rearrangement 120 bp 5' to the coding region results in different 5' transcript termini for the two genes. A comparison of several crucifer mitochondrial DNAs indicates that this rearrangement also occurs in the normal radish cytoplasm and is, therefore, not involved in Ogura CMS. Sequences present at the coxI locus belong to at least two different dispersed repeat families, members of which are also associated with other rearranged genes in radish.