ORGANIZATION AND EXPRESSION OF THE MITOCHONDRIAL GENOME IN THE NICOTIANA-SYLVESTRIS CMSII MUTANT

Previous analyses suggested that the Nicotiana sylvestris CMSII mutant carried a large deletion in its mitochondrial genome. Here, we show b y cosmid mapping that the deletion is 60 kb in length and contains sev eral mitochondrial genes or ORFs, including the complex I nad7 gene. H owever, due to the presence of large duplications in the progenitor mi tochondrial genome, the only unique gene that appears to be deleted is nad7. RNA gel blot data confirm the absence of nad7 expression, stron gly suggesting that the molecular basis for the CMSII abnormal phenoty pe, poor growth and male sterility, is the altered complex I structure . The CMSII mitochondrial genome appears to consist essentially of one of two subgenomes resulting from recombination between direct short r epeats. In the progenitor mitochondrial genome both recombination prod ucts are detected by PCR and, reciprocally, the parental fragments are detected at the substoichiometric level in the mutant. The CMSII mtDN A organization has been maintained through six sexual generations.