The tobacco apocytochrome b gene predicts sensitivity to the respiratory inhibitors antimycin A and myxothiazol

The potential for use of the cytochrome-pathway electron-transfer inhibitor s antimycin A and myxothiazol in the selection of plant mitochondrial genom e transformants was investigated. The net growth of Nicotiana tabacum L. (t obacco) suspension-culture cells was reduced by these inhibitors, but compl ete repression of cell growth occurred only in the presence of both cytochr ome and alternative electron-transfer-pathway inhibitors. Antimycin A and m yxothiazol bind to and block electron transfer through different sites in t he cytochrome b (COB) subunit of the mitochondrial bcl respiratory complex (complex III). The nucleotide sequence of the tobacco cob gene was determin ed and found to predict highly conserved glycine and phenylalanine residues that are associated with sensitivity to antimycin A and myxothiazol, respe ctively. These residues are altered by mutations that confer resistance to antimycin A or myxothiazol in diverse organisms. Tobacco cob cDNA clones we re constructed and sequenced, revealing eight full and 11 partial RNA-editi ng sites. RNA editing did not: however, alter codons for the conserved glyc ine and phenylalanine residues associated with sensitivity to the respirato ry inhibitors. Antimycin A or myxothiazol, in conjunction with a modified c ob gene, may therefore be useful in the selection of tobacco cells carrying a genetically transformed mitochondrial genome.