Molecular analysis of the cms-inducing MAX1 cytoplasm in sunflower.

DNA from different male sterility-inducing sunflower cytoplasms was investigated in order to determine whether the cytoplasmic male sterility-inducing insertion of the PET1 mitochondrial DNA (mtDNA) is present in other cytoplasms. In one of these cytoplasms (MAX1) the mtDNA shows 93% sequence homology to the orfH522 of the PET1 mtDNA, which is probably responsible for cytoplasmic male sterility (cms) in the latter cytoplasm. In contrast to the situation in the PET1 mitochondrial genome, no transcription of the orfH522-related sequence could be detected in lines with the MAX1 cytoplasm. The organization of the MAX1 mtDNA and the mtDNA of a fertile line is shown to be widely different. In the study described here, homology to the mtDNA insertion was also detected in a fertile Helianthus maximiliani population, whereas DNA of four other H. maximiliani populations showed no hybridization signals.