A variant mitochondrial DNA arrangement specific toPetunia stable sterile somatic hybrids

We have characterized two related regions of twoPetunia mitochondrial genomes in order to understand how plant mt genomes from a cytoplasmic male sterile (cms) line and a fertile line diverge from one another. Restriction maps of these regions indicate that a sequence arrangement shared by the two genomes adjoins sequences which are not shared at the corresponding locations in the two genomes. A point where the mt genomes from the cms line and the fertile lines diverge from each other was identified and mapped. Previously we had observed that somatic hybrids constructed from the cms and the fertile line contained mt genomes carrying new combinations of parental mtDNA restriction fragments (3). Using the restriction maps of the two related mtDNA regions, a mtDNA arrangement unique to the cms parent could be shown to be present in all 17 stable sterile somatic hybrids tested and none of the 24 stable fertile somatic hybrids tested. This data does not exclude the possibility that additional, as yet unidentified, mtDNA arrangements unique to the cms parent might also be found exclusively in sterile somatic hybrids. Whether or not the sterile parental mtDNA arrangement reported here is functionally related to cms, it apparently segregates with cms in somatic hybrids.