Rearrangements in the Physarum polycephalum mitochondrial genome associated with a transition from linear mF-mtDNA recombinants to circular molecules.

Although mitochondrial DNA (mtDNA) is transmitted to progeny from one parent only in Physarum polycephalum, the mtDNAs of progeny of mF+ plasmodia vary in structure. To clarify the mechanisms associated with the mitochondrial plasmid mF that generate mtDNA polymorphisms, 91 progeny of four strains (KM88 x JE8, KM88 x TU111, KM88 x NG111, Je90) were investigated using RFLP analysis, PCR, and pulse-field gel electrophoresis (PFGE). Nine mtDNA rearrangement types were found, with rearrangements occurring exclusively in the mF regions. PFGE revealed that, in the groups containing rearranged mtDNA, the linear mF-mtDNA recombinants had recircularized. Sequencing the rearranged region of one of the progeny suggested that the mF plasmid and the mtDNA recombine primarily at the ID sequences, linearizing the circular mtDNA. Recombination between the terminal region of the mF plasmid and a region about 1 kbp upstream of the mitochondrial/plasmid ID sequence results in a rearranged circular mtDNA, with variations caused by differences in the secondary recombination region.