Mitochondrial DNA rearrangements associated with mF plasmid integration and plasmodial longevity in Physarum polycephalum

Plasmodial cultures of Physarum polycephalum have defined life spans and undergo a reproducible decline (senescence) before losing the ability to be subcultured. Studies of the mtDNA of a long-lived Physarum strain, which does not undergo senescence, revealed a 7.9-kb insertion in its mtDNA. This insertion is derived from a mitochondrial plasmid which enhances mitochondrial fusion and mtDNA recombination. Four different recombination events are required to convert the parental mtDNA to the form found in the long-lived strain. An additional recombination event, which deletes a 2.4-kb region of the insert from the long-lived strain, has been identified in the mtDNA of a normally senescing strain. These observations imply a mitochondrial involvement in the process of plasmodial senescence and implicate a region of the DNA derived from the mitochondrial plasmid as being necessary for plasmodial longevity. Received: 11 August / 18 November 1997