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

Abstract

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.

RNA editing is absent in a single mitochondrial gene ofDidymium iridis

“…It should be noted that ORFs are present in both P. polycephalum (Takano et al 2001) and D. iridis mitochondrial genomes (Buber and Silliker unpubl); however none of the ORFs encode typical mitochondrial genes. In P. polycephalum there is evidence that some of the ORFs are likely the result of recombination between the mitochondrial genome and a linear mitochondrial plasmid (Takano et al 1992, Nakagawa et al 1998, Nomura et al 2005. The lack of RNA editing in these ORFs might be due to their acquisition after extensive RNA editing evolved in the typical mitochondrial genes.…”

The mitochondrial plasmid pAL2-1 reduces calorie restriction mediated life span extension in the filamentous fungus Podospora anserina

“…The observed effects of these and similar plasmids obviously depend on whether or not the host senesces. For example, in the slime mold Physarum polycephalum that normally senesces, integration of a linear mitochondrial plasmid (Nakagawa et al, 1998) has been associated with longevity but not senescence. Despite the fact that plasmid integration has been associated with longevity both in Podospora and Physarum, overall the plasmids are more likely to shorten life span rather than lengthen it.…”

Inheritance and recombination of mitochondrial genomes in plants, fungi and animals

“…A number of selfish mitochondrial genomes and selfish mitochondrial plasmids are known from several taxa of obligate aerobic fungi. These selfish mitochondrial elements arise from rearrangements, deletions, and insertions in mtDNA, and are implicated in phenotypes such as increased cell senescence, decreased cell senescence, and retarded hyphal growth (Bertrand et al ., 1980; Griffiths, 1992; Nakagawa et al ., 1998). Despite this wide range of genomic and phenotypic effects, all of these selfish mitochondrial genomes and mitochondrial plasmids over‐replicate at the expense of wild‐type mitochondrial genomes and plasmids.…”

“…Plasmids insert into and bud off from the mitochondrial genome. These interactions can affect both the transmission properties and the degree of selfishness of the mitochondrial plasmids (Yang & Griffiths, 1993; Nakagawa et al ., 1998).…”