DNA deletion of mitochondrial introns is correlated with the process of senescence in Podospora anserina.

In the filamentous fungus Podospora anserina, the unavoidable phenomenon of senescence is associated with specific mitochondrial rearrangements and particularly with the amplification of some regions of the mitochondrial chromosome. Mechanisms responsible for these rearrangements are still unknown. The implication in this phenomenon, of the first intron of the mitochondrial gene cox1 (intron alpha), a class II intron that presents significant amino acid similarity with retroviral reverse transcriptases, was postulated several years ago. We demonstrate here by polymerase chain reaction experiments: (1) that senescent and young cultures contain DNA molecules precisely deleted for intronic sequences; (2) that these deletions are found to a much greater extent in senescent than in young cultures; (3) that DNA intron deletion likely results from a reverse transcriptase-mediated mechanism as indicated by the detection of copies of the gene 1 cox1 completely devoid of its 15 introns; (4) that the intron alpha-encoded protein could intervene in this process. On the whole, these results strongly suggest that in Podospora, an increase in a mitochondrial reverse transcriptase activity probably mediated by the intron alpha-encoded protein is involved in the process of senescence.