Mitochondrial Excision-Amplification Plasmids in Senescent and Long-Lived Cultures of Podospora Anserina
Part of the
Basic Life Sciences
book series (BLSC, volume 40)
Senescence in the filamentous fungus Podospora anserina is maternally inherited. Several laboratories, including our own, have shown that specific regions of the mitochondrial genome excise and replicate as autonomous plasmids during senescence. One particular plasmid, termed α senDNA, is found most often, but others (β, ε, and θ senDNAs) are also observed. DNA sequence analysis has shown that the 2.6-kbp α senDNA is a complete group II intron of the cytochrome oxidase subunit I (COI) gene. Like other group II introns, α senDNA codes for amino acid sequences that have considerable homology with retroviral reverse transcriptase. Beta senDNA is a 9.8-kbp element, and, of the 5 kbp sequenced thus far, no introns have been noted. Epsilon senDNA is 5.5 kbp, and, while it contains no group II introns, three group I introns were detected.
To determine the relevance of these senDNAs, especially α, with senescence, we have isolated and characterized several long-lived strains of P. anserina. In most, a novel family of small, autonomously replicating elements, derived from the 3′ end of the EcoRI-7 region of the mitochondrial genome, are found. We termed these sMt-1, sMt-2, and sMt-3. DNA sequence analysis has shown that sMt-1 is 368 bp, sMt-2 is 114 bp, and sMt-3 is 67 bp. The sMt-2 and sMt-3 elements overlap and are completely contained within the sMt-1 element. The 5′ and 3′ termini of sMt-1 are unique, as are the 5′ ends of sMt-2 and sMt-3, but the sMt-2 and sMt-3 elements share the same 3′ terminus. Palindromic sequences and direct repeats are present, and their locations suggest a role in the excision process of the sMt DNAs. In early stages of their growth, several of these long-lived strains contain a senDNA but none of the sMt plasmids. Later in vegetative growth, large quantities of the sMt elements are observed. Concomitant with the appearance of these sMt plasmids, gene rearrangements of the mitochondrial genome are common. We argue that the senDNAs and the sMt elements play an antagonistic role in the determination of life span.
KeywordsMitochondrial Genome Gene Rearrangement Palindromic Sequence Excision Site Mitochondrial Plasmid
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
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