Mitochondrial Group II Introns, Cytochrome c Oxidase, and Senescence in Podospora anserina

Abstract

Podospora anserina is a filamentous fungus with a limited life span. It expresses a degenerative syndrome called senescence, which is always associated with the accumulation of circular molecules (senDNAs) containing specific regions of the mitochondrial chromosome. A mobile group II intron (alpha) has been thought to play a prominent role in this syndrome. Intron alpha is the first intron of the cytochrome c oxidase subunit I gene (COX1). Mitochondrial mutants that escape the senescence process are missing this intron, as well as the first exon of the COX1 gene. We describe here the first mutant of P. anserina that has the alpha sequence precisely deleted and whose cytochrome c oxidase activity is identical to that of wild-type cells. The integration site of the intron is slightly modified, and this change prevents efficient homing of intron alpha. We show here that this mutant displays a senescence syndrome similar to that of the wild type and that its life span is increased about twofold. The introduction of a related group II intron into the mitochondrial genome of the mutant does not restore the wild-type life span. These data clearly demonstrate that intron alpha is not the specific senescence factor but rather an accelerator or amplifier of the senescence process. They emphasize the role that intron alpha plays in the instability of the mitochondrial chromosome and the link between this instability and longevity. Our results strongly support the idea that in Podospora, "immortality" can be acquired not by the absence of intron alpha but rather by the lack of active cytochrome c oxidase.

The Ll.LtrB intron from Lactococcus lactis excises as circles in vivo: insights into the group II intron circularization pathway

“…It was previously reported that when intron RNA circles are found, intron DNA circles or at least head-to-tail intron DNA junctions could also be detected (Osiewacz and Esser 1984;Schmidt et al 1994;Begel et al 1999;Murray et al 2001;Molina-Sánchez et al 2006;Federova and Zingler 2007). However, the origin, the nature, and the significance of these head-to-tail intron DNA junctions are still unclear.…”

“…Intron RNA circles were previously observed in vitro (Murray et al 2001;Nagy et al 2013) and in vivo (Li-Pook-Than and Bonen 2006;Molina-Sánchez et al 2006Dalby and Bonen 2013) but the circularization pathway was not addressed. Interestingly, the presence of intron RNA circles in vivo can be accompanied by traces of head-to-tail intron DNA junctions (Osiewacz and Esser 1984;Schmidt et al 1994;Begel et al 1999;Murray et al 2001;Molina-Sánchez et al 2006;Federova and Zingler 2007). The nature, the origin and the function of these intron DNA junctions where the 5 ′ and 3 ′ end of the intron are precisely joined is still unclear.…”

Two Copies of mthmg1 , Encoding a Novel Mitochondrial HMG-Like Protein, Delay Accumulation of Mitochondrial DNA Deletions in Podospora anserina

“…Implants were removed at approximately 1 cm from the margin of dead mycelia. The specific probes used to reveal senDNA␣ and -␥ have been described previously (5). Total RNA was extracted according to the method of Lecellier and Silar (28) for 5Ј rapid amplification of cDNA ends (RACE) or by the guanidinium thiocyanate-phenol-chloroform method (20) for cDNA preparation and Northern blotting.…”

Suppression of Mitochondrial DNA Instability of Autosomal Dominant Forms of Progressive External Ophthalmoplegia-AssociatedANT1Mutations inPodospora anserina

“…The resulting vector, pPableDPaAnt Mitochondrial DNA analysis: The mtDNA of the different growing or dying cultures was extracted by minipreparation (Lecellier and Silar 1994). The probes used in this study were EcoIV, EcoI, and 2604 ( described previously by Begel et al 1999); they cover $80% of the mitochondrial genome.…”