Mitochondrial DNA amplification in senescent cultures of Podospora anserina: Variability between the retained, amplified sequences

Belcour, Léon; Begel, Odile; Mossé, Marie-Odile; Vierny, Corinne

doi:10.1007/bf00419575

Cited by 80 publications

(12 citation statements)

References 16 publications

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“…This DNA species is not found in juvenile mycelia and has the following properties: contour length, 0.75 tkm; buoyant density, 1.699 g/ cm3; and molecular size, 2.4 kilobases (kb). Confirmative observations were recently reported by Belcour et al (5).…”

supporting

confidence: 92%

Replication and expression of a bacterial--mitochondrial hybrid plasmid in the fungus Podospora anserina.

Ståhl¹,

Tudzynski²,

Kück³

et al. 1982

Proc. Natl. Acad. Sci. U.S.A.

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Hybrid plasmids consisting of the bacterial plasmid pBR322 and plasmid-like DNA (pl DNA) sequences from the fungus Podospora anserina are not only able to replicate in Escherichia coli but also in the fungus. This was proved by both biophysical and biological evidence involving buoyant density profiles, DNADNA hybridization, and restriction analysis-all confirming that pl DNA behaves as a true plasmid. During its amplification in P. anserina, the hybrid plasmid does not lose its prokaryotic coding capacity as shown after retransfer and subsequent cloning in E. coli P. ansermna is able to express both the eukaryotic and the prokaryotic genetic information of the hybrid plasmid because the occurrence of senescence and the production of .-lactamase could be shown in experiments involving specific hybrid plasmids. In the same systems, it was possible to demonstrate that a hybrid plasmid containing, instead of p1 DNA, a pl DNA homologous region of native mtDNA also could function as a true plasmid. This hybrid plasmid contained about 25% of the genetic information of pl DNA, which corresponds to about 6% of the genetic information of mtDNA. Thus, the data show that hybrid plasmids may be used to shuttle genetic information between P. anserina and E. coli Hence, through the use of a mtDNA replicon, as evidenced by the pl DNA of P. anserina, another pathway in genetic engineering is established.The senescence that occurs regularly in wild strains of the ascomycete Podospora anserina (1) is caused by an infective agent (2) identical with plasmid-like DNA (pl DNA) (3,4). This DNA species is not found in juvenile mycelia and has the following properties: contour length, 0.75 tkm; buoyant density, 1.699 g/ cm3; and molecular size, 2.4 kilobases (kb). Confirmative observations were recently reported by Belcour et al. (5).The pl DNA inserted into the prokaryotic plasmid pBR322 (6) has been cloned in Escherichia coli, and the hybrid plasmid pSP17 that was isolated from the bacterium was able to induce senescence in juvenile cultures of P. anserina (4). Furthermore, heteroduplex analysis and DNA-DNA hybridization (Southern blotting method) have established that pl DNA is an integral part of mtDNA from juvenile mycelia of P. anserina (7,8).The discovery ofpl DNA of mitochondrial origin in a eukaryotic organism has raised the following questions. (i) Is the pl DNA of P. anserina a true plasmid, having the characteristics attributed to bacterial plasmids-i.e., self-replication and expression? The latter has already been shown for pl DNA by induction of senescence in juvenile cultures through transformation experiments (4). Experimental evidence for pl DNA selfreplication will be given in data confirming that pl DNA contains an origin of replication (replicon). Plasmids. Single (pSP4, pSP24) or double (pSP17) copies of pl DNA were integrated in the Sal

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supporting

confidence: 92%

Replication and expression of a bacterial--mitochondrial hybrid plasmid in the fungus Podospora anserina.

Ståhl¹,

Tudzynski²,

Kück³

et al. 1982

Proc. Natl. Acad. Sci. U.S.A.

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“…The only example of a mobile element with some attributes of a retrotransposon in this species is the mitochondrial intron pl, which appears to move via an RNA intermediate. This thoroughly investigated element is involved in gross rearrangements of the mitochondrial DNA (mtDNA) that occur regularly during aging of cultures (Stahl et al 1978;Belcour et al 1981;Osiewacz and Esser 1984;KuÈ ck 1989). In the nuclear DNA, only a putative solo-LTR of an unknown LTR retrotransposon, termed repa, has been reported previously (Deleu et al 1990).…”

Section: Introductionmentioning

confidence: 96%

The degenerate DNA transposon Pat and repeat-induced point mutation (RIP) in Podospora anserina

2000

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A degenerate DNA transposon, Pat, was identified in the genomes of various wild-type strains of the filamentous fungus Podospora anserina. In these strains, the number (approximately 20-25 copies per genome) and location of Pat sequences appear to be conserved. Two copies of Pat, one complete and one partial, were cloned and characterized. The sequence of the complete element is 1856 bp long and contains imperfect inverted terminal repeats (ITRs) of 53 bp. The target site duplication comprises the sequence TA. The amino acid sequence derived from one reading frame of Pat shows significant homology to members of the Fot1 family of transposons. However, this reading frame is interrupted by numerous stop codons. Since no transcripts of Pat were identified in different P. anserina strains grown under standard conditions and under increased stress, we conclude that none of the copies of Pat is active in the strains analyzed, under the environmental conditions investigated. Comparison of the sequences of the two cloned Pat sequences revealed 89% (589/747 nucleotides) identity. Most of the differences (82%, 129/158) can be attributed to transitions preferentially at CpA:TpG and CpT:ApG dinucleotides. The dinucleotide ratios in Pat are similar to those in a Neurospora crassa transposon which was subject to repeat-induced mutation (RIP), but differ significantly from those found in single-copy genes of P. anserina and in fungal DNA transposons not modified by this mechanism. Molecular analysis of the progeny of a cross between the wild-type strain and a transgenic strain in which a nuclear gene was duplicated by transformation yielded the first clear evidence that a RIP-like process is active in P. anserina.

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“…It is well documented that gross mtDNA rearrangements regularly appear during senescence of P. anserina cultures (36)(37)(38). To investigate a potential role of grisea in the control of these agerelated mtDNA rearrangements, we analyzed DNA of the wild-type, the long-lived mutant grisea, and cultures of grisea that were transformed with the cloned wild-type copy of grisea and displayed wild-type characteristics.…”

Section: Resultsmentioning

confidence: 99%

Mitochondrial DNA rearrangements of Podospora anserina are under the control of the nuclear gene grisea

Borghouts

Kimpel²,

Osiewacz³

1997

Proc. Natl. Acad. Sci. U.S.A.

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Podospora anserina is a filamentous fungus with a limited life span. Life span is controlled by nuclear and extranuclear genetic traits. Herein we report the nature of four alterations in the nuclear gene grisea that lead to an altered morphology, a defect in the formation of female gametangia, and an increased life span. Three sequence changes are located in the 5 upstream region of the grisea ORF. One mutation is a G 3 A transition at the 5 splice site of the single intron of the gene, leading to a RNA splicing defect. This loss-of-function affects the amplification of the first intron of the mitochondrial cytochrome c oxidase subunit I gene (COI) and the specific mitochondrial DNA rearrangements that occur during senescence of wild-type strains. Our results indicate that the nuclear gene grisea is part of a molecular machinery involved in the control of mitochondrial DNA reorganizations. These DNA instabilities accelerate but are not a prerequisite for the aging of P. anserina cultures.Aging of biological systems, as the progressive functional impairment of living beings leading to an increase in agerelated mortality, is a complex process that is dependent on both environmental and genetic factors. With regard to the genetic basis, instabilities of the mitochondrial DNA (mtDNA) were reported in various organisms to be involved in aging leading to mitochondrial dysfunction and degeneration (for reviews, see refs. 1 and 2). Moreover, increased instabilities of the mtDNA were found to lead to premature degeneration processes. Examples of this type are premature death syndromes in fungi and various neuromuscular diseases in humans (for reviews, see refs. 3-5). Interestingly, in some cases, these syndromes are due to the mutation of a nuclear gene that demonstrate that the integrity of the mtDNA is under the control of nuclear factors (6-10). Unfortunately, until now, the molecular mechanisms involved in this maintenance function have not been elucidated in any case.In the filamentous fungus Podospora anserina, all wildstrains are characterized by a limited life span. After prolonged vegetative growth, they display various symptoms of senescence. Since the first description of this syndrome (11), it has become clear that nuclear-mitochondrial interactions are crucially involved in its control (for reviews, see refs. 12-15). Detailed molecular investigations revealed that gross reorganizations of the mtDNA occur during senescence. These reorganizations are almost quantitative and lead to impairment of the energy-generating system located in mitochondria. Similar processes were subsequently reported to occur in senescing strains of Neurospora (16)(17)(18). In all cases, the activity of mobile genetic elements of circular or linear structure were found to be relevant. More specifically, in P. anserina, it appears that the mobility of a circular plasmid, termed plasmid-like DNA (plDNA) or ␣senDNA (19,20), which is a derivative of the first intron of the cytochrome oxidase gene subunit I (COI), is responsible f...

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Mitochondrial DNA amplification in senescent cultures of Podospora anserina: Variability between the retained, amplified sequences

Cited by 80 publications

References 16 publications

Replication and expression of a bacterial--mitochondrial hybrid plasmid in the fungus Podospora anserina.

Replication and expression of a bacterial--mitochondrial hybrid plasmid in the fungus Podospora anserina.

The degenerate DNA transposon Pat and repeat-induced point mutation (RIP) in Podospora anserina

Mitochondrial DNA rearrangements of Podospora anserina are under the control of the nuclear gene grisea

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