Unstable mitochondrial DNA in natural-death nuclear mutants of Neurospora crassa.

Abstract

The natural-death mutant of Neurospora crassa has an accelerated senescence phenotype caused by a recessive mutation, nd, in a nuclear gene that is located in linkage group I. An examination of mitochondrial functions, however, revealed that the mutant has phenotypic and molecular defects similar to those commonly associated with maternally transmitted fungal senescence syndromes, including (i) deficiencies in cytochromes aa3 and b; (ii) a deficit in small subunits of mitochondrial ribosomes, and hence defective mitochondrial protein synthesis; and (iii) accumulation of gross rearrangements, including large deletions, in the mitochondrial chromosome of vegetatively propagated cells. These traits indicate that the nd+ allele codes for a function that is essential for stable maintenance of the mitochondrial chromosome, possibly a protein involved in replication, repair, or recombination.

Deletion of a Novel F-Box Protein, MUS-10, in Neurospora crassa Leads to Altered Mitochondrial Morphology, Instability of mtDNA and Senescence

“…Similar to nd and sen, strains deficient for mus-10 displayed a shortened life span and accumulated mtDNA deletions (Seidel-Rogol et al 1989;Bertrand et al 1993;Navaraj et al 2000;D'Souza et al 2005). Analysis of the mtDNA deletion observed in latter subcultures of mus-10 revealed the absence of EcoRI-3 and parts of EcoRI-5 and EcoRI-10.…”

“…mtDNA deletions in the mus-10 mutant: The nd and sen mutants of N. crassa suffer from a shortened life span that correlates with the accumulation of mtDNA rearrangements (Sheng 1951;Seidel-Rogol et al 1989;Bertrand et al 1993;Navaraj et al 2000;D'Souza et al 2005). To investigate whether mtDNA rearrangements became more prevalent in mus-10 as it aged, we isolated mtDNAs from five sequential subcultures of agematched wild type and mus-10.…”

“…Isolation of mtDNA: Sucrose gradient-purified mitochondria were isolated from mycelia using previously described methods (Lambowitz 1979;Seidel-Rogol et al 1989;Rowley et al 1994). TE200 (200 mm Tris-HCl pH 8.0, 1 mm EDTA) was mixed with the mitochondria and then centrifuged at 15,000 rpm for 15 min.…”

“…However, replicative life span is also influenced by genetic background as certain mutations can cause progressive deterioration of growth, ultimately leading to death. One such example is the nuclear-encoded natural death (nd ), which when mutant causes a senescence phenotype correlating with the accumulation of multiple mtDNA deletions (Sheng 1951;Seidel-Rogol et al 1989). The deletions of mtDNA in nd occurred between two 70-to 701-bp direct repeats, suggesting that the nd gene product regulates recombination, repair, or replication of mtDNA (Bertrand et al 1993).…”

A site-specific deletion in mitochondrial DNA of Podospora is under the control of nuclear genes.

“…In some cases, nuclear genes have been shown to control the mtDNA rearrangements (5,6). The molecular mechanisms producing these rearrangements and the role played by nuclear-encoded proteins remain unclear in all cases.…”