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Characterization and prevalence of a circular mitochondrial plasmid in senescence-prone isolates of Neurospora
Anthony D D'Souza1, Shahana Sultana, Ramesh Maheshwari
1Department of Biochemistry, Indian Institute of Science, Bangalore, 560 012, India.
Abstract:
Genetic and molecular analyses of the phenomenon of senescence-i.e., irreversible loss of growth and reproductive potential upon subculturing-in Neurospora intermedia strain M1991-60A, collected from Maddur in southern India, showed the presence of plasmid pMaddur1, which is homologous to the senescence-inducing circular mitochondrial plasmid, pVarkud. Maternal inheritance of senescence in M1991-60A correlated to the formation of variant pMaddur1, its subsequent insertion into mitochondrial (mt)DNA and the accumulation of defective mtDNA with the pMaddur1insert. PCR-based analyses for similar plasmids in 147 natural isolates of Neurospora from Maddur showed that nearly 40% of the strains had pMaddur1 or pMaddur2 that shared 97-98% sequence homology with pVarkud and pMauriceville. Nearly 50% of the strains that harbored either pMaddur1 or pMaddur2, also contained a circular Varkud satellite plasmid (pVS). Size polymorphism maps to the cluster of PstI sites in the non-coding region. Whereas senescence of nearly 40% of N. intermedia strains may be due to pMaddur, the presence in seven strains of pVS but not pMaddur and the absence of either of these two plasmids in other senescence-prone isolates suggests yet undiscovered mechanisms of senescence in the Maddur strains.
Insights
Senescence in Neurospora intermedia is linked to mitochondrial plasmids like pMaddur1. These plasmids can integrate into mtDNA, causing defects and maternal inheritance of senescence, though other mechanisms may also exist.
Area of Science:
- Genetics
- Molecular Biology
- Mycology
Background:
- Senescence, an irreversible loss of growth and reproductive potential, is observed in Neurospora intermedia strains.
- The Maddur strain M1991-60A from India exhibits this phenomenon.
- Circular mitochondrial plasmids are implicated in senescence in some fungal species.
Purpose of the Study:
- To investigate the genetic and molecular basis of senescence in Neurospora intermedia M1991-60A.
- To identify and characterize plasmids associated with senescence in this strain.
- To explore the prevalence and role of similar plasmids in other natural isolates.
Main Methods:
- Genetic and molecular analyses of Neurospora intermedia.
- Plasmid isolation and characterization (pMaddur1).
- Polymerase Chain Reaction (PCR) to screen natural isolates for specific plasmids.
- DNA sequencing and homology analysis.
Main Results:
- Plasmid pMaddur1, homologous to the senescence-inducing pVarkud plasmid, was identified in M1991-60A.
- Senescence correlated with pMaddur1 variant formation, mtDNA integration, and defective mtDNA accumulation.
- Approximately 40% of 147 natural isolates harbored pMaddur1 or pMaddur2, showing high homology to known plasmids.
- Nearly 50% of these strains also contained the Varkud satellite plasmid (pVS).
- Some senescence-prone strains lacked pMaddur or pVS, suggesting alternative senescence mechanisms.
Conclusions:
- Mitochondrial plasmids, particularly pMaddur1 and its variants, play a significant role in inducing senescence in Neurospora intermedia.
- The integration of these plasmids into mtDNA is a key mechanism leading to senescence.
- The presence of pVS in some strains and the absence of identified plasmids in others indicate diverse and potentially undiscovered pathways for senescence in this species.
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