Senescence in fungi: the view from Neurospora

Area of Science:

• Mycology
• Cell Biology
• Genetics

Background:

• Some fungal strains exhibit senescence, ceasing growth during subculturing.
• Senescence in Neurospora is often associated with intramitochondrial plasmids integrating into mitochondrial DNA (mtDNA).
• This integration causes insertional mutagenesis, leading to defective mitochondria.

Purpose of the Study:

• To investigate the mechanisms underlying fungal senescence.
• To explore the role of mitochondrial DNA instability and nuclear gene mutations in senescence.
• To understand the implications for fungal growth and cellular function.

Main Methods:

• Analysis of senescing fungal strains, including Neurospora.
• Examination of intramitochondrial plasmids and their integration into mtDNA.
• Study of nuclear gene mutations and their phenotypic effects.
• Investigation of mitochondrial replication and spread in interconnected hyphae.

Main Results:

• Senescing strains frequently harbor plasmids that integrate into mtDNA, causing mutations.
• Defective mitochondria replicate faster and spread, leading to impaired oxidative phosphorylation.
• Nuclear gene mutations can also cause senescence, with effects masked until spore germination.
• mtDNA appears inherently unstable, requiring nuclear-encoded factors for stability.

Conclusions:

• Fungal senescence results from mtDNA instability or nuclear mutations affecting mitochondrial function.
• Dysfunctional mitochondria and impaired oxidative phosphorylation ultimately halt colony growth.
• The findings support the endosymbiotic theory of eukaryotic cell origins.