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High natural prevalence of a fungal prion

Alfons J M Debets1, Henk J P Dalstra, Marijke Slakhorst

  • 1Laboratory of Genetics, Wageningen University, 6708 PB Wageningen, The Netherlands. fons.debets@wur.nl

Proceedings of the National Academy of Sciences of the United States of America
|June 14, 2012
PubMed

Insights

Fungal prions like [Het-s] in Podospora anserina are widespread. The [Het-s] prion is selected due to meiotic drive, but balanced by allorecognition polymorphism.

Area of Science:

  • Mycology
  • Molecular Biology
  • Evolutionary Biology

Background:

  • Prions, infectious proteins causing fatal mammalian diseases, are also found in fungi, but their natural roles are poorly understood.
  • The biological significance of fungal prions is debated, ranging from detrimental to beneficial.
  • [Het-s] is a well-characterized prion in the fungus Podospora anserina, associated with an allorecognition system involving two antagonistic alleles: het-s (prion-forming) and het-S (non-prion-forming).

Purpose of the Study:

  • To investigate the prevalence and evolutionary dynamics of the [Het-s] prion in a natural Podospora anserina population.
  • To elucidate the selective forces shaping the frequency of het-s and het-S alleles.
  • To explore the interplay between the [Het-s]/HET-S allorecognition system and prion infection dynamics.

Main Methods:

  • Population genetics analysis of allele frequencies in 112 natural isolates.
  • Prevalence assessment of [Het-s] prion infection within het-s isolates.
  • Investigating the influence of the allorecognition system on the spread of a senescence plasmid.

Main Results:

  • het-s alleles were found to be nearly twice as frequent as het-S alleles in the natural population.
  • A high prevalence (92%) of [Het-s] prion infection was observed among het-s isolates.
  • Evidence suggests the [Het-s]/HET-S allorecognition system influences infection by a deleterious senescence plasmid.

Conclusions:

  • The [Het-s] prion is selected for and widespread, acting as a selfish genetic element.
  • Balancing selection for allorecognition polymorphism counteracts the prion's selfish activity.
  • The allele ratio is explained by frequency-dependent selection during somatic stages and meiotic drive during sexual reproduction.

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