A%20study%20of%20the%20genetic%20mechanisms%20which%20generate%20diversity%20in%20a%20self-fertile%20mushroom,%20Volvariella

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A study of the genetic mechanisms which generate
diversity in a self-fertile mushroom, Volvariella

• Siu Wai Chiu David Moore
• The Chinese University of Hong Kong
• University of Manchester

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Main points of the typical life cycle

• Two haploid nuclei brought together
• From different parents
• A diploid forms which undergoes meiosis
• Progeny are haploid and genetically diverse

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V. volvacea is cross-fertile

• No barriers to cross-fertility
• No evidence for mating type factors
• Different isolates can mate
• Mendelian segregations of genetic markers

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V. volvacea is homothallic

• The mycelium from a single basidiospore can
  produce fruit bodies

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V. volvacea is homothallic

• Basidiospores are haploid and have only one
  nucleus
• So only one haploid set of genes can occur in a
  self-fertilized fruit body

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V. volvacea is homothallic

• If only one haploid set of genes occurs in a
  self-fertilized fruit body,
• we expect the progeny to be identical to each
  other and to the parent

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Outcome unexpected

• Progeny of a self-fertilized fruit body look
  very different

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Even into the next (selfed) generation

• The F2 is also diverse

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And segregation of culture morphology continues
for four generations of selfing
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Another peculiarity is that progeny segregate
into self-fertile and self-sterile

• Most (16 out of 21) progenies studied segregated
  self-fertile to self-sterile in a 11 ratio

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Segregation also evident at the DNA level

• DNA fingerprints of progeny from a selfed
  mushroom

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Possible mechanisms to continue segregation after
selfing

• High mutation rate
• Transposon activity
• Mating type switching
• DNA hybridization

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Summary and Conclusions - I

• Many fungi have a highly evolved sexual cycle
• Many others modify sexual reproduction strategy
  to their own circumstances

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Summary and Conclusions - II

• Volvariella volvacea is an extreme
• Hybridizes readily in nature
• But the organism has a mechanism to maintain
  genetic diversity when isolated

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Were still discussing it!