1. 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

2. 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

3. 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

4. V. volvacea is homothallic
The mycelium from a single basidiospore can produce fruit bodies

5. 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

6. 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

7. Outcome unexpected
Progeny of a ‘self-fertilized’ fruit body look very different

8. Even into the next (selfed) generation
The F2 is also diverse

9. And segregation of culture morphology continues for four generations of ‘selfing’

10. 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 1:1 ratio

11. Segregation also evident at the DNA level
DNA fingerprints of progeny from a ‘selfed’ mushroom

12. Possible mechanisms to continue segregation after selfing
High mutation rate
Transposon activity
Mating type switching
DNA hybridization

13. Summary and Conclusions - I
Many fungi have a highly evolved sexual cycle
Many others modify sexual reproduction strategy to their own circumstances

14. 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

15. We’re still discussing it!