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Fruiting Body Formation in Volvariella volvacea Can Occur Independently of its MAT-A-Controlled Bipolar Mating System, Enabling Homothallic and Heterothallic Life Cycles

Summary

This research investigated how the edible straw mushroom (Volvariella volvacea) reproduces and forms mushrooms. The study revealed that this fungus has multiple ways of reproducing, which helps explain why mushroom production can be unpredictable in commercial farming. Understanding these mechanisms could help improve cultivation methods. Impacts on everyday life: – Better understanding could lead to more reliable mushroom crops for farmers – May help develop improved strains for commercial production – Could reduce crop failures and make mushrooms more consistently available – May lower production costs and consumer prices for this nutritious food – Provides knowledge that could be applied to other edible mushroom species

Background

Volvariella volvacea is an important edible mushroom crop in Southeast Asia, but erratic fruiting presents challenges for production and breeding. The fungus has multinucleate hyphae, typically lacks clamp connections, and has an incompletely identified sexual reproductive system. Previous microscopy indicated possible coexistence of heterothallic and homothallic life cycles.

Objective

To investigate and characterize the life cycle and mating system of V. volvacea using whole genome sequencing, cloning of MAT loci, karyotyping of spores, and fruiting assays.

Results

Analysis showed that only MAT-A, not MAT-B, controlled heterokaryotization, indicating a bipolar mating system. Karyotyping supported the existence of heterokaryotic spores, but most single spore isolates contained structural variation markers from both parents without being clearly heterokaryotic. Some isolates with single MAT-A loci could produce fruiting bodies, demonstrating that self-fertile isolates were not necessarily secondary homothallic. Recombination between markers was normal, but many markers showed unusual 1:2 or 1:3 distribution ratios in spores.

Conclusion

V. volvacea employs multiple life cycles including bipolar heterothallic, secondary homothallic, and homothallic mechanisms. The bipolar system appears most prevalent. Genetic content is distributed unequally in many spores, possibly due to partial aneuploidy combined with other mechanisms. This explains the irregular fruiting patterns and provides new insights into the complex reproductive biology of this important mushroom species.
  • Published in:G3: Genes | Genomes | Genetics,
  • Study Type:Genomic Analysis,
  • Source: 10.1534/g3.116.030700
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