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Stepwise Recombination Suppression Around the Mating-Type Locus in an Ascomycete Fungus with Self-Fertile Spores

Summary

This research investigated how certain fungi control their mating and reproduction through changes in their DNA organization. The study found that different species of fungi have independently evolved similar strategies for maintaining self-fertility, which involves suppressing genetic mixing around key mating genes. This research impacts everyday life in several ways: • Helps understand fundamental processes of evolution and how organisms adapt over time • Provides insights into breeding systems that could be relevant for improving fungal strains used in agriculture and industry • Advances our knowledge of how organisms maintain genetic diversity while being able to self-reproduce • Could lead to better understanding of fungal reproduction for applications in biotechnology and medicine • Demonstrates how different species can arrive at similar solutions to biological challenges

Background

Recombination is often suppressed at sex-determining loci in plants and animals, and at self-incompatibility or mating-type loci in plants and fungi. In fungal ascomycetes, recombination suppression around the mating-type locus is associated with pseudo-homothallism, which produces self-fertile dikaryotic sexual spores carrying two opposite mating types. This has been well studied in two species complexes but it remains unclear if this association holds in other species.

Objective

To investigate whether Schizothecium tetrasporum, a fungus from a third family in Sordariales, also produces mostly self-fertile dikaryotic spores carrying opposite mating types, and to study the mechanisms and evolution of recombination suppression around its mating-type locus.

Results

S. tetrasporum was found to produce mostly self-fertile dikaryotic spores carrying opposite mating types, due to high frequency second meiotic division segregation at the mating-type locus. This indicated a single systematic crossing-over event between the mating-type locus and centromere. The researchers identified a 1.47 Mb region of recombination suppression around the mating-type locus with three evolutionary strata, indicating stepwise extension of recombination suppression. Gene losses and disruptions were found precisely at the strata margins.

Conclusion

The study revealed convergent evolution of self-fertile dikaryotic sexual spores across multiple ascomycete fungi. The particular pattern of meiotic segregation at the mating-type locus was associated with recombination suppression that had extended stepwise. This association between pseudo-homothallism and recombination suppression across lineages, and the presence of gene disruption at strata limits, supports a recently proposed mechanism of sheltering deleterious alleles to explain stepwise recombination suppression.
  • Published in:PLOS Genetics,
  • Study Type:Genomic Analysis,
  • Source: 10.1371/journal.pgen.1010347
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