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A Deviation from the Bipolar-Tetrapolar Mating Paradigm in an Early Diverged Basidiomycete

Summary

This research revealed a new type of mating system in fungi that helps us understand how organisms evolve different ways to reproduce sexually. The scientists discovered that a species of red yeast has a unique hybrid system that combines features of two previously known mating systems. This finding provides important insights into how complex mating systems evolved over millions of years. Impacts on everyday life: – Helps understand how organisms evolve and adapt their reproductive strategies – Provides insights that could be useful for breeding beneficial fungi – Advances our knowledge of basic biological processes that affect many organisms – Could lead to better control of harmful fungal pathogens – Demonstrates how studying simple organisms can reveal fundamental principles of life

Background

In fungi, sexual identity is determined by specialized genomic regions called MAT loci which are equivalent to sex chromosomes in animals and plants. Usually only two sexes or mating types exist, determined by two alternate sets of genes at the MAT locus (bipolar system). However, in the phylum Basidiomycota, a unique tetrapolar system emerged where four different mating types are generated per meiosis due to two functionally distinct molecular recognition systems encoded by separate MAT regions.

Objective

To characterize the mating system in the red yeast Sporidiobolus salmonicolor and investigate how HD1/HD2 transcription factors and the pheromone receptor system interact to produce bipolar mating behavior. The study aimed to understand the content and organization of MAT loci in the Pucciniomycotina, an early diverged lineage of basidiomycetes that had been poorly explored.

Results

The study revealed that S. salmonicolor has a novel mating system unlike any previously described, termed ‘pseudo-bipolar’. While normally bipolar, occasional disruptions of genetic cohesion of the bipolar MAT locus can create new mating types. Multiple HD1/HD2 alleles were found associated with each receptor type, but heterozygosity at both MAT regions was required for mating. Meiotic recombination was shown to occur within the bipolar MAT locus, explaining tetrapolar-like features such as increased allele numbers and evolution rates of some MAT genes.

Conclusion

The researchers discovered a new intermediate mating system in S. salmonicolor that is neither strictly bipolar nor tetrapolar. This pseudo-bipolar system may represent a previously unforeseen gradual form of transition from an ancestral tetrapolar system to bipolarity. The findings suggest this system may be common among red yeasts and provides new insights into the evolution of fungal mating systems.
  • Published in:PLOS Genetics,
  • Study Type:Experimental Research,
  • Source: 10.1371/journal.pgen.1001052
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