Establishment of a Congenic Strain for the Oyster Mushroom Reveals the Structure and Evolution of Mating-Type Loci

Pleurotus ostreatus, a widely cultivated edible oyster mushroom, is an ecologically versatile species with applications in biotechnology, agriculture, and food production. It functions as a decomposer and in nutrient-limited conditions it enhances its survival by using a potent toxin to prey on nematodes. Its adaptability is further regulated by sexual reproduction, which follows a tetrapolar mating system governed by two unlinked, multiallelic loci, matA and matB. The two mating-compatible monokaryotic strains PC9 and PC15, derived from the parental dikaryon strain N001, exhibit significant physiological differences. PC9 grows robustly in laboratory conditions, whereas PC15 grows more slowly, making PC9 the preferred strain for research. To advance P. ostreatus as a genetic model, we characterized the mating-type (MAT) loci of both monokaryon strains and developed a congenic strain. We analyzed the MAT loci in multiple P. ostreatus strains, and identified 11 A and 12 B alleles among twelve haplotypes, confirming their multiallelic nature. Using genetic backcrosses, we introgressed the matA and matB loci from PC15 into the PC9 genetic background to generate the congenic strain PC9.15. After sequencing and assembling a high-quality and contiguous genome for PC9.15, we confirmed that the genomes of PC9.15 and PC9 are 99% similar, with the only major difference placed at the matA and matB loci. Author SummaryMushrooms are not just decomposers-they can also be predators. The oyster mushroom Pleurotus ostreatus is an ecologically adaptable species that thrives by breaking down plant material and preying on nematodes using a potent toxin that triggers rapid paralysis of nematode prey. In addition to its ability to switch from saprophyte to predator, another feature contributing to the ecological success of Pleurotus is its reproductive strategy. P. ostreatus reproduces sexually through a tetrapolar mating-type system, governed by two unlinked mating loci, matA and matB. These loci determine mating compatibility and contribute to genetic diversity, yet their precise structure and allelic diversity remain unclear. In this study, we characterized the matA and matB loci in P. ostreatus strains PC9 and PC15 and analyzed MAT loci across multiple strains, confirming their multiallelic nature. To enhance P. ostreatus as a genetic model, we developed the congenic strain PC9.15 by introgressing MAT alleles from PC15 into the PC9 genetic background through genetic backcrosses. Genome sequencing confirmed that PC9.15 closely matches the genome of PC9, except at the MAT loci. This study expands our understanding of mating-type diversity in P. ostreatus, introduces PC9.15 as a valuable tool for genetic studies and controlled crosses, and facilitates the development of P. ostreatus as a model system for fungal biology.