Evidence for the Existence of Mating Subtypes Within the Schizophyllum commune: Mating Behavior and Genetic Divergence

<i>Schizophyllum commune</i>, a Basidiomycota fungus with a tetrapolar mating system, serves as a key model for studying sexual reproduction. In this study, two distinct mating subtypes (I and II) were identified in strain 20R-7-ZF01, isolated from subseafloor sediment, which exhibited eight different mating interaction phenotypes. Intra-subtypes exhibited colony-symmetric tetrapolar interactions (G1), whereas inter-subtype crosses yielded colony-asymmetric phenotypes (G2) and a reduced number of fruiting bodies. Nuclear migration analysis revealed that both subtypes follow the same sexual reproductive process, suggesting functional similarities despite the different reproductive outcomes. Gene silencing of mating-type loci identified the genes <i>bbp2-9</i> and <i>bbp2-7</i> within the B locus as key factors in determining mating subtype identity. Additionally, a similar pattern of mating subtype differentiation was observed in five other <i>S. commune</i> strains from both subseafloor and terrestrial environments. These findings highlight the genetic diversity within <i>S. commune</i>, challenge the classical understanding of fungal mating systems, and provide new insights into the genetic evolutionary mechanisms governing fungi with tetrapolar mating systems.