The Mating-Type Genes of the Basidiomycetes
Basidiomycete mating-type genes are encoded by two different factors resulting in a tetrapolar mating system where a cross can lead to one of four different reactions, only one of which results in a fertile state. Pairs of homeodomain transcription factors termed HD1 and HD2 classes constitute one factor (b genes in the smut fungi, A genes in the hymenomycete basidiomycetes). With the evolution of basidiomycetes, pheromone/receptor (P/R) systems (a genes in smut fungi and Bgenes in hymenomycetes) were co-opted to become independent master regulators constituting the second factor. Subsequently, the two sets of genes underwent evolutionary radiation with duplications, inversions and gene shuffling leading to the development of multiallelic HD and P/R systems, each functioning independently of the other. The multiallelic loci each developed many allelic specificities, resulting in tens of thousands of potential mating types for some species. An additional complexity of receptor gene homologues directly involved in mate discrimination has been revealed with the ready availability of genome sequences. Using examples derived from some model species, the molecular nature of the mating-type genes, the evolution of multiallelic and multispecific mating-type loci and the potential roles of newly detected receptor-like genes are discussed.
Freihorst, D., Fowler, T.J., Bartholomew, K., Raudaskoski, M., Horton, J.S., Kothe, E. (2016). The mating-type genes of the basidiomycetes. In J. Wendland (Ed.), Growth, Differentiation, and Sexuality (Updated and rev. 3rd ed.), (pp. 329-349). Updated and New York:Springer.