Evolution of Mating in the Saccharomycotina.

The fungal phylum Ascomycota comprises three subphyla: Saccharomycotina, Pezizomycotina, and Taphrinomycotina. In many Saccharomycotina species, cell identity is determined by genes at the MAT (mating-type) locus; mating occurs between MATa and MATα cells. Some species can switch between MATa and MATα mating types. Switching in the Saccharomycotina originated in the common ancestor of the Saccharomycetaceae, Pichiaceae, and Metschnikowiaceae families, as a flip/flop mechanism that inverted a section of chromosome. Switching was subsequently lost in the Metschnikowiaceae, including Candida albicans, but became more complex in the Saccharomycetaceae when the mechanism changed from inversion to copy-and-paste between HML/HMR and MAT. Based on their phylogenetic closeness and the similarity of their MTL (mating-type like) loci, some Metschnikowia species may provide useful models for the sexual cycles of Candida species. Conservation of synteny demonstrates that, despite changes in its gene content, a single orthologous locus (MAT/MTL) has controlled cell type throughout ascomycete evolution.