Essential genes encoded by the mating-type locus of the human fungal pathogen .

Fungal sexual reproduction is controlled by the mating-type () locus. In contrast to a majority of species in the phylum Basidiomycota that have tetrapolar mating-type systems, the opportunistic human pathogen employs a bipolar mating-type system, with two mating types ( and α) determined by a single locus that is unusually large (~120 kb) and contains more than 20 genes. While several genes are associated with mating and sexual development, others control conserved cellular processes (e.g. cargo transport and protein synthesis), of which five (, , , , and ) have been hypothesized to be essential. In this study, through genetic analysis involving sporulation of heterozygous diploid deletion mutants, as well as in some cases construction and analyses of conditional expression alleles of these genes, we confirmed that with the exception of , both alleles of the other four genes are indeed essential for cell viability. We further showed that while is not essential, its function is critical for infectious spore production, faithful cytokinesis, adaptation for growth at high temperature, and pathogenicity . Our results demonstrate the presence of essential genes in the locus that are divergent between cells of opposite mating types. We discuss possible mechanisms to maintain functional alleles of these essential genes in a rapidly-evolving genomic region in the context of fungal sexual reproduction and mating-type evolution.