Fungal sex: The basidiomycota
In the phylum Basidiomycota, a wide variety of lifestyles are represented. These range from well-known and conspicuous wood-decaying mushrooms, plant growth-promoting and mutualistic mycorrhizae, and crop-destroying smut and rust fungi, to yeast-like human pathogens. Lifestyle differences have consequences for the mating and breeding systems of these fungi (see "Glossary," below, for definitions of specialist terms used in this article), which are reflected in the genetic evolution of mating-type determination. For over a century fungi have been recognized as having diverse breeding systems, from homothallism (i.e., universal compatibility among gametes, including among clonemates) to heterothallism (i.e., mating among haploid gametes carrying different mating-type alleles). The study of breeding systems, for example, led to the discovery of the astounding variability in mating-type alleles among mushrooms, with thousands of different mating types in some species (1), and to the realization that in many fungal pathogens the process of sexual reproduction is closely linked to infection and pathogenicity (2) (Fig. 1). The importance of basidiomycete fungi and their great research tractability, from ecology to genomics, have brought major insights into the diversification of genetic mechanisms used to achieve sexual reproduction.
