Evolution of the Mating-Type Locus: The Basidiomycetes
Of all the fungi, production of sexual structures is most prominent in the members of the phylum Basidiomycota. The sexual cycles of fungi have been well studied for several decades. Research has shown that although enormous variation exists between the sexual processes of different fungal species, there are two common, underlying paradigms: the bipolar and the tetrapolar mating-type systems. The sexual cycles of fungi have been well studied for several decades. Research has shown that although enormous variation exists between the sexual processes of different fungal species, there are two common, underlying paradigms: the bipolar and the tetrapolar mating-type systems. In a typical basidiomycete sexual cycle, cells undergo chemoattraction, fuse to form a dikaryon, and nuclear migration is orchestrated by a complex regulatory process involving clamp cell formation and fusion. The genes encoding pheromone produce an immature product that requires extensive posttranslational modification, with the immature peptide undergoing prenylation, proteolytic cleavage, and carboxy-terminal methylation to produce the mature, biologically active form. Ustilago maydis is a phytopathogen that infects maize plants, a process that occurs only when the fungus is in the dikaryotic filamentous phase produced by mating. The smut Sporisorium reilianum is closely related to U. maydis and infects both maize and sorghum. Unlike its better-known relative, the role of the sexual cycle in infection in S. reilianum is currently unknown, but the potential link between infection and mating has encouraged analysis of the mating-type system in this pathogen.
