title: Linkage of mating-type loci distinguishes bipolar from tetrapolar mating in basidiomycetous smut fungi.
abstract: Sexual compatibility requires self vs. non-self recognition. Genetically, two compatibility or mating-type systems govern recognition in heterothallic basidiomycete fungi such as the edible and woodrotting mushrooms and the economically important rust and smut phytopathogens. A bipolar system is defined by a single genetic locus (MAT) that can have two or multiple alleles. A tetrapolar system has two loci, each with two or more specificities. We have employed two species from the genus Ustilago (smut fungi) to discover a molecular explanation for the genetic difference in mating systems. Ustilago maydis, a tetrapolar species, has two genetically unlinked loci that encode the distinct mating functions of cell fusion (a locus) and subsequent sexual development and pathogenicity (b locus). We have recently described a b locus in a bipolar species, Ustilago hordei, wherein the existence of an a locus has been suspected, but not demonstrated. We report here the cloning of an allele of the a locus (a1) from U. hordei and the discovery that physical linkage of the a and b loci in this bipolar fungus accounts for the distinct mating system. Linkage establishes a large complex MAT locus in U. hordei; this locus appears to be in a region suppressed for recombination.
authors.affiliation: Biotechnology Laboratory, University of British Columbia, Vancouver, Canada.
authors.forename: G
authors.initials: G
authors.lastname: Bakkeren
authors.forename: J W
authors.initials: JW
authors.lastname: Kronstad
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D004271:DNA, Fungal; D005656:Fungal Proteins / Q000235:genetics*; D005800:Genes, Fungal; D049770:Genes, Mating Type, Fungal; D008040:Genetic Linkage; D014644:Genetic Variation; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D011956:Receptors, Cell Surface; D051964:Receptors, Mating Factor; D018000:Receptors, Peptide / Q000235:genetics*; D043563:Receptors, Pheromone; D011995:Recombination, Genetic / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors; D014588:Ustilago / Q000235:genetics*
chemical_list: D004271:DNA, Fungal; D005656:Fungal Proteins; C499529:PRA1 protein, Ustilago hordei; D011956:Receptors, Cell Surface; D051964:Receptors, Mating Factor; D018000:Receptors, Peptide; D043563:Receptors, Pheromone; D014157:Transcription Factors