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Linkage of Mating-Type Loci Distinguishes Bipolar from Tetrapolar Mating in Basidiomycetous Smut Fungi

Guus Bakkeren and James W. Kronstad
Proceedings of the National Academy of Sciences of the United States of America
Vol. 91, No. 15 (Jul. 19, 1994), pp. 7085-7089
Stable URL: http://www.jstor.org/stable/2365224
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Linkage of Mating-Type Loci Distinguishes Bipolar from Tetrapolar Mating in Basidiomycetous Smut Fungi
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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.

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