Conservation of the b mating-type gene complex among bipolar and tetrapolar smut fungi.

Abstract

In the phytopathogenic fungus Ustilago hordei, one locus with two alternate alleles, MAT.1 and MAT-2, controls mating and the establishment of the infectious dikaryon (bipolar mating). In contrast, for U. maydis, these functions are associated with two different gene complexes, called a and b (tetrapolar mating); the a complex has two alternate specificities, and the b gene complex is multiallelic. We have found homologs for the b gene complex in U. bordei and have cloned one from each mating type using sequences f" one bEast allele of U. maydis as a probe. Sequence analysis revealed two divergent open reading frames in each b complex, which we called bW (bWest) and bE (bEast) in analogy with the b gene complex of U. maydis. The predicted bW and bE gene products from the two different mating types showed .v75% identity when homologous polypeptides were compared. All of the characterized bW and bE gene products have variable amino-terminal regions, consenred carboxy-terminal regions, and similar homeodomain motifs. Sequence comparisons with the bW1 and bE1 genes of U. maydis showed conservation in organization and structure. Ransformation of the U. bordei b gene complex into a U. bordei strain of opposite mating type showed that the b genes from the two mating types are functional alleles. The U. hordei b genes, when introduced into 0. maydis, rendered the haploid transforniants weakly pathogenic on maize. These results indicate that structurally and functionally consenred b genes are present in U, bordei.

Mating Type Loci of Sporisorium reilianum : Novel Pattern with Three a and Multiple b Specificities

“…However, in that study it was analyzed whether bE or bW of U. hordei can function in combination with the bW or bE protein of U. maydis. The chimeric b proteins triggered filamentous growth, while pathogenicity symptoms were weak or absent (5). These experiments are not directly comparable to our experiments, where we analyzed the ability of the bE/bW heterodimer of S. reilianum to trigger the regulatory cascade in U. maydis.…”

“…A similar set of experiments has been carried out with the b proteins of U. hordei in U. maydis (5). However, in that study it was analyzed whether bE or bW of U. hordei can function in combination with the bW or bE protein of U. maydis.…”

Evolution of Mating Systems in Basidiomycetes and the Genetic Architecture Underlying Mating-Type Determination in the YeastLeucosporidium scottii

“…This suggests that the P/R system functions essentially as premating determinant, but is still required for normal spore production. Such a situation would parallel the findings reported for U. maydis, in which diploid strains homozygous at the P/R locus and heterozygous at the HD locus (either naturally occurring or genetically transformed with an HD1/HD2 gene pair of a different allelic specificity) are only able to generate incipient hyphae and teliospores that undergo meiosis and are weakly pathogenic on maize (Banuett and Herskowitz 1989;Bakkeren and Kronstad 1993).…”

Tetrapolar fungal mating types: Sexes by the thousands

“…It has been postulated that tetrapolar mating type systems might be exclusive to the basidiomycetes, while ascomycetes display bipolar mating types. This discussion is kindled by the findings in U. hordei and awaits further investigation [57]. In homobasidiomycetes, bipolarity has also been reported !…”