Conservation of the b mating-type gene complex among bipolar and tetrapolar smut fungi.
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. hordei and have cloned one from each mating type using sequences from 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 approximately 75% identity when homologous polypeptides were compared. All of the characterized bW and bE gene products have variable amino-terminal regions, conserved carboxy-terminal regions, and similar homeodomain motifs. Sequence comparisons with the bW1 and bE1 genes of U. maydis showed conservation in organization and structure. Transformation of the U. hordei b gene complex into a U. hordei 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 U. maydis, rendered the haploid transformants weakly pathogenic on maize. These results indicate that structurally and functionally conserved b genes are present in U. hordei.
Bakkeren
G
G
Biotechnology Laboratory, University of British Columbia, Vancouver, Canada.
Kronstad
J W
JW
D000483:Alleles; D001483:Base Sequence; D001487:Basidiomycota / Q000235:genetics* / Q000254:growth & development / Q000472:pathogenicity; D002874:Chromosome Mapping; D004271:DNA, Fungal / Q000235:genetics; D005800:Genes, Fungal; D049770:Genes, Mating Type, Fungal; D008969:Molecular Sequence Data; D010944:Plants / Q000382:microbiology; D010957:Plasmids; D012689:Sequence Homology, Nucleic Acid; D014170:Transformation, Genetic
D004271:DNA, Fungal