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Conservation of the b mating-type gene complex among bipolar and tetrapolar smut fungi
1Biotechnology Laboratory, University of British Columbia, Vancouver, Canada.
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. 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.
Insights
The study identified conserved b mating genes in Ustilago hordei, similar to Ustilago maydis. These U. hordei b genes are functional alleles and confer weak pathogenicity in U. maydis.
Area of Science:
- Mycology
- Fungal Genetics
- Plant Pathology
Background:
- Ustilago hordei exhibits bipolar mating controlled by a single locus with two alleles (MAT-1, MAT-2).
- Ustilago maydis displays tetrapolar mating involving two gene complexes (a and b), with the b complex being multiallelic.
- The genetic control of mating in phytopathogenic fungi varies significantly between species.
Purpose of the Study:
- To investigate the presence and characteristics of b mating gene homologs in Ustilago hordei.
- To compare the structure and function of U. hordei b genes with those of U. maydis.
- To assess the functional conservation and pathogenic potential of U. hordei b genes.
Main Methods:
- Cloning of U. hordei b gene complexes using U. maydis bEast alleles as probes.
- Sequence analysis of cloned bW (bWest) and bE (bEast) open reading frames.
- Functional analysis through transformation of U. hordei strains and pathogenicity assays in U. maydis.
Main Results:
- Homologs of the b gene complex were identified and cloned from both mating types of U. hordei.
- Sequence analysis revealed two divergent open reading frames (bW and bE) in U. hordei, showing approximately 75% identity to their U. maydis counterparts.
- The cloned U. hordei b genes were functional alleles and conferred weak pathogenicity when introduced into U. maydis.
Conclusions:
- Structurally and functionally conserved b genes exist in Ustilago hordei.
- The b mating gene complex plays a conserved role in fungal mating and pathogenicity across different Ustilago species.
- Comparative genomics and functional studies highlight conserved mechanisms in fungal mating systems.