TheaandbLoci ofUstilago maydisHybridize with DNA Sequences from Other Smut Fungi

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

“…Our earlier hybridization results showed that homologous sequences were present in smut fungi with bipolar mating systems (Bakkeren et al, 1992). We have expanded on the hybridization results by characterizing b sequences from one representative smut fungus with bipolar mating, U. hordei.…”

“…A U. maydis-derived DNA probe corresponding to the carboxyterminal, constant domain of the bEl protein, was found to hybridize under moderately stringent conditions to genomic DNA of U. hordei (Bakkeren et al, 1992). The probe revealed a single restriction fragment, different in size, in (haploid) strains of the opposite mating type: that is, a 1.5-kb BamHl fragment in a MAT-2 strain (Uh100) and a 2.8-kb BamHl fragment in a MAT-7 strain (Uh112).…”

“…We have previously shown, in a survey of 23 different fungal strains (Bakkeren et al, 1992), that hybridization probes from the U. maydis a and b genes recognize homologs in the genomic DNA of all smut fungi tested. Based on these data, we have concluded that other small grain-infecting smut fungi from the bipolar group (e.g., U. kolleri, U. avenae, U. nigra, and U. bullata) possess b homologs.…”

Regulation of haplid phenotypes in Ustilago maydis by ammonium transporters and components of the b mating locus.

“…Like all smuts, the two fungal pathogens share many life cycle features, including a yeast-like stage and an infectious dikaryon arising from the fusion of two haploid cells (Bakkeren et al, 1992). Unlike the U. maydis mating system which is tetrapolar, the a and b loci being on different chromosomes, U. hordei has a bipolar mating system in which the a and b loci are physically linked on the same chromosome and designated as one of two mating types, MAT-1 or MAT-2 (Bakkeren & Kronstad, 1993).…”

“…Also similar to the other smut, the b locus contains two homeodomain proteins that during mating dimerize to create a transcription factor to regulate expression of mating-related genes (Bakkeren, Kamper, & Schirawski, 2008). Interestingly, there is a high degree of sequence similarity between the U. hordei mating type locus and MAT loci of other closely related organisms, including U. maydis and S. cerevisiae (Bakkeren et al, 1992). In fact, If the homeodomain of "opposite mating type" from U. maydis is expressed in U. hordei, and vice versa, there is a positive mating reaction on charcoal plates, although pathogenicity in corn is markedly reduced, resulting in no teliospores and only weak symptoms of infection (Bakkeren & Kronstad, 1996).…”