The mating-type and pathogenicity locus of the fungus Ustilago hordei spans a 500-kb region - PubMed (original) (raw)

The mating-type and pathogenicity locus of the fungus Ustilago hordei spans a 500-kb region

N Lee et al. Proc Natl Acad Sci U S A. 1999.

Abstract

The fungal pathogen Ustilago hordei causes the covered smut disease of barley and oats. Mating and pathogenicity in this fungus are controlled by the MAT locus, which contains two distinct gene complexes, a and b. In this study, we tagged the a and b regions with the recognition sequence for the restriction enzyme I-SceI and determined that the distance between the complexes is 500 kb in a MAT-1 strain and 430 kb in a MAT-2 strain. Characterization of the organization of the known genes within the a and b gene complexes provided evidence for nonhomology and sequence inversion between MAT-1 and MAT-2. Antibiotic-resistance markers also were used to tag the a gene complex in MAT-1 strains (phleomycin) and the b gene complex in MAT-2 strains (hygromycin). Crosses were performed with these strains and progeny resistant to both antibiotics were recovered at a very low frequency, suggesting that recombination is suppressed within the MAT region. Overall, the chromosome homologues carrying the MAT locus of U. hordei share features with primitive sex chromosomes, with the added twist that the MAT locus also controls pathogenicity.

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Figures

Figure 1

Chromosomal organization of the MAT-1 (A) and MAT-2 (B) loci. The two thick lines represent the MAT chromosomes. The thin lines represent inserts of plasmid constructs used to tag the respective mating-type loci. The mfa, pra, bE, and bW ORFs are shown as black boxed arrows denoting the direction of transcription. The direction of transcription of pan1 and its location in MAT-2 are not known. The locations of probes used for the hybridizations are shown as gray bars. For details on the organization of the gene complexes, see ref. .

Figure 2

Determination of the size and organization of the MAT locus of U. hordei by hybridization with probes from the b gene complex. (A) Ethidium-bromide-stained CHEF gel. (B_–_D) DNA gel blots of the same gel hybridized with the probes indicated. Lane 1, I-_Sce_I-digested 4857–4 (a1b1); lane 2, I-_Sce_I-digested 364–86 (a1b1; single tag at a1); lane 3, undigested 364–86dt21 (a1b1; double tag at a1, b1); lane 4, I-_Sce_I-digested 364–86dt21 (a1b1; double tag at a1, b1); lane 5, I-_Sce_I-digested 365–57dt51 (a2b2; double tag at a2, b2); lane 6, undigested 365–57dt51 (a2b2; double tag at a2, b2); lane 7, I-_Sce_I-digested 365–57 (a2b2; single tag at b2); lane 8, I-_Sce_I-digested 4857–5 (a2b2). Note that probes b1–1, be and bw recognize homologous sequences in both MAT loci.

Figure 3

Determination of the size and organization of the MAT locus of U. hordei by hybridization with probes from the a gene complex. (A and D) Ethidium-bromide-stained CHEF gels. (B, C, and _E-_-G) DNA gel blots of the corresponding gels hybridized with the probes as indicated. Lanes are as described in Fig. 2.

Figure 4

Determination of the chromosomal position of the MAT locus by hybridization with probes from the a and b gene complexes. (A) Ethidium-bromide-stained CHEF gel. (B_–_D) DNA gel blots of the corresponding gels hybridized with the probes as indicated. Lanes are as described in Fig. 2.

Figure 5

Identification of mating-type-specific sequences in the drp by hybridization with probes from the a and b gene complexes. DNA gel blots of _Bam_HI-digested genomic DNA from representative drp (see text) and both parental strains were hybridized with the probes indicated.

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The mating-type and pathogenicity locus of the fungus Ustilago hordei spans a 500-kb region - PubMed (original) (raw)