Construction of chimeric alleles with altered specificity at the b incompatibility locus of Ustilago maydis.

AUTOR(ES)

Yee, A R

RESUMO

Multiallelic incompatibility systems found in many fungi and plants function to limit inbreeding by mediating self versus nonself recognition. The plant pathogenic fungus Ustilago maydis has a locus called b that governs incompatibility. Two multiallelic genes, bE and bW, are present at the b locus. Fusion of haploid strains carrying different alleles at bE and bW establishes an infectious dikaryon capable of pathogenesis on maize (Zea mays). Cells carrying a single type of b locus, whether haploid or dikaryotic, are nonpathogenic. To identify sequences within the bE gene that determine allelic specificity, targeted gene replacement was employed to produce a series of chimeras between the b1E and b2E alleles. Incompatibility tests with strains carrying the chimeric alleles identified a 30- to 48-amino acid region responsible for specificity. Suprisingly, the chimeras with recombination points within this region had a specificity different from both parent alleles. Overall, these results define an important domain in bE involved in self versus nonself recognition.

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