Analysis of mating-type genes in the chestnut blight fungus, Cryphonectriaparasitica

McGuire, I. C., Marra, R. E., Turgeon, B. G., and Milgroom, M. G. 2001. Ana lysis of mating-type genes in the chestnut blight fungus, Cryphonectria par asitica. Fungal Genetics and Biology 34, 131-144. In nature, the chestnut b light fungus, Cryphonectria parasitica, has a mixed mating system; i.e., in dividuals in the same population have the ability to self and outcross. In the laboratory, C. parasitica appears to have a bipolar self-incompatibilit y system, typical of heterothallic ascomycetes; selfing is rare, although d emonstrable. In this report we describe the cloning and sequencing of both mating-type idiomorphs and their flanking regions at the MAT locus in C. pa rasitica. The two idiomorphs, MAT1-1 and MAT1-2, are structurally similar t o those of other pyrenomycetes described to date. MAT1-1 encodes three gene s (MAT1-1-1, MAT1-1-2, and MAT1-1-3) and MAT1-2 encodes a single gene (MAT1 -2-1). Unlike MAT idiomorphs in some ascomycetes, the sequences at both end s of the idiomorphs in C. parasitica show a relatively gradual, rather than abrupt, transition from identity in the flanking regions to almost complet e dissimilarity in the coding regions. The flanking regions have repetitive polypyrimidine (T/C) and polypurine (A/G) tracts; the significance of thes e repetitive tracts is unknown. Although we found repetitive tracts in the flanks and gradual transition zones at the ends of the idiomorphs, we found no special features that would explain how selfing occurs in an otherwise self-incompatible fungus. (C) 2001 Academic Press.