title: Mating-type heterokaryosis and selfing in Cryphonectria parasitica.
abstract: Selfing in the chestnut blight fungus, Cryphonectria parasitica, occurs by two different genetic mechanisms. Most self-fertile isolates of C. parasitica are heterokaryotic for mating type, and the progeny from selfing segregate for mating type. Further, we resolved mating-type (MAT) heterokaryons into homokaryons of both mating types by isolating uninucleate asexual spores (conidia). However, because ascospore progeny, with rare exceptions, are not MAT heterokaryons, C. parasitica must lack a regular mechanism to maintain heterokaryosis by selfing. We hypothesize that heterokaryon formation may occur either because of recurrent biparental inbreeding, or by mating-type switching, possibly one involving some kind of parasexual process. The second mechanism found for selfing in C. parasitica occurred less frequently. Three single-conidial isolates (MAT-1 and MAT-2) selfed and produced progeny that did not segregate for mating type. It is currently not known if meiosis occurs during ascospore formation by this mechanism.
authors.affiliation: Department of Plant Pathology, Cornell University, 334 Plant Science Building, Ithaca, NY 14853, USA.
authors.forename: I Cristina
authors.initials: IC
authors.lastname: McGuire
authors.forename: Robert E
authors.initials: RE
authors.lastname: Marra
authors.forename: Michael G
authors.initials: MG
authors.lastname: Milgroom
mesh_terms: D000483:Alleles; D001203:Ascomycota / Q000235:genetics* / Q000502:physiology*; D002467:Cell Nucleus / Q000235:genetics; D003433:Crosses, Genetic; D004271:DNA, Fungal / Q000032:analysis; D005800:Genes, Fungal; D049770:Genes, Mating Type, Fungal; D005838:Genotype; D016133:Polymerase Chain Reaction; D013172:Spores, Fungal / Q000235:genetics
chemical_list: D004271:DNA, Fungal