Sexual reproduction and recombination in the aflatoxin-producing fungus Aspergillus parasiticus

The fungal phylum Ascomycota comprises a large proportion of species with no known sexual stage, despite high genetic variability in field populations. One such asexual species, Aspergillus parasiticus, is a potent producer of carcinogenic and hepatotoxic aflatoxins, polyketide-derived secondary metabolites that contaminate a wide variety of agricultural crops. In this study, individuals of A. parasiticus from a population showing an evolutionary history of recombination were examined for sexual reproduction. Crosses between strains with opposite mating-type genes MAT1-1 and MAT1-2 resulted in the development of ascospore-bearing ascocarps embedded within stromata. Sexually compatible strains belonged to different vegetative compatibility groups. Recombination through the independent assortment of chromosomes 3 and 6 was detected using loci for mating type, aflatoxin gene cluster, and a protein-encoding gene. Our discovery of the sexual stage in A. parasiticus has important implications for current biological control strategies using nontoxigenic strains to reduce aflatoxin contamination in crops. (C) 2008 Elsevier Inc. All rights reserved.