Submitted to: Fungal Genetics and Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/7/2008
Publication Date: 2/2/2009
Citation: Horn, B.W., Ramirez-Prado, J.H., Carbone, I. 2009. Sexual reproduction and recombination in the aflatoxin-producing fungus Aspergillus parasiticus. Fungal Genetics and Biology. 46(2):169-175. Interpretive Summary: Aflatoxins are potent carcinogens produced by fungi in agricultural commodities such as corn and peanuts. The two aflatoxin-producing species, Aspergillus flavus and A. parasiticus, reproduce through the formation of nonsexual spores and have no previously known sexual stage. Here we show that A. parasiticus is capable of reproducing sexually. Sexual reproduction in A. parasiticus accounts for the high variability in aflatoxin production by this fungus and will influence our strategies for controlling aflatoxins in agricultural crops.
Technical Abstract: 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.