ARS | Publication request: Characterization and Population Analysis of the Mating-Type Genes in Aspergillus flavus and A. parasiticus

Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 20, 2008
Publication Date: August 29, 2008
Citation: Ramirez-Prado, J.H., Moore, G.G., Horn, B.W., Carbone, I. 2008. Characterization and population analysis of the mating-type genes in Aspergillus flavus and A. parasiticus. Fungal Genetics and Biology. 45:1292-1299.

Interpretive Summary: Aflatoxins are carcinogenic compounds produced by certain molds (Aspergillus flavus and A. parasiticus) in agricultural commodities such as peanuts, corn, cottonseed, tree nuts and spices. Reproduction by these molds in the form of spores is thought to be strictly nonsexual. Sexual reproduction could explain the high levels of genetic variation in field populations, but sex has never been reported in these molds. In this research we show that the genes necessary for sexual reproduction are present in A. flavus and A. parasiticus. Sexual reproduction in aflatoxin-producing molds is an important consideration when devising strategies for controlling aflatoxin contamination.

Technical Abstract: Aflatoxins (AF) are acutely toxic and carcinogenic polyketides produced by several Aspergillus species. A. flavus and A. parasiticus are the most common agents of AF contamination of crops. Previously, we sequenced 21 intergenic regions in the aflatoxin gene cluster for 43 isolates of A. flavus and 24 isolates of A. parasiticus, both sampled from a single peanut field in Georgia. Our analyses revealed a history of recombination indicative of sexual reproduction between different vegetative compatibility groups (VCGs) and haplotypes in each species. To explore this further, we examined homologous mating-type genes MAT1-1 and MAT1-2 to identify highly conserved domains, which then allowed us to amplify and sequence the MAT genes in A. flavus, A. parasiticus and several allied species. Heterothallism seemed to predominate in A. flavus and A. parasiticus and only one strain, an O-methylsterigmatocystin-accumulating A. parasiticus, was homothallic. Mating-type frequencies were determined for the total population samples and for samples that were clone-corrected based on VCGs and haplotypes. There was no significant difference in the frequency of the two mating types for A. flavus and A. parasiticus in either VCG or haplotype clone-corrected samples. The existence of both mating-type genes in equal proportions in A. flavus and A. parasiticus populations indicates the potential for a cryptic sexual state in these agriculturally important species.