|RAMIREZ PRADO, J - NC STATE UNIVERSITY
|MOORE, G - NC STATE UNIVERSITY
|CARBONE, IGNAZIO - NC STATE UNIVERSITY
Submitted to: Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 10/30/2007
Publication Date: 12/8/2007
Citation: Ramirez Prado, J.H., Moore, G.G., Horn, B.W., Carbone, I. 2007. The population genetics of aflatoxin and mating type evolution in aspergillus. Meeting Proceedings.
Interpretive Summary: none required.
Technical Abstract: Aflatoxins (AF) are toxic polyketides produced by several Aspergillus species that contaminate crops worldwide. A. parasiticus and A. flavus are the most common agents of AF contamination of corn, peanuts, cottonseed, figs and tree nuts in the US. The biosynthesis of AF involves over 20 enzymatic reactions that converts acetate and malonate to the intermediates sterigmatocystin (ST) and O-methylsterigmatocystin (OMST), the respective penultimate and ultimate precursors of AF. The genes encoding these enzymes are clustered together. Previously, we sequenced 21 intergenic regions in the AF gene cluster for 24 isolates of A. parasiticus and 43 isolates of A. flavus, both sampled from a single peanut field in Georgia. Linkage disequilibrium analyses revealed several distinct recombination blocks that separate contiguous genes in the cluster. The inferred recombination events were between different haplotypes and vegetative compatibility groups (VCGs) in each species. Most Aspergillus species are thought to be strictly asexual but A. fumigatus was recently reported to comprise complementary mating type idiomorphs, suggesting that this species may be undergoing sexual reproduction. We therefore hypothesized the existence of a heterothallic mating system in A. parasiticus and A. flavus. We examined homologous mating type idiomorphs, MAT1-1 and MAT1-2, to identify highly conserved domains, which further allowed us to amplify and sequence the MAT locus in A. parasiticus, A. flavus, and several allied species. Although heterothallism seems to predominate, a few OMST-accumulating A. parasiticus isolates were homothallic. Mating type frequencies were determined for the total population sample, and for clone-corrected samples based on haplotype or VCG data in A. parasiticus and A. flavus. There was no significant difference in the frequency of the two mating types for A. flavus and A. parasiticus in either haplotype or VCG clone-corrected samples. This near 1:1 distribution of mating types indicates the potential for a sexual state in these agriculturally important species.