Title: Structural variation of trichothecene mycotoxins has resulted from multiple evolutionary processes in the fungal order Hypocreales Authors
Submitted to: Fungal Genetics Conference/Asilomar
Publication Type: Abstract Only
Publication Acceptance Date: March 17, 2013
Publication Date: March 17, 2013
Citation: Proctor, R., Stanley, A.M., Mallmierca, M.G., Alexander, N.J., Gutierrez, S., McCormick, S.P. 2013. Structural variation of trichothecene mycotoxins has resulted from multiple evolutionary processes in the fungal order Hypocreales. Fungal Genetics Conference/Asilomar. Abstract. Technical Abstract: Trichothecenes are secondary metabolites produced by fungi in at least six genera of the order Hypocreales. These metabolites are of concern because they are toxic to humans and other animals and can accumulate in grain used for food and feed. They also contribute to plant pathogenesis of Fusarium and to biological control activity of Trichoderma. Although all trichothecenes share the same molecular skeleton, a tricyclic structure with a12,13-epoxide, different genera produce trichothecenes that differ in patterns of oxygenation and acylation. To investigate how such structural variation has evolved, we examined 1) variation in gene function and content in homologs of the trichothecene biosynthetic gene (TRI) cluster and 2) phylogenetic relationships of TRI genes among trichothecene-producing genera. The results suggest that the ancestral hypocrealean TRI cluster consisted of at least seven genes, including the enzyme-encoding genes TRI4 and TRI5 responsible for synthesis of the trichothecene skeleton, the regulatory genes TRI6 and TRI10, and the transporter gene TRI12. Phylogenetic analyses indicate that oxygenation of carbon atom 4 (C-4), which occurs in all trichothecene-producing genera, likely arose when different genera acquired different C-4 hydroxylase genes: e.g. TRI11b in Trichoderma and Myrothecium and TRI13 in Fusarium. In contrast, C-3 oxygenation, which occurs in only one genus, likely arose by a change in function of TRI4, a gene that exists in all genera. These results, and those from studies of Fusarium and Trichoderma, indicate that structural variation of trichothecenes has arisen by recruitment, changes in function, and deletion of TRI genes during evolution of the Hypocreales.