Secondary metabolite profile of Canadian NX-2 Fusarium graminearum chemotypes.
Blackwell, B., Bahadoor, A., Bosnich, W., Schneiderman, D., Herweyer, D., Gräfenhan, T., Harris, L.J. Secondary metabolite profile of Canadian NX-2 Fusarium graminearum chemotypes. Proceedings of the 8th Can. Workshop on Fusarium Head Blight, Ottawa, ON Nov. 20-22, 2016. P. 66, Poster presentation.
Fusarium graminearum isolates have traditionally been known to produce type B trichothecenes, either 15-ADON, 3-ADON or nivalenol. Recent surveys of F. graminearum from North America identified a “Northland” population that produced NX-2, a type A trichothecene that is not hydroxylated at the C-8 position1. Sequence diversity of the trichothecene biosynthetic enzyme Tri8 determines whether a strain produces trichothecenes acetylated at the C-3 or C-15 positions while ~9 amino acid changes within the Tri1 protein determine the production of type A or type B trichothecenes2. We had surveyed 43 F. graminearum strains isolated from Canadian wheat and grass samples collected in 2010 and 2011. Sequencing the Tri8 gene of these isolates revealed that 22 possessed the 3-ADON genotype while sequencing the Tri1 gene revealed that two showed genetic similarity to the NX-2 genotype. One NX-2 strain, DAOM242077 was from Nova Scotia while the other, DAOM250010, was from central Alberta.
When cultured in two stage liquid media, the crude extract of the fungal medium showed that both isolates produced substantial quantities of NX-2 (7-hydroxy-15-deacetylcalonectrin). In addition, the minor trichothecenes detected were consistent in lacking an OH at C-8, including 7-hydroxycalonectrin, 7-hydroxyisotrichodermin and two unidentified trichothecenes. Significant quantities of culmorin, sambucinol, and some butenolide were produced, demonstrating that the biosynthetic pathways to alternate sequiterpenes and modified trichothecenes were unaffected. When inoculated into wheat heads and subsequently analysed using DON ELISA, the de-acetylated NX (equivalent to DON) showed cross reactivity (extent of cross reactivity yet to be determined).
1. Varga et al. 2015, doi:10.1111/1462-2920.12718.
2. Kelly et al. 2016, doi:10.1016/j.fgb.2016.08.003.