Submitted to: National Fusarium Head Blight Forum Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 11/9/2007
Publication Date: 12/2/2007
Citation: Garvey, G., Mc Cormick, S.P., Rayment, I. 2007. Structural and functional studies of trichothecene biosynthetic enzymes: a novel approach to combating fusarium head blight [abstract]. National Fusarium Head Blight Forum Proceedings. p. 29. Interpretive Summary:
Technical Abstract: Fusarium Head Blight (FHB) is a plant disease with serious economic and health impacts. Although it has proved difficult to combat this disease, one strategy that has been examined is the introduction of an indigenous fungal protective gene into cereals such as wheat, barley, and rice. Thus far the gene of choice has been tri101, whose gene product catalyses the transfer of an acetyl group from acetyl Coenzyme A to the C3 hydroxyl moiety of several trichothecene mycotoxins. In vitro this has been shown to reduce the toxicity of the toxins by approximately 100 fold but has demonstrated limited resistance to FHB in transgenic cereal. In order to understand the molecular basis for the differences between in vitro and in vivo resistance, the three-dimensional structures and kinetic properties of two TRI101 orthologs isolated from Fusarium sporotrichioides and Fusarium graminearum have been determined. The kinetic results reveal important differences in activity of these enzymes towards B-type trichothecenes such as deoxynivalenol. These differences in activity can be explained in part by the three dimensional structures for the ternary complexes for both these enzymes with Coenzyme A and trichothecene mycotoxins. The structural and kinetic results together emphasize that the choice of an enzymatic resistance gene in transgenic crop protection strategies must take into account the kinetic profile of the selected protein. Examination of the trichothecene biosynthetic pathway suggests that other enzymes might provide a more suitable scaffold for engineering new degradative activities for improved resistance. Therefore, it is planned to continue the biochemical characterization and three-dimensional structure determination of the remaining enzymes in the biosynthetic pathways for deoxynivalenol, nivalenol, and T-2 toxin. To date, the crystal structure for FsTRI3 both apo and in complex with 15-decalonectrin have been determined, and the kinetics of this enzyme towards native substrate and final toxins have been evaluated. This structural information will be used to create new enzymes by directed evolution utilizing a yeast selection system to detect new activities that degrade or inactivate the toxins.