Title: Virulence of Gibberella zeae on Wheat following Independent Disruptions of Trichothecene Biosynthetic Genes Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: December 4, 2008
Publication Date: December 4, 2008
Citation: Alexander, N.J., Mccormick, S.P., Desjardins, A.E. 2008. Virulence of Gibberella zeae on Wheat following Independent Disruptions of Trichothecene Biosynthetic Genes [abstract]. Proceedings of the 2008 National Fusarium Head Blight Forum. Poster No. 52. p. 79. Technical Abstract: The plant-fungal interaction that occurs when Fusarium graminearum invades small grains such as wheat and barley is complicated and involves many interactions between the invading fungus and the plant host. Although trichothecene toxins are not required for the initial infection of wheat, they are involved in the progression of Fusarium Head Blight (FHB) disease. Mutants of F. graminearum (tri5-) blocked in the first committed step in the trichothecene biosynthetic pathway do not produce deoxynivalenol (DON) or any other trichothecenes, and are reduced in virulence on wheat. In order to test if biosynthetic precursors of DON are sufficient for disease progression, we disrupted the coding region sequence of 5 genes (FgTri1, FgTri3, FgTri8, FgTri11, and FgTri101) to produce mutants blocked at various steps in the trichothecene biosynthetic pathway. The mutants were analyzed for production of trichothecenes in liquid media, in a rice solid medium, and in planta, and for ability to cause head blight on the FHB-susceptible wheat cultivar Wheaton. Disruption mutants of the esterase FgTri8 did not show a significant reduction in virulence. However, FgTri8- mutants accumulated 3,15-diacetylDON in culture, while in the infected seed DON as well as 3,15 diacetylDON was detected. These results suggest that esterases in wheat can contribute to the deacetylation that produces DON following infection by strains that produce 3-acetylDON. Disruptions of four genes, FgTri1, FgTri3, FgTri11, and FgTri101 blocked production of DON and led to the accumulation in culture of early pathway intermediates, such as isotrichodermol and its 3-acetylated derivative isotrichodermin, or calonectrin and its 3 and 15-deacetylated derivatives. Disruption mutants of FgTri1, FgTri3, and FgTri101 were reduced in virulence. However, disruption mutants of the cytochrome P450 monooxygenase FgTri11 retained wild-type virulence although they accumulated isotrichodermol and isotrichodermin in culture and in infected seed. In a previous study, both isotrichodermol and isotrichodermin were as phytotoxic as DON in an Arabidopsis thaliana bioassay. Together, these results suggest that some trichothecene early intermediates are as biologically active as DON, thus the earliest steps of the pathway should be high priority targets for trichothecene control.