Investigations into the Mechanisms of Resistance to Fusarium Head Blight in Wheat

Megan Eileen Gillespie, Purdue University

Abstract

Fusarium head blight (FHB), caused by the fungal pathogen Fusarium graminearum, is a devastating disease of wheat and barely. Control of FHB has proven to be especially difficult in wheat, where genetic resistance is infrequent, quantitative in nature, and often must be bred into elite lines from varieties of little commercial value. Resistance to the spread of the pathogen following infection of a single floret, known as type II resistance, is poorly understood at the molecular level and is therefore difficult to make use of in order to develop better performing varieties. The objective of this study was to gain a better understanding of the molecular mechanisms behind type II resistance to F. graminearum. In order to achieve this, a list of candidate genes with known or suspected general defense functions was compiled. These genes were targeted for silencing in a resistant variety using virus induced gene silencing (VIGS). This study demonstrates that ethylene (ET) signaling is vitally important to the type II resistance mechanism found naturally in the wheat variety Ning7840. Silencing of the ET biosynthesis gene SAMs and the transcription factor TaERF 7-1 resulted in the conversion to susceptibility in the resistant cultivar. The VIGS results were then confirmed by chemically manipulating ET signaling. Inhibition of ET signaling with the compound 1-MCP generated similar results in Ning and actually enhanced the susceptibility of the already susceptible line Bobwhite. 1-MCP treatment also rendered Ning more sensitive to deoxynivalenol, the toxin produced by F. graminearum when a single floret was exposed to the toxin alone. Augmentation of ET signaling with the immediate biological precursor 1-aminocycloproane-1-carboxylic acid (ACC), had no effect on the already resistant Ning, but significantly increased resistance in Bobwhite. ACC treatment in both varieties also caused an increase in lignin deposition. Furthermore, silencing of the genes BAK1, BRI1, CEBiP, Chorismate synthase, and Anthranilate N-benzoylransferase results in conversion of Ning to susceptibility. These genes are all linked with basal defense, and therefore, ethylene is likely modulating the resistance mechanism of wheat to F. graminearum by activating basal defense.

Degree

Ph.D.

Advisors

Johal, Purdue University.

Subject Area

Molecular biology|Plant Pathology

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