How Fusarium graminearum GPCRs Contribute To Fungal Virulence On Wheat
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Authors
Sridhar, Pooja
Date
Type
thesis
Language
eng
Keyword
Fusarium graminearum , Wheat pathogen , Chemotropism , G protein-coupled receptors
Alternative Title
Abstract
Fusarium graminearum is the principal causal agent of Fusarium Head Blight, one of the most destructive diseases of wheat. Infection of wheat by F. graminearum results in contamination of the grains with harmful mycotoxins and deterioration of grain quality. Infection begins when F. graminearum spores land on the wheat head. However, the host cues that activate directional growth, or chemotropism, of the fungus to enable infection are yet to be characterized. The fungal pheromone-sensing receptors Ste2 and Ste3 have been implicated in host sensing in multiple pathogens, shedding light on novel functions for these receptors. The experimental chapters in this thesis explore whether similar mechanisms of host-directed chemotropism are present in Fusarium graminearum. Through the studies described in Chapter 2, we have determined that F. graminearum exhibits Ste2-mediated chemotropic growth towards the catalytic product of wheat-secreted peroxidases. This chemotropic signal requires elements of the cell wall integrity mitogen-activated protein kinase (MAPK) signaling pathway. Furthermore, depletion of FgSte2 compromises the pathogenicity of F. graminearum on germinating wheat coleoptiles. Chapter 3 provides evidence that one substrate converted by the plant peroxidases is of fungal origin. Peroxidase treatment of F. graminearum conidia results in the conversion of this substrate into a FgSte2-activating ligand that can be extracted in an aqueous solution. Interestingly, the availability of this substrate is dependent on FgSte2 and FgSte3. Mass spectrometry identified a 400 Da carbohydrate whose abundance is significantly lower in solutions produced by peroxidase treatment of F. graminearum lacking FgSte2 or FgSte3. Transcriptomic profiling of genes impacted by FgSte2 in combination with glycosidase-based experiments suggests that this carbohydrate likely derives from a cell surface glycan. Finally, in Chapter 4, full-length FgSte2 was successfully expressed in an insect cell line. Conditions for detergent solubilization and purification were optimized, resulting in the capture of pure FgSte2 protein that could be visualized on a Coomassie-stained SDS-PAGE. These studies provide a basis for the purification of FgSte2 on a larger scale to facilitate the determination of its structure. Elucidating the mechanism of FgSte2-mediated chemotropism will deepen our understanding of fungal pathogenesis and provide a foundation for developing novel anti-fungal inhibitors.
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This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.
Attribution-NoDerivs 3.0 United States
ProQuest PhD and Master's Theses International Dissemination Agreement
Intellectual Property Guidelines at Queen's University
Copying and Preserving Your Thesis
This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.
Attribution-NoDerivs 3.0 United States