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Cell surface organization of the wheat pathogen Fusarium graminearum
Fungi comprise the largest group of plant pathogenic organisms. Regardless of the pathogen's strategy, large changes in gene transcription typically occur during plant infection. However, very little is known about the cell surface proteins that contribute to host invasion. The results presented in this dissertation describe the contribution of different fungal cell surface components to hyphal growth, differentiation, and plant infection.^ First, an in vitro system was developed to induce infection-related morphogenesis in the wheat pathogen F. graminearum. Using detached wheat glumes, I demonstrated that F. graminearum differentiates at least two distinct hyphal structures during glume invasion: subcuticular hyphae and bulbous infection hyphae. I further demonstrated that the mitogen activated protein kinase Gpmk1, which was previously implicated in the pathogenicity of F. graminearum, is essential for the differentiation of bulbous infection hyphae. ^ Second, two genes involved in plasma membrane organization ( mes1 and bar1) were deleted, and the resultant mutants were characterized. I demonstrated that mes1 is required for efficient reproduction, proper endomembrane organization, and full virulence on wheat heads. Deletion of ceramide synthase encoding gene bar1 caused a severe defect in colonial growth, which made a clear interpretation of pathogenicity assays difficult. However, I demonstrated that Bar1 is specifically necessary for the generation of glucosylceramides, a class of sphingolipids whose function is not yet clear. Also, I demonstrated that glucosylceramides likely mediate sensitivity to heat stable antifungal factor (HSAF) from biocontrol agent Lysobacter enzymogenes. ^ Finally, I demonstrated that the gene gpi7 contributes to cell wall integrity and in planta proliferation of F. graminearum, possibly by mediating resistance to plant defense compounds. I also generated a list of putative GPI-anchored proteins in the proteome of F. graminearum, some of which may play a role in virulence. Also, I demonstrated that at least two of these predicted GPI-anchored proteins show hypervariability among Nebraska isolates of F. graminearum, the first time that such variability was demonstrated for putative GPI-anchored proteins of a plant pathogenic fungus.^
Biology, Molecular|Biology, Microbiology|Agriculture, Plant Pathology
Rittenour, William R, "Cell surface organization of the wheat pathogen Fusarium graminearum" (2009). ETD collection for University of Nebraska - Lincoln. AAI3389922.