EAGER: Understanding the mechanisms of action of two diverse antifungal plant defensins

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Crop diseases caused by fungal pathogens lead to tremendous economic losses and threaten food security worldwide. Chemical fungicides, crop rotation and natural genetic resistance don't provide adequate control of these diseases. At present, fungal diseases remain a key battlefront for reducing pre-and post-harvest losses of crop yield. Plants produce a large number of antifungal peptides as part of a complex set of multi-tiered defense strategies. Small cysteine-rich antifungal peptides called defensins exhibit potent broad-spectrum antifungal activity. This project seeks insight into the mechanisms that govern antifungal activity of two very different antifungal defensins from a model legume. This knowledge will facilitate use of these peptides as effective and sustainable biological fungicides in agriculture. Importantly, this project provides the opportunity to train the postdoctoral fellow and under-represented minority undergraduate students. Students and the postdoctoral fellow will be broadly trained in protein biochemistry, molecular biology and fungal cell biology so as to better prepare them for future careers in science. Research experiences will also be provided to K-5 teachers from low performing public schools in the St Louis area so that they can make connections between knowledge acquired in the classroom and research conducted in the laboratory. The goal of this project is to elucidate molecular mechanisms governing the potent antifungal activity of two plant defensins from a model legume Medicago truncatula. These defensins kill economically important fungal pathogens at low concentrations. These peptides bind to bioactive phospholipids in the plasma membrane of a fungal pathogen and antifungal activity of each defensin is a function of which phospholipid(s) it targets. This project will uncover sequence motifs governing phospholipid specificity and recognition for these peptides. Molecular mechanisms by which these peptides gain access to the cytoplasm of a wheat fungal pathogen Fusarium graminearum will be identified. In addition, systematic biochemical and proteomics approaches will be undertaken to identify intracellular protein targets of these peptides in this pathogen. The fully completed and annotated genome sequence of this fungus and its functional genomics database will provide essential resources for the research. Detailed mechanistic understanding of the antifungal action of these peptides will enable a more realistic prediction of their antifungal activity in a complex environment of the host plant and design of more effective peptides for disease control.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.