Antimicrobial Plant Defensins:Structure-Activity Relationships and Modes of Action

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Intellectual Merit Plants constantly encounter pathogen attacks, especially from pathogenic fungi. As part of various defense strategies to protect themselves against fungal attack, plants produce small antifungal proteins known as defensins. Defensins are produced during the normal growth and development of plants and also in response to fungal attack. Some of these proteins are potent inhibitors of fungal pathogens. The PI and his research team have isolated two plant defensins, MsDef1 and MtDef4, from Medicago spp. that inhibit the growth of Fusarium graminearum, a fungal pathogen which causes devastating head blight disease in wheat and barley. The constitutive expression of these proteins in transgenic plants affords strong protection from fungal attack. A critical issue that needs to be addressed for effective use of these proteins in transgenic crops is understanding their structure-activity relationships, modes of action and the mechanisms by which fungal resistance to these proteins might emerge. Preliminary data suggest that MsDef1 and MtDef4 have different modes of antifungal action and act independently on F. graminearum. The planned research will identify the structural features and active sites that are essential for the unique antifungal activity of these proteins. In addition, the fungal toxicity pathway utilized by each protein will be elucidated. Broader ImpactsThe planned research will shed light on the molecular mechanisms by which antifungal plant defensins inhibit the growth of fungi. This knowledge will enable an effective long-term use of these proteins for biological control of fungal pathogens in transgenic crops. The research will also help establish the foundation for crop and mammalian safety, thus providing a greater sense of security about the use of these proteins in transgenic crops. Moreover, knowledge gained from the planned studies will facilitate future discovery of environmentally safe fungicides. In addition, this project provides a training opportunity for a postdoc as well as minority undergraduates and high school students. The PIs will continue to coordinate with and provide research opportunities through existing programs for students at the Danforth Center. Participants will learn not only protein biochemistry and engineering, but also cutting-edge fungal genomics and proteomics technologies. To enhance the wider scientific impact, presentations at professional meetings and publications in peer-reviewed journals are planned.