Seminar: Modes of antifungal activity of a fungal cell penetrating plant defensin

Dr. Kaoutar El Mounadi, Assistant Professor, Department of Biology, Kutztown University

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March 26, 2018, 3:35 PM - 4:30 PM

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Dr. El Mounadi is an assistant professor in the department of biology  at Kutztown University, PA.  She received a Bachelor’s from University Mohammed V in Morocco, a Master’s from the University of Seville in Spain and a doctoral degree in  Agricultural Sciences from Southern Illinois University at Carbondale. Dr. El Mounadi did her postdoctoral fellowship at the Danforth Plant Science Center in St. Louis, Mo where she started her research on studying the molecular mechanisms by which plant defensins inhibit the growth of plant fungal pathogens. Dr. El Mounadi’s research interests include understanding the mode of action of plant antifungal peptides and cellular and molecular biology of fungi.


Defensins are small cysteine-rich proteins present in all plants and constitute an ancient and diverse set of natural antimicrobial proteins. MtDef4 is a 47-amino acid cysteine-rich evolutionary conserved defensin from a model legume Medicago truncatula. It is an apoplast-localized plant defense protein that inhibits the growth of various plant pathogens in vitro at micromolar concentrations. Furthermore, overexpression of this defensin in wheat plants confers resistance to the biotrophic pathogen Puccinia graminis. In order to fully harness the potential of MtDef4 for bioengineering crops with robust resistance to fungal and oomycete pathogens, a thorough understanding of its mode of action is necessary.  Data showed that MtDef4 rapidly permeabilizes the fungal plasma membrane of Fusarium graminearum and is internalized by the fungal cells where it accumulates in the cytoplasm. Furthermore, analysis of the structure of MtDef4 revealed the presence of a positively charged γ-core motif composed of β2 and β3 strands connected by a positively charged RGFRRR loop. Amino acid subsitutions to the RGFRRR sequence abolish the ability of MtDef4 to enter fungal cells, suggesting that the RGFRRR loop is a translocation signal required for the internalization of the protein. Data also showed that MtDef4 binds to phosphatidic acid (PA) via the RGFRRR loop and that this binding is required for the antifungal activity. However, this mechanism of action is not conserved between fungi.  Neurospora crassa, for example, responds very differently to MtDef4 challenge compared to F. graminearum. MtDef4 does not permeabilize the plasma membrane of N. crassa. MDef4 is also targeted to different subcellular compartments in each fungus. Internalization of MtDef4 in N. crassa is energy-dependent and involves endocytosis. By contrast, in F. graminearum, the defensin is translocated autonomously using partially energy-dependent pathway. These data are crucial to our understanding of the molecular mechanisms that govern the antifungal activity of MtDef4 and other defensins.

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