Abstract

Antifungal Plant Defensins: Mechanisms of Action and Engineering Disease Resistant Crops

Dilip Shah, Principal Investigator, Donald Danforth Plant Science Center

Defensins are sequence divergent cysteine-rich effector proteins of innate immunity expressed in all plants. They exhibit potent antifungal activity and efficacy against filamentous fungi. Understanding the mechanisms by which these proteins perturb fungal cell processes and inhibit fungal growth is central to the study of plant-fungal interactions. MtDef4 and MtDef5 from Medicago spp. are two diverse apoplast-localized defensins with potent inhibitory activity against filamentous fungal pathogens. They are structurally similar, but exhibit different modes of antifungal action. MtDef4 and MtDef5 rapidly permeabilize the plasma membrane and translocate into the cytoplasm of fungal pathogens. MtDef4 is the first antifungal defensin that has been shown to interact specifically with membrane-resident bioactive phosphatidic acid (PA), whereas MtDef5 interacts with phosphatidylinositol monophosphates with high affinity. The overexpression of apoplast-targeted MtDef4 confers strong resistance to obligate biotrophic pathogens Hyaloperonospora arabidopsidis and Puccinia triticina, causal agents of downy mildew and leaf rust disease, in transgenic Arabidopsis and wheat, respectively. Studies on the expression of MtDef5 in transgenic plants are in progress. Our studies demonstrate that defensins with different modes of action have the potential to provide resistance to economically important fungal pathogens in transgenic crops.