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Transgenic expression of a plant defensin in alfalfa (Medicago sativa) leads to increased resistance to crown rot pathogens

Andrew Sathoff: University of Minnesota

<div>Plant defensins are small cationic peptides with a conserved signature of cysteines. These peptides inhibit the growth of a broad range of fungi and bacteria. Alfalfa crown rot is a disease complex that reduces alfalfa stand density and causes substantial losses in productivity in all alfalfa-growing areas. Currently, there are no effective methods of disease control. To evaluate plant defensins as a potential control for alfalfa crown rot, the amount of defensin needed to inhibit growth of pathogen strains by 50% (IC<sub>50</sub>) was calculated. MtDef5, a bi-domain defensin from <em>Medicago truncatula</em>, displayed high activity against both bacterial and fungal crown rot pathogens <em>in vitro</em>. MtDef5 had IC<sub>50</sub> values against <em>Pseudomonas syringae</em> pv. <em>syringae</em> and <em>Phoma medicaginis</em> of 0.198 μM and 1.50 μM, respectively. <em>Agrobacterium</em>-mediated transformation was used to create transgenic lines of alfalfa (cultivar Regen SY27x) constitutively expressing MtDef5. Expression of the transgene was confirmed by qRT-PCR and by Western blots using the polyclonal anti-MtDef5 antibody. Disease bioassays demonstrated increased resistance against fungal crown rot pathogens, especially against <em>P. medicaginis</em> in transgenic lines expressing MtDef5. These experiments show promise for not only controlling crown rot pathogens, but potentially a wide array of economically important fungal and bacterial pathogens through the transgenic expression of a plant defensin.</div>