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Apoplastic targeting of plant defensin MtDef4 confers strong resistance to leaf rust pathogen Puccinia triticina in transgenic wheat
J. KAUR (1), J. Fellers (2), T. Clemente (3), D. Shah (1). (1) Donald Danforth Plant Science Center, Saint Louis, MO, U.S.A.; (2) Dept. of Plant Pathology, Kansas State University, Manhattan, KS, U.S.A.; (3) Center for Biotechnology, University of Nebraska-Lincoln, Lincoln, NE, U.S.A.

Rust diseases caused by fungi of the order Pucciniales remain a major threat to global wheat production. Basidiomycete <i>Puccinia triticina</i>, an obligate biotroph causes leaf rust disease in wheat. Current disease management strategies involving the use of resistant wheat cultivars and fungicide application fail to provide complete resistance because of the rapid evolution of new virulent pathotypes. Genetic engineering of wheat using antifungal plant defensins can augment the current control strategies. MtDef4 is a 47 aa cysteine-rich defensin from <i>Medicago truncatula</i> with broad-spectrum antifungal activity. This plant defense effector protein contains an RxLR-like motif that is required for its entry into fungal cells. Expression of MtDef4 in the apoplast confers resistance to an obligate oomycete biotroph <i>Hyaloperonospora arabidopsidis </i>in transgenic <i>Arabidopsis</i>. We have generated transgenic wheat lines expressing apoplast-targeted MtDef4. Two of the four homozygous single-copy transgenic wheat lines showed strong resistance to <i>P. triticina </i>race MCPSS in the greenhouse, compared to non-transgenic controls. Histopathological observations and fungal gene expression profile data further support the resistance observed in transgenic wheat lines. This study demonstrates that expressing an apoplast-localized defensin is an effective strategy in providing resistance to a biotrophic basidiomycete fungal pathogen in transgenic wheat.

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