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SnTox1, a Parastagonospora nodorum necrotrophic effector, is a dual‐function protein that facilitates infection while protecting from wheat‐produced chitinases

Zhaohui Liu, Yuanyuan Gao, Yong Min Kim, Justin D. Faris, Weilin L. Shelver, Pierre J. G. M. de Wit, Steven S. Xu, Timothy L. Friesen
new phytologist 2016 v.211 no.3 pp. 1052-1064
saprotrophs, necrosis, wheat, genes, plant pathogenic fungi, nutrients, Phaeosphaeria, barley, cell walls, fluorescence, fungal diseases of plants, Triticum aestivum, disease resistance, mesophyll, gene expression regulation, mycelium, leaves, apoptosis, host range, sugar beet, Parastagonospora nodorum, resistance mechanisms, chitin, avirulent strains, host-pathogen relationships, fungal proteins, chitinase
SnTox1 induces programmed cell death and the up‐regulation of pathogenesis‐related genes including chitinases. Additionally, SnTox1 has structural homology to several plant chitin‐binding proteins. Therefore, we evaluated SnTox1 for chitin binding and localization. We transformed an avirulent strain of Parastagonospora nodorum as well as three nonpathogens of wheat (Triticum aestivum), including a necrotrophic pathogen of barley, a hemibiotrophic pathogen of sugar beet and a saprotroph, to evaluate the role of SnTox1 in infection and in protection from wheat chitinases. SnTox1 bound chitin and an SnTox1‐green fluorescent fusion protein localized to the mycelial cell wall. Purified SnTox1 induced necrosis in the absence of the pathogen when sprayed on the leaf surface and appeared to remain on the leaf surface while inducing both epidermal and mesophyll cell death. SnTox1 protected the different fungi from chitinase degradation. SnTox1 was sufficient to change the host range of a necrotrophic pathogen but not a hemibiotroph or saprotroph. Collectively, this work shows that SnTox1 probably interacts with a receptor on the outside of the cell to induce cell death to acquire nutrients, but SnTox1 accomplishes a second role in that it protects against one aspect of the defense response, namely the effects of wheat chitinases.