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A saponin-detoxifying enzyme mediates suppression of plant defences

Abstract

Plant disease resistance can be conferred by constitutive features such as structural barriers or preformed antimicrobial secondary metabolites. Additional defence mechanisms are activated in response to pathogen attack and include localized cell death (the hypersensitive response)1,2. Pathogens use different strategies to counter constitutive and induced plant defences, including degradation of preformed antimicrobial compounds3 and the production of molecules that suppress induced plant defences4,5,6. Here we present evidence for a two-component process in which a fungal pathogen subverts the preformed antimicrobial compounds of its host and uses them to interfere with induced defence responses. Antimicrobial saponins are first hydrolysed by a fungal saponin-detoxifying enzyme. The degradation product of this hydrolysis then suppresses induced defence responses by interfering with fundamental signal transduction processes leading to disease resistance.

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Figure 1: Infection of N. benthamiana by S. lycopersici strains.
Figure 2: Localized cell death induced by tomatinase-deficient mutants of S. lycopersici is SGT1-dependent.
Figure 3: Pre-infiltration with β2-tomatine compromises resistance to 2D2.
Figure 4: β2-Tomatine mediates suppression of bacterial disease resistance in N. benthamiana.

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Acknowledgements

We thank R. Sandrock and H. Van Etten for strains of S. lycopersici; P. Moffett for supplying SGT1-silenced N. benthamiana plants; and D. Holden and J. Rathjen for criticism of the manuscript. K.B. is supported by a Marie Curie European Community fellowship and the Sainsbury Laboratory is supported by the Gatsby Charitable Foundation.

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Bouarab, K., Melton, R., Peart, J. et al. A saponin-detoxifying enzyme mediates suppression of plant defences. Nature 418, 889–892 (2002). https://doi.org/10.1038/nature00950

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