Research ArticlePLANT DEFENSES

An engineered pathway for N-hydroxy-pipecolic acid synthesis enhances systemic acquired resistance in tomato

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Science Signaling  22 Oct 2019:
Vol. 12, Issue 604, eaay3066
DOI: 10.1126/scisignal.aay3066

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Enhancing defenses in crop plants

Localized exposure of a plant tissue to a pathogen stimulates systemic acquired resistance (SAR), a plant-wide immune response that protects it from further infection. SAR is induced by soluble factors, such as hormones and metabolites. Holmes et al. identified the minimal set of Arabidopsis thaliana enzymes required to synthesize the SAR-inducing metabolite NHP in a tobacco relative. Localized expression of these enzymes in tomato plant leaves or NHP treatment of sweet pepper plant leaves protected the plants from infection at distant sites. Thus, engineering crop plants to produce NHP constitutively or under the control of an inducible system may be useful for enhancing endogenous defenses, thus improving agricultural productivity.

Abstract

Systemic acquired resistance (SAR) is a powerful immune response that triggers broad-spectrum disease resistance throughout a plant. In the model plant Arabidopsis thaliana, long-distance signaling and SAR activation in uninfected tissues occur without circulating immune cells and instead rely on the metabolite N-hydroxy-pipecolic acid (NHP). Engineering SAR in crop plants would enable external control of a plant’s ability to mount a global defense response upon sudden changes in the environment. Such a metabolite-engineering approach would require the molecular machinery for producing and responding to NHP in the crop plant. Here, we used heterologous expression in Nicotiana benthamiana leaves to identify a minimal set of Arabidopsis genes necessary for the biosynthesis of NHP. Local expression of these genes in tomato leaves triggered SAR in distal tissues in the absence of a pathogen, suggesting that the SAR trait can be engineered to enhance a plant’s endogenous ability to respond to pathogens. We also showed tomato produces endogenous NHP in response to a bacterial pathogen and that NHP is present across the plant kingdom, raising the possibility that an engineering strategy to enhance NHP-induced defenses could be possible in many crop plants.

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