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

Systemic acquired resistance (SAR) is a powerful immune response that triggers broad-spectrum disease resistance throughout a plant. In the model plant , long-distance signaling and SAR activation in uninfected tissues occur without circulating immune cells and instead rely on the metabolite 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 leaves to identify a minimal set of 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.