Indole primes defense signaling and increases herbivore resistance in tea plants.

Upon herbivore attack, plants emit herbivore-induced plant volatiles (HIPVs). HIPVs can prime defenses and resistance of intact plants. However, how HIPVs are decoded and translated into functional defense responses is not well understood, especially in long-lived woody plants. Here, we investigated the impact of the aromatic HIPV indole on defense-related early signaling, phytohormone accumulation, secondary metabolite biosynthesis and herbivore resistance in tea plants. We find that tea plants infested with tea geometrid caterpillars release indole at concentrations > 450 ng*h-1 . Exposure to corresponding doses of synthetic indole primes the expression of early defense genes involved in calcium (Ca2+ ) signaling, MPK signaling and jasmonate biosynthesis. Indole exposure also primes the production of jasmonates and defense-related secondary metabolites. These changes are associated with higher herbivore resistance of indole-exposed tea plants. Chemical inhibition of Ca2+ and jasmonate signaling provides evidence that both are required for indole-mediated defense priming and herbivore resistance. Our systematic assessment of the impact of indole on defense signaling and deployment shows that indole acts by boosting Ca2+ signaling, resulting in enhanced jasmonate-dependent defense and resistance in a woody plant. Our work extends the molecular basis of HIPV-induced defense priming from annual plants to an economically important tree species. This article is protected by copyright. All rights reserved.