Priming in Systemic Plant Immunity

Abstract

Upon local infection, plants possess inducible systemic defense responses against their natural enemies. Bacterial infection results in the accumulation to high levels of the mobile metabolite C9-dicarboxylic acid azelaic acid in the vascular sap of Arabidopsis. Azelaic acid confers local and systemic resistance against Pseudomonas syringae. The compound primes plants to strongly accumulate salicylic acid (SA), a known defense signal, upon infection. Mutation of a gene induced by azelaic acid (AZI1) results in the specific loss in plants of systemic immunity triggered by pathogen or azelaic acid and of the priming of SA induction. AZI1, a predicted secreted protein, is also important for generating vascular sap that confers disease resistance. Thus, azelaic acid and AZI1 comprise novel components of plant systemic immunity involved in priming defenses.