The quest for long-distance signals in plant systemic immunity.

Plants induce long-lasting systemic immunity after local pathogen attack by emitting resistance-priming signals from infection sites. A number of plant molecules have been proposed as mobile factors for this response, but many do not fully satisfy criteria for timing and action in systemic immunity. Azelaic acid has been identified as a pathogen-induced metabolite in Arabidopsis vascular sap that has several properties of a long-distance resistance-priming signal.