Airborne signals synchronize the defenses of neighboring plants in response to touch

Plants activate defense-related pathways in response to subtle abiotic or biotic disturbances, changing their volatile profile rapidly. How such perturbations reach and potentially affect neighboring plants is less understood. We evaluated whether brief and light touching had a cascade effect on the profile of volatiles and gene expression of the focal plant and a neighboring untouched plant. Within minutes after contact, Zea mays showed an up-regulation of certain defense genes and increased the emission of specific volatiles that primed neighboring plants, making them less attractive for aphids. Exposure to volatiles from touched plants activated many of the same defense-related genes in non-touched neighboring plants, demonstrating a transcriptional mirroring effect for expression of genes up-regulated by brief contact. Perception of so-far-overlooked touch-induced volatile organic compounds was of ecological significance as these volatiles are directly involved in plant-plant communication as an effective trigger for rapid defense synchronization among nearby plants. Our findings shed new light on mechanisms of plant responses to mechanical contact at the molecular level and on the ecological role of induced volatiles as airborne signals in plant-plant interactions.