Volatile-Mediated Plant Defense Networks: Field Evidence for Isoprene as a Short-Distance Immune Signal.

Isoprene, the most abundant biogenic hydrocarbon in the atmosphere, is known to protect photosynthesis from abiotic stress and significantly impact atmospheric chemistry. While laboratory studies show that isoprene can enhance plant immunity, its role in plant-plant communication under natural field conditions remains unclear. In a 2-year field experiment, we used wild-type and transgenic silver birch (Betula pendula) lines with enhanced isoprene emission levels to examine their impact on neighboring Arabidopsis thaliana, including wild-type and immune signaling mutants (llp1: legume lectin-like protein 1; jar1: jasmonate resistant 1). Receiver plants exposed to higher isoprene levels showed increased resistance to Pseudomonas syringae, independent of jasmonate signaling but dependent on LLP1, a protein essential for systemic acquired resistance. Volatile analysis indicated isoprene as an airborne molecule that can also trigger an immune response in neighboring plants along with other terpenoids. Our study using transgenic birches in a complex environment provides new insights into the molecular mechanisms underlying plant volatile perception and expands our understanding of plant chemical communication in terrestrial ecosystems.