Interplant communication: From induced volatiles to signal transduction pathways
 
Jürgen Engelberth*, Irmgard Seidl-Adams, Jack C. Shultz, James H. Tumlinson
Penn State University, Dept. of Entomology, 117 A Chemical Ecology Lab, University Park, PA 16802, USA
*email: jee11@psu.edu
 

Plants under insect herbivore attack have evolved various mechanisms to counteract this threat. Among the measures plants undertake to survive with the least damage are the recognition of insect-derived elicitors, production of proteins that block digestion or disrupt intestinal tissue, and the production of defense-related secondary metabolites, which directly or indirectly affect the herbivore performance. Volatile organic compounds (VOC), a mixture of volatile secondary metabolites from various pathways, serve as signals not only to attract predators and parasites of attacking herbivores, but also can be recognized by neighboring plants resulting in defense-related gene expression. Jasmonic acid (JA) and other lipid-derived compounds (oxylipins), which are activated by wounding and insect elicitors, represent important signals in this process. In corn (Zea mays), insect-derived elicitors not only increase the production of oxylipins locally, but also induce JA distal from the application site within 5-10 min. Green leafy volatiles (GLV), which are rapidly emitted during herbivory, serve as potent volatile signals for neighboring receiver plants. By inducing specific sections of the octadecanoid signaling pathway GLV can act as priming signals preparing those plants against impending herbivory. Structure/function analysis of natural GLV as well as synthetic analogs clearly showed certain structural requirements, but excluded α,β-unsaturated carbonyls as active centers. A comparison of gene expression after wounding, wounding with application of crude regurgitant elicitors (CRE), and exposure to Z-3-hexenyl acetate (Z-3-HAC) further demonstrated the specificity of the GLV signal in plant-plant communication through selective activation of genes involved in JA biosynthesis. In conclusion, inter-plant communication via GLV results in an enhanced preparedness specifically directed against insect herbivore attack mediated by specific activation of distinct parts of the octadecanoid signaling pathway.

 
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