Intercepting Plant Defense Signaling

Abstract

Herbivorous insects stimulate signaling cascades in the plants being eaten that help the plants mount a defense against these voracious enemies. Plant defense mechanisms can involve the activation of the jasmonate and salicylate pathways that can stimulate the production of toxic chemicals known as allelochemicals. Li et al. report that the gene expression of the cytochrome P450 genes involved in allelochemical detoxification in the corn earworm, Helicoverpa zea , can be stimulated in response to ingestion of jasmonate or salicylate. When worms were allowed to eat celery leaves that had been previously damaged to stimulate jasmonate and salicylate production, the cytochrome P450 genes were stimulated in the worms. These damaged leaves had not yet accumulated allelochemicals, which are known to stimulate detoxifying enzyme production in insects. Finally, previous exposure to jasmonate or salicylate enhanced survival of worms ingesting celery leaves. The authors call this process "signal eavesdropping" and suggest that the ability to enhance the synthesis of detoxifying enzymes before the toxins accumulate may provide the insects with prophylactic protection from plant defenses. For biochemical details of jasmonate signaling, see the Connections Map by Liechti and Farmer. X. Li, M. A. Schule, M. R. Berenbaum, Jasmonate and salicylate induce expression of herbivore cytochrome P450 genes. Nature 419 , 712-715 (2002). [Online Journal] R. Liechti, E. E. Farmer, Jasmonate biochemical pathway. Science's STKE (Connections Map as seen October 2002), http://stke.sciencemag.org/cgi/cm/CMP_7361. [Pathway]