Early herbivore-elicited events in terpenoid biosynthesis

Volatile terpenoids, the major products among the herbivore-induced plant volatiles in the legume, mediate interactions that attract herbivores' natural enemies and serve as signals to neighboring plants. We recendy demonstrated cross-talk among the signaling components involving Ca²⁺, jasmonic acid and ethylene, which are altogether responsible for volatile terpenoid formation in Medicago truncatula. Herbivore-stimulated Ca²⁺ transients are an additional element that has an impact on the composition of the blend of terpenoids, whose biosynthesis depends on the jasmonic acid/ethylene pathway. The molecular diversity of the blend is expanded and modulated by the transcriptional regulation of terpene synthases, some of which are multi-functional enzymes producing a large set of sesqui- and monotepenes or precursors of C₁₁ and C₁₆ homoterpenes from different prenyl diphosphates. In this addendum, we discuss a new perspective on early events leading to terpenoid biosynthesis.