Volatile defence signalling: molecular basis of herbivory-induced terpene biosynthesis and emission in purple willow leaves

Volatiles play an important role in biotic plant-environment interactions. While major research has been conducted on the emission of herbivore-induced plant volatiles in annual herbaceous species, little comparable information is available about long-living plant species. This study shows that herbivory by gypsy moth (Lymantria dispar) caterpillars or poplar leaf beetles (Chrysomela populi) on purple willow (Salix purpurea) leaves led to the induced emission of complex volatile bouquets, including a wide range of mono- and sesquiterpenes. Further comprehensive sequence and phylogenetic analyses enabled the identification of a mid-sized terpene synthase (TPS) family within the S. purpurea genome. The heterologous overexpression of identified S. purpurea TPS candidate genes in E. coli revealed their respective activities in the formation of the monoterpene alcohol linalool, as well as the sesquiterpenes (E,E)-α-farnesene and germacrene D, among others. Moreover, the majority of the herbivore-induced terpenoid volatile bouquet of S. purpurea leaves could be reconstituted in the volatile blend of the heterologous host Nicotiana benthamiana by overexpression of the respective TPS candidate genes.