In response to herbivory, many plants produce defense compounds which can either be toxic or repellant for the herbivore or attractive for natural enemies of the herbivore. These direct and indirect defense mechanisms often present strong barriers against various attackers. Such induced plant defense mechanisms have been intensively studied above-ground, but little is known about the induced defenses of roots, especially those of trees. In this project we will investigate the formation and biological role of volatile and non-volatile defense compounds produced in poplar roots after insect attack. Preliminary experiments revealed that feeding of cockchafer (Melolontha melolontha) larvae on poplar roots induces the emission of volatiles (terpenes, aldehydes) and leads to an increased accumulation of non-volatile defense compounds such as phenolic glycosides in the roots. Using a transcriptomic approach, we will identify candidate genes involved in poplar root defense. The identified genes will be heterologously expressed in bacteria or yeast to characterize the encoded enzymes. RNAi will be used to generate transgenic poplar trees with either decreased or increased levels of terpenes, aldehydes or phenolic glycosides.
After a comprehensive metabolomic analysis using GC-MS, LC-MS/MS, and NMR, the transgenic trees will be used in behavioral assays with cockchafer larvae in order to elucidate the biological role of the different volatile and non-volatile defense compounds. The project will provide excellent training in plant biochemistry, enzymology and molecular biology as well as analytical chemistry and ecological assays. The candidate for this project should have a Master degree or equivalent in biochemistry or biology and previous experience in biochemistry, enzymology, and/or molecular biology.