Defence from the wild Specialised metabolism in tomato glandular trichomes

Glandular trichomes are small, hair-like structures found on the above-ground surfaces of about 30% of the higher plants. Consisting of one or more glandular cells, oftentimes on top of a basal-and a stalk cell, glandular trichomes synthesise, store and/or secrete so-called specialised metabolites. These metabolites are produced in complex blends and can contribute to the plant’s defence e.g. by having deterrent, antifeedant or toxic effects to the attacking organism. This thesis focusses on the specialised metabolism in glandular trichomes of wild tomato species (Solanum sp.) that are, unlike the cultivated species, often resistant to agronomically important pests. The thesis starts by linking metabolites produced by various wild-and cultivated tomato species to insect resistance by making use of the natural variation that occurs between the species and accessions. Follow-up studies demonstrate how one of the wild species (S. habrochaites accession PI127826) synthesises a sesquiterpene derivative (9-hydroxy-10,11-epoxyzingiberene) in its trichomes that is toxic to whiteflies (Bemisia tabaci) and several micro-organisms. The introgression of this trait from PI127826 into a cultivated tomato background was shown to be successful, although terpene quantities produced seem to be constrained. Experiments indicate that terpene biosynthesis in tomato glandular trichomes run primarily via the plastidial biosynthetic pathway (MEP), and, while this pathway is highly active in the wild species, seems to be repressed in cultivated tomato. Finally, a method is presented to modulate the MEP pathway, and thereby terpene levels, in glandular trichomes of cultivated tomato by genetic engineering.