The surface of plants plays a critical role in the interaction with their environment and their ability to protect themselves against biotic and abiotic stresses. The epidermal layer is therefore a tissue with a number of features of particular significance to its localization at the interface between the inside and the outside of the plant. One of these is the presence of protuberances which cover the aerial parts of the plant. These protuberances, or trichomes, come in a large variety of shapes, sizes, structures and metabolic capacity. Despite this diversity, trichomes can be classified in two main categories according to their ability to synthesize and secrete large quantities of metabolites. Non-glandular trichomes, or hairs, produce little specialized metabolites, and represent a purely physical protection barrier. For example the model plant Arabidopsis thaliana is covered exclusively with unicellular non-glandular trichomes. In contrast, glandular trichomes typically contain at their top one to a dozen secretory cells, which are true cell factories, producing, secreting and in some cases storing, abundant metabolites. These are in general hydrophobic, such as terpenoids or fatty acid derivatives. They can be volatile, such as the essential oils of many aromatic plants, or make an oily and sticky resin, forming a deadly trap for insects. Glandular and non-glandular trichomes can coexist on the same plant, even with different types of glandular trichomes, resulting in a complex leaf surface landscape.
The fact that the biosynthesis of secreted compounds takes place in the glandular cells has greatly facilitated the elucidation of the pathways involved, notably through expressed sequence tag (EST) collections. Glandular trichomes are also the tissues where a number of industrially relevant compounds are produced. This includes the aromatic and fragrant essential oils of many species of the Lamiaceae family, e.g. mint, basil, lavender, thyme, sage and oregano, but also pharmaceutical ingredients like artemisinin, a sesquiterpene from sweet wormwood, Artemisia annua, which is at the origin of novel treatments for malaria. In addition, there are numerous reports pointing to a role of glandular trichome secretions in the defense against insects. Finally, as metabolic cell factories, the secretory cells of the glandular trichomes represent an interesting target for metabolic engineering for the production of novel compounds.
We are interested in various aspects of glandular trichome biology including terpenoid biosynthesis, metabolic engineering, and development. Our model species for this are plants of the Solanaceae family, namely tomato and tobacco, which present the advantage of good genetic resources, extensive transcriptome sequences, interesting natural variation and genetic diversity. In addition, the genome of cultivated tomato (Solanum lycopersicum) was recently sequenced, and 100 more Solanaceae genomes will be sequenced in the near future, thus providing a valuable resource for gene identification and characterization.