Glandular trichomes: micro-organs with model status?

Abstract

Glandular trichomes are epidermal outgrowths that are the site of biosynthesis and storage of large quantities of specialized metabolites. Besides their role in the protection of plants against biotic and abiotic stresses, they have attracted interest due to the importance of the compounds they produce for human use, for example as pharmaceuticals, flavor and fragrance ingredients or pesticides. Here, we review what novel concepts investigations on glandular trichomes have brought to the field of specialized metabolism, in particular with respect to chemical and enzymatic diversity. Furthermore, understanding the metabolic network underlying the high productivity of glandular trichomes, as well as the transport and storage of metabolites, represent the next challenges in the field. Another emerging area is the development of glandular trichomes. Studies in some model species, essentially tomato, tobacco and Artemisia, are now providing the first molecular clues, but many open questions remain: how is the distribution and density of different trichome types on the leaf surface controlled? When is the decision for an epidermal cell to differentiate into one type of trichome or another taken? Recent advances in gene editing make it now possible to address these questions and promise exciting discoveries in the near future.