Trichomes, the epidermal outgrowths covering most of aerial plant tissues, are found in a very large number of plant species and are composed of single-cell or multicellular structures. They can be glandular or non-glandular and several types of trichomes can be observed in a single plant species. Among those, multicellular glandular trichomes are characterized by the presence of a head made of cells that have the ability to secrete or store large quantities of specialized metabolites with antimicrobial and/or insecticidal properties. These compounds also act as a defense barrier to herbivorous attacks. These specialized metabolites have been largely exploited over the centuries. One of the most ancient uses originates from the aromatic properties and fragrance of some of those secretions referred to as essential oils. Many of these secreted secondary metabolites are also used for their medicinal properties, and in some cases the active ingredients have been marketed as drugs
The development of multicellular glandular trichomes proceeds through the enlargement of single epidermal cells, followed by several cell divisions to generate a structure perpendicular to the epidermal surface (see Figure 1). This highly regulated differentiation program also includes a polarized and localized cell wall lysis and remodelling. A precise understanding of the transcriptional control of glandular trichome development is still fragmentary.
Glandular trichome initiation and development in Nicotiana tabacum. A-F/ Confocal microscopy pictures showing early steps of glandular trichome development.
The number of cells forming the developing glandular trichome is shown at the bottom of each frame. A differentiating protodermal cell enlarges and forms a protuberance (A), the cell nuclei migrates to the tip of the protuberance (B), cell division takes place (C) forming a structure made of two cells (D). The upper cell protruding from the epidermis then undergoes an asymmetric division forming one large cell (which will form the multicellular stalk after several round of controlled cell division) and one small cell (which will give rise to the multicellular glandular head). A developing trichome made of five cells is shown in F. Magenta: cell wall (propodium iodide staining), Blue: nuclei (DAPI staining), Green: chloroplasts (Chlorophyll a autofluorescence). G / Scanning electron micrograph showing the typical cell architecture of a mature long glandular trichome.
Our lab is interested in the elucidation of this specific developmental process down to a molecular level. Using cutting edge molecular-, cell- and systems-biology approaches, we are working to unravel the genetic mechanisms that initiate, control and drive the development of these fascinating plant structures.
In the future, awareness of, and detailed knowledge on, the biology of plant glandular trichome development and metabolism could generate new leads to tap the largely unexploited potential of glandular trichomes in plant resistance to pests, and lead to the improved plant-based production of specialized metabolites.