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Our lab is interested in the elucidation of the molecular genetic framework governing the development of glandular trichomes in the leaf epidermis of Nicotiana tabacum and their patterning at the leaf surface.
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 developmental program also includes a polarized and localized cell wall lysis and remodelling.
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.
听G/听Photo d鈥橝ntoine Champagne
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Plant glandular trichomes are elaborated and highly organized cell structures, suggesting the existence of an intricate array of molecular processes controlling the different steps of their patterning on the leaf epidermis and subsequent development. A detailed understanding of the molecular genetic framework governing the development and patterning of these tiny cell factories is however still missing.
- What are the different steps of the differentiation process of glandular trichomes in N.tabacum?
- How do such specialized multicellular plant structures differentiate from the protodermis?
- Which genes are pivotal to initiate, control, and drive this differentiation process?
A complete circuit for glandular trichome development and patterning in the leaf epidermis will require knowledge of the genes that regulate cell division, that participate in cell signaling, and that promote specialized cell fate. It will also require understanding how this developmental regulatory network impinges on cellular biological targets such as the core cell cycle machinery. A particularly large gap in our knowledge is the identification of regulators of entry into the glandular trichome cell fate and of progression through the pathway (Figure 2).
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.
Glandular trichome initiation and development, a process with many unknowns.
A differentiating protodermal cell integrates both environmental and endogenous signals. Such signal integration results in the selection of a pool of trichome cell precursors which will initiate a specific developmental program. In these trichome initials, cell-specific transcriptional control of gene expression and cell cycle regulation results in the onset of a controlled cell division and trichome morphogenesis program, most of which is still not so well understood in case of glandular trichomes. It probably also involves some cell-cell signaling promoting the 鈥渙ne cell-spacing rule鈥� which allows a specific patterning of trichomes in the epidermis. Morphogenesis of the trichomes glandular head also necessitates extensive remodeling of the cell wall. The extent of endoreduplication in glandular trichomes is still mostly uncharacterized. The illustration shows a modified confocal picture of a long glandular trichome initial from Nicotiana. tabacum. Chloroplasts are shown in green, propidium iodide-stained cell walls in magenta and nuclei in cyan
Awareness of, and detailed knowledge on, the biology of plant glandular trichome development and metabolism will generate new leads to tap the largely unexploited potential of glandular trichomes in plant resistance to pests, and lead to the improved production of specialized metabolites with high industrial or pharmacological value.