Plant Glandular Trichomes: Natural Cell Factories of High Biotechnological Interest

Abstract

ORCID IDs: 0000-0001-9302-405X (A.H.); 0000-0002-2315-6900 (M.B.); 0000-0002-3688-7614 (C.H.).Multicellular glandular trichomes are epidermal outgrowths characterized by the presence of a head made of cells that have the ability to secrete or store large quantities of specialized metabolites. Our understanding of the transcriptional control of glandular trichome initiation and development is still in its infancy. This review points to some central questions that need to be addressed to better understand how such specialized cell structures arise from the plant protodermis. A key and unique feature of glandular trichomes is their ability to synthesize and secrete large amounts, relative to their size, of a limited number of metabolites. As such, they qualify as true cell factories, making them interesting targets for metabolic engineering. In this review, recent advances regarding terpene metabolic engineering are highlighted, with a special focus on tobacco (Nicotiana tabacum). In particular, the choice of transcriptional promoters to drive transgene expression and the best ways to sink existing pools of terpene precursors are discussed. The bioavailability of existing pools of natural precursor molecules is a key parameter and is controlled by so-called cross talk between different biosynthetic pathways. As highlighted in this review, the exact nature and extent of such cross talk are only partially understood at present. In the future, 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.

TRANSPARENT TESTA GLABRA1 (TTG1) regulates leaf trichome density in tea Camellia sinensis

“…To date, many genes and transcription factors, such as GL3, EGL3 and NAC, have been identified to be involved in the control of trichome formation in Antirrhinum, A. thaliana and species of Solanaceae. Some of the functions of these genes have been documented in detail and were found to be conserved among species (Huchelmann et al 2017). In this study, we found that the transcription level of CsTTG1 is positively correlated with the trichome density of a majority of the investigated tea cultivars.…”

“…In addition, a large number of animals, insects and pathogens live in these areas, and trichomes protect the plants from herbivores and pathogens (Ehleringer 1984, Brewer andSmith 1997). Some of the functions of these genes have been documented in detail and were found to be conserved among species (Huchelmann et al 2017). We also observed that trichome density varies considerably among different varieties.…”

“…Trichomes can synthesize, store and sometimes secrete large amounts and various types of specialized metabolites, such as terpenes, phenylpropanoid derivatives and flavonoids (van Der Hoeven et al 2000, Gang et al 2001, Valkama et al 2003. Secondary metabolites have become popular not only because of their significance in the protection of plants against environmental stressors but also because they have great commercial value as food additives or pharmaceuticals (Schilmiller et al 2008, Glas et al 2012, Chen et al 2017, Huchelmann et al 2017, Yan et al 2017, Sun et al 2019a. For example, Cistus salvifolius trichomes synthesize and store polyphenols that affect both radiation absorbance and plant desiccation, which evolved for adaptation to high light stress and poor soil conditions along Mediterranean coasts (Tattini et al 2007).…”

Genes regulating gland development in the cotton plant

“…Because we found no visible glands in the embryos at 14 dpa, we hypothesized that comparative transcriptomics at this time-point would reveal the identity of the genes that play an important role in initiating gland formation. The later stages of embryo development are likely to reveal the genes that are involved in gland maturation and biosynthesis of secondary metabolites, including gossypol (Huchelmann et al, 2017).…”

Identification of two new trichome-specific promoters of Nicotiana tabacum

“…From these trials, N. tabacum has emerged as one of the most suitable plant hosts (Moses and Pollier 2013;Lange et al 2013;Wang et al 2016). N. tabacum synthesizes an important pool of terpenoid precursors (IPP/DMAPP) and, besides the essential metabolites derived from the isoprenoid biosynthesis pathways, it also produces a very high amount of a limited range of specialized metabolites (Huchelmann et al 2017).…”