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Isoprenoids constitute a wide range of metabolites with diverse functions as plant hormones (gibberellins, abscisic acid, strigolactones, brassinosteroids) or house-keeping constituents (e.g. sterols), but also contain a large group of structurally diverse secondary metabolites with roles in plant protection against insects and pathogens, attraction of pollinators or seed dispersal. Furthermore, some plant terpenoids are used industrially as pharmaceutics, flavour or fragrance ingredients. The co-existence, in the same metabolic network, of signalling molecules in extremely low concentration (nM range), of structural components, and of secondary metabolites which can be produced in high concentrations in specific tissues or even specific organelles, raises the issue of how plant cells manage to appropriately balance the flux towards these distinct isoprenoid classes with highly divergent concentrations and in competition for the same building blocks. In plants the universal isoprenoid precursors, isopentenyl diphosphate (IPP) and dimethyl-allyl diphosphate (DMAPP), are produced via two distinct routes, the cytosolic mevalonate pathway (MEV) and the plastidic deoxy-xylulose phosphate pathway (DXP). Although the allocation of precursors from these two sources is relatively strict, there is now mounting evidence that cross-talk exists, implicating most likely the transport of isoprenyl diphosphates (IPP, DMAPP, GPP or FPP) between compartments. The identity of these putative transporters is however still elusive. The production of industrially relevant terpenoids often resides in specialized cells or structures, such as the glandular trichomes. The study of isoprenoid flux in glandular trichomes is advantageous, since they are separated from the rest of the plant and are not vital organs, thus allowing the study of components of isoprenoid pathways which are otherwise essential for plant growth and development. Using two species of the Solanaceae, tomato (food) and tobacco (non-food), as model plants with glandular trichomes, we will implement a multi-disciplinary approach, including proteomics, interactomics, cell biology, biochemistry and molecular genetics, to deepen our understanding of isoprenoid metabolism. The major objectives of this project are to 1) identify transporters of intracellular isoprenoid intermediates and of terpenoid secretion; 2) determine flux through the two isoprenoid biosynthesis pathways in different types of glandular trichomes; 3) establish a complete and detailed map of sub-cellular localization of all enzymes involved in isoprenoid precursor pathways; 4) explore the interactome of isoprenoid pathway enzymes. This research programme will shed new light on how glandular trichomes achieve such massive flux towards specialized terpenoid metabolites while maintaining homeostasis, and establish new ground for a knowledge-based exploitation of these natural cell factories. |
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