Comparative Genomics of Secretory Trichomes - Biofactories for Production of Plant Secondary Metabolites

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A genomics approach to the synthesis and secretion of bioactive plant natural productsPI Richard Dixon, Samuel Roberts Noble Foundation coPI M. David Marks University of MinnesotaCollectively, plants are a rich source of natural products, chemicals that often function to protect the plant from infection or insect pests. Natural products also form the basis of many currently used drugs, such as aspirin, morphine, taxol or the antimalarial compound artemesinin. Plant natural products are often synthesized and accumulated in secretory trichomes, which are appendages found on the aerial organs of plants. Trichomes have a unique capacity for chemical synthesis and secretion, and have been described as biofactories for the production of natural products. However, with few exceptions, little is known about the molecular aspects of trichome metabolism and secretion. The production of many natural products in specialized trichome cells facilitates genomics-based approaches to characterize biosynthetic and secretory processess. In this project, a large number of expressed sequence tags (ESTs) will be generated corresponding to genes expressed in trichomes of five species representing different plant families and both model and crop plants; Medicago truncatula and M. sativa (alfalfa), Leguminosae; Nicotiana benthamiana and Lycopersicum esculentum (cultivated tomato), Solanaceae; and hops (Humulus lupulus). Potato leafhopper resistant and susceptible alfalfa lines will be compared. At the same time, the full spectrum of natural products produced in the trichomes of these five species will be determined. The EST collection will be mined for genes involved in the regulation, biosynthesis and transport of natural products, and the functions of a selection of those genes that are common to multiple species will be determined by over- or under-expressing them in Arabidopsis thaliana.The project is multidisciplinary, combining genomics, informatics and molecular biology with analytical biochemistry, enzymology, and metabolic engineering, and provides excellent training for postdoctoral fellows and undergraduate students in the skills increasingly required in the post-genomics age. The Noble Foundation and University of Minnesota will link the subject area of the project to the curricula of their existing student outreach programs. A major deliverable of the project, TrichOME, a publicly available database of genes and metabolites expressed in plant trichomes, will be an important addition to plant genome sequence information, as genes only expressed in trichomes may be under-represented in non-tissue-targeted EST sequencing projects. As the project develops, gene sequences in the database will be linked to functional information describing the involvement of the genes in trichome-specific processes. The project will also improve our understanding of the synthesis, storage and secretion of a range of useful bioactive natural products, from anti-insect lipid amides in alfalfa to heath-beneficial prenyl chalcones and bitter acid flavors/antimicrobials in hops.