Control of Natural Product Production in Aromatic Herbs

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Culinary and other aromatic herbs make a significant contribution to improving the appeal of foodstuff and play increasingly important roles in our society as components of the herbal remedies and supplements industry. However, the biosynthesis of almost all bioactive secondary compounds or natural products is still poorly understood. The plant family Lamiaceae (e.g., sweet basil and mint) includes many species that are rich in such natural products. Natural product production by the plant is believed to be associated with defense against herbivores and pathogens, and Lamiaceae species have evolved elaborate structures on the surface of their leaves, known as peltate glands, where these chemicals are synthesized and stored. Basil is a particularly noteworthy herb because it synthesizes relatively high amounts of both terpenoids and phenylpropanoids, two large classes of compounds that include many plant defense and medicinally important natural products, including paclitaxel (Taxol) and podophyllotoxin (derivatized to form Etoposide and Teniposide) that are used to treat cancer. Aside from some focused efforts to delineate the pathways to specific compounds, such as paclitaxel and podophyllotoxin, very little is known about the biochemical reactions that produce the great diversity of compounds that result from these two biosynthetic pathways. Even less is known about the genes and enzymes that control or regulate these pathways. This research project aims to identify how secondary compounds are produced in basil peltate glands and to begin to identify and define the mechanisms that control their production. Specifically, this research will: 1) use metabolic profiling to characterize levels of known metabolites and potential intermediates in the phenylpropanoid pathway in peltate glands of select basil lines; and 2) use a functional genomics approach to determine what roles specific enzymes and other regulatory factors play in controlling the flux into and through the phenylpropanoid pathway in basil peltate glands.The research results and developed tools will form a foundation that should facilitate research of other plant secondary metabolic pathways. In addition to the intrinsic scientific value of understanding how plants produce natural products, such knowledge is essential for rational design of breeding strategies to produce plants with targeted natural product profiles. This knowledge will also help in the application of genetic engineering to improve and develop new aromatic plants, which could then serve as feed stocks for the pharmaceutical and other industries.