471323 Plants 2.0: Towards Metabolic Engineering of Natural Product Biosynthesis into Crops

Friday, November 18, 2016: 1:06 PM
Continental 7 (Hilton San Francisco Union Square)
Amy Calgaro, Andrew P. Klein and Elizabeth Sattely, Department of Chemical Engineering, Stanford University, Stanford, CA

By 2050, 9.7 billion people will inhabit the earth. To feed this growing population, we need to combat plant pathogens, which cause 65% of crop damage in the United States alone. One solution is to engineer production of natural defense metabolites from wild, or even domesticated, plants into crops. When attacked by pathogens, a few cruciferous plants, such as Chinese cabbage (Brassica rapa) and watercress (Nasturtium officinale), produce a group of secondary metabolites called phytoalexins. Indole phytoalexins (brassinins) and benzyl phytoalexins (nasturlexins) are especially affective against bacterial and fungal pathogens1. They can improve human health as well; in vitro studies show brassinin is highly affective against cancer cell lines2.

By engineering brassinin synthesis into a crop, we introduce not just a single anti-fungal, anti-cancer compound, but potentially over a dozen brassinin derivatives, each with unique defense and therapeutic properties. Towards this end, we recently discovered a 10 gene pathway in B. rapa for the synthesis of brassinin and two more enzymes responsible for its derivatization. Furthermore, preliminary results show this pathway is active in planta when transiently and constitutively expressed in tobacco (Nicotiana benthamiana ). However, transient engineering is unacceptable for a crop trait that must be passed through generations and constitutive production of brassinin enzymes and intermediates appears to have detrimental effects on plant health. Therefore, our ultimate goal is creation of a stable engineered crop line which produces brassinin only under pathogen stress.

Here we present our progress towards introduction of phytoalexin biosynthesis in planta. We first focus on initial transient expression of these pathways in tobacco and the model plant Arabidopsis thaliana. Then we discuss our progress toward engineering of A. thaliana stable lines which both synthesize brassinin and, with careful promotor design, regulate brassinin biosynthesis. We chose to create an A. thaliana prototype both as a proof of concept and to study the effect of this pathway on plants and their commensal microbial communities. Finally, we present our outlook for the characterization of brassinins on the plant-microbe system and the introduction of this pathway into a crop, such as soybean (Glycine max). Understanding these phenotypes and initial engineering of these pathways will be extremely important for successful integration of aromatic defense molecules into crop plants and improved food yield.

1 Pedras, M. Soledade C., Estifanos E. Yaya, and Erich Glawischnig. "The phytoalexins from cultivated and wild crucifers: chemistry and biology."Natural product reports 28.8 (2011): 1381-1405.

2 Kim, Sung‐Moo, et al. "Brassinin Induces Apoptosis in PC‐3 Human Prostate Cancer Cells through the Suppression of PI3K/Akt/mTOR/S6K1 Signaling Cascades." Phytotherapy Research 28.3 (2014): 423-431.

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