Accelerated Discovery and Engineering of Medicinal Plant Alkaloid Biosynthetic Pathways

Plants have served as crucial medicines for thousands of years, and continue to supply us with clinical pharmaceuticals and novel compounds with diverse bioactivities. However, our ability to access the molecules produced by medicinal plants is often limited by their slow growth, difficulty in cultivation, and the threat of over-harvesting native populations. One potential strategy to alleviate these challenges is through the metabolic engineering of plant biosynthetic pathways for medicinal compounds, but this requires underlying knowledge of the requisite metabolic genes, as well as a heterologous system in which pathways can be rapidly tested and assembled. By leveraging the conditional production of plant-derived molecules in native plants, we have been able to utilize a combined metabolomic and transcriptomic approach for the rapid discovery of biosynthetic pathways for multiple medicinal plant alkaloids. This includes a near complete pathway for huperzine A, a psychoactive compound with potential as a treatment for neurological diseases, as well as a full biosynthetic pathway for colchicine, an ancient and still-utilized treatment for inflammatory conditions. Critically, we have not only established a full set of genes for colchicine biosynthesis, but we have also engineered its complete pathway, consisting of 20 genes, into the model plant Nicotiana benthamiana, thereby demonstrating an alternative means to produce this pharmaceutical molecule. Our results highlight a powerful strategy for the discovery of plant biosynthetic pathways, and further provide a proof-of-concept for the engineered production of medicinal alkaloids. Additionally, our insight into the biosynthetic reactions used to produce these molecules has led to the discovery of novel catalytic mechanisms for well-known enzyme families, as well as the identification of new classes of specialized metabolic enzymes, thereby expanding our understanding of the remarkable breadth and diversity of chemistry used within plant metabolism.