Balancing Flux through Secondary Metabolic Pathways in Plant Culture Systems

Plants are a valuable source of chemical compounds with applications ranging from fragrances and flavors to pharmaceuticals. Due to their sophisticated structures, chemical synthesis of these compounds is often difficult, necessitating biological production platforms. Metabolic engineering can be used to improve product yields in both whole plant and cell culture systems. However, due to the complex interactions between plant primary and secondary metabolism and within cooperating and competing secondary pathways, it is difficult to predict the effect of single gene overexpression or silencing on overall cellular metabolism. To begin to understand these complex relationships, we developed assays to map flux through key pathways to general classes of secondary products (i.e., phenolics, flavonoids, alkaloids), as well as relevant endpoint products (lignin and taxanes). Using the Taxus suspension culture system that uniquely accumulates the anti-cancer drug paclitaxel, we studied distribution of flux through secondary metabolic pathways upon induction with the abiotic elicitor methyl jasmonate. Results demonstrate that individual cell lines respond variably to methyl jasmonate by upregulating different secondary metabolic pathways. In addition, we studied the heterogeneity in secondary metabolic flux distribution over multiple generations of growth, identifying key competing pathways for paclitaxel accumulation in each cell line. These studies are amongst the first to study global secondary metabolism in a non-model plant species and provide valuable insight into the design of effective metabolic engineering strategies to promote production of a particular class of secondary products.