Rewiring Photosynthesis for Terpene Production

One of the most fundamental challenges in agriculture and bioenergy is the efficient partition of photosynthates toward a target carbon sink. We used squalene as a model carbon sink to evaluate how photorespiratory glycolate could be redirected to pyruvate and subsequently terpene biosynthesis. Both computational and experimental studies suggested that a functional C2 redirection could increase terpene yield without significantly impacting photosynthetic carbon fixation. The squalene yield in transgenic tobacco implemented with various C2 redirection designs increased up-to four-fold as compared to the lines engineered for terpene biosynthesis only. The C2 redirection has enabled a record level production of squalene at 2.7 mg/g fresh weight (FW) of tobacco leave. Further analysis of carbon flux by feeding of radioactive labelled glycolate indicated that C2 redirection led to increased carbon flux from glycolate to malate and squalene. The C2 redirection plants provided optimal models to study how photosynthesis might be rewired to increase a target compound yield. Metabolomics analysis revealed a significant carbon repartition, as a decrease in the intermediates of sucrose and starch biosynthesis correlated with an increase in malate and pyruvate in the C2 redirection lines. Correlating with the computational study, we have established that redirecting phtorespiratory C2 products to pyruvate could result in significant carbon repartition from storage carbohydrates to terpene without compromising photosynthesis.  In addition, recent advances indicated that the integration of carbon repartition by C2 redirection with improved carbon fixation can further increase squalene production to more than 7mg/g FW in tobacco, which represented a more than 10 fold increase of the current state-of-the-art. Together, the results indicated that photosynthetic organisms have the potential to be engineered for efficient production of high value terpene compounds, when proper strategies for carbon repartition and photosynthesis improvement were integrated. The study has provided a new platform for the production of nutraceutical and pharmaceutical compounds.