Re-routing plant terpene biosynthesis enables momilactone pathway elucidation

Momilactones from rice have allelopathic activity, the ability to inhibit growth of competing plants. Transferring momilactone production to other crops is a potential approach to combat weeds, yet a complete biosynthetic pathway remains elusive. Here, we address this challenge through rapid gene screening in N. benthamiana, a heterologous plant host. To do so, we solved a central problem with this technique: diminishing yields remain a bottleneck for multi-step pathways. We increased intermediate and product titers by re-routing diterpene biosynthesis from the chloroplast to the cytosolic, high-flux mevalonate pathway. This enabled the discovery and reconstitution of a complete route to momilactones (>10-fold yield improvement versus rice). Pure momilactone B isolated from N. benthamiana inhibits germination and root growth in Arabidopsis, validating allelopathic activity. We demonstrate the broad utility of this approach by applying it to forskolin, a hedgehog inhibitor, and taxadiene, an intermediate in taxol biosynthesis (~10-fold improvement versus chloroplast expression).