Microbial-type terpene synthases enable enhanced insect and fungal resistance in engineered plants

A major challenge in crop improvement is enhancing resistance to diverse biotic stresses. Because terpenoids play key roles in chemical defense, an envisioned strategy is to introduce new terpene metabolic pathways into crops through engineering. Microbial-type terpene synthase-like (MTPSL) genes are widespread in nonseed plants but absent in seed plants. Here, we engineered terpene metabolism in Nicotiana benthamiana using MTPSL genes, enabling production of sesquiterpenes absent in flowering plants and enhanced resistance to pest insects and fungal pathogens. Two liverwort MTPSL genes, RlMTPSL3 and RlMTPSL4, which produce sesquiterpenes absent from flowering plants, were selected for metabolic engineering. In N. benthamiana, both genes generated sesquiterpenes consistent with their in vitro activities, and co-expression yielded combined profiles. Co-expression of RlMTPSL3 and RlMTPSL4, individually or together, with 3-hydroxy-3-methylglutaryl-CoA reductase, the rate-limiting enzyme in sesquiterpene pathway, substantially increased sesquiterpene production. Bioassays of engineered tissues with two defoliating herbivores beet armyworm (Spodoptera exigua) and Colorado potato beetle (Leptinotarsa decemlineata) showed growth suppression and up to 30% mortality. The gut microbiome of beet armyworm feeding on engineered tissues showed differences from those feeding on control tissues, suggesting a potential mechanism underlying reduced pest insect performance. Engineered sesquiterpenes were recovered from larval frass, indicating stability through digestion. Transformed leaves emitted elevated sesquiterpenes as volatiles that repelled beet armyworm. In addition, extracts of engineered tissues inhibited the growth of Fusarium oxysporum, a fungal pathogen, by ∼50%. Together, these results demonstrate that MTPSL-based engineering can introduce new sesquiterpenes into flowering plants, providing a promising strategy for broad-spectrum crop protection.