Functional identification of 10-hydroxygeraniol oxidoreductases related to camptothecin biosynthesis in Ophiorrhiza pumila.

As a leading cause of death worldwide, cancer severely threatens human health and life. Camptothecin, a plant-derived monoterpene indole alkaloid (MIA) has been extensively used to treat various cancers. However, the camptothecin production in its plants sources is low and cannot meet the global need. Identifying enzyme-encoding genes related to camptothecin biosynthesis could provide parts for the reconstruction of camptothecin biosynthetic pathway in heterologous systems using synthetic biology tools, thus guaranteeing the camptothecin supply. In this study, 15 10-hydroxygeraniol oxidoreductases (10HGOs) were genome-wide identified in O. pumila, and three Op10HGOs namely Op10HGO1, Op10HGO2, and Op10HGO3 were subjected to the enzymatic activity assays. Op10HGO2 and Op10HGO3 exhibited the ability to convert 10-hydroxygeraniol into 10-oxogeraniol, 10-oxogeranial, and 10-hydroxygeranial in the presence of NADP, whereas Op10HGO1 catalyzed the production of 10-oxogeraniol and 10-hydroxygeranial. Overexpression of Op10HGO2 led to increased camptothecin content in Ophiorrhiza pumila hairy roots, whereas knock-out of Op10HGO2 markedly decreased the camptothecin content, indicating its important roles in the biosynthesis of camptothecin. This work provided a candidate gene for enhancing the camptothecin production in O. pumila using transgenic approaches, as well as offered available DNA parts for reconstructing the MIAs biosynthetic pathway.