Streamlined screening platforms lead to the discovery of pachysiphine synthase from Tabernanthe iboga

Plant-specialized metabolism is largely driven by the oxidative tailoring of key chemical scaffolds catalyzed by cytochrome P450 (CYP450s) enzymes. Monoterpene indole alkaloids (MIAs) tabersonine and pseudo-tabersonine, found in the medicinal plant Tabernanthe iboga (commonly known as iboga), are tailored with oxidations, and the enzymes involved remain unknown. Here, we developed a streamlined screening strategy to test the activity of T. iboga CYP450s in Nicotiana benthamiana. Using multigene constructs encoding the biosynthesis of tabersonine and pseudo-tabersonine scaffolds, we aimed to uncover the CYP450s responsible for oxidative transformations in these scaffolds. Our approach identified two T. iboga cytochrome P450 enzymes: pachysiphine synthase (PS) and 16-hydroxy-tabersonine synthase (T16H). These enzymes catalyze an epoxidation and site-specific hydroxylation of tabersonine to produce pachysiphine and 16-OH-tabersonine, respectively. This work provides new insights into the biosynthetic pathways of MIAs and underscores the utility of N. benthamiana and Catharanthus roseus as platforms for the functional characterization of plant enzymes.