Genome-based discovery of pachysiphine synthases in Tabernaemontana elegans

Plant specialized metabolism represents an inexhaustible source of active molecules, some of which have been used in human health for decades. Among these, monoterpene indole alkaloids (MIAs) include a wide range of valuable compounds with anticancer, antihypertensive, or neuroactive properties. This is particularly the case for the pachysiphine derivatives which show interesting antitumor and anti-alzheimer activities but accumulate at very low levels in several Tabernaemontana species. Unfortunately, genome data in Tabernaemontanaceae are lacking and knowledge on the biogenesis of pachysiphine-related MIAs in planta remains scarce, limiting the prospects for biotechnological supply of many pachysiphine-derived biopharmaceuticals. Here, we report a raw version of the toad tree (Tabernaemontana elegans) genome sequence. These new genomic resources led to the identification and characterization of a couple of genes encoding cytochrome P450 with pachysiphine synthase activity. Our phylogenomic and docking analyses highlights the different evolutionary processes that have been recruited to epoxidize the pachysiphine precursor tabersonine at a specific position and in a dedicated orientation, thus enriching our understanding of the diversification and speciation of the MIA metabolism in plants. These gene discoveries also allowed us to engineer the synthesis of MIAs in yeast through the combinatorial association of metabolic enzymes resulting in the tailor-made synthesis of non-natural MIAs. Overall, this work represents a step forward for the future supply of pachysiphine-derived drugs by microbial cell factories. Significance StatementWhile pachysiphine is a monoterpene indole alkaloid of high interest and the precursor of an anti-Alzheimer compound, its biosynthesis involving the epoxidation of tabersonine remains uncharacterized. By sequencing and assembling the genome of Tabernaemontana elegans, we identified two P450s exhibiting a pachysiphine synthase activity that we modelized to explore the evolutionary scenario leading to the acquisition of this expoxidase activity; and used to engineer yeast cell factories for securing pachysiphine supply and producing new-to-nature alkaloids.