Characterization of a cytosol-localized dual prenyl diphosphate synthase involved in monoterpene and sesquiterpene biosynthesis in strawberry

Plants produce more than a million metabolites, most of which are compounds from specialized metabolism. The biosynthesis of these metabolites is controlled by different organelles within cells. For terpenoids in particular, plant cells have two independent pathways: the methylerythritol phosphate pathway in plastids and the mevalonate pathway in the cytosol. Monoterpenes, a class of C10 compounds, play important roles in plant communication with other organisms, such as pollinators and herbivores, to aid reproduction and deter predators, respectively. Monoterpenes are generally produced by terpene synthases, which are responsible for each end product from the common substrate, geranyl diphosphate (GPP), via the methylerythritol phosphate pathway in plastids, where GPP biosynthesis also occurs. However, linalool, a major monoterpene found in strawberries (Fragaria × ananassa), is synthesized via the mevalonate pathway in the cytosol by a cytosol-localized terpene synthase, FaNES1. The enzyme that provides its substrate remains unknown. In this study, we identified two strong candidates for cytosol-localized trans-prenyltransferases. Both candidates were functionally characterized, and we demonstrated that one yielded both GPP and farnesyl diphosphate (FPP), with a higher efficiency for GPP. The other protein exclusively yielded FPP. Both proteins lack a transit peptide and are localized in the cytosol. Gene expression analysis revealed that GPP/FPP synthase is almost constantly expressed in strawberries. We also discuss a putative molecular evolution of the unique strawberry GPP synthase.