Floral scent emission ofEpiphyllum oxypetalum: identification of a novel cytosol-localized geraniol biosynthesis pathway

Summary Epiphyllum oxypetalum , a renowned ornamental species in Cactaceae, releases attractive fragrance during its infrequent, transient and nocturnal flowering, the nature and biosynthesis of the volatiles for this floral scent, however, remained unexplored. Employing volatilomic, transcriptomic and biochemical approaches, we systematically characterized the composition, emission dynamics and biosynthesis of E. oxypetalum floral scent. Floral scent composition was highly dynamic, with trans-geraniol comprising 72.54% of the total emission at full bloom, followed by benzyl alcohol (12.96%) and methyl salicylate (3.75%), which predominantly emanated from petals and sepals. Transcriptomic analysis and inhibition assay using pathway-specific inhibitors revealed the mevalonate (MVA) pathway as the precursor source for trans-geraniol biosynthesis. Together with elevated expression of both cytosol-localized geraniol pyrophosphate synthase EoGDPS and geraniol synthase EoTPSa1, we elucidated an unusual cytosolic biosynthesis route for geraniol in E. oxypetalum petals. Our study on E. oxypetalum scent emission and its biosynthesis offers a comprehensive profile of cactus floral scent profiles and presents a rare case of cytosolic geraniol biosynthesis using MVA pathway-derived substrates. These findings underline the unique metabolism of cactus flower volatiles, which hold a promise to be applied in the development of novel perfumes.