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

O_LIEpiphyllum 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. C_LIO_LIEmploying volatilomic, transcriptomic and biochemical approaches, we systematically characterized the composition, emission dynamics and biosynthesis of E. oxypetalum floral scent. C_LIO_LIFloral 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. C_LIO_LIOur 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. C_LI