How the ‘Queen of the night’ flower rapidly produces its iconic scent

Floral scents play essential ecological roles, attracting pollinators and deterring herbivores. Geraniol, a monoterpene with a sweet, rose-like aroma, is a major commercial fragrance component widely used in the perfume and flavor industries. In most flowering plants, geraniol biosynthesis occurs in plastids and relies on precursors from the methylerythritol phosphate (MEP) pathway.

Alternative pathways in monoterpene synthesis

However, emerging evidence suggests that alternative cytosolic pathways may also contribute to monoterpene synthesis in certain species. Yet, the extent, regulation, and biological relevance of such pathways remain unclear. Due to these uncertainties, a deeper investigation was needed to clarify how Epiphyllum oxypetalum produces its strong nocturnal fragrance.

Researchers from Sichuan University and collaborating institutes reported new insights into the floral scent biosynthesis of E. oxypetalum in a study published in Horticulture Research. Using volatilomics, transcriptomics, enzymatic assays, and subcellular localization, the team uncovered the molecular basis of geraniol production in the night-blooming cactus. They demonstrated that a cytosolic terpene synthase is responsible for geraniol formation, representing a departure from the classical plastid-localized monoterpene biosynthetic model.

Key findings on geraniol production

The researchers first quantified floral volatile emissions throughout the blooming process and identified 49 compounds, among which geraniol accounted for over 70% of total scent release during peak bloom. Petals and sepals were found to be the primary tissues responsible for fragrance emission. Integrating gene expression data with protein functional assays, the team identified EoTPSa1, a highly upregulated terpene synthase localized to the cytosol, as the key enzyme responsible for geraniol synthesis. Biochemical experiments confirmed that EoTPSa1 efficiently converts geranyl diphosphate (GPP) into geraniol.

Crucially, inhibitor assays revealed that the precursor pool for geraniol originates predominantly from the mevalonate (MVA) pathway rather than the MEP pathway. This finding indicates that E. oxypetalum synthesizes monoterpenes in the cytosol through an MVA-TPS biosynthetic route—a previously undocumented mechanism in cactus floral scent biosynthesis. Metabolite profiling further showed that rapid starch breakdown coincides with geraniol emission, providing the necessary carbon substrates for volatile production during the short nighttime flowering window.

Implications for plant biology and biotechnology

“This discovery reveals an elegant and efficient strategy by which E. oxypetalum orchestrates its signature fragrance within a remarkably short time,” the authors noted.

“The identification of a cytosolic geraniol biosynthetic route challenges long-standing assumptions about monoterpene production in plants. These findings expand our understanding of specialized metabolism and highlight the biochemical sophistication underlying transient nocturnal flowering events.”

This study provides new opportunities for fragrance biotechnology and ornamental plant improvement. The identification of cytosolic geraniol biosynthesis offers a promising molecular target for enhancing or modifying floral scents in horticultural breeding.

Additionally, the efficient, high-output fragrance pathway of E. oxypetalum may inspire metabolic engineering approaches for sustainable industrial geraniol production. The work also sheds light on chemical signaling strategies in night-pollinated species, paving the way for future studies on plant–pollinator interactions and adaptive floral evolution.