Floral scent profiling and candidate gene discovery in Hesperis oreophila

Hesperis oreophila is a wild cruciferous aromatic plant endemic to North China, valued for both ornamental appeal and fragrance development. However, the molecular regulatory mechanisms underlying floral scent formation in Hesperis have not been systematically elucidated. In this study, HS-SPME-GC-MS-based VOC profiling was performed across four floral developmental stages, including small bud (P1), large bud (P2), initial bloom (P3), and full bloom (P4), whereas transcriptome sequencing was conducted for three scent-transition stages, P2, P3, and P4. A total of 1,211 volatile organic compounds (VOCs) were detected and putatively annotated. Terpenoids were the predominant scent constituents at the initial and full bloom stages, reaching 166.25 μg·g^-1 at full bloom. Relative odor activity value (rOAV) analysis suggested that citronellol, myrcene, and limonene may be important putative aroma-contributing compounds, and the initial bloom stage was revealed as a major developmental transition associated with increased VOC accumulation. Genes involved in the MVA pathway showed relatively higher expression at the large bud stage, whereas several MEP pathway genes and terpene synthase genes were upregulated at the initial bloom stage, suggesting stage-specific transcriptional patterns associated with terpenoid accumulation. Concurrently, several phenylpropanoid-related genes also showed elevated expression at P3, suggesting coordinated developmental changes in scent-related pathways. A gene-metabolite correlation network identified MVK, DXS, and TPS22 as candidate genes associated with terpenoid VOC accumulation. Among them, TPS22 was significantly positively correlated with multiple characteristic terpenoids and may represent a promising candidate gene associated with terpenoid compositional variation. This study provides initial molecular and metabolic insights into floral scent formation in H. oreophila, providing a theoretical foundation and candidate gene resources for germplasm conservation, molecular breeding, and industrial development.