Combined Analysis of Metabolome and Transcriptome Reveals Bauhinia variegata-Specific Floral Scent Profile and Key Aroma Components

Background: Bauhiniavariegata is a plant with considerable application potential owing to its combined ornamental, edible, aromatic, and medicinal values. However, research on this species remains limited and superficial both domestically and internationally, and systematic investigation of floral volatile organic compounds (VOCs) is still lacking. Methods: Through integrated metabolome and transcriptome analyses. Results: This study first comprehensively characterizes the VOC composition, floral scent profile, key aroma components, and the molecular mechanisms underlying VOC variation during anthesis in floral buds and flowers of B. variegata. A total of 1214 volatile compounds were identified across buds and flowers, including 239 odor-active compounds and 35 differential odor-active compounds. Flavor statistics revealed that the floral scent profile of B. variegata is dominated by fruity, sweet, floral, green, woody, herbal, citrus, phenol, fresh, and spicy notes. Compared to floral buds, most differential odor-active compounds were markedly upregulated in flowers, including key floral aroma constituents such as phenylacetaldehyde, rose oxide, (Z)-β-ocimene, 2-methylbenzaldehyde, and melon heptenal. Conversely, (R)-(+)-citronellal, which possesses defensive functions, and the bitter-tasting compound 1-methyl-4-nitro-benzene were significantly downregulated in flowers, reflecting a shift from a defense-oriented mode at the bud stage to an attraction-oriented mode at anthesis. Upregulation of phenylalanine/histidine ammonia-lyase, acyl-CoA synthetase, and squalene synthetase genes and downregulation of copper amine oxidase, O-methyltransferase, and aldo–keto reductase genes synergistically promoted accumulation of floral aroma compounds such as phenylacetaldehyde and facilitated the floral transition. Conclusions: This study provides important data support for understanding the ecological interactions between B. variegata floral scent and its pollinators, as well as the molecular mechanisms governing floral scent formation. Furthermore, it contributes to the application of B. variegata in landscaping, edible flower utilization, and fragrance development.