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

Bauhinia variegata 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 the volatile organic compounds (VOCs) emitted from its flowers is still lacking. Through integrated metabolome and transcriptome analyses, this study provides the first comprehensive characterization of the VOC composition, floral scent profile, key aroma components, and the molecular mechanisms underlying VOC variation during anthesis in Bauhinia variegata floral buds and fully opened flowers. A total of 1,214 volatile compounds were identified across buds and flowers, including 239 odor-active compounds and 37 differential odor-active compounds. Flavor statistics revealed that the floral scent profile of Bauhinia variegata is dominated by fruity, sweet, floral, green, woody, herbal, citrus, phenol, fresh, and spicy. Compared to floral buds, the majority of differential odor-active compounds were markedly up-regulated in fully opened flowers, notably including key floral aroma constituents such as phenylacetaldehyde, rose oxide, beta-ocimene, (Z)-beta-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 down-regulated in flowers, reflecting an ecological strategy shift from a defense-oriented mode at the bud stage to an attraction-oriented mode at anthesis. The up-regulation of Phenylalanine/histidine ammonia-lyase, Acyl-CoA synthetase, and Squalene synthetase genes, together with the down-regulation of Copper amine oxidase, O-methyltransferase, and Aldo/keto reductase genes, synergistically promoted the accumulation of floral aroma compounds such as phenylacetaldehyde and facilitated the floral transition. This study provides an important theoretical foundation for understanding the ecological interactions between Bauhinia variegata floral scent and its pollinators, as well as the molecular mechanisms governing floral scent formation. Furthermore, it contributes to the application of Bauhinia variegata in landscape beautification, edible flower utilization, and fragrance development.