Analysis of the Origin of Lilac Fragrance: Insights from Volatile Metabolomics and Transcriptomics

Lilac (Syringa oblata Lindl.) is an important eco-economic aromatic shrub in northern China; however, the key volatile organic compounds (VOCs) responsible for its floral aroma and their origin remain largely unexplored. In this study, we conducted an integrated analysis of volatile metabolomics and transcriptomics to elucidate the composition, dynamic changes, and potential regulatory network of VOCs across different floral organs and petal developmental stages. A total of 1440 VOCs were identified in the stamens, pistils, and petals, with petals being the primary contributors to the overall floral aroma. Analysis of different petal developmental stages revealed that the full-bloom stage (S3) is critical for VOCs emission. The floral aroma of S. oblata is primarily composed of terpenoids, alcohols, and aldehydes. By relative odor activity value (rOAV) with multivariate statistical screening, seven key VOCs with high contributions to the floral aroma were identified. Transcriptome analysis identified 69,935 differentially expressed genes (DEGs) across petal developmental stages, which were predominantly enriched in metabolic pathways and the biosynthesis of secondary metabolites. The expression patterns of these DEGs were highly consistent with the accumulation trends of VOCs, increasing at stages S2 and S3 and subsequently declining at stage S4. Integrative analysis of VOCs and gene expression further identified candidate genes significantly correlated with the key aroma volatiles. Specifically, the carotenoid pathway-related genes CYP97A3 and LYC may influence the formation of carotenoid-derived volatiles and floral aroma. Additionally, genes associated with the fatty acid-lipoxygenase pathway, transport-related genes, and transcription factors are potentially involved in the formation and regulation of aldehyde and alcohol volatiles. These findings advance our understanding of the floral aroma formation in S. oblata and provide metabolic basis, candidate gene resources and a theoretical foundation for the genetic improvement of aroma traits and the breeding of new cultivars.