OfWRKY48 coordinates floral aroma biosynthesis by dual regulation of MEP pathway and carotenoid metabolism in Osmanthus fragrans.

The flowers of Osmanthus fragrans are widely appreciated for their distinctive fragrance, predominantly derived from monoterpenes and apocarotenoid volatiles. However, the transcriptional mechanisms coordinating the production of these scent compounds remain poorly understood. In this study, integrated transcriptomic and metabolomic analyses of five cultivars with varying scent profiles identified OfWRKY48, a Group II-c WRKY TF. Functional studies demonstrated that transient overexpression and virus-induced gene silencing of OfWRKY48 significantly altered the accumulation of key scent terpenoids, including linalool, its oxides, and the apocarotenoids β-ionone, α-ionone, and dihydro-β-ionone. Mechanistic investigations revealed that OfWRKY48 activated key genes in the methylerythritol phosphate (MEP) pathway, including OfDXS, OfCMK, OfTPS1, and OfTPS2, thereby promoting linalool synthesis. Furthermore, OfWRKY48 upregulated upstream carotenogenic genes (OfPSY, OfPDS2, and OfLCYb2) and, in parallel, enhanced the expression of the carotenoid cleavage gene OfCCD4, collectively boosting the production of ionone derivatives. DNA-binding assays, including yeast one-hybrid (Y1H), luciferase reporter, and electrophoretic mobility shift assays, confirmed that OfWRKY48 bound to the promoters of OfTPS1, OfCMK, and OfLCYb2. These findings establish OfWRKY48 as a key regulator that orchestrates the biosynthesis of both monoterpene and apocarotenoid volatiles. Our work reveals a coordinated regulatory mechanism that synchronizes precursor supply in the MEP pathway with branching points in the carotenoid pathway, providing new insights into the complexity of floral fragrance regulation and suggesting a promising target for molecular breeding of aroma traits in horticultural crops.