Sweet osmanthus is prized for a scent dominated by terpenoids, especially linalool and the apocarotenoids β-ionone, α-ionone and dihydro-β-ionone. Their production depends on interconnected metabolic routes: the plastid-localized methylerythritol phosphate (MEP) pathway provides precursors for monoterpenes and carotenoids, while carotenoid-cleaving enzymes release volatile ionones. Many enzymes responsible for these steps have already been characterized, but pathway enzymes alone do not explain how plants coordinate precursor supply, branch-point decisions and the final balance between fragrance and pigmentation. Transcription factors can regulate several genes at once, yet the upstream control linking these two scent-producing systems in O. fragrans has remained unclear. Against these challenges, a deeper investigation was needed into how transcriptional regulators coordinate floral aroma biosynthesis across connected metabolic pathways.
On April 24, 2026, researchers from the National Key Laboratory for Germplasm Innovation & Utilization of Horticultural Crops and the College of Horticulture and Forestry Sciences at Huazhong Agricultural University, together with Panasia Aromatech Wuhan Company Ltd., published (DOI: 10.1093/hr/uhag167) the study in Horticulture Research. The team combined metabolite profiling, transcriptomics and functional experiments across five O. fragrans cultivars to identify OfWRKY48 and test how it controls both monoterpene and apocarotenoid production, revealing a regulatory link between precursor generation, carotenoid cleavage and floral scent output.
The researchers first profiled three pale-flowered ‘Albus’ cultivars and two orange ‘Aurantiacus’ cultivars using headspace solid-phase microextraction (HS-SPME) and gas chromatography–mass spectrometry (GC–MS). They detected 66 volatile and 91 free aroma compounds, with terpenoids dominating the volatile fraction. The ‘Albus’ cultivars showed especially strong scent chemistry: total volatile apocarotenoids were, on average, 4.2 times higher than in ‘Aurantiacus’ flowers. Transcriptome sequencing then identified 5,474 differentially expressed genes (DEGs), while weighted gene co-expression network analysis (WGCNA) linked gene modules to linalool and ionone accumulation. Among candidate regulators, expression of the gene OfWRKY48 was 3.2-fold higher in ‘Albus’ cultivars and peaked at full bloom. Functional tests strengthened the connection. Transient overexpression of OfWRKY48 increased linalool, its oxides and ionones, whereas virus-induced gene silencing (VIGS) produced the opposite effect. Overexpression also reduced total carotenoids and lightened petals, revealing a trade-off between volatile scent production and pigment deposition. Finally, yeast one-hybrid (Y1H), luciferase reporter (LUC) and electrophoretic mobility shift assays (EMSAs) showed that the OfWRKY48 protein directly binds and activates the promoters of OfTPS1, OfCMK and OfLCYb2, while other pathway genes appear to be regulated indirectly.
The authors said the importance of OfWRKY48 lies in its ability to coordinate several steps that had often been considered separately. Rather than switching on a single scent enzyme, the transcription factor helps increase precursor supply, activates a linalool-producing branch and promotes carotenoid metabolism toward ionone release. They said this integrated control offers a clearer explanation for why osmanthus cultivars can differ in fragrance even when changes in individual structural genes are not uniformly large. The scent–color trade-off also suggests that breeding for aroma may influence visible floral traits, making pathway-wide regulation an important consideration in future crop improvement.
The findings provide a framework for molecular breeding aimed at adjusting fragrance intensity and composition in sweet osmanthus and potentially other aromatic horticultural crops. Because OfWRKY48 connects monoterpene production with carotenoid-derived volatiles, manipulating its activity could offer a way to tune multiple aroma compounds at once rather than targeting individual enzymes. However, the study relied heavily on transient overexpression and gene-silencing systems, and the authors indicate that additional work is needed to identify interacting proteins and clarify the indirect regulatory network around OfWRKY48. Future genetic studies could test whether the same control system can be used predictably without undesirable effects on pigmentation, plant performance or ecological interactions. This could support more precise breeding of fragrance, color and related quality traits.
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References
DOI
10.1093/hr/uhag167
Original Source URL
https://doi.org/10.1093/hr/uhag167
Funding information
National Natural Science Foundation of China (32172621)；Fundamental Research Funds for the Central Universities (2662024YLPY006 and 2662024FW013)；Wuhan Metropolitan Circle Collaborative Innovation Technology Project (2025070604020035)；Hubei Provincial Sci-Tech Innovation Talents Program (2025DJB042).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.