Insights into F-box proteins with C-terminal PP2 domain and characterization of the role of OfFBP3 in regulating VOCs in sweet osmanthus

Osmanthus fragrans is a valuable ornamental plant known for its pleasant floral fragrance. The PP2-type F-box proteins (FBPs), characterized by a conserved PP2 domain at the C-terminus, represent a distinct subfamily within the F-box protein family. Although FBPs function as core components of the SCF (SKP1–Cullin–F-box) ubiquitin ligase complex, their roles in floral aroma biosynthesis remain largely unexplored. In this study, 26 OfFBP genes were identified through a genome-wide analysis and classified into three subgroups. Although tissue-specific expression profiling indicated that both OfFBP3 and OfFBP21 are highly expressed in flowers, OfFBP3 was selected for further characterization due to its stronger positive correlation with three key aroma biosynthesis genes: OfCCD4 (carotenoid cleavage dioxygenase 4), OfTPS1a (terpene synthase 1a), and OfTPS1b (terpene synthase 1b). Subcellular localization assays revealed that OfFBP3 is localized in the nucleus but lacks transcriptional activation activity, suggesting it likely functions as a post-translational regulator rather than a direct transcriptional activator. Functional validation demonstrated that OfFBP3 overexpression up-regulated the expression of aroma-related genes and promoted the accumulation of β-ionone and linalool, whereas tobacco rattle virus (TRV)-mediated transient silencing of OfFBP3 exerted the opposite effect. This study not only clarifies the characteristics of the OfFBP gene family in O. fragrans but also provides bidirectional evidence confirming that OfFBP3 plays a positive regulatory role in the biosynthesis of volatile organic compounds (VOCs) by modulating aroma-related genes. These findings lay a theoretical foundation for further deciphering the FBP-mediated post-translational regulatory mechanisms of floral aroma and offer valuable candidate genes for improving aroma quality in ornamental plants.