Role of geranylgeranyl diphosphate synthases in carotenoid biosynthesis in Osmanthus fragrans petals

Geranylgeranyl diphosphate synthase (GGPPS) plays a pivotal role in the biosynthetic pathway of plant terpenoids, producing geranylgeranyl diphosphate (GGPP), a precursor for secondary metabolites, such as carotenoids, phytol, and plastoquinone. In Osmanthus fragrans , carotenoids function as, the primary pigments responsible for the vibrant color of its flowers, providing not only pigmentation but also profoundly contributing to the production of floral fragrance. However, the regulatory mechanisms through which GGPPS governs carotenoid biosynthesis in O. fragrans remain unclear. This study aimed to explore the intricate relationship between GGPPS and carotenoid biosynthesis in O. fragrans . Using transcriptome analysis, a total of eight GGPPS gene sequences encoding five large subunits (LSUs) and three small subunits (SSUs) were identified. Despite similarities in subcellular localization among different members, their spatiotemporal gene expression profiles suggested potential functional diversity. Pigment complementation tests identified two key members of LSU—OfLSU1 and OfLSU5—which exhibited catalytic activity. These two members displayed notable differences in their ability to form homodimers and heterodimers. Furthermore, SSUII activated OfLSU1’s ability to synthesize carotenoids, whereas SSUI reduced OfLSU5’s ability. Overexpression of OfLSU1 and OfLSU5 in planta confirmed that OfLSU1 plays a more specific role in carotenoid biosynthesis, shedding light on the mechanism by which OfGGPPS regulates this process. This study provides insights into the regulatory mechanism of OfGGPPS family members in carotenoid biosynthesis, laying a foundation for further research on the regulation of flower color and fragrance biosynthesis in O. fragrans , as well as for the directional breeding of this species. • Eight GGPPS genes were identified in Osmanthus fragrans , including five LSUs and three SSUs . • Among the five OfLSUs, only OfLSU1 and OfLSU5 exhibited true GGPPS activity. • SSUII activated OfLSU1’s ability to synthesize carotenoids, whereas SSUI reduced OfLSU5’s ability. • Compared with OfLSU5, OfLSU1 plays a more specific role in carotenoid biosynthesis.