Insights into the geranylgeranyl pyrophosphate synthase (GGPPS) gene family in Osmanthus fragrans and the role of OfGGPPS13 in the formation of floral color and aroma

Osmanthus fragrans is most famous for its strong aroma, and different varieties have different degrees of fragrance and color. Fragrance and color are important factors affecting the ornamental quality of O. fragrans. Terpenoids are important secondary metabolites in plants, with β-carotene (C40) being the major pigment substance and linalool (C10) being the key aromatic component in O. fragrans. The geranylgeranyl pyrophosphate synthase genes (GGPPSs) play important roles in secondary metabolism in plants. However, the functions of the GGPPS family in floral color and fragrance formation has rarely been reported in O. fragrans. In this study, 24 OfGGPPS genes were identified and classified into two subfamilies. The OfGGPPSs showed tissue-specific expression and OfGGPPS13 had highest expression in flowers. The OfGGPPS13 protein was localized to chloroplasts. The transcriptome data of OfGGPPS13 was verified by qRT-PCR and the expression level in ‘Wanyingui’ with strong aroma was higher than that in ‘Zhuangyuanhong’ with deep color at different flower development stages. Transient overexpression of OfGGPPS13 in O. fragrans petals showed that OfGGPPS13 increased the β-carotene content, the main color substance of O. fragrans, but decreased the linalool content, the main volatile organic compound (VOC) in the floral aroma of O. fragrans. OfGGPPS13 was indicated as the critical gene related to terpenoid synthesis in the floral aroma and color formation in O. fragrans. Our findings provide gene resources on the GGPPS gene family for further revealing the molecular regulation mechanism of the floral color and aroma formation in O. fragrans.