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.

Flower color is an essential trait in ornamental plant breeding. Lycoris longituba is a popular ornamental plant native to central eastern China. The decrease in anthocyanin accumulation causes L. longituba petal color fading during flower development, which considerably affects the ornamental value of L. longituba. However, mechanisms underlying anthocyanin biosynthesis inhibition during L. longituba petal development remain unclear. In this study, three LlDFR genes were confirmed to be involved in anthocyanin biosynthesis and LlDFRc exerted the strongest promoting effect on anthocyanin accumulation. According to the correlation analysis results, LlbHLH12 exhibited the strongest negative correlation with LlDFRc. Quantitative real-time PCR analysis showed that LlbHLH12 was highly expressed during the medium bud and full bloom stages of flower development. LlbHLH12 was identified as a member of subgroup XII of bHLH transcription factor family. Subcellular localization and transcriptional activation ability assay revealed that LlbHLH12 was located in the nucleus without transcriptional activation activity. Overexpression of LlbHLH12 in Nicotiana tabacum and L. longituba inhibited anthocyanin accumulation by suppressing the expression of anthocyanin biosynthetic pathway genes. Furthermore, yeast one-hybrid, dual-luciferase, and β-glucuronidase activity assays showed that LlbHLH12 directly bound to the promoters of LlPAL and LlDFRc and suppressed their expression to inhibit anthocyanin biosynthesis. Overall, our study identified a novel bHLH repressor negatively regulating anthocyanin biosynthesis and provided new insights into the molecular mechanisms underlying color fading in L. longituba petals.