Multi-omics analysis revealed the difference in pigment accumulation profiles between Syringa oblata and S. oblata var. alba

Abstract

Syringa oblata (So) and its variety S. oblata var. alba (Soa) are famous flowering shrubs with high ornamental value due to their beautiful inflorescence. The flower colors of So (purple) and Soa (white) differ significantly. In this study, pigment contents were detected and flavonoid and anthocyanin metabolites were determined by UPLC-ESI-MS/MS methods. Combined with transcriptome analysis, the key genes related to anthocyanin accumulation were obtained to explore the reasons for the difference in flower colors. The results showed that the total anthocyanin content was obviously higher in So than in Soa. The differential metabolites annotated in anthocyanin biosynthesis were significantly up-regulated, and conversely, the differential metabolites in biosynthesis of secondary metabolites and flavone and flavonol biosynthesis were down-regulated in So compared by Soa, with similar results revealed by the analysis of the top 20 fold change metabolites. It is explained that the anthocyanins and chlorophylls were the key pigment for the difference in flower color between So and Soa. Furthermore, the quantitative analysis of anthocyanins showed that delphinidin-3-O-rutinoside and cyanidin-3-O-rutinoside were the major anthocyanins in So, and their contents were significantly higher than other anthocyanins. However, the levels of major anthocyanins in Soa were very low, resulting in its white flower. In addition, high levels of kaempferol-3-O-rutinoside, rutin, quercetin-3-O-glucoside and naringenin were detected in flowers. These metabolites could play the roles of co-pigments in So and major pigments in Soa, respectively. Cyanidin-3-O-rutinoside were markedly elevated from initial flower bud (IFB) to flower bud (FB), which contributed to the anthocyanin accumulation and the flower color change in So, while the reduction of chlorophyll content was the main reason for the change in flower color from green to white in Soa. The integrated analysis showed that the genes (F3GT, FLS and F3H) might play the key roles in flower color formation. The study revealed the reason for the flower color variation between So and Soa and the flower color change during the development. It will provide the metabolites fundamental for research on flower color breeding in Syringa.