Molecular Mechanism of Selenium Affecting the Synthesis of Flavonoids in G. biloba Leaves

Flavonoids from Ginkgo biloba have antioxidant and free radical scavenging activity. In the present study, we used different concentrations of OS (organic selenium), NS (nano-selenium), and IS (inorganic selenium) to treat the 2-year-old Ginkgo seedlings and studied the effects of different concentrations of selenium treatment on the physiological indexes and flavonoid content of Ginkgo at different growth stages. Our results showed that the content of chlorophyll, soluble sugar, and total flavonoid glycosides in the 1.6-mM NS treatment group increased significantly in July and September (by 43.87%, 59.92%, and 43.99% and 13.86%, 18.60%, and 35.04%), compared to the control respectively, all P < 0.05. To further analyze the changes of flavonoid content and gene expression levels in Ginkgo leaves, transcriptome sequencing analysis was performed on the treated seedlings. Sequencing analysis results showed that NS could promote PAL, COMT, CAD, and F6H gene expression levels in the flavonoid synthesis pathway; OS up-regulates the CCR and HCT genes. IS promotes the expression of C3'H, CCoAOMT, CYP, DFR, and HCT genes. Furthermore, the increase of key genes and enzyme levels promotes the increase of total flavonoid content. These data suggest that the appropriate concentration of OS and NS can promote the expression level of flavonoid synthesis genes and further promote the increase of total flavonoid content in Ginkgo leaves, which is beneficial to the medicinal value of Ginkgo extract.