Integration of morphological, physiological, cytological, metabolome and transcriptome analyses reveal age inhibited accumulation of flavonoid biosynthesis in Ginkgo biloba leaves

Age affects the content of flavonoids in ginkgo (Ginkgo biloba L.) leaves, such that only 1-to-5-year-old ginkgo leaves are suitable for the extraction of medicinal compounds. Nevertheless, the relationship between age and flavonoids in ginkgo leaves is unclear. In this study, we compared 1-to-7-year-old ginkgo trees, and found that the flavonoid content decreased with age. The total flavonol aglycones content of 1-year old ginkgo was 9.88 ± 0.27 mg/g, significantly higher than those of 4- and 7-year-old gingko, and there was a marked difference in quercetin content. Next, we extensively compared the transcriptome and metabolome in leaves of 1-, 4-, and 7-year-old ginkgo. Metabolome profiles showed that flavonoid metabolites were the most abundant in different metabolities, and 82 % of the flavonoids exhibited a decreasing trend with increasing age. Downregulation of key structural genes (chalcone synthase, CHS; flavanone 3-hydroxylase, F3H; flavonol synthase, FLS) in the flavonoid biosynthesis pathway may explain the decreased flavonoid content with age. Furthermore, GO and KEGG analysis revealed photosynthesis- and hormone-related genes were downregulated with increasing age, implying that photosynthesis, salicylic acid, and jasmonic acid influence the flavonoid content. These results provide a theoretical basis for leaves ginkgo seedlings and new clues for understanding how age regulates flavonoids.