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.