The most unique components of Ginkgo biloba extracts are terpene trilactones (TTLs) including ginkgolides and bilobalide. Study of TTLs biosynthesis has been stagnant in recent years. Metabolic profiling of 40 compounds, including TTLs, flavonoids, and phenolic acids, were globally analyzed in leaf, fibrous root, main root, old stem and young stem extracts of G. biloba. Most of the flavonoids were mainly distributed in the leaf and old stem. Most of phenolic acids were generally distributed among various tissues. The total content of TTLs decreased in the order of the leaf, fibrous root, main root, old stem and young stem. The TTLs were further analyzed in different parts of the main root and old stem. The content of TTLs decreases in the order of the main root periderm, the main root cortex and phloem and the main root xylem. In old stems, the content of TTLs in the cortex and phloem was much higher than both the old stem periderm and xylem. The expression patterns of five key genes in the ginkgolide biosynthetic pathway were measured by real-time quantitative polymerase chain reaction (RT-Q-PCR). Combining metabolic profiling and RT-Q-PCR, the results showed that the fibrous root and main root periderm tissues were the important biosynthesis sites of ginkgolides. Based on the above results, a model of the ginkgolide biosynthesis site and transport pathway in G. biloba was proposed. In this putative model, ginkgolides are synthesized in the fibrous root and main root periderm, and these compounds are then transported through the old stem cortex and phloem to the leaves.
A matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) assisted genome mining strategy was developed for the discovery of glycosyltransferase (GT) from the root of Platycodon grandiflorum. A di-O-glycosyltransferase PgGT1 was discovered and characterized that is capable of catalyzing platycoside E (PE) synthesis through the attachment of two β-1,6-linked glucosyl residues sequentially to the glucosyl residue at the C3 position of platycodin D (PD). Although UDP-glucose is the preferred sugar donor for PgGT1, it could also utilize UDP-xylose and UDP-N-acetylglucosamine as weak donors. Residues S273, E274, and H350 played important roles in stabilizing the glucose donor and positioning the glucose in the optimal orientation for the glycosylation reaction. This study clarified two key steps involved in the biosynthetic pathway of PE and could greatly contribute to improving its industrial biotransformation.
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