Combining Metabolic Profiling and Gene Expression Analysis to Reveal the Biosynthesis Site and Transport of Ginkgolides in Ginkgo biloba L.

Xu Lu,Hua Yang,Lian-Wen Qi,Ping Li,Ning Wang,Qian Shen,Xinguang Liu

doi:10.3389/fpls.2017.00872

Xu Lu, Hua Yang + Show 5 more

Open Access

https://doi.org/10.3389/fpls.2017.00872

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Abstract

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.

Highlights

The ‘living fossil’ Ginkgo biloba, which is a typical gymnosperm species with great economic and ecological values, has existed for more than 200 million years on Earth (Sabater-Jara et al, 2013; Zhang et al, 2015)
The content of terpene lactones was further analyzed in the main root periderm (R1), the main root cortex and phloem (R2), the main root xylem (R3), the old stem periderm (S1), the old stem cortex and phloem (S2) and the old stem xylem (S3)
The results showed that GbLPS is expressed in R1, which implies that the site of ginkgolides biosynthesis should be in R1 (Figure 6C)

Summary

Introduction

The ‘living fossil’ Ginkgo biloba, which is a typical gymnosperm species with great economic and ecological values, has existed for more than 200 million years on Earth (Sabater-Jara et al, 2013; Zhang et al, 2015). An increasing number of researchers have focused their studies on the TTLs of G. biloba. Despite their very complex structures, ginkgolides, and bilobalide are both biosynthesized from the basic isoprene units, dimethylallyl diphosphate (DMAPP) and isopentenyl diphosphate (IPP) (Figure 1). A series of genes in the MEP pathway, such as 1-deoxy-D-xylulose-5-phosphate synthase (DXS), 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR) and isopentenyl diphosphate isomerase (IDS), were cloned in G. biloba (Gong et al, 2005; Gao et al, 2006; Kim et al, 2006a,b, 2008a,b; Lu et al, 2008). Through a series of complex reactions including several cytochrome P450-dependent oxidoreductase (CYP450s) mediated oxidation steps and skeletal rearrangement, dehydroabietane is converted into ginkgolides (Schwarz and Arigoni, 1999). Some authors have suggested that bilobalide is most likely a product of partially degraded ginkgolide, but others have reported that bilobalide is derived from farnesyl diphosphate (FPP) (Peñuelas and Munné-Bosch, 2005; Dewick, 2009)

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