Identification and Characterization of Glucosyltransferase That Forms 1-Galloyl-β-d-Glucogallin in Canarium album L., a Functional Fruit Rich in Hydrolysable Tannins.

Qinghua Ye,Nana Qiu,Wei Wang,Linmin Liu,Shiyan Zhang,Qian Xie,Qiang Chang,Qingxi Chen

doi:10.3390/molecules26154650

Abstract

Hydrolysable tannins (HTs) are useful secondary metabolites that are responsible for pharmacological activities and astringent taste, flavor, and quality in fruits. They are also the main polyphenols in Canarium album L. (Chinese olive) fruit, an interesting and functional fruit that has been cultivated for over 2000 years. The HT content of C. album fruit was 2.3–13 times higher than that of berries with a higher content of HT. 1-galloyl-β-d-glucose (βG) is the first intermediate and the key metabolite in the HT biosynthesis pathway. It is catalyzed by UDP-glucosyltransferases (UGTs), which are responsible for the glycosylation of gallic acid (GA) to form βG. Here, we first reported 140 UGTs in C. album. Phylogenetic analysis clustered them into 14 phylogenetic groups (A, B, D–M, P, and Q), which are different from the 14 typical major groups (A~N) of Arabidopsis thaliana. Expression pattern and correlation analysis showed that UGT84A77 (Isoform0117852) was highly expressed and had a positive correlation with GA and βG content. Prokaryotic expression showed that UGT84A77 could catalyze GA to form βG. These results provide a theoretical basis on UGTs in C. album, which will be helpful for further functional research and availability on HTs and polyphenols.

Highlights

The role of secondary metabolites has been of interest to scientists for a long time
Hydrolysable tannins (HTs) consist of multiple esters of gallic acid (GA) with glucose and products of their oxidative reactions, which can be generally classified into gallotannins and ellagitannins depending on the residues to which the hydroxyl group of glucose forms an ester linkage [5,14]
C. album fruit is a natural candidate for dietary supplements, and studies have shown that its pharmacological action is closely related to phenolic compounds, especially HTs [37,38,42,44,45]

Summary

Introduction

The role of secondary metabolites has been of interest to scientists for a long time. Hydrolysable tannins (HTs) are one category of useful secondary metabolites, which are a heterogeneous groups of water-soluble polyphenolic compounds of high molecular weight (500–3000 Daltons) with up to 20 hydroxyl groups [1]. Strong antioxidant and radical scavenging capacities make HTs play a role in the treatment of various diseases. The antioxidant activity and scavengers of hydroxyl, superoxide, and peroxyl radicals largely depend on their structure [2,3,4]; for example, an increase in anti-radical effects was observed with an increase in the degree of polymerization [5]. HTs consist of multiple esters of gallic acid (GA) with glucose and products of their oxidative reactions, which can be generally classified into gallotannins and ellagitannins depending on the residues to which the hydroxyl group of glucose forms an ester linkage [5,14]

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Conclusion