Characterization of the UDP-glycosyltransferase UGT72 Family in Poplar and Identification of Genes Involved in the Glycosylation of Monolignols.

Nathanael Speeckaert,Hadjara Amadou Hassane,Geert Goeminne,Fabien Baldacci-Cresp,Pierre Duez,Nassirou Mahamadou Adamou,Simon Hawkins,Wilfried Schwab,Marc Behr,Marie Baucher,Wout Boerjan,Godfrey Neutelings,Thomas Hoffmann,Adeline Mol,Mondher El Jaziri

doi:10.3390/ijms21145018

Abstract

Monolignols are the building blocks for lignin polymerization in the apoplastic domain. Monolignol biosynthesis, transport, storage, glycosylation, and deglycosylation are the main biological processes partaking in their homeostasis. In Arabidopsis thaliana, members of the uridine diphosphate-dependent glucosyltransferases UGT72E and UGT72B subfamilies have been demonstrated to glycosylate monolignols. Here, the poplar UGT72 family, which is clustered into four groups, was characterized: Group 1 UGT72AZ1 and UGT72AZ2, homologs of Arabidopsis UGT72E1-3, as well as group 4 UGT72B37 and UGT72B39, homologs of Arabidopsis UGT72B1-3, glycosylate monolignols. In addition, promoter-GUS analyses indicated that poplar UGT72 members are expressed within vascular tissues. At the subcellular level, poplar UGT72s belonging to group 1 and group 4 were found to be associated with the nucleus and the endoplasmic reticulum. However, UGT72A2, belonging to group 2, was localized in bodies associated with chloroplasts, as well as possibly in chloroplasts. These results show a partial conservation of substrate recognition between Arabidopsis and poplar homologs, as well as divergent functions between different groups of the UGT72 family, for which the substrates remain unknown.

Highlights

Glycosyltransferases (GT) (EC 2.4.x.y) are defined as enzymes that utilize an activated donor sugar substrate that contains a phosphate leaving group [1]
Our results showed that poplar UGT72 family members clustered into four groups
Ten sequences homologous to Arabidopsis UGT72s were identified in the P. trichocarpa genome sequence

Summary

Introduction

Glycosyltransferases (GT) (EC 2.4.x.y) are defined as enzymes that utilize an activated donor sugar substrate that contains a (substituted) phosphate leaving group [1]. Based on available genome sequences, GT are ubiquitous enzymes, and 110 families have been identified so far, from which 42 are present in both model plants Arabidopsis thaliana and Populus trichocarpa (http://www.cazy.org/ GlycosylTransferases.html [4]). GT1, comprising the uridine diphosphate glycosyltransferases (UGT) that use uridine diphosphate (UDP)-activated sugars as donor molecules, is the largest GT family in plant [5]. UGT (E.C. 2.4.1.x) share a conserved motif, the Plant Secondary Product Glycosyltransferase (PSPG) box, consisting of 44 aa at the C-terminal part of the protein and which is involved in the binding of the UDP-sugar molecule [6]. UGTs glycosylate a large array of secondary metabolites, such as terpenoids, alkaloids, steroids, and flavonoids, as well as phenylpropanoids [7,8]

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