UDP-GLYCOSYLTRANSFERASE 72E3 Plays a Role in Lignification of Secondary Cell Walls in Arabidopsis

Abstract

Lignin is present in plant secondary cell walls and is among the most abundant biological polymers on Earth. In this work we investigated the potential role of the UGT72E gene family in regulating lignification in Arabidopsis. Chemical determination of floral stem lignin contents in ugt72e1, ugt72e2, and ugt72e3 mutants revealed no significant differences compared to WT plants. In contrast, the use of a novel safranin O ratiometric imaging technique indicated a significant increase in the cell wall lignin content of both interfascicular fibers and xylem from young regions of ugt72e3 mutant floral stems. These results were globally confirmed in interfascicular fibers by Raman microspectroscopy. Subsequent investigation using a bioorthogonal triple labelling strategy suggested that the augmentation in lignification was associated with an increased capacity of mutant cell walls to incorporate H-, G-, and S-monolignol reporters. Expression analysis showed that this increase was associated with an up-regulation of LAC17 and PRX71, which play a key role in lignin polymerization. Altogether, these results suggest that UGT72E3 can influence the kinetics of lignin deposition by regulating monolignol flow to the cell wall as well as the potential of this compartment to incorporate monomers into the growing lignin polymer.

UGT72, a Major Glycosyltransferase Family for Flavonoid and Monolignol Homeostasis in Plants

“…Functional characterization of mutants has evidenced phenotypes to clarify this question. Although single ugt72e1, ugt72e2 or ugt72e3 Arabidopsis mutants do not show any difference in lignin quantity in the floral stem when using the acetyl bromide method, a higher proportion of lignin in the xylem and interfascicular fiber cell walls of the ugt72e3 mutant was evidenced by Raman microspectroscopy and safranin O ratiometric imaging technique, as compared to the wild type [40]. This difference was only observed in the young part and not in the old part of the floral stem and indicates a role of UGT72E3 in cell wall lignification during vascular cells development.…”

“…Moreover, a higher capacity of incorporation of the three fluorescently labeled monolignols into lignin was found in the ugt72e3 young stem as compared to the wild type. This phenotype was related to an increased expression of lignin-specific PRX71 and LAC17 [40]. The ugt72b1 mutant exhibits a higher lignin content in the whole floral stem, as well as an ectopic lignification in the interfascicular fibers and the pith as compared to the wild type and the rescued line (insertion of the UGT72B1 cDNA under the control of the native gene promoter) [39].…”

“…Reducing the lignin content in the cell wall and/or altering its composition are considered as two strategies to improve pulping and saccharification [124]. The investigation of the role of UGT72s in monolignol homeostasis has revealed an additional novel regulation process for lignification in Arabidopsis [39,40]. In poplar, the role of UGT72s in lignin regulation is less clear and is worth further investigation according to the importance of trees in wood, paper pulp, and bioethanol production.…”

“…allows predicting their recognition by UGTs, as well as the regiospecificity of the enzyme [22]. This review focuses on the UGT72 family, whose members are known for their role in the homeostasis of two groups of compounds, the monolignols and the flavonoids (and their derivatives), and thereby on plant development [35][36][37][38][39][40].…”

PbUGT72AJ2-Mediated Glycosylation Plays an Important Role in Lignin Formation and Stone Cell Development in Pears (Pyrus bretschneideri)

“…Histochemical assays and thioacidolysis analysis confirmed the enhanced lignification and increased lignin biosynthesis in the ugt72b1 mutant [ 33 ]. Recent research has found that the use of a novel safranin O ratiometric imaging technique indicated a significant increase in the cell wall lignin content of both interfascicular fibres and xylem from young regions of ugt72e3 mutant floral stems [ 34 ].…”