Effects of P-Coumarate 3-Hydroxylase Downregulation on the Compositional and Structural Characteristics of Lignin and Hemicelluloses in Poplar Wood (Populus alba × Populus glandulosa).

Xiao-Peng Peng,Cheng-Ye Ma,Jia-Long Wen,Shuang-Quan Yao,Jing Bian

doi:10.3389/fbioe.2021.790539

Abstract

Elucidating the chemical and structural characteristics of hemicelluloses and lignin in the p-coumarate 3-hydroxylase (C3H) down-regulated poplar wood will be beneficial to the upstream gene validation and downstream biomass conversion of this kind of transgenic poplar. Herein, the representative hemicelluloses and lignin with unaltered structures were prepared from control (CK) and C3H down-regulated 84K poplars. Modern analytical techniques, such as 13C NMR, 2D-HSQC NMR, and gel chromatography (GPC), were performed to better delineate the structural changes of hemicelluloses and lignin caused by transgenesis. Results showed that both the hemicelluloses (H-CK and H-C3H) extracted from control and C3H down-regulated poplar wood have a chain backbone of (1→4)-β-D-Xylan with 4-O-Me-α-D-GlcpA as side chain, and the branch degree of the H-C3H is higher than that of H-CK. With regarding to the lignin macromolecules, NMR results demonstrated that the syringyl/guaiacyl (S/G) ratio and dominant substructure β-O-4 linkages in C3H down-regulated poplar were lower than those of control poplar wood. By contrast, native lignin from C3H down-regulated poplar wood exhibited higher contents of p-hydroxybenzoate (PB) and p-hydroxyphenyl (H) units. In short, C3H down-regulation resulted in the chemical and structural changes of the hemicelluloses and lignin in these poplar wood. The identified structures will facilitate the downstream utilization and applications of lignocellulosic materials in the biorefinery strategy. Furthermore, this study could provide some illuminating results for genetic breeding on the improvement of wood properties and efficient utilization of poplar wood.

Highlights

With the consumption of petrochemical resources and environmental concerns related to global warming and pollution, the search and development of renewable alternatives to petroleum-based resources have gained worldwide attraction (Himmel et al, 2007; Ragauskas et al, 2014)
The representative alkaline hemicelluloses (KOH hemicelluloses) and lignin were respectively extracted from control (CK) and C3Hdownregulated 84K (C3H) poplars, which can better characterize the structural variations of hemicelluloses and lignin macromolecules in control and coumarate 3-hydroxylase (C3H)-downregulated poplars
Results showed that H-Control 84K (CK) and H-C3H were mainly composed of a linear backbone of (1→4)-β-D-Xylp with 4-OMe-α-D-GlcpA attached as side chain, and the branching degree of H-CK was more than that of H-C3H

Summary

Introduction

With the consumption of petrochemical resources and environmental concerns related to global warming and pollution, the search and development of renewable alternatives to petroleum-based resources have gained worldwide attraction (Himmel et al, 2007; Ragauskas et al, 2014). Lignocellulosic biomass represents a readily available renewable feedstock with the potential to be converted into a variety of fuels and chemicals (Ragauskas et al, 2006). Lignocellulosic biomass consists of three main components: lignin, hemicelluloses, and cellulose (Wang et al, 2019). Cellulose is a homopolymer which accounts for 30–50 wt% in lignocellulose, consisting of β-D-glucopyranose units linked by glycosidic bonds. Hemicelluloses are amorphous polymers (15–30 wt% of lignocellulosic biomass) and consisted of C5 and C6 sugars. Due to the higher reactive activation than cellulose, hemicelluloses are easier to remove from lignocellulose to produce furfural and related chemicals (Peng et al, 2009). Lignin is composed of aromatic monomers, which is an amorphous polymer accounting for 15–30 wt% in biomass (Wen et al, 2013b; Ragauskas et al, 2014)

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Conclusion