Evolution of glucuronoxylan side chain variability in vascular plants and the compensatory adaptations of cell wall-degrading hydrolases

Gene regulatory network analysis of silver birch reveals the ancestral state of secondary cell wall biosynthesis in core eudicots

The compact genome and lack of recent whole-genome multiplication (WGM) events make the boreal pioneer tree silver birch (Betula pendula) a promising model for primary and secondary cell wall (PCW and SCW) regulation in forest trees. Here, we constructed regulatory networks through combined co-expression and promoter motif analysis and carried out a tissue-wide analysis of xylan using mass spectrometry. Analyses confirm the evolutionarily conserved model of superimposed layers of regulation and suggest a relatively simple ancestral state still retained in birch. Multispecies network analysis, including birch, poplar, and eucalyptus, identified conserved regulatory interactions, highlighting lignin biosynthesis as least conserved. The SCW biosynthesis co-expression module was enriched with WGM duplicates. While regulator genes were under positive selection, others evolved under relaxed purifying selection, possibly linked with diversification, as indicated by expression and regulatory motif differences. Xylan composition varied between PCW and SCW, revealing unique acetylation patterns. PCW xylan biosynthesis genes showed distinct expression and regulatory motifs, with a novel acetyl transferase potentially involved. This work highlights birch as a valuable model for understanding wood formation, vascular development, and cell wall composition in eudicots.

Influence of potassium on the degradative solvent extraction process of biomass components cellulose, hemicelluloses and lignin

Lignocellulosic biomass mainly consists of three organic components (cellulose, hemicelluloses, and lignin) and inorganic potassium. The potential influence of potassium on the degradative solvent extraction (DSE) process of the three biomass components remains unknown and requires to be elucidated. In this study, the influence of potassium species (potassium chloride [KCl] and potassium acetate [CK]) on the DSE process of biomass organic components was systematically investigated. The results showed that KCl had a greater influence than CK on the yield distribution and chemical structure of the extraction products during the DSE process of cellulose and hemicelluloses. KCl had the most significant influence on the cellulose extract yield, reducing it from 48.96 % to 23.98 %. Both KCl and CK facilitated the decarboxylation and decarbonylation reactions of cellulose and hemicelluloses, and increased the yield of CO2. In addition, KCl and CK inhibited the formation of light components in extracts during the DSE process of cellulose and hemicelluloses. Both KCl and CK had limited effects on the DSE process of lignin because of lignin's thermally stable structure. The presence of KCl inhibited the aromatization reactions during the formation of cellulose extracts, and this inhibitory effect was enhanced at elevated temperatures. These findings can help elucidate the complex reaction mechanisms underlying the DSE process of biomass and provide guidance for improving the yield and quality of the extraction products by regulating the potassium content or by conducting deashing pretreatments of raw biomass.

Enzymatic Routes to Designer Hemicelluloses for Use in Biobased Materials

Various enzymes can be used to modify the structure of hemicelluloses directly in vivo or following extraction from biomass sources, such as wood and agricultural residues. Generally, these enzymes can contribute to designer hemicelluloses through four main strategies: (1) enzymatic hydrolysis such as selective removal of side groups by glycoside hydrolases (GH) and carbohydrate esterases (CE), (2) enzymatic cross-linking, for instance, the selective addition of side groups by glycosyltransferases (GT) with activated sugars, (3) enzymatic polymerization by glycosynthases (GS) with activated glycosyl donors or transglycosylation, and (4) enzymatic functionalization, particularly via oxidation by carbohydrate oxidoreductases and via amination by amine transaminases. Thus, this Perspective will first highlight enzymes that play a role in regulating the degree of polymerization and side group composition of hemicelluloses, and subsequently, it will explore enzymes that enhance cross-linking capabilities and incorporate novel chemical functionalities into saccharide structures. These enzymatic routes offer a precise way to tailor the properties of hemicelluloses for specific applications in biobased materials, contributing to the development of renewable alternatives to conventional materials derived from fossil fuels.

Evolutionary arms race: the role of xylan modifications in plant-pathogen interactions

This article is a Commentary on Yu et al. (2024), 244: 1024–1040.

Carbohydrate-active enzymes involved in rice cell wall metabolism

Plant cell walls are complex, multifunctional structures, built up of polysaccharides and proteins. The configuration and abundance of cell wall constituents determine cellular elongation and plant growth. The emphasis of this review is on rice, a staple crop with economic importance, serving as model for grasses/cereals. Recent advancements have contributed to a better understanding of the grass/cereal cell wall. This review brings together current knowledge of the organization and metabolism of the rice cell wall, and addresses gaps in the information regarding the cell wall and enzymes involved. Several cell wall fractions, including cellulose, mixed-linkage glucans, and glucuronoarabinoxylans, are well understood in rice and other grasses/grains. Conversely, there are still open questions and missing links in relation to xyloglucans, glucomannans, pectin, lignin, and arabinogalactan proteins. There is still a large and untapped potential to identify carbohydrate-active enzymes (CAZymes), to characterize their activity, and to elucidate their involvement in the metabolism of the mentioned cell wall fractions. This review highlights the involvement of carbohydrate-active enzymes in rice cell wall metabolism, providing an update of current understanding with the aim of demarcating research areas with potential for further investigations.

Structure, Modification Pattern, and Conformation of Hemicellulose in Plant Biomass

Different forms of plant biomass have been utilised for various applications in daily life and have gained increasing attention as replacements for fossil fuel-based products in the pursuit of a sustainable society. Plant cell walls, the primary carbon sink of plant biomass, have a high-order polysaccharide architecture consisting of cellulose, hemicelluloses, pectins, lignin and some proteins. Hemicelluloses are a group of polysaccharides that interact with cellulose, which is fundamental to the different properties and functionality of the plant cell walls. However, for industrial applications, the complex polysaccharide architecture poses a barrier to their efficient use. Understanding the molecular basis of plant cell walls - especially cellulose-hemicellulose interactions - is therefore critical to improving the utilisation of plant biomass. Recent research has revealed that the detailed structures, modification patterns, and conformation of hemicelluloses play an influential role in their interaction with cellulose. In this review, we discuss the latest insights into hemicelluloses across different forms of plant biomass and how their structures affect cell wall assembly. Additionally, we explore recent findings on how alterations in hemicellulose structure and modification patterns affect the usability of plant biomass, including the extractability of polysaccharides and the digestibility of biomass by glycoside hydrolases for biofuel production. Furthermore, we address unsolved questions in the field and propose future strategies to maximize the potential of plant biomass.