How Does Plant Cell Wall Nanoscale Architecture Correlate with Enzymatic Digestibility?

Multiscale dynamics and molecular mobility in cellulose-rich materials

Cellulose, an abundant biopolymer in nature as a structural component of plant cell walls, has a native semi-crystalline structure in which the arrangement of amorphous-crystalline domains governs its key properties such as mechanical and physico-chemical properties. The performance of the material in different situations is shaped by molecular mobility, which affects attributes such as mechanical properties, chemical reactivity, and water absorption. Nevertheless, it is difficult to investigate experimentally the structural and dynamic properties of cellulose-rich materials. This is especially the case for the glass transition, which impacts its quality and properties. This experimental challenge is notably evidenced by the considerable variability in data across the literature. The purpose of this study is to offer a comprehensive multi-scale exploration of dynamics within cellulose-rich materials, emphasizing literature data on cellulose glass transition and molecular relaxations, and providing insights into methods for characterizing their physical state and underscoring the impact of water-cellulose interactions on molecular mobility in these systems. The promising results obtained using multiple approaches bring out the importance of combining methods to achieve a more accurate and detailed understanding of the complex thermal transition in cellulose materials, particularly when considering the influence of water on their thermal dynamics and properties.

Distribution of xylan linked glucuronic acid labelled by molecularly imprinted polymers on pulp fiber surface

Efficiently utilization of plant resources is heavily restricted by the resistance of lignocellulose in plant cells, which is related to the interlinkages of lignocellulose components. Hemicellulose in plant cell wall is bound to cellulose by hydrogen bond and linked with lignin in lignin-carbohydrate complex (LCC). In the xylan chain of hemicellulose, glucuronic acid (GA) is a typical side-group, which provides clues for us to label and locate hemicellulose. The way to label GA on the surface of pulp fibers obtained from pulping process is benefit to explore the deconstruction of lignocellulose. Herein, a new visualization method, fluorescence modified molecularly imprinted polymers (MIP) were applied to recognize and locate GA on the pulp fiber surface. The method combining fluorescence imaging and integrated 3D fiber structure verified the feasibility of the MIP for specific GA recognition. The results showed that xylan (represented by GA) was closely attached to lignin, distributed along the inner wall of pulp fiber cells, and gradually taken off from the inside edge of fiber cells with the deconstruction of lignocellulose. This research provided a basis to develop visualization bioimaging technology to identify biomass components.

High-throughput prediction of stalk cellulose and hemicellulose content in maize using machine learning and Fourier transform infrared spectroscopy

Cellulose and hemicellulose are key cross-linked carbohydrates affecting bioethanol production in maize stalks. Traditional wet chemical methods for their detection are labor-intensive, highlighting the need for high-throughput techniques. This study used Fourier transform infrared (FTIR) spectroscopy combined with machine learning (ML) algorithms on 200 large-scale maize germplasms to develop robust predictive models for stalk cellulose, hemicellulose and holocellulose content. We identified several peak height features correlated with three contents, used them as input data for model building. Four ML algorithms demonstrated higher predictive accuracy, achieving coefficient of determination (R2) ranging from 0.83 to 0.97. Notably, the Categorical Boosting algorithm yielded optimal models with coefficient of determination (R2) exceeding 0.91 for the training set and over 0.81 for the test set. The approach combined FTIR spectroscopy with ML algorithms offers a precise and high-throughput tool for predicting stalk cellulose, hemicellulose and holocellulose contents, benefiting maize genetic breeding for bioenergy and biofuels.

Imaging Metabolic Flow of Water in Plants with Isotope-Traced Stimulated Raman Scattering Microscopy

Water plays a vital role in the life cycle of plants, participating in various critical biochemical reactions during both non-photosynthetic and photosynthetic processes. Direct visualization of the metabolic activities of water in plants with high spatiotemporal resolution is essential to reveal the functional utilization of water. Here, stimulated Raman scattering (SRS) microscopy is applied to monitor the metabolic processes of deuterated water (D2O) in model plant Arabidopsis thaliana (A. thaliana). The work shows that in plants uptaking D2O/water solution, proton-transfer from water to organic metabolites results in the formation of C-D bonds in newly synthesized biomolecules (lipid, protein, and polysaccharides, etc.) that allow high-resolution detection with SRS. Reversible metabolic pathways of oil-starch conversion between seed germination and seed development processes are verified. Spatial heterogeneity of metabolic activities along the vertical axis of plants (root, stem, and tip meristem), as well as the radial distributions of secondary growth on the horizontal cross-sections are quantified. Furthermore, metabolic flow of protons from plants to animals is visualized in aphids feeding on A. thaliana. Collectively, SRS microscopy has potential to trace a broad range of matter flows in plants, such as carbon storage and nutrition metabolism.

Photodegradation in terrestrial ecosystems

The first step in carbon (C) turnover, where senesced plant biomass is converted through various pathways into compounds that are released to the atmosphere or incorporated into the soil, is termed litter decomposition. This review is focused on recent advances of how solar radiation can affect this important process in terrestrial ecosystems. We explore the photochemical degradation of plant litter and its consequences for biotic decomposition and C cycling. The ubiquitous presence of lignin in plant tissues poses an important challenge for enzymatic litter decomposition due to its biological recalcitrance, creating a substantial bottleneck for decomposer organisms. The recognition that lignin is also photolabile and can be rapidly altered by natural doses of sunlight to increase access to cell wall carbohydrates and even bolster the activity of cell wall degrading enzymes highlights a novel role for lignin in modulating rates of litter decomposition. Lignin represents a key functional connector between photochemistry and biochemistry with important consequences for our understanding of how sunlight exposure may affect litter decomposition in a wide range of terrestrial ecosystems. A mechanistic understanding of how sunlight controls litter decomposition and C turnover can help inform management and other decisions related to mitigating human impact on the planet.

Establishment of efficient system for bagasse bargaining: Combining fractionation of saccharides, recycling of high-viscosity solvent and dismantling

Sugarcane bagasse (SCB) has a recalcitrant structure, which hinders its component dismantling and subsequent high value utilization. Some organic solvents are favorable to dismantle lignocellulose, but their high viscosity prevents separation of components and reuse of solvents. Herein, ethylene glycol phenyl ether (EGPE)-acid system is used as an example to develop green and efficient methods to dismantle SCB, purify polysaccharides and lignin, and reuse solvents. Results show that dismantling SCB at 130 °C, 0.5 % H2SO4, and 100 min can obtain 85.5 % cellulose recovery, 94.1 % hemicellulose removal and 83.7 % lignin removal. Different molecular weight saccharides are separated by membranes filtration and centrifugation, and lignin recovered by antisolvent precipitation. The solvent recovered by distillation, achieving high dismantling efficiency of 89.2 % cellulose recovery, 94.1 % hemicellulose removal and 94.4 % lignin removal after four recycles. Results show a promising approach for the closed-loop process of dismantling lignocellulose, fractionating saccharides, and reusing solvents in high-viscosity systems.

Structural elucidation of lignin, hemicelluloses and LCC from both bamboo fibers and parenchyma cells

Biomass recalcitrance, a key challenge in biomass utilization, is closely linked to the architectural composition and cross-linkages of molecules within cell walls. With three bamboo species investigated, this study aims to elucidate the inherent molecular-scale structural differences between bamboo fibers and parenchyma cells through a systematic chemical extraction and structural characterization of isolated hemicelluloses, lignin, and lignin-carbohydrate complexes (LCC). We observed that parenchyma cells exhibit superior alkaline extractability compared to fibers. Additionally, we identified the hemicelluloses in parenchyma cells as L-arabino-4-O-methyl-D-glucurono-D-xylan, displaying a highly branched structure, while that in fibers is L-arabino-D-xylan. Furthermore, the parenchyma cell lignin exhibited a higher syringyl-to-guaiacyl (S/G) ratio and β-O-4 linkage content compared to fibers, whereas fibers contain more carbon‑carbon linkages including β-β, β-5, and β-1. This notable structural difference suggests a denser and more stable lignin in bamboo fibers. Importantly, we found that LCC in parenchyma cells predominantly comprises γ-ester linkages, which exhibit an alkaline-unstable nature. In contrast, fibers predominantly contain phenyl glycoside linkages, characterized by their alkaline-stable nature. These findings were observed for all the tested bamboo species, indicating the conclusions should be also valid for other bamboo species, suggesting the competitiveness of bamboo parenchyma cells as a valuable biofuel feedstock.

Enhanced fermentation and deconstruction of natural wheat straw by Trichoderma asperellum T-1 and its positive transcriptional response

Microorganisms harvest energy from agricultural waste by degrading its structure. By comparing with Trichoderma reesei QM6a in cellulase production, straw deconstruction and transcriptome response, Trichoderma asperellum T-1 was identified to be prioritized for the fermentation of natural straw. Cellulase activity of T-1 was 50%-102% higher than QM6a. And the degradation rate of hemicellulose and ligin in wheat straw by T-1 reached 40% and 42%. Time-driven changes in the gene expression of extracellular proteins involved in polysaccharide, xylan, and hemicellulose metabolism and hydrolysis indicated that T-1 positively responded in both solid state fermentation and submerged fermentation for lignocellulose degradation. A significantly enriched category encoding carbohydrate-binding modules is considered critical for the deconstruction of the natural structure by T-1. The findings highlight the superiority of T. asperellum T-1 in straw fermentation, base on which, the construction of efficient microbial agents is expected to enhance the utilization of biomass.

Acidothermus cellulolyticus E1 endoglucanase expressed in planta undergoes extensive hydroxyproline-O-glycosylation and exhibits enhanced impact on biomass digestibility

KEY MESSAGE

E1 holoenzyme was extensively Hyp-O-glycosylated at the proline rich linker region in plants, which substantially increased the molecular size and improved the enzymatic digestibility of the biomass of transgenic plants. Thermophilic E1 endo-1,4-β-glucanase derived from Acidothermus cellulolyticus has been frequently expressed in planta to reconstruct the plant cell wall to overcome biomass recalcitrance. However, the expressed holoenzyme exhibited a larger molecular size (~ 100 kDa) than the theoretical one (57 kDa), possibly due to posttranslational modifications in the recombinant enzyme within plant cells. This study investigates the glycosylation of the E1 holoenzyme expressed in tobacco plants and determines its impact on enzyme activity and biomass digestibility. The E1 holoenzyme, E1 catalytic domain (E1cd) and E1 linker (E1Lk) were each expressed in tobacco plants and suspension cells. The accumulation of holoenzyme was 2.0- to 2.3- times higher than that of E1cd. The proline-rich E1Lk region was extensively hydroxyproline-O-glycosylated with arabinogalactan polysaccharides. Compared with E1cd, the holoenzyme displayed a broader optimal temperature range (70 to 85 ºC). When grown in greenhouse, the expression of E1 holoenzyme induced notable phenotypic changes in plants, including delayed flowering and leaf variegation post-flowering. However, the final yield of plant biomass was not significantly affected. Finally, plant biomass engineering with E1 holoenzyme showed 1.7- to 1.8-fold higher saccharification efficiency than the E1cd lines and 2.4- to 2.7-fold higher than the wild-type lines, which was ascribed to the synergetic action of the E1Lk and cellulose binding module in reducing cell wall recalcitrance.

Production, Purification, and Characterization of a Cellulase from Paenibacillus elgii

Cellulases are one of the most essential natural factors for cellulose degradation and, thus, have attracted significant interest for various applications. In this study, a cellulase from Paenibacillus elgii TKU051 was produced, purified, and characterized. The ideal fermentation conditions for cellulase productivity were 2% carboxymethyl cellulose (CMC) as the growth substrate, pH = 8, temperature of 31 °C, and 4 days of culturing. Accordingly, a 45 kDa cellulase (PeCel) was successfully purified in a single step using a High Q column with a recovery yield of 35% and purification of 42.2-fold. PeCel has an optimal activity at pH 6 and a temperature of 60 °C. The activity of cellulase was significantly inhibited by Cu2+ and enhanced by Mn2+. The PeCel-catalyzed products of the CMC hydrolysis were analyzed by high-performance liquid chromatography, which revealed chitobiose and chitotriose as the major products. Finally, the clarity of apple juice was enhanced when treated with PeCel.

Biological pretreatment with white rot fungi for preparing hierarchical porous carbon from Banlangen residues with high performance for supercapacitors and dye adsorption

White rot fungi possess superior infiltrability and biodegradability on lignocellulosic substrates, allowing them to form tailored microstructures which are conducive to efficient carbonization and chemical activation. The present research employed white rot fungus pretreatment as a viable approach for preparing porous carbon from Banlangen residues. The resultant F-A-BLGR-PC prepared by pretreating Banlangen residues with white rot fungi followed by carbonization and activation has a hierarchical porous structure with a high specific surface area of 898 m2 g-1, which is 43.4% greater than that of the unprocessed sample (R-BLGR-PC). When used as an electrode for supercapacitors, the F-A-BLGR-PC demonstrated a high specific capacitance of 308 F g-1 at 0.5 A g-1 in 6 M KOH electrolyte in three-electrode configuration. Moreover, the F-A-BLGR-PC based symmetric supercapacitor device achieved a superb cyclic stability with no obvious capacitance decay after 20,000 cycles at 5 A g-1 in 1 M Na2SO4 electrolyte. Additionally, the F-A-BLGR-PC sample was found to be an ideal adsorbent for removing methyl orange (MO) from water, exhibiting an adsorption ability of 173.4 mg g-1 and a maximum removal rate of 86.6%. This study offers a promising method for the preparation of a porous carbon with a high specific surface area in a biological way using white rot fungi pretreatment, and the derived carbon can not only be applied in energy storage but also in environmental remediation, catalysis, and so on.

Altering the substitution and cross-linking of glucuronoarabinoxylans affects cell wall architecture in Brachypodium distachyon

The Poaceae family of plants provides cereal crops that are critical for human and animal nutrition, and also, they are an important source of biomass. Interacting plant cell wall components give rise to recalcitrance to digestion; thus, understanding the wall molecular architecture is important to improve biomass properties. Xylan is the main hemicellulose in grass cell walls. Recently, we reported structural variation in grass xylans, suggesting functional specialisation and distinct interactions with cellulose and lignin. Here, we investigated the functions of these xylans by perturbing the biosynthesis of specific xylan types. We generated CRISPR/Cas9 knockout mutants in Brachypodium distachyon XAX1 and GUX2 genes involved in xylan substitution. Using carbohydrate gel electrophoresis, we identified biochemical changes in different xylan types. Saccharification, cryo-SEM, subcritical water extraction and ssNMR were used to study wall architecture. BdXAX1A and BdGUX2 enzymes modify different types of grass xylan. Brachypodium mutant walls are likely more porous, suggesting the xylan substitutions directed by both BdXAX1A and GUX2 enzymes influence xylan-xylan and/or xylan-lignin interactions. Since xylan substitutions influence wall architecture and digestibility, our findings open new avenues to improve cereals for food and to use grass biomass for feed and the production of bioenergy and biomaterials.

Interaction between lignin and cellulose during the pyrolysis process

The hierarchical and heterogeneous structures and the interactions between biomass components within cell walls are closely related to the pyrolysis characteristics. In this work, thermogravimetric analysis (TGA) and pyrolysis kinetics analysis were used to investigate the pyrolysis characteristics of windmill palm (Trachycarpus fortunei (Hook.) H. Wendl.) culm and silk after delignification. The results demonstrate cellulose pyrolysis temperature of silk is much higher than that of culm, attributed to the higher lignin content of the former. After delignification, the cellulose pyrolysis temperature of silk decreased by 48 °C, which is much higher than that of culm by 18 °C, suggesting a strong interaction between lignin and cellulose during the pyrolysis process. Futhermore, pyrolysis kinetics analysis also found that the frequency factor of slik and culm increased by 129 % and 26 %, respectively, attributed to the disappearance of the carbon layer formed by lignin pyrolysis process. And, differ in lignin content is responsible for the discrepancy of frequency factor increase. In conclusion, we propose a mechanism model for lignin hindering cellulose pyrolysis, which is of great significance for understanding the pyrolysis interactions of biomass components in complex supramolecular cell wall.

Xylan-directed cell wall assembly in grasses

Xylan is the most abundant hemicellulosic polysaccharide in the cell walls of grasses and is pivotal for the assembly of distinct cell wall structures that govern various cellular functions. Xylan also plays a crucial role in regulating biomass recalcitrance, ultimately affecting the utilization potential of lignocellulosic materials. Over the past decades, our understanding of the xylan biosynthetic machinery and cell wall organization has substantially improved due to the innovative application of multiple state-of-the-art techniques. Notably, novel xylan-based nanostructures have been revealed in the cell walls of xylem vessels, promoting a more extensive exploration of the role of xylan in the formation of cell wall structures. This Update summarizes recent achievements in understanding xylan biosynthesis, modification, modeling, and compartmentalization in grasses, providing a brief overview of cell wall assembly regarding xylan. We also discuss the potential for tailoring xylan to facilitate the breeding of elite energy and feed crops.

Highly-efficient lipid production from hydrolysate of Radix paeoniae alba residue by oleaginous yeast Cutaneotrichosporon oleaginosum

Valorization of herbal extraction residues (HERs) into value-added products is pivotal for the sustainability of Chinese medicine industry. Here, seven different enzymatic hydrolysates of dilute acid pretreated HERs were evaluated for lipid production by Cutaneotrichosporon oleaginosum. Among them, the highest sugar yield via hydrolysis and the maximum lipid production were obtained from Radix paeoniae alba residue (RPAR). More interestingly, high proportion of sugar polymers was disintegrated into fermentable sugars during the pretreatment step, allowing a cheap non-enzymatic route for producing sugars from RPAR. A repeated dilute acid pretreatment gained a high sugar concentration of 241.6 g/L through reusing the pretreatment liquor (PL) for four times. Biomass, lipid concentration, and lipid content achieved 49.5 g/L, 35.7 g/L and 72.2 %, respectively, using fed-batch culture of PL. The biodiesel parameters indicated lipids produced from HERs were suitable for biodiesel production. This study offers a cost-effective way to upgrade the HERs waste into micro-biodiesel.

An aggregated understanding of the influence of aqueous ammonia pretreatment on the physical deconstruction of cell walls in sugar beet pulp

The underlying interplay between physicochemical property and enzymatic hydrolysis of cellulose still remains unclear. The impacts of matrix glycan composition of sugar beet pulp (SBP) on physical structure and saccharification efficiency were emphasized. The results showed that aqueous ammonia (AA) pretreatment could remove the non-cellulosic polysaccharides and destroy the linkage between the pectin and lignin. The cellulose supramolecule was changed significantly after AA pretreatment, in terms of the decline in hardness, gumminess, springiness, thickness and degree of polymerization. Furthermore, vascular cell was exposed and degraded. The highest reducing sugar yield of 355.06 mg/g was obtained from the pretreated SBP (80 °C) with enzyme loading of 30 U/g, which was 1.01 times higher than that of the untreated SBP. This research also supported the idea that recognizing and precisely removing the primary epitopes in cell walls might be an ideal strategy to accomplish the improved enzymatic hydrolysis through mild pretreatment.

Manipulating microRNA miR408 enhances both biomass yield and saccharification efficiency in poplar

The conversion of lignocellulosic feedstocks to fermentable sugar for biofuel production is inefficient, and most strategies to enhance efficiency directly target lignin biosynthesis, with associated negative growth impacts. Here we demonstrate, for both laboratory- and field-grown plants, that expression of Pag-miR408 in poplar (Populus alba × P. glandulosa) significantly enhances saccharification, with no requirement for acid-pretreatment, while promoting plant growth. The overexpression plants show increased accessibility of cell walls to cellulase and scaffoldin cellulose-binding modules. Conversely, Pag-miR408 loss-of-function poplar shows decreased cell wall accessibility. Overexpression of Pag-miR408 targets three Pag-LACCASES, delays lignification, and modestly reduces lignin content, S/G ratio and degree of lignin polymerization. Meanwhile, the LACCASE loss of function mutants exhibit significantly increased growth and cell wall accessibility in xylem. Our study shows how Pag-miR408 regulates lignification and secondary growth, and suggest an effective approach towards enhancing biomass yield and saccharification efficiency in a major bioenergy crop.

Maize Internode Autofluorescence at the Macroscopic Scale: Image Representation and Principal Component Analysis of a Series of Large Multispectral Images

A quantitative histology of maize stems is needed to study the role of tissue and of their chemical composition in plant development and in their end-use quality. In the present work, a new methodology is proposed to show and quantify the spatial variability of tissue composition in plant organs and to statistically compare different samples accounting for biological variability. Multispectral UV/visible autofluorescence imaging was used to acquire a macroscale image series based on the fluorescence of phenolic compounds in the cell wall. A series of 40 multispectral large images of a whole internode section taken from four maize inbred lines were compared. The series consisted of more than 1 billion pixels and 11 autofluorescence channels. Principal Component Analysis was adapted and named large PCA and score image montages at different scales were built. Large PCA score distributions were proposed as quantitative features to compare the inbred lines. Variations in the tissue fluorescence were clearly displayed in the score images. General intensity variations were identified. Rind vascular bundles were differentiated from other tissues due to their lignin fluorescence after visible excitation, while variations within the pith parenchyma were shown via UV fluorescence. They depended on the inbred line, as revealed by the first four large PCA score distributions. Autofluorescence macroscopy combined with an adapted analysis of a series of large images is promising for the investigation of the spatial heterogeneity of tissue composition between and within organ sections. The method is easy to implement and can be easily extended to other multi-hyperspectral imaging techniques. The score distributions enable a global comparison of the images and an analysis of the inbred lines' effect. The interpretation of the tissue autofluorescence needs to be further investigated by using complementary spatially resolved techniques.

Efficient production of high concentration monosaccharides and ethanol from poplar wood after delignification and deacetylation

Efficient enzymatic hydrolysis is required for production of high concentration monosaccharides and ethanol. The lignin and acetyl group in poplar can limit the enzymatic hydrolysis. However, the effect of delignification combined with deacetylation on the saccharification of poplar for high concentration monosaccharides was not clear. Herein, hydrogen peroxide-acetic acid (HPAA) was used for delignification and sodium hydroxide was used for deacetylation to enhance the hydrolyzability of poplar. Delignification with 60% HPAA at 80 °C could remove 81.9% lignin. Acetyl group was completely removed with 0.5% NaOH at 60 °C. After saccharification, 318.1 g/L monosaccharides were obtained with a poplar loading of 35% (w/v). After simultaneous saccharification and fermentation, 114.9 g/L bioethanol was gained from delignified and deacetylated poplar. Those results showed the highest monosaccharides and ethanol concentrations in reported research. This developed strategy with relatively low temperature could effectively improve the production of high concentration monosaccharide and ethanol from poplar.

Structure of cellulose in birch phloem fibres in tension wood: an X-ray nanodiffraction study

BACKGROUND

To gain a better understanding of bark layer structure and function, especially of the phloem fibres and their contribution to the posture control of trees, it is important to map the structural properties of these cells. The role of bark can also be linked to the reaction wood formation and properties which are essential when it comes to studying the questions related to tree growth. To offer new insights into the role of bark in the postural control of trees, we studied the micro- and nanoscale structures of the phloem and its nearest layers. This study is the first time, in which phloem fibres in trees have been extensively examined using X-ray diffraction (XRD). We determined the orientation of cellulose microfibrils in phloem fibres of Silver birch saplings by using scanning synchrotron nanodiffraction. The samples consisted of phloem fibres extracted from tension, opposite and normal wood (TW, OW, NW).

RESULTS

Using scanning XRD, we were able to obtain new information about the mean microfibril angle (MFA) in cellulose microfibrils in phloem fibres connected to reaction wood. A slight but consistent difference was detected in the average MFA values of phloem fibres between the TW and OW sides of the stem. Using scanning XRD, different contrast agents (intensity of the main cellulose reflection or calcium oxalate reflection, mean MFA value) were used to produce 2D images with 200 nm spatial resolution.

CONCLUSIONS

Based on our results, the tension wood formation in the stem might be related to the structure and properties of phloem fibres. Thus, our results suggest that the nanostructure of phloem fibres is involved in the postural control of trees containing tension and opposite wood.

Identification of ZmBK2 Gene Variation Involved in Regulating Maize Brittleness

Maize stalk strength is a crucial agronomic trait that affects lodging resistance. We used map-based cloning and allelic tests to identify a maize mutant associated with decreased stalk strength and confirmed that the mutated gene, ZmBK2, is a homolog of Arabidopsis AtCOBL4, which encodes a COBRA-like glycosylphosphatidylinositol (GPI)-anchored protein. The bk2 mutant exhibited lower cellulose content and whole-plant brittleness. Microscopic observations showed that sclerenchymatous cells were reduced in number and had thinner cell walls, suggesting that ZmBK2 affects the development of cell walls. Transcriptome sequencing of differentially expressed genes in the leaves and stalks revealed substantial changes in the genes associated with cell wall development. We constructed a cell wall regulatory network using these differentially expressed genes, which revealed that abnormal cellulose synthesis may be a reason for brittleness. These results reinforce our understanding of cell wall development and provide a foundation for studying the mechanisms underlying maize lodging resistance.

Exploring how lignin structure influences the interaction between carbohydrate-binding module and lignin using AFM

Nonproductive adsorption of cellulase onto the residual lignin in substrate seriously hinders the enzymatic hydrolysis. To understand how lignin structure affects lignin-cellulase interaction, the carbohydrate-binding module (CBM) functionalized atomic force microscope tip was used to measure CBM-lignin interaction by single-molecule dynamic force spectroscopy in this work. The results showed that sulfonated lignin (SL) has the greatest adhesion force to CBM (4.74 nN), while those of masson pine milled wood lignin (MWL), poplar MWL and herbaceous MWLs were 2.85, 1.03 and 0.27-0.61 nN, respectively. It provides direct quantitative evidence for the significance of lignin structure on lignin-cellulase interaction. The CBM-MWLs interaction decreased sharply to 0.054-0.083 nN while SL was added, indicating the primary mechanism of SL promoting lignocellulose hydrolysis was significantly reducing the nonproductive adsorption of substrate lignin on cellulase. Finally, the "competitive adsorption" mechanism was proposed to interpret why SL effectively promotes the enzymatic hydrolysis of lignin-containing substrates.

Light scattering in stacked mesophyll cells results in similarity characteristic of solar spectral reflectance and transmittance of natural leaves

Solar spectral reflectance and transmittance of natural leaves exhibit dramatic similarity. To elucidate the formation mechanism and physiological significance, a radiative transfer model was constructed, and the effects of stacked mesophyll cells, chlorophyll content and leaf thickness on the visible light absorptance of the natural leaves were analyzed. Results indicated that light scattering caused by the stacked mesophyll cells is responsible for the similarity. The optical path of visible light in the natural leaves is increased with the scattering process, resulting in that the visible light transmittance is significantly reduced meanwhile the visible light reflectance is at a low level, thus the visible light absorptance tends to a maximum and the absorption of photosynthetically active radiation (PAR) by the natural leaves is significantly enhanced. Interestingly, as two key leaf functional traits affecting the absorption process of PAR, chlorophyll content and leaf thickness of the natural leaves in a certain environment show a convergent behavior, resulting in the high visible light absorptance of the natural leaves, which demonstrates the PAR utilizing strategies of the natural leaves. This work provides a new perspective for revealing the evolutionary processes and ecological strategies of natural leaves, and can be adopted to guide the improvement directions of crop photosynthesis.

Fungi-enabled pore channel regulation and defect engineering of a novel micro-reactor for treating complex effluents

Defect engineering has become a significant research area in recent years; however, little has been reported on the biological method for modulating the intrinsic carbon defects of the biochar framework. Herein, a fungi-enabled method for the fabrication of porous carbon/Fe₃O₄/Ag (PC/Fe₃O₄/Ag) composites was developed, and the mechanism underlying the hierarchical structure is elucidated for the first time. By regulating the cultivation process of fungi on water hyacinth biomass, a well-developed interconnected structure and carbon defects acting as potential catalytic active sites were formed. This new material with antibacterial, adsorption and photodegradation properties could be an excellent choice for treating the mixed dyestuff effluents with oils and bacteria, also guiding pore channel regulation and defect engineering in materials science. Numerical simulations were carried out to demonstrate the remarkable catalytic activity.

A comprehensive review of the synthesis strategies, properties, and applications of transparent wood as a renewable and sustainable resource

The uncertainties of the environment and the emission levels of nonrenewable resources have compelled humanity to develop sustainable energy savers and sustainable materials. One of the most abundant and versatile bio-based structural materials is wood. Wood has several promising advantages, including high toughness, low thermal conductivity, low density, high Young's modulus, biodegradability, and non-toxicity. Furthermore, while wood has many ecological and structural advantages, it does not meet optical transparency requirements. Transparent wood is ideal for use in various industries, including electronics, packaging, automotive, and construction, due to its high transparency, haze, and environmental friendliness. As a necessary consequence, current research on developing fine wood is summarized in this review. This review begins with an explanation of the history of fine wood. The concept and various synthesis strategies, such as delignification, refractive index measurement methods, and transparent lumber polymerization, are discussed. Approaches and techniques for the characterization of transparent wood are outlined, including microscopic, Fourier transform infrared (FTIR), and X-ray diffraction (XRD) analysis. Furthermore, the characterization, physical properties, mechanical properties, optical properties, and thermal conductivity of transparent wood are emphasized. Eventually, a brief overview of the various applications of fine wood is presented. The present review summarized the first necessary actions toward future transparent wood applications.

Single-molecular insights into the breakpoint of cellulose nanofibers assembly during saccharification

Plant cellulose microfibrils are increasingly employed to produce functional nanofibers and nanocrystals for biomaterials, but their catalytic formation and conversion mechanisms remain elusive. Here, we characterize length-reduced cellulose nanofibers assembly in situ accounting for the high density of amorphous cellulose regions in the natural rice fragile culm 16 (Osfc16) mutant defective in cellulose biosynthesis using both classic and advanced atomic force microscopy (AFM) techniques equipped with a single-molecular recognition system. By employing individual types of cellulases, we observe efficient enzymatic catalysis modes in the mutant, due to amorphous and inner-broken cellulose chains elevated as breakpoints for initiating and completing cellulose hydrolyses into higher-yield fermentable sugars. Furthermore, effective chemical catalysis mode is examined in vitro for cellulose nanofibers conversion into nanocrystals with reduced dimensions. Our study addresses how plant cellulose substrates are digestible and convertible, revealing a strategy for precise engineering of cellulose substrates toward cost-effective biofuels and high-quality bioproducts.

Biosynthesis of artificial starch and microbial protein from agricultural residue

Growing populations and climate change pose great challenges to food security. Humankind is confronting a serious question: how will we feed the world in the near future? This study presents an out-of-the-box solution involving the highly efficient biosynthesis of artificial starch and microbial proteins from available and abundant agricultural residue as new feed and food sources. A one-pot biotransformation using an in vitro coenzyme-free synthetic enzymatic pathway and baker's yeast can simultaneously convert dilute sulfuric acid-pretreated corn stover to artificial starch and microbial protein under aerobic conditions. The β-glucosidase-free commercial cellulase mixture plus an ex vivo two-enzyme complex containing cellobiose phosphorylase and potato α-glucan phosphorylase displayed on the surface of Saccharomyces cerevisiae, showed better cellulose hydrolysis rates than a commercial β-glucosidase-rich cellulase mixture. This is because the channeling of the hydrolytic product from the solid cellulosic feedstock to the yeast mitigated the inhibition of the cellulase cocktail. Animal tests have shown that the digestion of artificial amylose results in slow and relatively small changes in blood sugar levels, suggesting that it could be a new health food component that prevents obesity and diabetes. A combination of the utilization of available agricultural residue and the biosynthesis of starch and microbial protein from non-food biomass could address the looming food crisis in the food-energy-water nexus.

Superstrong Carbon Nanotube Yarns by Developing Multiscale Bundle Structures on the Direct Spin-Line without Post-Treatment

Super strong fibers, such as carbon or aramid fibers, have long been used as effective fillers for advanced composites. In this study, the highest tensile strength of 5.5 N tex-1 for carbon nanotube yarns (CNTYs) is achieved by controlling the micro-textural structure through a facile and eco-friendly bundle engineering process in direct spinning without any post-treatment. Inspired by the strengthening mechanism of the hierarchical fibrillary structure of natural cellulose fiber, this study develops multiscale bundle structures in CNTYs whereby secondary bundles, ≈200 nm in thickness, evolve from the assembly of elementary bundles, 30 nm in thickness, without any damage, which is a basic load-bearing element in CNTY. The excellent mechanical performance of these CNTYs makes them promising substitutes for the benchmark, lightweight, and super strong commercial fibers used for energy-saving structural materials. These findings address how the tensile strength of CNTY can be improved without additional post-treatment in the spinning process if the development of the aforementioned secondary bundles and the corresponding orientations are properly engineered.

Role of hydrothermal pretreatment towards sustainable biorefinery

Recently, the world is experiencing a shift from petroleum refineries to biorefineries due to fossil fuel depletion and environmental concerns. To achieve sustainable development of biorefineries and other components of the biofuel production process, eco-friendly and cost-effective approaches are necessary. Therefore, lignocellulosic biomass (LCB) must be exploited in biorefineries for the generation of a broad spectrum of products. The complex structure of LCB prevents its direct saccharification by enzymatic means, so pretreatment is necessary. There are several pretreatment technologies for disrupting the lignocellulosic structure, but hydrothermal pretreatment is the leading pretreatment technology for recovering hemicellulose fraction with a low number of inhibitors and an increased amount of cellulose. The severity of hydrothermal pretreatment plays a principal role in affecting cellulose, hemicellulose, and lignin structure. A detailed account of microwave-assisted hydrothermal pretreatment technologies and the cost-effectiveness, eco-friendliness, and upcoming challenges of this technology for commercialization with the probable solution is presented.

Evaluation of Biological Pretreatment of Wormwood Rod Reies with White Rot Fungi for Preparation of Porous Carbon

In this work, the wormwood rod residues are pretreated with white rot fungi as the precursor to preparing porous carbon following a simple carbonization and activation process (denoted herein as FWRA sample). The FWRA sample possesses abundant hierarchical pores structure with high specific surface area (1165.7 m² g^-1) and large pore volume (1.02 cm³ g^-1). As an electrode for supercapacitors, the FWRA sample offers a high specific capacitance of 443.2 F g^-1 at 0.5 A g^-1 and superb rate ability holding a specific capacitance of 270 F g^-1 at 100 A g^-1 in 6 M KOH electrolyte. The corresponding symmetrical capacitor has a superb cyclic stability with a low specific capacitance decay rate of 0.4% after 20,000 cycles at 5 A g^-1 in 1 M Na₂SO₄ electrolyte. Moreover, measurements revealed that when used as adsorbent, the FWRA sample is ideal for removing methyl orange (MO) from water, exhibiting a superior adsorption ability of 260.8 mg g^-1. Therefore, this study is expected to provide a simple and environmentally friendly technique for the generation of value-added and functional porous carbon materials from Chinese medicinal herbal residues, thus offering promising candidates for broad application areas.

Enzyme Discovery in Anaerobic Fungi (Neocallimastigomycetes) Enables Lignocellulosic Biorefinery Innovation

Lignocellulosic biorefineries require innovative solutions to realize their full potential, and the discovery of novel lignocellulose-active enzymes could improve biorefinery deconstruction processes. Enzymatic deconstruction of plant cell walls is challenging, as noncarbohydrate linkages in hemicellulosic sidechains and lignin protect labile carbohydrates from hydrolysis. Highly specialized microbes that degrade plant biomass are attractive sources of enzymes for improving lignocellulose deconstruction, and the anaerobic gut fungi (Neocallimastigomycetes) stand out as having great potential for harboring novel lignocellulose-active enzymes. We discuss the known aspects of Neocallimastigomycetes lignocellulose deconstruction, including their extensive carbohydrate-active enzyme content, proficiency at deconstructing complex lignocellulose, unique physiology, synergistic enzyme complexes, and sizeable uncharacterized gene content. Progress describing Neocallimastigomycetes and their enzymes has been rapid in recent years, and it will only continue to expand. In particular, direct manipulation of anaerobic fungal genomes, effective heterologous expression of anaerobic fungal enzymes, and the ability to directly relate chemical changes in lignocellulose to fungal gene regulation will accelerate the discovery and subsequent deployment of Neocallimastigomycetes lignocellulose-active enzymes.

Lignocellulose dissociation with biological pretreatment towards the biochemical platform: A review

Lignocellulose utilization has been gaining great attention worldwide due to its abundance, accessibility, renewability and recyclability. Destruction and dissociation of the cross-linked, hierarchical structure within cellulose hemicellulose and lignin is the key procedure during chemical utilization of lignocellulose. Of the pretreatments, biological treatment, which can effectively target the complex structures, is attractive due to its mild reaction conditions and environmentally friendly characteristics. Herein, we report a comprehensive review of the current biological pretreatments for lignocellulose dissociation and their corresponding degradation mechanisms. Firstly, we analyze the layered, hierarchical structure of cell wall, and the cross-linked network between cellulose, hemicellulose and lignin, then highlight that the cracking of β-aryl ether is considered the key to lignin degradation because of its dominant position. Secondly, we explore the effect of biological pretreatments, such as fungi, bacteria, microbial consortium, and enzymes, on substrate structure and degradation efficiency. Additionally, combining biological pretreatment with other methods (chemical methods and catalytic materials) may reduce the time necessary for the whole process, which also help to strengthen the lignocellulose dissociation efficiency. Thirdly, we summarize the related applications of lignocellulose, such as fuel production, chemicals platform, and bio-pulping, which could effectively alleviate the energy pressure through bioconversion into high value-added products. Based on reviewing of current progress of lignocellulose pretreatment, the challenges and future prospects are emphasized. Genetic engineering and other technologies to modify strains or enzymes for improved biotransformation efficiency will be the focus of future research.

Enzymatic biotransformation of Rb3 from the leaves of Panax notoginseng to ginsenoside rd by a recombinant β-xylosidase from Thermoascus aurantiacus

Given the important pharmacological activity of ginsenoside Rd but its low content in plants, the production of Rd by enzymatic transformation is of interest. In this study, a β-xylosidase gene Ta-XylQS from Thermoascus aurantiacus was cloned and overexpressed in Komagataella phaffii. Purified recombinant Ta-XylQS specifically hydrolyzes substrates with xylosyl residues at the optimal pH of 3.5 and temperature of 60 °C. This study established a process for producing Rd by transforming ginsenoside Rb3 in the saponins of Panax notoginseng leaves via recombinant Ta-XylQS. After 60 h, 3 g L^- 1 of Rb3 was transformed into 1.46 g L^- 1 of Rd, and the maximum yield of Rd reached 4.31 g kg^- 1 of Panax notoginseng leaves. This study is the first report of the biotransformation of ginsenoside Rb3 to Rd via a β-xylosidase, and the established process could potentially be adopted for the commercial production of Rd from Rb3.

Production of xylo-oligosaccharides and ethanol from corncob by combined tartaric acid hydrolysis with simultaneous saccharification and fermentation

In organic acid hydrolysis for xylo-oligosaccharides (XOS) production, organic acids with low flash points and explosion limits can lead to explosion and fire risk. Herein, tartaric acid (TA) as an organic acid with high flash point and no explosion limit was used in the hydrolysis of corncob to produce XOS. Then, the TA-hydrolyzed corncob was used for ethanol production. In TA hydrolysis of corncob, a 56.4 % XOS yield was obtained from the hydrolysate with the conditions of 170 °C, 60 mM TA and 10 min. Meanwhile, 92.1 % TA was recovered from the hydrolysate by the addition of calcium hydroxide. After simultaneous saccharification and fermentation of TA-hydrolyzed corncob, an 82.4 % ethanol yield was obtained with a solid loading of 25 % (w/v, 250 g/L) by Saccharomyces cerevisiae H06. This research provided a relatively safe, simple, and efficient technology for producing XOS and ethanol from corncob.

Heat production and volatile biosynthesis are linked via alternative respiration in Magnolia denudata during floral thermogenesis

Floral thermogenesis is coupled with odor emission in known thermogenic plants. It is widely accepted that elevation in floral temperature can help release of volatile organic compounds (VOCs). However, no information is available about whether floral thermogenesis is associated with VOC biosynthesis. Here, we used RNA-Sequencing (RNA-Seq) to draw a gene expression atlas of floral thermogenesis in Magnolia denudata and captured an upregulation of Alternative Oxidase (AOX) during floral thermogenesis. Western blot analyses also suggested upregulation of AOX during floral thermogenesis. Moreover, oxygen consumption analyses revealed increased activity of the AOX respiration pathway during floral thermogenesis. Using HPLC analyses, we further found that increased AOX respiration substantially promoted production of citric acid by 1.35 folds, which provided fundamental metabolite skeletons for biosynthesis of VOCs. RNA-Seq also showed upregulation of genes regulating lignin catabolism, which was in agreement with in situ Raman chemical imaging of lignin. Taken together, our results suggest the central role of AOX by coupling heat production and VOC biosynthesis in floral thermogenesis of M. denudata.

Comparative Transcriptome and Anatomic Characteristics of Stems in Two Alfalfa Genotypes

Stems are more important to forage quality than leaves in alfalfa. To understand lignin formation at different stages in alfalfa, lignin distribution, anatomical characteristics and transcriptome profile were employed using two alfalfa cultivars. The results showed that the in vitro true digestibility (IVTD) of stems in WL168 was significantly higher than that of Zhungeer, along with the significantly lower neutral detergent fiber (NDF), acid detergent fiber (ADF) and lignin contents. In addition, Zhungeer exhibited increased staining of the xylem areas in the stems of different developmental stages compared to WL168. Interestingly, the stems of WL168 appeared intracellular space from the stage 3, while Zhungeer did not. The comparative transcriptome analysis showed that a total of 1993 genes were differentially expressed in the stem between the cultivars, with a higher number of expressed genes in the stage 4. Of the differentially expressed genes, starch and sucrose metabolism as well as phenylpropanoid biosynthesis pathways were the most significantly enriched pathways. Furthermore, expression of genes involved in lignin biosynthesis such as PAL, 4CL, HCT, CAD, COMT and POD coincides with the anatomic characteristics and lignin accumulation. These results may help elucidate the regulatory mechanisms of lignin biosynthesis and improve forage quality in alfalfa.

Naturally Derived Janus Cellulose Nanomaterials: Anisotropic Cellulose Nanomaterial Building Blocks and Their Assembly into Asymmetric Structures

Naturally derived cellulose nanomaterials (CNMs) with desirable physicochemical properties have drawn tremendous attention for their versatile applications in a broad range of fields. More recently, Janus amphiphilic cellulose nanomaterial particles with asymmetric structures (i.e., reducing and nonreducing ends and crystalline and amorphous domains) have been in the spotlight, offering a rich and sophisticated toolbox for Janus nanomaterials. With careful surface and interfacial engineering, Janus CNM particles have demonstrated great potential as surface modifiers, emulsifiers, stabilizers, compatibilizers, and dispersants in emulsions, nanocomposites, and suspensions. Naturally derived Janus CNM particles offer a fascinating opportunity for scaling up the production of self-standing Janus CNM membranes. Nevertheless, most Janus CNM membranes to date are constructed by asymmetric fabrication or asymmetric modification without considering the Janus traits of CNM particles. More future research should focus on the self-assembly of Janus CNM particles into bulk self-standing Janus CNM membranes to enable more straightforward and sustainable approaches for Janus membranes. This review explores the fabrication, structure-property relationship, and Janus configuration mechanisms of Janus CNM particles and membranes. Janus CNM membranes are highlighted for their versatile applications in liquid, thermal, and light management. This review also highlights the significant advances and future perspectives in the construction and application of sustainable Janus CNM particles and membranes.

Root Hair Apex is the Key Site for Symplastic Delivery of Graphene into Plants

Uptake kinetics and delivery mechanisms of nanoparticles (NPs) in crop plants need to be urgently understood for the application of nanotechnology in agriculture as delivery systems for eco-friendly nanoagrochemicals. Here, we investigated the uptake kinetics, translocation pathway, and key internalization process of graphene in wheat (Triticum aestivum L.) by applying three specific hydroponic cultivation methods (submerging, hanging, and split-root). Quantification results on the uptake of carbon-14 radiolabeled graphene in each tissue indicated that graphene could enter the root of wheat and further translocate to the shoot with a low delivery rate (<2%). Transmission electron microscopy (TEM) images showed that internalized graphene was transported to adjacent cells through the plasmodesmata, clearly indicating the symplastic pathway of graphene translocation. The key site for the introduction of graphene into root cells for translocation through the symplastic pathway is evidenced to be the apex of growing root hair, where the newly constructed primary cell wall is much thinner. The confirmation of uptake kinetics and delivery mechanisms is useful for the development of nanotechnology in sustainable agriculture, especially for graphene serving as the delivery vector for pesticides, genes, and sensors.

Building an extensible cell wall

This article recounts, from my perspective of four decades in this field, evolving paradigms of primary cell wall structure and the mechanism of surface enlargement of growing cell walls. Updates of the structures, physical interactions, and roles of cellulose, xyloglucan, and pectins are presented. This leads to an example of how a conceptual depiction of wall structure can be translated into an explicit quantitative model based on molecular dynamics methods. Comparison of the model's mechanical behavior with experimental results provides insights into the molecular basis of complex mechanical behaviors of primary cell wall and uncovers the dominant role of cellulose-cellulose interactions in forming a strong yet extensible network.

Fabrication of uniform lignin nanoparticles with tunable size for potential wound healing application

The construction of lignin nanoparticles (LNPs) with both lignin properties and nanomaterial properties through controlling the morphologies and structures of lignin is one of the effective ways to realize its application in the field of biomedicine. Firstly, the morphology and chemical structure of LNPs were studied in detailed. The results showed that the chemical structural characteristics of LNPs had not changed significantly and its morphology was more regular shape and narrower size distribution (50-350 nm). Besides, LNPs also exhibited excellent water dispersion stability and high negative zeta potential. Subsequently, LNPs as wound dressings had good antioxidant property, excellent adsorption capacity of protein, outstanding bactericidal activity and remarkable biocompatibility, suggesting that LNPs did not interfere with cell proliferation during wound healing. Finally, the in vivo results of mouse wounds further illustrated that treatment of wounded skin wounds with LNPs enhanced its effective healing. After 15 days, as compared with the untreated control and original lignin (OL) groups, the wounds treated of LNPs was completely closed and granulation tissue formation was advanced. Overall, this study can be a good method for high-value applications of LNPs, and highlighting the advantages of using lignin as medical adjuvant nanomaterials to accelerate wound healing.

Structural elucidation and targeted valorization of poplar lignin from the synergistic hydrothermal-deep eutectic solvent pretreatment

Elucidating the structural variations of lignin during the pretreatment is very important for lignin valorization. Herein, poplar wood was pretreated with an integrated process, which was composed of AlCl₃-catalyzed hydrothermal pretreatment (HTP, 130-150 °C, 1.0 h) and mild deep-eutectic solvents (DES, 100 °C, 10 min) delignification for recycling lignin fractions. Confocal Raman Microscopy (CRM) was developed to visually monitor the delignification process during the HTP-DES pretreatment. NMR characterizations (2D-HSQC and ³¹P NMR) and elemental analysis demonstrated that the lignin fractions had undergone the following structural changes, such as dehydration, depolymerization, condensation. Molecular weights (GPC), microstructure (SEM and TEM), and antioxidant activity (DPPH analysis) of the lignins revealed that the DES delignification resulted in homogeneous lignin fragments (1.32 < PDI < 1.58) and facilitated the rapid assemblage of lignin nanoparticles (LNPs) with controllable nanoscale sizes (30-210 nm) and excellent antioxidant activity. These findings will enhance the understanding of structural transformations of the lignin during the integrated process and maximize the lignin valorization in a current biorefinery process.

Efficient fractionation of bamboo residue by autohydrolysis and deep eutectic solvents pretreatment

Bamboo processing residue, which is rich in parenchyma cells, was treated as huge waste in bamboo processing industry, such as reassemble bamboo and bamboo flooring. Herein, autohydrolysis and rapid different deep eutectic solvents (DES) delignification strategy were consecutively performed to remove hemicelluloses and lignin from bamboo processing residue. The xylooligosaccharides (XOS) with high yield (34.35%) was achieved in the autohydrolysis process. Results showed that alkaline DES pretreatment resulted in the highest glucose yield (88.22%) and relatively high delignification rate (83.75%) as well as well-preserved lignin structures. However, the lignin fractions obtained under acidic DES conditions were tending to assemble into lignin nanoparticles (LNPs) and having excellent antioxidant activity as compared to those obtained from alkaline DES system. In brief, the combination of autohydrolysis and rapid DES delignification can achieve orientated fractionation of the components from the industrialized bamboo.

Real-time imaging of enzymatic degradation of pretreated maize internodes reveals different cell types have different profiles

This work presents a dynamic view of the enzymatic degradation of maize cell walls, and sheds new light on the recalcitrance of hot water pretreated maize stem internodes. Infra-red microspectrometry, mass spectrometry, fluorescence recovery after photobleaching and fluorescence imaging were combined to investigate enzymatic hydrolysis at the cell scale. Depending on their polymer composition and organisation, cell types exhibits different extent and rate of enzymatic degradation. Enzymes act sequentially from the cell walls rich in accessible cellulose to the most recalcitrant cells. This phenomenon can be linked to the heterogeneous distribution of enzymes in the liquid medium and the adsorption/desorption mechanisms that differ with the type of cell.

Dissolved xylan inhibits cellulosome-based saccharification by binding to the key cellulosomal component of Clostridium thermocellum

Polysaccharides derived from lignocellulose are promising sustainable carbon sources. Cellulosome is a supramolecular machine integrating multi-function enzymes for effective lignocellulose bio-saccharification. However, how various non-cellulose components of lignocellulose affect the cellulosomal saccharification is hitherto unclear. This study first investigated the stability and oxygen sensitivity of the cellulosome from Clostridium thermocellum during long-term saccharification process. Then, the differential inhibitory effects of non-cellulose components, including lignin, xylan, and arabinoxylan, on the cellulosome-based saccharification were determined. The results showed that lignin played inhibitory roles by non-productively adsorbing extracellular proteins of C. thermocellum. Differently, arabinoxylan preferred to bind with the cellulosomal components. Almost no adsorption of cellulosomal proteins on solid xylan was detected. Instead, xylan in water-dissolved form interacted with the cellulosomal proteins, especially the key exoglucanase Cel48S, leading to the xylan inhibitory effect. Compared to xylan, xylooligosaccharides influenced the cellulosome activity slightly. Hence, this work demonstrates that the timely hydrolysis or removal of dissolved xylan is important for cellulosome-based lignocellulose saccharification.

Fluorescent Imaging of Extracellular Fungal Enzymes Bound onto Plant Cell Walls

Lignocelluloytic enzymes are industrially applied as biocatalysts for the deconstruction of recalcitrant plant biomass. To study their biocatalytic and physiological function, the assessment of their binding behavior and spatial distribution on lignocellulosic material is a crucial prerequisite. In this study, selected hydrolases and oxidoreductases from the white rot fungus Phanerochaete chrysosporium were localized on model substrates as well as poplar wood by confocal laser scanning microscopy. Two different detection approaches were investigated: direct tagging of the enzymes and tagging specific antibodies generated against the enzymes. Site-directed mutagenesis was employed to introduce a single surface-exposed cysteine residue for the maleimide site-specific conjugation. Specific polyclonal antibodies were produced against the enzymes and were labeled using N-hydroxysuccinimide (NHS) ester as a cross-linker. Both methods allowed the visualization of cell wall-bound enzymes but showed slightly different fluorescent yields. Using native poplar thin sections, we identified the innermost secondary cell wall layer as the preferential attack point for cellulose-degrading enzymes. Alkali pretreatment resulted in a partial delignification and promoted substrate accessibility and enzyme binding. The methods presented in this study are suitable for the visualization of enzymes during catalytic biomass degradation and can be further exploited for interaction studies of lignocellulolytic enzymes in biorefineries.

Development of different pretreatments and related technologies for efficient biomass conversion of lignocellulose

Lignocellulose, a kind of biological resource widely existing in nature, which can be transformed into value-added biochemical products through saccharification, fermentation or chemical catalysis. Pretreatments are the necessary step to increase the accessibility and digestibility of lignocellulose. This paper comprehensively reviewed different pretreatment progress of lignocellulose in recent year, including mechanical/thermal, biological, inorganic solvent, organic solvent and unconventional physical-chemical pretreatments, focusing on quantifying the influence of pretreatments on subsequent biomass conversion. In addition, related pretreatment techniques such as genetic engineering, reactor configurations, downstream process and visualization technology of pretreatment were discussed. Finally, this review presented the challenge of lignocellulose pretreatment in the future.

Reconsidering the function of the xyloglucan endotransglucosylase/hydrolase family

Plants possess an outer cell layer called the cell wall. This matrix comprises various molecules, such as polysaccharides and proteins, and serves a wide array of physiologically important functions. This structure is not static but rather flexible in response to the environment. One of the factors responsible for this plasticity is the xyloglucan endotransglucosylase/hydrolase (XTH) family, which cleaves and reconnects xyloglucan molecules. Since xyloglucan molecules have been hypothesised to tether cellulose microfibrils forming the main load-bearing network in the primary cell wall, XTHs have been thought to play a central role in cell wall loosening for plant cell expansion. However, multiple lines of recent evidence have questioned this classic model. Nevertheless, reverse genetic analyses have proven the biological importance of XTHs; therefore, a major challenge at present is to reconsider the role of XTHs in planta. Recent advances in analytical techniques have allowed for gathering rich information on the structure of the primary cell wall. Thus, the integration of accumulated knowledge in current XTH studies may offer a turning point for unveiling the precise functions of XTHs. In the present review, we redefine the biological function of the XTH family based on the recent architectural model of the cell wall. We highlight three key findings regarding this enzyme family: (1) XTHs are not strictly required for cell wall loosening during plant cell expansion but play vital roles in response to specific biotic or abiotic stresses; (2) in addition to their transglycosylase activity, the hydrolase activity of XTHs is involved in physiological benefits; and (3) XTHs can recognise a wide range of polysaccharides other than xyloglucans.