Cell Wall Polymers Research Articles

Architecture of the dynamic fungal cell wall.

The fungal cell wall is essential for growth and survival, and is a key target for antifungal drugs and the immune system. The cell wall must be robust but flexible, protective and shielding yet porous to nutrients and membrane vesicles and receptive to exogenous signals. Most fungi have a common inner wall skeleton of chitin and β-glucans that functions as a flexible viscoelastic frame to which a more diverse set of outer cell wall polymers and glycosylated proteins are attached. Whereas the inner wall largely determines shape and strength, the outer wall confers properties of hydrophobicity, adhesiveness, and chemical and immunological heterogeneity. The spatial organization and dynamic regulation of the wall in response to prevailing growth conditions enable fungi to thrive within changing, diverse and often hostile environments. Understanding this architecture provides opportunities to develop diagnostics and drugs to combat life-threatening fungal infections.

Genome-edited rice deficient in two 4-COUMARATE:COENZYME A LIGASE genes displays diverse lignin alterations.

The 4-coumarate:coenzyme A ligase (4CL) is a key enzyme that contributes to channeling metabolic flux in the cinnamate/monolignol pathway, leading to the production of monolignols, p-hydroxycinnamates, and a flavonoid tricin, the major building blocks of lignin polymer in grass cell walls. Vascular plants often contain multiple 4CL genes; however, the contribution of each 4CL isoform to lignin biosynthesis remains unclear, especially in grasses. In this study, we characterized the functions of two rice (Oryza sativa L.) 4CL isoforms (Os4CL3 and Os4CL4) primarily by analyzing the cell wall chemical structures of rice mutants generated by CRISPR/Cas9-mediated targeted mutagenesis. A series of chemical and nuclear magnetic resonance analyses revealed that loss-of-function of Os4CL3 and Os4CL4 differently altered the composition of lignin polymer units. Loss of function of Os4CL3 induced marked reductions in the major guaiacyl and syringyl lignin units derived from both the conserved non-γ-p-coumaroylated and the grass-specific γ-p-coumaroylated monolignols, with more prominent reductions in guaiacyl units than in syringyl units. In contrast, the loss-of-function mutation to Os4CL4 primarily decreased the abundance of the non-γ-p-coumaroylated guaiacyl units. Loss-of-function of Os4CL4, but not of Os4CL3, reduced the grass-specific lignin-bound tricin units, indicating that Os4CL4 plays a key role not only in monolignol biosynthesis but also in the biosynthesis of tricin used for lignification. Further, the loss-of-function of Os4CL3 and Os4CL4 notably reduced cell-wall-bound ferulates, indicating their roles in cell wall feruloylation. Overall, this study demonstrates the overlapping but divergent roles of 4CL isoforms during the coordinated production of various lignin monomers.

P017 Echinocandin resistance mechanism in Candida tropicalis and Candida glabrata

Poster session 1, September 21, 2022, 12:30 PM - 1:30 PMObjective Candida tropicalis and Candida glabrata account for 41.6% and 7.08% of total Candidaemia cases in India. Echinocandins are the first-line treatment option for these infections. Resistance to Echinocandins is rare with Candida sp. However, in recent years, has been noted across many centers. We determined the mechanism of echinocandin resistance in C. tropicalis and C. glabrata.Methods C. tropicalis and C. glabrata isolated from Candidaemia patients over a period of 3 years (August 2016-July 2019), identified by MALDI-TOF-MS were used in this study. Antifungal susceptibility testing was done following CLSI broth microdilution reference method (M 27A). FKS1 gene was sequenced using species-specific primers for the presence of any mutation. To determine any changes in the cell wall chitin and glucan contents, expression fold changes of chitin synthase (CHS1, CHS2, and CHS3), and glucan synthase genes upon caspofungin treatment were determined using real-time qPCR. These findings were correlated with cell wall chitin and glucan content determined by flowcytometry.ResultsA total of 3558 Candida species were isolated from patients of all age groups at our hospital. C. tropicalis was the predominant agent (34%), while the prevalence of C. glabrata was 6%. A total of 17 (8.5%) C. glabrata and 3 (0.25%) C. tropicalis exhibited reduced susceptibility to echinocandins. All these isolates carried a wild-type FKS genes.In C. tropicalis, inducible expression of Chs1, Chs2 and Chs3 genes were comparable among susceptible and resistant isolates1.8 (0.4-2.8) vs. 2.5 (0.9-6.6), P = .247); [0.7 (0.3-1.8) vs. 0.7 (0.2-1.6), P = .793]; [1.3 (0.14-4.8) vs. 1.1(0.48-1.7), P = .522], respectively. In concordance with gene expression, there was no significant difference in cell wall chitin contents among resistant and susceptible [14.37 (6.5-24.8) vs 16.28 (6.0-24.7), P = .114] C. tropicalis isolates. In contrast in resistant isolates of C. glabrata, caspofungin treatment resulted in significantly higher induction of chitin synthase genes compared to susceptible isolates; Chs1 [2.34 (0.24-9.71) vs. 1.56 (0.55-4.5) (P = .007)], CHS2 [1.59 (0.33-8.0) vs. (2.3 (0.69-6.15), P = .0006], and CHS3 gene [3.8 (0.13-12.73) vs. 1.9 (0.56-7.16), P <.0001]. Flowcytometric data in terms of chitin content, correlated well with expression changes as staining index was significantly higher in resistant compared to susceptible isolates [320 (198-535) vs. 164 (5.34-254.10) P = .0001]. Glucan synthase expression was comparable in susceptible and resistant isolates of C. tropicalis [3.47 (1.57-7.63) vs. 4.41 (0.41-17.51), (P = .518)]. However, glucan synthase gene expression was found significantly increased in resistant C. glabrata isolates compared to susceptible isolates; 3.10 (1.02-16.45) vs. 1.61 (0.13-7.67), P <.001.ConclusionWe evaluated the role of cell wall components in echinocandin resistance in isolates with reduced susceptibility to echinocandins but lacking an FKS1 mutation. While chitin was induced at higher levels in C. glabrata, a similar finding was not observed in C. tropicalis. This warrants further studies to elucidate the role of fungal cell wall polymers in resistance.

Why Do Bamboo Parenchyma Cells Show Higher Nanofibrillation Efficiency than Fibers: An Investigation on Their Hierarchical Cell Wall Structure.

The cell walls of parenchyma cells and fibers in bamboo are both highly lignified with secondary thickening. However, the former were found to have much higher nanofibrillation efficiency than fibers via both protocols of ultrasonication and high pressure homogenization. To elucidate the inherent mechanism, detailed comparisons of chemical composition, cell morphology, cell wall density, pore structures, and structural organization of cell wall polymers were performed on native and pretreated cell walls of both parenchyma cells and fibers. Chemical compositional analysis showed that fibers have much higher cellulose (49.8% to 35.5%) but lower xylan content (21.1% to 36.2%) than parenchyma, while their lignin contents were similar (24.9% vs 22.9%). Polarized FTIR further revealed clear differences in the structural organization of polymers between the two types of cells, with all the polymers of fibers being more orderly assembled than those of parenchyma cells. The compact arrangement of polymers in the fibers was also supported by the much higher cell wall density (1.52 vs 1.28 g/cm3) and lower porosity (0.007 vs 0.013 cc/g after chemical pretreatments), as compared to the parenchyma cells. The study provides evidence that the anatomical characteristics of huge cavity-wall ratio, higher cell wall porosity, and less ordered arrangement of cell wall matrix polymers (mainly lignin) in parenchyma cells contribute to their higher nanofibrillation efficiency compared to fibers.

Proteomic analysis response of rice (Oryza sativa) leaves to ultraviolet-B radiation stress.

Rice (Oryza sativa) is a human staple food and serves as a model organism for genetic and molecular studies. Few studies have been conducted to determine the effects of ultraviolet-B (UV-B) stress on rice. UV-B stress triggers morphological and physiological changes in plants. However, the underlying mechanisms governing these integrated responses are unknown. In this study, we conducted a proteomic response of rice leaves to UV-B stress using two-dimensional gel electrophoresis and identified the selected proteins by mass spectrometry analysis. Four levels of daily biologically effective UV-B radiation intensities were imposed to determine changes in protein accumulation in response to UV-B stress: 0 (control), 5, 10, and 15 kJ m−2 d−1in two cultivars, i.e., IR6 and REX. To mimic the natural environment, we conducted this experiment in Sunlit Soil-Plant-Atmosphere-Research (SPAR) chambers. Among the identified proteins, 11% of differentially expressed proteins were found in both cultivars. In the Rex cultivar, only 45% of proteins are differentially expressed, while only 27.5% were expressed in IR6. The results indicate that REX is more affected by UV-B stress than IR6 cultivars. The identified protein TSJT1 (spot 16) in both cultivars plays a crucial role in plant growth and development during stress treatment. Additionally, we found that UV-B stress altered many antioxidant enzymes associated with redox homeostasis and cell defense response. Another enzyme, the glyceraldehyde-3-phosphate dehydrogenase (GAPDH), has been identified as spot 15, which plays an essential role in glycolysis and cellular energy production. Another vital protein identified is glycosyl hydrolase (GH) as spot 9, which catalyzes the hydrolysis of glycosidic bonds in cell wall polymers and significantly affects cell wall architecture. Some identified proteins are related to photosynthesis, protein biosynthesis, signal transduction, and stress response. The findings of our study provide new insights into understanding how rice plants are tailored to UV-B stress via modulating the expression of UV-B responsive proteins, which will help develop superior rice breeds in the future to combat UV-B stress. Data are available via ProteomeXchange with identifier PXD032163.

Central Sugar Metabolism and the Cell Wall.

ABSTRACTThe human opportunistic pathogen Aspergillus fumigatus is recognized for its versatile cell wall when it comes to remodeling its components in adaptation to external threats, and this remodeling renders it refractory to antifungals targeting cell wall biosynthesis. A specific role for general sugar metabolism in the regulation of the synthesis of cell wall polymers has been previously demonstrated. Delving deeper into central sugar metabolism may reveal unexpected fundamental aspects in cell wall construction, as shown by the work of Zhou and coworkers (Y. Zhou, K. Yan, Q. Qin, O.G. Raimi, et al., mBio 13:e01426-22, 2022, https://doi.org/10.1128/mbio.01426-22) on the roles of the phosphoglucose isomerase of A. fumigatus in cell wall biosynthesis.

Genome-wide identification of CrRLK1L gene family and desiccation-induced expression profiles in Boea hygrometrica

Catharanthus roseus receptor-like kinase 1-like (CrRLK1L) proteins constitute a subfamily of receptor-like kinases (RLKs) that play diverse roles during fertilization, vegetative development and plant pathogen interactions. CrRLK1Ls possess a unique malectin-like domain at N-terminal that bind to oligo- or polysaccharides from cell wall polymers, byproducts of cell wall degradation, or membrane-associated or secreted glycosylated proteins. CrRLK1L members have been identified in many organisms, however, the study of this gene family in resurrection plant species has not been reported to date. Resurrection plants are a kind of extremophiles that can survive extreme drought stress (desiccation) and recover rapidly after rehydration, and display specific and reversible cell wall structure and component changes during dehydration and rehydration. Here, we identified 18 CrRLK1L protein members in the resurrection plant Boea hygrometrica genome and classified them into 9 clades based on the conserved amino acid sequences. Phylogenetic analysis reveals the expansion of FER clade, the absence of MEDOS and CVY clades and the emergence of a new Bh-specific clade in BhCrRLK1L protein family. Analysis of cis-regulatory elements has predicted several types of drought induced elements and/or drought related hormone responsiveness elements in the promoter regions of all BhCrRLK1Ls. In agreement, we found 15 members of BhCrRLK1Ls change their expression pattern in response to drought stress, based on a previous transcriptome survey. Subsequent qRT-PCR validation of selected 7 BhCrRLK1L genes confirmed that BhFER1, BhCrRLK1L14 and BhCrRLK1L15 are induced by desiccation, and BhFER3, BhCrRLK1L17 and BhCrRLK1L18 are repressed by desiccation. Our study systematically identified the CrRLK1L members in B. hygrometrica, and analyzed the gene expression profiles in response to desiccation stresses, which lays a foundation for exploring the function of BhCrRLK1Ls in desiccation signal transduction in B. hygrometrica.

The influence of key reactions during hydrothermal carbonization of sewage sludge on aqueous phase properties: A review

Hydrothermal carbonization (HTC) emerges as a promising technology to reduce the volume of activated sewage sludge (SS) and generate solid products as fuels. During HTC, extracellular polymeric substance and cell wall degrade to form low molecular compounds, which can further carry out hydrolysis, dehydration, polymerization, etc. The temperature has a notable impact on the HTC, which ultimately changes the composition of the aqueous phase. A large amount of the aqueous phase remains a by-product containing high amounts of organic and inorganic compounds. Herein, the HTC of SS process and aqueous phase treatment were discussed, especially in industrial applications within China. This review depicts the influence of aqueous phase properties on the hydrochar properties of SS, especially using the aqueous phase recirculation process. The mechanism during HTC of SS has been discussed, especially Maillard reaction, which would significantly influence the aqueous phase and hydrochar. The systematic information on the current research, new applications and new perspectives in this field to promote its further development were provided.

Contribution of TagA-Like Glycosyltransferases to the Assembly of the Secondary Cell Wall Polysaccharide in Bacillus anthracis.

Bacillus anthracis elaborates a secondary cell wall polysaccharide (SCWP) made of 6 to 12 trisaccharide units. Pyruvyl and acetyl substitutions of the distal unit are prerequisites for the noncovalent retention of 22 secreted Bacillus S-layer (Bsl)-associated proteins bearing an S-layer homology (SLH) domain. Surface display of Bsl proteins contributes to cell separation as well as virulence. Earlier work suggested that TagO initiates the synthesis of SCWP while GneY and GneZ, two UDP-GlcNAc 2-epimerases, synthesize ManNAc that is later incorporated in the repeat unit (→4)-ManNAc-(β1→4)-GlcNAc-(β1→6)-GlcNAc-(α1→). In organisms that synthesize wall teichoic acid, TagA catalysts have been shown to form the glycosidic bond ManNAc-(β1→4)-GlcNAc. Here, we show that genes bas2675 and bas5272, predicted to encode glycosyltransferases of the WecB/TagA/CpsF family (PFAM03808; CAZy GT26), are required for B. anthracis SCWP synthesis and S-layer assembly. Similar to tagO or gneY gneZ mutants, B. anthracis strains depleted of tagA1 (bas5272) cannot maintain cell shape, support vegetative growth, or synthesize SCWP. Expression of tagA2 (bas2675), or Staphylococcus aureus tagA on a plasmid, rescues the nonviable tagA1 mutant. We propose that TagA1 and TagA2 fulfill overlapping and key glycosyltransferase functions for the synthesis of repeat units of the SCWP of B. anthracis. IMPORTANCE Glycosyltransferases (GTs) catalyze the transfer of sugar moieties from activated donor molecules to acceptor molecules to form glycosidic bonds using a retaining or inverting mechanism. Based on the structural relatedness of their catalytic and carbohydrate-binding modules, GTs have been grouped into 115 families in the Carbohydrate-Active EnZyme (CAZy) database. For complex products, the functional assignment of GTs remains highly challenging without the knowledge of the chemical structure of the assembled polymer. Here, we propose that two uncharacterized GTs of B. anthracis belonging to the WecB/TagA/CpsF family incorporate ManNAc in repeat units of the secondary cell wall polymer of bacilli species.

Raman spectroscopy mapping of changes in the organization and relative quantities of cell wall polymers in bast fiber cell walls of flax plants exposed to gravitropic stress.

Flax is an important fiber crop that is subject to lodging. In order to gain more information about the potential role of the bast fiber cell wall in the return to the vertical position, 6-week-old flax plants were subjected to a long-term (6 week) gravitropic stress by stem tilting in an experimental set-up that excluded autotropism. Stress induced significant morphometric changes (lumen surface, lumen diameter, and cell wall thickness and lumen surface/total fiber surface ratio) in pulling- and opposite-side fibers compared to control fibers. Changes in the relative amounts and spatial distribution of cell wall polymers in flax bast fibers were determined by Raman vibrational spectroscopy. Following spectra acquisition, datasets (control, pulling- and opposite sides) were analyzed by principal component analysis, PC score imaging, and Raman chemical cartography of significant chemical bonds. Our results show that gravitropic stress induces discrete but significant changes in the composition and/or spatial organization of cellulose, hemicelluloses and lignin within the cell walls of both pulling side and opposite side fibers.

Sweetpotato chip texture and fat content: Effects of enzymatic modification of cell wall polymers.

Impacts of cell wall polymers on sweetpotato chip texture and fat content were investigated through enzymatic modification. Covington sweetpotato slices were treated with cellulase, hemicellulase, pectinase, pectin methyl esterase, protease, the enzyme blend Viscozyme, or no enzymes (control) at 40-45°C for 0.5-2 h. Treated slices were blanched, dried, and fried in triplicate per experimental condition. Breaking forces of 20 chips per frying replicate were measured followed by chip fat, moisture, sugar, alcohol insoluble solids, glass transition temperature, and color analyses. Untreated slices from each batch (daily check) were fried and analyzed to account for starting material variability. Viscozyme and protease-treated chips had the greatest reduction in breaking force from untreated chips (-30.9% and -23.7%, respectively), while pectin methyl esterase-treated chips had the lowest reduction in breaking force (-9.0%). Chips treated with Viscozyme for 2 h were 6.7-6.3 percentiles lower in fat than the control. Principal component analysis elucidated that chip breaking force was associated with unfried slice puncture force, alcohol insoluble solids, and chip color, and chip fat content was inversely associated with maltose content and glass transition temperature. Breaking down multiple cell wall polysaccharides or structural proteins weakened chip textures, while strengthening the pectic fraction resulted in harder chips. Chip fat reduction also occurred when multiple cell wall polysaccharides were broken down. Therefore, cell wall polymers impact sweetpotato chip texture and fat contents, and their attributes should be considered when selecting cultivars and processes for sweetpotato chips. PRACTICAL APPLICATION: Sweetpotato chips are an increasingly popular snack, but there is little understanding how cell wall polymers impact chip textures and fat contents. Raw sweetpotato slices were enzymatically treated to selectively modify cell wall polymers before frying. Chip breaking forces were lowered by protease or Viscozyme (cell wall enzyme blend) treatments, while breaking forces were increased with pectin methyl esterase. In addition, chip fat contents were reduced by the Viscozyme treatment. Since cell wall modifications could impact chip texture and fat content, cell wall polymer attributes should be considered in selection and processing of sweetpotatoes for chip manufacturing.

STUDY OF THE BIOCHEMICAL CHARACTERISTICS OF GLYCOSYLATED RECOMBINANT XYLANASE

The main renewable source of energy and raw materials on Earth is plant biomass, most of which consists of plant cell wall polymers: cellulose, hemicellulose, and lignin. Hemicelluloses are divided into three main types: xylans, mannans and arabinogalactans. Xylan is the second most abundant carbohydrate in nature after cellulose. The specific enzymes that hydrolyze xylan into xylooligosaccharides and D-xylose are xylanases. Prospective xylanases are enzymes derived from bacteria and mycelial fungi. Bacterial xylanases are characterized by high unitary activity, and additional manose chains can significantly increase the stability of the enzyme protein globule. Obtaining a glycosylated variant of bacillary xylanase, which are known for their high specific activity, seems promising. The Bacillus sonorensis T6 xylanase gene was cloned and expressed in the yeast Pichia pastoris. The recombinant xylanase was isolated and purified. The biochemical characteristics of the glycosylated recombinant xylanase were studied. It was found that the recombinant xylanase had maximum activity at 47-50°C and pH 6.0. The Km, Vmax and Kcat values are 3.037 ± 0.362 (mg/ml), 667.8 ± 31 (units/mg) and 100.3 ± 4.6 (s-1), respectively. The unitary activity of the recombinant enzyme is 873.8 units/mg. The glycosylated recombinant xylanase was found to have high temperature stability and retained 47% activity after a 2-hour incubation at 55°C. In addition to temperature stability, recombinant xylanase showed high pH stability - 10 h incubation in buffers with pH 3-11 did not decrease the activity. The effect of metal ions, detergents, and organic solvents on the activity of recombinant glycosylated xylanase was studied. The high biochemical parameters of recombinant glycosylated xylanase from Bacillus sonorensis T6 suggest that this enzyme is promising for use in the biotechnology and food industry.

Genetic Determinants of Xylan Utilization in Humisphaera borealis M1803T, a Planctomycete of the Class Phycisphaerae

—Planctomycetes of the class Phycisphaerae are aerobic and anaerobic heterotrophic bacteria that colonize a wide range of marine and terrestrial habitats. Their functional roles in the environment, however, are still poorly understood. Humisphaera borealis M1803T is one of the very few characterized planctomycetes of this class. It is also the first described representative of the previously uncultured group WD2101, which is commonly detected in soils and peatlands. This work analyzed the genetic determinants that define the ability of Humisphaera borealis M1803T to grow on xylan, one of the plant cell wall polymers. The whole genome sequence analysis of this planctomycete resulted in identification of five genes encoding the proteins homologous to previously described endo-β-xylanases. For two of these proteins, evolutionarily closer experimentally characterized homologs with other substrate specificities were found. In a member of the GH10 family of glycoside hydrolases, the active center of the enzyme was destroyed. We consider two proteins from GH62 and GH141 families as the most likely candidates for the role of β-xylanase responsible for xylan utilization. Phylogenetic analysis of proteins of GH10, GH62, and GH141 families was carried out. The role of lateral transfers in the evolution of the genes for glycoside hydrolases and their close homologs is discussed.

Characterization of the Cell Wall Component through Thermogravimetric Analysis and Its Relationship with an Expansin-like Protein in Deschampsia antarctica.

Deschampsia antarctica Desv. (Poaceae) is one of the two vascular plants that have colonized the Antarctic Peninsula, which is usually exposed to extreme environmental conditions. To support these conditions, the plant carries out modifications in its morphology and metabolism, such as modifications to the cell wall. Thus, we performed a comparative study of the changes in the physiological properties of the cell-wall-associated polysaccharide contents of aerial and root tissues of the D. antarctica via thermogravimetric analysis (TGA) combined with a computational approach. The result showed that the thermal stability was lower in aerial tissues with respect to the root samples, while the DTG curve describes four maximum peaks of degradation, which occurred between 282 and 358 °C. The carbohydrate polymers present in the cell wall have been depolymerized showing mainly cellulose and hemicellulose fragments. Additionally, a differentially expressed sequence encoding for an expansin-like (DaEXLA2), which is characterized by possessing cell wall remodeling function, was found in D. antarctica. To gain deep insight into a probable mechanism of action of the expansin protein identified, a comparative model of the structure was carried out. DaEXLA2 protein model displayed two domains with an open groove in the center. Finally, using a cell wall polymer component as a ligand, the protein–ligand interaction was evaluated by molecular dynamic (MD) simulation. The MD simulations showed that DaEXLA2 could interact with cellulose and XXXGXXXG polymers. Finally, the cell wall component description provides the basis for a model for understanding the changes in the cell wall polymers in response to extreme environmental conditions.

Arabidopsis GELP7 functions as a plasma membrane-localized acetyl xylan esterase, and its overexpression improves saccharification efficiency.

Acetyl substitution on the xylan chain is critical for stable interaction with cellulose and other cell wall polymers in the secondary cell wall. Xylan acetylation pattern is governed by Golgi and extracellular localized acetyl xylan esterase (AXE). We investigated the role of Arabidopsis clade Id from the GDSL esterase/lipase or GELP family in polysaccharide deacetylation. The investigation of the AtGELP7 T-DNA mutant line showed a decrease in stem esterase activity and an increase in stem acetyl content. We further generated overexpressor AtGELP7 transgenic lines, and these lines showed an increase in AXE activity and a decrease in xylan acetylation compared to wild-type plants. Therefore, we have named this enzyme as AtAXE1. The subcellular localization and immunoblot studies showed that the AtAXE1 enzyme is secreted out, associated with the plasma membrane and involved in xylan de-esterification post-synthesis. The cellulose digestibility was improved in AtAXE1 overexpressor lines without pre-treatment, after alkali and xylanases pre-treatment. Furthermore, we have also established that the AtGELP7 gene is upregulated in the overexpressor line of AtMYB46, a secondary cell wall specific transcription factor. This transcriptional regulation can drive AtGELP7 or AtAXE1 to perform de-esterification of xylan in a tissue-specific manner. Overall, these data suggest that AtGELP7 overexpression in Arabidopsis reduces xylan acetylation and improves digestibility properties of polysaccharides of stem lignocellulosic biomass.

Eco-friendly preparation of high-quality mineralized wood via thermal modification induced silica sol penetration

Application of wood as a green and sustainable material is restricted due to its easy wrapping property, deformation, biological degradation and thermal instability. Coupling thermal treatment and silica sol penetration could overcome the weakness of natural wood, and synergistically improve the overall performance. Thermal treatment showed a significant effect on hydrophobicity, hygroscopicity, surface color and compressive strength. It reduced the compressive strength to some extent due to the degradation of cell wall polymers (hemicellulose, lignin and cellulose). At above 200 ℃, the degradation of cell wall polymers, rather than hornification, was in the leading position, dominating the compressive strength. Changes in the component and structure of cell walls (chemical and physical environment) helped the penetration and deposition of silica sol owing to extra channels and enlarged pore size. Satisfied silica sol incorporation in thermally treated wood further improved the surface hydrophobicity, dimensional stability, surface hardness, and compensated the reduction on compressive strength. It was attributed to the -OH consumption (cell wall polymers degradation) and filling effect caused by silica sol networks (Si-O-Si and Si-O-C bonds) in wood. The improved thermal stability was ascribed to the coverage effect of silica sol on the inner-surfaces of wood, which could be treated as a physical barrier to prevent heat conduction. Eventually, we proposed a mechanism concerning the combination treatment for preparing silica-mineralized wood. This work opens an eco-friendly way to produce bio-based materials with high quality to be used in outdoor applications or humid environments.

Desiccation Tolerance in Ramonda serbica Panc.: An Integrative Transcriptomic, Proteomic, Metabolite and Photosynthetic Study.

The resurrection plant Ramonda serbica Panc. survives long desiccation periods and fully recovers metabolic functions within one day upon watering. This study aimed to identify key candidates and pathways involved in desiccation tolerance in R. serbica. We combined differential transcriptomics and proteomics, phenolic and sugar analysis, FTIR analysis of the cell wall polymers, and detailed analysis of the photosynthetic electron transport (PET) chain. The proteomic analysis allowed the relative quantification of 1192 different protein groups, of which 408 were differentially abundant between hydrated (HL) and desiccated leaves (DL). Almost all differentially abundant proteins related to photosynthetic processes were less abundant, while chlorophyll fluorescence measurements implied shifting from linear PET to cyclic electron transport (CET). The levels of H2O2 scavenging enzymes, ascorbate-glutathione cycle components, catalases, peroxiredoxins, Fe-, and Mn superoxide dismutase (SOD) were reduced in DL. However, six germin-like proteins (GLPs), four Cu/ZnSOD isoforms, three polyphenol oxidases, and 22 late embryogenesis abundant proteins (LEAPs; mainly LEA4 and dehydrins), were desiccation-inducible. Desiccation provoked cell wall remodeling related to GLP-derived H2O2/HO● activity and pectin demethylesterification. This comprehensive study contributes to understanding the role and regulation of the main metabolic pathways during desiccation aiming at crop drought tolerance improvement.

Enzymatic Synthesis of Xylan Microparticles with Tunable Morphologies.

Xylans are a diverse family of hemicellulosic polysaccharides found in abundance within the cell walls of nearly all flowering plants. Unfortunately, naturally occurring xylans are highly heterogeneous, limiting studies of their synthesis and structure–function relationships. Here, we demonstrate that xylan synthase 1 from the charophyte alga Klebsormidium flaccidum is a powerful biocatalytic tool for the bottom-up synthesis of pure β-1,4 xylan polymers that self-assemble into microparticles in vitro. Using uridine diphosphate-xylose (UDP-xylose) and defined saccharide primers as substrates, we demonstrate that the shape, composition, and properties of the self-assembling xylan microparticles could be readily controlled via the fine structure of the xylan oligosaccharide primer used to initiate polymer elongation. Furthermore, we highlight two approaches for bottom-up and surface functionalization of xylan microparticles with chemical probes and explore the susceptibility of xylan microparticles to enzymatic hydrolysis. Together, these results provide a useful platform for structural and functional studies of xylans to investigate cell wall biosynthesis and polymer–polymer interactions and suggest possible routes to new biobased materials with favorable properties for biomedical and renewable applications.

Effect of the thermal treatment on the chemical components, sorption, and shrinkage properties of Tectona grandis juvenile wood

The effect of thermal treatment on the chemical components, equilibrium moisture content (EMC), and shrinkage of teak juvenile wood was studied. Heartwood and sapwood samples were thermally-treated at 180 ºC and 200 ºC. Extractive, Klason lignin, holocellulose, and α-cellulose contents, as well as pH on untreated and thermally-treated woods, were determined. The EMC was reached at five relative humidity (RH) levels using saturated salt solutions: 86 % (KCl), 76 % (NaCl), 58 % (NaBr), 33 % (MgCl2), and 0 % (P2O5). Linear and volumetric shrinkages were calculated for all EMCs. The ratio of sorption (S), coefficient of shrinkage (h), and fiber saturation point (FSP) were also determined. Thermally-treated wood exhibited lower holocellulose and α-cellulose contents than untreated wood and increased acidity due to degradation of the hemicelluloses. The thermal treatment reduced the EMC of heartwood and sapwood. However, sapwood was more sensitive to RH variations than heartwood regardless of the treatment. Thermally-treated woods had higher hygroscopic and dimensional stabilities, and lower FSP than untreated wood. The thermal treatment did not affect radial shrinkage of the heartwood between 33 % and 86 % RH. Heartwood was more sensitive to the effect of the thermal treatment on shrinkage and degradation of cell wall polymers compared to sapwood.

Cell wall biology of the moss Physcomitrium patens.

The moss Physcomitrium (previously Physcomitrella) patens is a non-vascular plant belonging to the bryophytes that has been used as a model species to study the evolution of plant cell wall structure and biosynthesis. Here, we present an updated review of the cell wall biology of P. patens. Immunocytochemical and structural studies have shown that the cell walls of P. patens mainly contain cellulose, hemicelluloses (xyloglucan, xylan, glucomannan, and arabinoglucan), pectin, and glycoproteins, and their abundance varies among different cell types and at different plant developmental stages. Genetic and biochemical analyses have revealed that a number of genes involved in cell wall biosynthesis are functionally conserved between P. patens and vascular plants, indicating that the common ancestor of mosses and vascular plants had already acquired most of the biosynthetic machinery to make various cell wall polymers. Although P. patens does not synthesize lignin, homologs of the phenylpropanoid biosynthetic pathway genes exist in P. patens and they play an essential role in the production of caffeate derivatives for cuticle formation. Further genetic and biochemical dissection of cell wall biosynthetic genes in P. patens promises to provide additional insights into the evolutionary history of plant cell wall structure and biosynthesis.