Wall Polymers Research Articles

Elongated galactan side chains mediate cellulose-pectin interactions in engineered Arabidopsis secondary cell walls.

The plant secondary cell wall is a thickened matrix of polysaccharides and lignin deposited at the cessation of growth in some cells. It forms the majority of carbon in lignocellulosic biomass, and it is an abundant and renewable source for forage, fiber, materials, fuels, and bioproducts. The complex structure and arrangement of the cell wall polymers mean that the carbon is difficult to access in an economical and sustainable way. One solution is to alter the cell wall polymer structure so that it is more suited to downstream processing. However, it remains difficult to predict what the effects of this engineering will be on the assembly, architecture, and properties of the cell wall. Here, we make use of Arabidopsis plants expressing a suite of genes to increase pectic galactan chain length in the secondary cell wall. Using multi-dimensional solid-state nuclear magnetic resonance, we show that increasing galactan chain length enhances pectin-cellulose spatial contacts and increases cellulose crystallinity. We also found that the increased galactan content leads to fewer spatial contacts of cellulose with xyloglucan and the backbone of pectin. Hence, we propose that the elongated galactan side chains compete with xyloglucan and the pectic backbone for cellulose interactions. Due to the galactan topology, this may result in comparatively weak interactions and disrupt the cell wall architecture. Therefore, introduction of this strategy into trees or other bioenergy crops would benefit from cell-specific expression strategies to avoid negative effects on plant growth.

Endosidin 5 disruption of the Golgi Apparatus and extracellular matrix secretion in the unicellular charophyte, Penium margaritaceum.

Endosidins are a group of small molecular weight compounds, first identified by "chemical biology" screening assays, that have been used to target specific components of the endomembrane system. In this study, we employed multiple microscopy-based screening techniques to elucidate effects of Endosidin 5 (ES5) on the Golgi Apparatus and the secretion of extracellular matrix (ECM) components, Penium margaritaceum. These effects were compared with those caused by treatments with brefeldin A and concanamycin A. Penium margaritaceum's extensive Golgi Apparatus and endomembrane system make it an outstanding model organism for screening changes to the endomembrane system. Here we detail changes to the Golgi Apparatus and secretion of ECM material caused by Endosidin 5. Changes to extracellular polymeric substance (EPS) secretion and cell wall expansion were screened using fluorescence microscopy. Confocal laser scanning microscopy, and transmission electron microscopy were used to assess changes to the Golgi Apparatus, the cell wall and the vesicular network. Electron tomography was also performed in order to detail the changes to the Golgi Apparatus. While other endosidins were able to impact EPS secretion and cell wall expansion only ES5 completely inhibited EPS secretion and cell wall expansion over 24h. Short treatments of ES5 resulted in displacement of the Golgi bodies from their typical linear alignment. The number of cisternae decreased per Golgi stack and trans face cisternae in-curled to form distinct elongate circular profiles. Longer treatment resulted in a transformation of the Golgi body to an irregular aggregate of cisternae. These alterations could be reversed by removal of ES5 and returning cells to culture. ES5 alters secretion of ECM material in Penium by affecting the Golgi apparatus and does so in a markedly different way than other endomembrane inhibitors such as Brefeldin A and Concanamycin A.

Identification of d-arabinan-degrading enzymes in mycobacteria

Bacterial cell growth and division require the coordinated action of enzymes that synthesize and degrade cell wall polymers. Here, we identify enzymes that cleave the d-arabinan core of arabinogalactan, an unusual component of the cell wall of Mycobacterium tuberculosis and other mycobacteria. We screened 14 human gut-derived Bacteroidetes for arabinogalactan-degrading activities and identified four families of glycoside hydrolases with activity against the d-arabinan or d-galactan components of arabinogalactan. Using one of these isolates with exo-d-galactofuranosidase activity, we generated enriched d-arabinan and used it to identify a strain of Dysgonomonas gadei as a d-arabinan degrader. This enabled the discovery of endo- and exo-acting enzymes that cleave d-arabinan, including members of the DUF2961 family (GH172) and a family of glycoside hydrolases (DUF4185/GH183) that display endo-d-arabinofuranase activity and are conserved in mycobacteria and other microbes. Mycobacterial genomes encode two conserved endo-d-arabinanases with different preferences for the d-arabinan-containing cell wall components arabinogalactan and lipoarabinomannan, suggesting they are important for cell wall modification and/or degradation. The discovery of these enzymes will support future studies into the structure and function of the mycobacterial cell wall.

Life cycle energy analysis of houses incorporating conventional and alternative masonry units

ABSTRACT The use of alternative masonry units and technologies in traditional masonry work could reduce the life cycle energy of buildings. This study investigates the life cycle energy assessment of houses constructed using concrete blocks, eco-bricks and polymer bricks to evaluate the impacts of masonry units on the life cycle energy of buildings. Three bungalows of approximately 110 m2 each, having the same geometry but different types of wall materials, namely eco-bricks, polymer bricks, and concrete blocks, were used for the analysis. The study found embodied manufacturing energy of 0.346 MJ/kg for eco-bricks and 0.518 MJ/kg for polymer bricks. Approximately 85-86% of the total life cycle energy constitutes the operational phase energy. The polymer brick and eco-brick buildings had the least embodied construction energy of 14% of the total life cycle energy. The life cycle energy of concrete block buildings was 17.547 GJ/m2 at 50 years of service life. Buildings made of polymer bricks and eco-bricks had lower life cycle energy than the concrete block building. The study suggests a prudent selection of building materials by developers and construction professionals based on life cycle energy assessment to reduce the energy consumption of the building sector. Although the study focus is limited to eco-bricks, polymer bricks, and concrete blocks as masonry units in the Nigerian construction context, the method employed in the study is applicable to the energy analysis of other construction materials and geographical locations.

Atomic Level Interactions and Suprastructural Configuration of Plant Cell Wall Polymers in Dialkylimidazolium Ionic Liquids.

Ionic liquids (ILs) have been widely investigated for the pretreatment and deconstruction of lignocellulosic feedstocks. However, the modes of interaction between IL-anions and cations, and plant cell wall polymers, namely, cellulose, hemicellulose, and lignin, as well as the resulting ultrastructural changes are still unclear. In this study, we investigated the atomic level and suprastructural interactions of microcrystalline cellulose, birchwood xylan, and organosolv lignin with 1,3-dialkylimidazolium ILs having varying sizes of carboxylate anions. Analysis by 13C NMR spectroscopy indicated that cellulose and lignin exhibited stronger hydrogen bonding with acetate ions than with formate ions, as evidenced by greater chemical shift changes. Small-angle X-ray scattering analysis showed that while both cellulose and xylan adopted a single-stranded conformation in acetate-ILs, twice as many acetate ions were bound to one anhydroglucose unit than to an anhydroxylose unit. We also determined that a minimum of seven representative carbohydrate units must interact with an anion for that IL to effectively dissolve cellulose or xylan. Lignin is associated as groups of four polymer molecules in formate-ILs and dispersed as single molecules in acetate-ILs, which indicates that it is highly soluble in the latter. In summary, our study demonstrated that 1,3-dialkylimidazolium acetates displayed stronger binding interactions with cellulose and lignin, as compared to formates, and thus have superior potential to fractionate these polymers from lignocellulosic feedstocks.

Truxene-Based Porous Triazole-Linked Polymers for Dye Removal through Synergetic Adsorption and Photodegradation

Two high surface area porous polymers (TxTri and PhTxTri) consisting of semiconducting truxene units connected through triazole nodes have been synthesized via Cu(I)-catalyzed azide–alkyne click polymerization, and their ability to remove different organic dyes (Nile blue, Rhodamine B, and Methyl orange) from aqueous solutions has been investigated. The presence of triazole moieties in the polymer walls, capable of binding guest molecules through different intermolecular interactions (such as dipole–dipole interactions, hydrogen bonding, and π–π interactions), is expected to benefit dye capture. We have found that these materials show a high adsorption capacity toward cationic dyes (reaching values as high as 1562 mg g–1 for Nile blue). This preference is probably due to the high electron density of the polymeric networks, which will favor electrostatic interactions with electron-deficient dyes. Interestingly, owing to the semiconducting nature of the truxene units, these polymers also act as photocatalysts in the oxidative degradation of the dyes, allowing for easy recovery and reuse of the polymers without the need for additional cleaning steps to remove trapped dyes. This interesting adsorption/photodegradation synergy represents a huge advantage compared to common dye adsorbents and makes them promising candidates for water remediation.

BsEXLX of engineered Trichoderma reesei strain as dual-active expansin to boost cellulases secretion for synergistic enhancement of biomass enzymatic saccharification in corn and Miscanthus straws

In this study, bacterial BsEXLE1 gene was overexpressed into T. reesei (Rut-C30) to generate a desirable engineered TrEXLX10 strain. While incubated with alkali-pretreated Miscanthus straw as carbon source, the TrEXLX10 secreted the β-glucosidases, cellobiohydrolases and xylanses with activities raised by 34%, 82% and 159% compared to the Rut-C30. Supplying EXLX10-secreted crude enzymes and commercial mixed-cellulases for two-step lignocellulose hydrolyses of corn and Miscanthus straws after mild alkali pretreatments, this work measured consistently higher hexoses yields released by the EXLX10-secreted enzymes for synergistic enhancements of biomass saccharification in all parallel experiments examined. Meanwhile, this study detected that the expansin, purified from EXLX10-secreted solution, was of exceptionally high binding activities with wall polymers, and further determined its independent enhancement for cellulose hydrolysis. Therefore, this study raised a mechanism model to highlight EXLX/expansin dual-activation roles for both secretion of stable biomass-degradation enzymes at high activity and biomass enzymatic saccharification in bioenergy crops.

FERONIA and wall-associated kinases coordinate defense induced by lignin modification in plant cell walls

Altering the content or composition of the cell wall polymer lignin is a favored approach to valorize lignin toward biomaterial and chemical production in the biorefinery. However, modifying lignin or cellulose in transgenic plants can induce expression of defense responses and negatively affect growth. Through genetic screening for suppressors of defense gene induction in the low lignin ccr1-3 mutant of Arabidopsis thaliana, we found that loss of function of the receptor-like kinase FERONIA, although not restoring growth, affected cell wall remodeling and blocked release of elicitor-active pectic polysaccharides as a result of the ccr1-3 mutation. Loss of function of multiple wall-associated kinases prevented perception of these elicitors. The elicitors are likely heterogeneous, with tri-galacturonic acid the smallest but not necessarily the most active component. Engineering of plant cell walls will require development of ways to bypass endogenous pectin signaling pathways.

Glucuronic acid: not just another brick in the cell wall.

This article is a Commentary on Debra‐Maceluch et al. (2023), 238: 297–312.

Exploiting Underutilised crops

Exploiting Underutilised crops

PEGylated and functionalized polylactide-based nanocapsules: An overview

Polymeric nanocapsules (NC) are versatile mixed vesicular nanocarriers, generally containing a lipid core with a polymeric wall. They have been first developed over four decades ago with outstanding applicability in the cosmetic and pharmaceutical fields. Biodegradable polyesters are frequently used in nanocapsule preparation and among them, polylactic acid (PLA) derivatives and copolymers, such as PLGA and amphiphilic block copolymers, are widely used and considered safe for different administration routes. PLA functionalization strategies have been developed to obtain more versatile polymers and to allow the conjugation with bioactive ligands for cell-targeted NC. This review intends to provide steps in the evolution of NC since its first report and the recent literature on PLA-based NC applications. PLA-based polymer synthesis and surface modifications are included, as well as the use of NC as a novel tool for combined treatment, diagnostics, and imaging in one delivery system. Furthermore, the use of NC to carry therapeutic and/or imaging agents for different diseases, mainly cancer, inflammation, and infections is presented and reviewed. Constraints that impair translation to the clinic are discussed to provide safe and reproducible PLA-based nanocapsules on the market. We reviewed the entire period in the literature where the term “nanocapsules” appears for the first time until the present day, selecting original scientific publications and the most relevant patent literature related to PLA-based NC. We presented to readers a historical overview of these Sui generis nanostructures.

Identifying plant cell wall remnants in detritus of a subtropical wetland with fluorescence labeling

Sediment accretion in wetlands represents a significant carbon burial pathway. While litter studies can quantify the loss rates of plant leaf material, those studies do not provide insight into the specific cell wall polymers being retained or lost within the detrital matrix. The Everglades ecosystem has been dramatically altered due to anthropogenic eutrophication and hydrologic modifications. The results are changes in macrophyte species composition and sediment accretion- and loss- rates. To improve ecological conditions, active management strategies are re-establishing open water slough environments. A question remains about the persistence of new- and old- plant cell wall material in sediments because of active management. In this pilot project we utilized immuno-fluorescence labeling with lectins applied to plant leaf material and detrital flocculent collected from created open and control plots in the Everglades to observe the presence, absence, and overlap of specific cell wall polymers between macrophytes and detrital flocculent in increasingly recalcitrant materials that would most likely contribute to peat accumulation. The persistence and loss of specific polymers between treatment and control plots provided insight into the differing levels of recalcitrance amongst plant cell walls and their relative potential as a carbon sink. This study provides a novel method for testing for the presence and persistence of specific cell wall polymers in detritus to gain a better understanding of plant material persistence in wetland ecosystems.

A dive into the cell wall with Arabidopsis.

One of the many legacies of the work of Michel Caboche is our understanding of plant cell wall synthesis and metabolism thanks to the use of Arabidopsis mutants. Here I describe how he was instrumental in initiating the genetic study of plant cell walls. I also show, with a few examples for cellulose and pectins, how this approach has led to important new insights in cell wall synthesis and how the metabolism of pectins contributes to plant growth and morphogenesis. I also illustrate the limitations of the use of mutants to explain processes at the scale of cells, organs or whole plants in terms of the physico-chemical properties of cell wall polymers. Finally, I sketch how new approaches can cope with these limitations.

The Light-Controlled Release of 2-fluoro-l-fucose, an Inhibitor of the Root Cell Elongation, from a nitrobenzyl-caged Derivative.

Glycan metabolic engineering is a powerful tool for studying the glycosylation in living plant cells. The use of modified monosaccharides such as deoxy or fluorine-containing glycosides has been reported as a powerful pharmacological approach for studying the carbohydrate metabolism. 1,3,4-tri-O-acetyl-2-fluoro-l-fucose (2F-Fuc) is a potent inhibitor of the plant cell elongation. After feeding plant seedlings with 2F-Fuc, this monosaccharide derivative is deacetylated and converted by the endogenous metabolic machinery into the corresponding nucleotide-sugar, which then efficiently inhibits Golgi-localized fucosyltransferases. Among plant cell wall polymers, defects in the fucosylation of the pectic rhamnogalacturonan-II cause a decrease in RG-II dimerization, which in turn induce the arrest of the cell elongation. In order to perform the inhibition of the cell elongation process in a spatio-temporal manner, we synthesized a caged 3,4-di-O-acetyl-1-hydroxy-2-fluoro-l-fucose (1-OH-2F-Fuc) derivative carrying a photolabile ortho-nitrobenzyl alcohol function at the anomeric position: 3,4-di-O-acetyl-1-ortho-nitrobenzyl-2-fluoro-l-fucose (2F-Fuc-NB). The photorelease of the trapped 1-OH-2F-Fuc was performed under a 365 nm LED illumination. We demonstrated that the in planta elimination by photoexcitation of the photolabile group releases free 2F-Fuc in plant cells, which in turn inhibits in a dose-dependent manner and, reversibly, the root cell elongation.

Chlorine dioxide gas slow-release film for strawberry preservation

The polymeric wall material of microcapsules has the function of encapsulation, protection, and controlled release of the active core material. In this study, sodium alginate (SA)-NaClO2 solution was encapsulated in ethylcellulose (EC) microcapsules using an emulsion-solvent evaporation method. The EC/SA-NaClO2 microcapsules were doped into polyvinyl alcohol (PVA) solution containing HCl, and an antimicrobial film was prepared using the solution casting method. Water vapor drives HCl into the interior of the microcapsules and reacts with NaClO2 in the microcapsules to release ClO2 gas to achieve antimicrobial properties. ClO2 gas can effectively inhibit the growth and reproduction of bacteria and molds on strawberry surfaces. The antimicrobial film inhibited the growth of E. coli by 99.9% and reduced the area of B. cinerea to <10%. Storage bags prepared from antimicrobial films could extend the shelf life of strawberries and maintain their sensory characteristics such as color, hardness, and moisture.

Modification of plant cell walls with hydroxycinnamic acids by BAHD acyltransferases.

In the last decade it has become clear that enzymes in the "BAHD" family of acyl-CoA transferases play important roles in the addition of phenolic acids to form ester-linked moieties on cell wall polymers. We focus here on the addition of two such phenolics-the hydroxycinnamates, ferulate and p-coumarate-to two cell wall polymers, glucuronoarabinoxylan and to lignin. The resulting ester-linked feruloyl and p-coumaroyl moities are key features of the cell walls of grasses and other commelinid monocots. The capacity of ferulate to participate in radical oxidative coupling means that its addition to glucuronoarabinoxylan or to lignin has profound implications for the properties of the cell wall - allowing respectively oxidative crosslinking to glucuronoarabinoxylan chains or introducing ester bonds into lignin polymers. A subclade of ~10 BAHD genes in grasses is now known to (1) contain genes strongly implicated in addition of p-coumarate or ferulate to glucuronoarabinoxylan (2) encode enzymes that add p-coumarate or ferulate to lignin precursors. Here, we review the evidence for functions of these genes and the biotechnological applications of manipulating them, discuss our understanding of mechanisms involved, and highlight outstanding questions for future research.

Small-scale OrganoCat processing to screen rapeseed straw for efficient lignocellulose fractionation

Agricultural residues such as rapeseed straw can be a valuable source of cellulose, sugars, and aromatic molecules like lignin. Understanding its composition is crucial in order to develop suitable processing technology for the production of biofuel or biochemicals from rapeseed straw. Here, we developed a small-scale OrganoCat system to screen multiple technical conditions and different samples at higher throughput and utilize this system to analyze straw samples from a set of 14 genetically different Brassica lines on their processability. Correlation analysis was performed to investigate the effects of cell wall polymer features on rapeseed biomass disintegration. At comparably mild reaction conditions, the differences in recalcitrance towards OrganoCat fractionation within the set were especially associated with parameters such as pectic polysaccharide content, acetylation, and hemicellulose composition. These findings can subsequently be used to optimize and scale up the pretreatment and fractionation of lignocellulose derived from rapeseed straw.

Fluorogenic properties of 4-dimethylaminocinnamaldehyde (DMACA) enable high resolution imaging of cell-wall-bound proanthocyanidins in plant root tissues.

Proanthocyanidins (PAs) are polymeric phenolic compounds found in plants and used in many industrial applications. Despite strong evidence of herbivore and pathogen resistance-related properties of PAs, their in planta function is not fully understood. Determining the location and dynamics of PAs in plant tissues and cellular compartments is crucial to understand their mode of action. Such an approach requires microscopic localization with fluorescent dyes that specifically bind to PAs. Such dyes have hitherto been lacking. Here, we show that 4-dimethylaminocinnamaldehyde (DMACA) can be used as a PA-specific fluorescent dye that allows localization of PAs at high resolution in cell walls and inside cells using confocal microscopy, revealing features of previously unreported wall-bound PAs. We demonstrate several novel usages of DMACA as a fluorophore by taking advantage of its double staining compatibility with other fluorescent dyes. We illustrate the use of the dye alone and its co-localization with cell wall polymers in different Populus root tissues. The easy-to-use fluorescent staining method, together with its high photostability and compatibility with other fluorogenic dyes, makes DMACA a valuable tool for uncovering the biological function of PAs at a cellular level in plant tissues. DMACA can also be used in other plant tissues than roots, however care needs to be taken when tissues contain compounds that autofluoresce in the red spectral region which can be confounded with the PA-specific DMACA signal.

The unique sugar conversion and complex CAZyme system of Trichoderma brev T069 during solid-state fermentation of cassava peel

Cassava peel is a lignocellulose-based agricultural by-product that can be degraded into reducing sugars as a raw material for energy. However, chemical and enzymatic treatment processes of cell wall polymers are expensive. We found that the filamentous fungus Trichoderma brev T069 can grow in a cassava peel matrix without any additional nutrient and degrade macromolecular carbohydrates, producing high levels of glucose and valuable hydrolytic enzymes. Therefore, this paper investigated the utilization strategy of T. brev T069 on cassava peels by dynamically analyzing its growth and hydrolytic enzyme system during solid fermentation, degradation of cassava peel components, and changes in reducing sugars. Results showed that T. brev T069 uses a "borrow-return" method of reducing sugar conversion, first absorbing fructose for growth for 3 days and later releasing glucose (99.56 mg/g) and cellobiose (24.69 mg/g) via hydrolases and high levels of β-glucosidase (1196.05 IU/g). Scanning electron microscopy and Fourier transform infrared spectrometry revealed the compositional breakdown and decreased carbohydrate contents of the peels. Label-free proteomics identified 257 carbohydrate-active enzymes (CAZymes), and functional annotation indicated that hemicellulases, lignin-modifying enzymes, and pectinases were induced at early stages, whereas amylases and cellulases were induced at later stages. A protein–protein interaction network revealed that protein degradation-related proteases and α-mannosidases may be involved in the realignment of enzymatic degradation strategies. This study explored the hydrolytic enzymatic potential of the Trichoderma CAZyme system and provided a practical approach for the biotransformation of tropical agricultural wastes into value-added products.

Insights from molecular dynamics simulations for interfacial effects between polylactic acid and wood cell wall constituents

• The interface structure between wood cell wall components and polymer is studied. • Molecular insights into the differences in the adhesion behavior of polymers on the surface of wood cell wall component. • Provides insights for the structural design of biomass composites. Knowledge of the interfacial structure from an atomic or molecular perspective helps to optimize the manufacturing of nanocomposite materials with bottom-up structural design and controls the performance more effectively. In this work, molecular dynamics simulation was used to study the composition, structure, and mechanism of interactions at the interface between wood cell wall constituents (cellulose, lignin, and hemicellulose) and polylactic acid (PLA). Results showed that the interfacial adhesion between the components and polymer was affected by the surface structure and the diffusion and aggregation of the polymer. Compared with the crystalline surface, the amorphous structure could achieve greater bonding energy and lower surface energy, and thus improving the dispersibility of fillers in the polymer matrix. An orderly arrangement and denser packing of the polymer were observed on the crystalline surface and the diffusion capacity of the polymer was reduced due to reduction in local free volume.