The plant cell wall-dynamic, strong, and adaptable-is a natural shapeshifter

Cell wall composition in relation to photosynthesis across land plants' phylogeny: crops as outliers

See also the Commentary on this article by Salesse‐Smith & Xiao, 246 : 2375–2376 .

Mucilicious methods: Navigating the tools developed to Arabidopsis Seed Coat Mucilage analysis

During the last decades, Arabidopsis seed mucilage has been extensively studied to gain insight into the metabolism of pectin, hemicellulose and cellulose. This review aims to provide a comprehensive examination of the techniques used to understand the composition and structure of Arabidopsis mucilage. Moreover, we present novel findings from mucilage analysis, including the separation of pectic domains within the mucilage, offering a fresh perspective on utilizing traditional techniques to analyze mucilage mutant lines.

The tri-molecular interaction controlling plant cell structure

The plant cell wall is a dynamic envelope crucial for cell structure. Recent insights highlight the pivotal roles of RAPID ALKALINIZATION FACTOR (RALF) peptides, LEUCINE-RICH REPEAT EXTENSINS (LRX), and the FERONIA (FER) receptor kinase in maintaining cell wall integrity. This tri-molecular complex, along with other membrane receptors, modulates cell wall mechanics through interactions with de-methylesterified homogalacturonan (HG) in a feedback-controlled manner along with other intra-cellular responses. Through the characterization of this complex, critical questions have emerged regarding the mechanistic details of RALF-induced HG modulation, the mechanosensing role of FER, and the structural roles of extensins in modulating cell wall dynamics. This review underscores the intricate feedback mechanisms involved in the maintenance of cell wall integrity and cellular growth dynamics, offering strategies to enhance crop productivity.

Changes in the assembly and functional adaptation of endophytic microbial communities in Amorphophallus species with different levels of resistance to necrotrophic bacterial pathogen stress

Pcc is one of the key pathogenic factors responsible for destructive soft rot in konjac. To date, the assembly and functional adaptation of the plant endophytic microbiome under Pcc stress remain poorly understood. Here, we found that Pcc stress leads to rapid reorganization of the endogenous microbiome in multiple organs of both susceptible and resistant konjac plants. Under Pcc stress, the negative interactions within the bacterial-fungal interdomain network intensified, suggesting an increase in ecological competition between bacterial and fungal taxa. We further discovered that the relative abundance dynamics of the classes Dothideomycetes and Sordariomycetes, as core fungal taxa, changed in response to Pcc stress. By isolating culturable microorganisms, we demonstrated that 46 fungal strains strongly inhibited the growth of Pcc. This implies that endophytic fungal taxa in konjac may protect the host plant through ecological competition or by inhibiting the growth of pathogenic bacteria. Metagenomic analysis demonstrated that microbial communities associated with resistant Amorphophallus muelleri exhibited unique advantages over susceptible Amorphophallus konjac in enhancing environmental adaptability, regulating plant immune signaling, strengthening cell walls, and inducing defense responses. Our work provides important evidence that endophytic fungal taxa play a key role in the host plant's defense against necrotizing bacterial pathogens.

Inheritance of acquired adaptive cold tolerance in rice through DNA methylation

Epigenetic pathways could provide a mechanistic explanation for the inheritance of acquired characteristics, as proposed by Lamarck in 1802, but epigenetic alterations that endow adaptive hereditary traits have rarely been observed. Here, in cultivated Asian rice (Oryzasativa L.), we identified an epiallele conferring acquired and heritable cold tolerance, an adaptive trait enabling northward spread from its tropical origins. We subjected cold-sensitive rice to multigenerational cold stress and identified a line with acquired stable inheritance of cold tolerance. DNA-hypomethylation variation in the acquiredcoldtolerance 1 (ACT1) promoter region rendered its expression insensitive to cold. This change is, in large part, responsible for the acquired cold tolerance, as confirmed by DNA-methylation editing. Natural variation in ACT1 DNA hypomethylation is associated with cold tolerance and rice geographic distribution. Hypomethylation at ACT1 triggers adaptive cold tolerance, presenting a route to epigenetic-variation-driven inheritance of acquired characteristics.

A Role for the Plastidial GPT2 Translocator in the Modulation of Lignin Biosynthesis

Engineering plants with reduced lignin content can result in pleiotropic growth defects. In stems of Arabidopsis plants with reduced expression of hydroxycinnamoyl CoA: shikimate hydroxycinnamoyl transferase (HCT), the plastidial glucose 6-phosphate: phosphate co-transporter GPT2 is highly overexpressed, and this coincides with reduced lignin levels and extensive transcriptional and metabolic reprogramming. To explore the potential relationship between GPT2 expression and lignin accumulation, GPT2 transcript levels were evaluated in a suite of Arabidopsis thaliana and Medicago truncatula lignin-defective lines. We also examined lignin levels and composition, and transcriptomic and metabolic profiles in GPT2 loss-of-function, GPT2 overexpression, and wild-type Arabidopsis plants. Loss of GPT2 had no effect on lignin, but its overexpression caused a decrease in stem lignin levels due to reduced accumulation of both guaiacyl and syringyl lignins and their associated monolignol pools. HCT transcript levels were diminished in 35S-GPT2 lines, indicating a potential transcriptional regulatory connection between lignin biosynthesis and GPT2. Based on our transcriptomic and metabolomic analyses, we suggest that GPT2 operates to balance the flux between the biosynthesis of lignin and light-protective phenylpropanoid derivatives.

Lettuce immune responses and apoplastic metabolite profile contribute to reduced internal leaf colonization by human bacterial pathogens

BACKGROUND

Human bacterial pathogens such as Salmonella enterica and Escherichia coli can colonize the apoplast of leafy greens, where they may evade standard sanitization measures and persist until produce consumption. Bacterial survival in this niche is influenced by plant immune responses that may vary according to bacterial species and plant genotypes. The variability in immune responses has been associated with differences in pathogen persistence capacity within the phyllosphere. In addition, emerging evidence suggests that preexisting and inducible plant metabolites contribute to either restricting or facilitating colonization of human pathogens in plant tissues. Identifying the molecular mechanisms underlying these interactions is crucial for developing strategies to mitigate contamination in fresh produce.

RESULTS

We characterized whole-leaf transcriptome and apoplast metabolome profiles of three lettuce cultivars upon exposure to the human pathogenic bacteria S. enterica ser. Typhimurium 14028s and E. coli O157:H7. The lettuce genotypes Lollo Rossa and Green Towers exhibited stronger transcriptional modulation, primarily associated with defense-related processes and showed reduced bacterial survival in their apoplast. Surprisingly, Green Towers did not generate callose deposition or reactive oxygen species burst responses at levels comparable to that of Lollo Rossa, suggesting it has distinct modifications in the apoplastic conditions that restrict pathogen persistence. Apoplastic metabolomic profiling revealed specific compounds alterations in Green Towers linked to bacterial survival, indicating their potential role in this genotype's defense mechanism. In contrast, the lettuce cultivar Red Tide exhibited minimal transcriptional and metabolic modulation, lack of robust defense activation, which was accompanied by apoplastic bacterial survival.

CONCLUSIONS

This study provides evidence that lettuce cultivars exhibit distinct molecular responses that may influence the persistence of human bacterial pathogens in the leaf apoplast. The results indicate that both immune response activation and metabolite composition may contribute to restrict apoplastic bacterial persistence or growth. These findings offer novel insights into the genetic and biochemical factors shaping lettuce-pathogen interactions, which might inform breeding programs and agronomic practices aimed at enhancing food safety.

Pectins and hemicelluloses from cell walls of hulls from developing soybean seeds

Soybean is the most cultivated legume in the world because of the nutrition quality of its seeds. Developing seeds of soybean crops can be damaged by stink bugs (Nezara viridula), which must penetrate hulls to feed on them. In this work, hulls were extracted sequentially with aqueous solvents of increasing alkalinity, and the major extracts were further purified. The fine structure of fractions was studied by chemical and spectroscopic methods. Pectins were obtained in all the extracts but containing different amounts of homogalacturonans (HG) and rhamnogalacturonans I. Galactomannans (GM) were extracted with water and with 4 M KOH (molar ratio Gal:Man, 1:1.8 and 1:3, respectively); glucuronoxylans (GX) and xyloglucans (XG) were also present, but in minor amounts. The residue obtained after exhaustive extraction contained 72 % cellulose, but also HG, GM, and GX. Estimation of the contribution of the different polysaccharides showed that they are composed of around 54 % cellulose, 31 % pectins, and 15 % hemicelluloses, and they represent as a whole, lesser amounts than those reported for mature hulls. This work would indicate more hydrated cell walls with lesser proportions of secondary structures in immature hulls. This characterization could help understanding the susceptibility of soybeans seeds to the cosmopolitan stink bugs.

Impact of pectin structural diversity on gut microbiota: A mechanistic exploration through in vitro fermentation

Pectins have demonstrated significant prebiotic potential in modulating gut microbiota and enhancing microbial metabolic functions. Nevertheless, the exact relationship between pectin structure and related properties on gut microbiota regulation is yet to be fully elucidated. To explore this, the interactions between four purified pectins with specific structural characteristics and gut microbiota were examined and compared through in vitro fecal fermentation, followed by full-length 16S rRNA gene sequencing, metabolomics, and bioinformatic analysis. The result shows that the pectins selectively modulated the composition of gut microbiota while being degraded into different levels of SCFAs. Moreover, the metabolite profiles in the pectin groups were also qualitatively and quantitatively different, suggesting that the structural variations in pectins further impacted the metabolic functionality of gut microbiota. The bioinformatic analysis revealed that various structural parameters of pectins, including the α-(1 → 4)-linked galacturonic acid composed linear chain in smooth region, arabinose residue determined hair region contribution, conjugated protein content, and molecular weight, are crucial factors in controlling their interaction with gut microbiota, the bacterial cross-feeding, and finally the microbial metabolic outcomes. This research advances our current understanding of the connection between pectin structure and its regulatory properties on gut microbiota at the level of purified pectin molecules.

"Shape of Cell"-An Auxin and Cell Wall Duet

Understanding the mechanisms underlying cell shape acquisition is of fundamental importance in plant science, as this process ultimately defines the structure and function of plant organs. Plants produce cells of diverse shapes and sizes, including pavement cells and stomata of leaves, elongated epidermal cells of the hypocotyl, and cells with outgrowths such as root hairs, and so forth. Plant cells experience mechanical forces of variable magnitude during their development and interaction with neighboring cells and the surrounding environment. From the time of cytokinesis, they are encaged in a complex cell wall matrix, which offers mechanical support and enables directional growth and a differential rate of expansion towards adjacent cells via its mechanochemical heterogeneity. The phytohormone auxin is well characterized for its role in cell expansion and cell elasticity. The interaction between dynamic auxin redistribution and the mechanical properties of the cell wall within tissues drives the development of specific cell shapes. Here, we focus on the regulatory feedback loop involving auxin activity, its influence on cell wall chemistry and mechanical properties, and the coordination of cell shape formation. Integrating insights from molecular and cell biology, biophysics, and computational modeling, we explore the mechanistic link between auxin signaling and cell wall dynamics in shaping plant cells.

Carrageenan-Based Hydrogels for Advanced Wound Healing and Controlled Drug Delivery in Tissue Engineering

Carrageenan (CGN) is a high molecular weight polysaccharide that is extracted from red seaweeds. It is made up of D-galactose residues connected by β-1,4 and α-1,3 galactose-galactose bonds. As a result of its ability to thicken, emulsify, and stabilize food, it is frequently used as a food additive in processed food. Its consumption has surged in recent years due to the Western diet's (WD) spread. Carrageenan has the ability to change the thickness of the mucus barrier, the composition of the gut microbiota, and the innate immune pathway that causes inflammation. Also, its inherent qualities, which include biodegradability, biocompatibility, resemblance to native glycosaminoglycans, antioxidants, anticancer, immunomodulatory, and anticoagulant activities, Carrageenan-based hydrogels have been the subject of numerous investigations lately for biomedical applications. The brittle hydrogel and uncontrollably exchanged ions, however, are two drawbacks to the application of this polysaccharide, but these can be avoided by making straightforward chemical changes to polymer networks, which create chemically bonded hydrogels with important mechanical characteristics and regulated degradation rates. Furthermore, the addition of diverse kinds of nanoparticles, as well as polymer networks, to carrageenan hydrogels results in hybrid platforms with noteworthy mechanical, chemical, and biological characteristics, which qualify them as appropriate biomaterials for tissue engineering (TE), drug delivery (DD), and also wound healing applications. Our goal in this article is to provide an overview of the most current developments in hybrid carrageenan-based platforms and several chemical modification techniques for TE and DD applications.

CarboTag: a modular approach for live and functional imaging of plant cell walls

Plant cells are contained within a rigid network of cell walls. Cell walls serve as a structural material and a crucial signaling hub vital to all aspects of the plant life cycle. However, many features of the cell wall remain enigmatic, as it has been challenging to map its functional properties in live plants at subcellular resolution. Here, we introduce CarboTag, a modular toolbox for live functional imaging of plant walls. CarboTag uses a small molecular motif, a pyridine boronic acid, that directs its cargo to the cell wall. We designed a suite of cell wall imaging probes based on CarboTag in various colors for multiplexing. Additionally, we developed new functional reporters for live quantitative imaging of key cell wall characteristics: network porosity, cell wall pH and the presence of reactive oxygen species. CarboTag paves the way for dynamic and quantitative mapping of cell wall responses at subcellular resolution.

Probing homogalacturonan in situ: A comprehensive review of available molecular recognition tools

Among the major plant cell wall components, pectic-type homogalacturonan emerges as a chemically and spatiotemporally dynamic matrix-forming agent embedded within the cell wall through various inter- and intramolecular interactions. Its abundance, localization, and chemistry profoundly influence cell wall biomechanics and all facets of plant physiology. Precise tracking of homogalacturonan in a native context is crucial for understanding cell wall organization, particularly the relation between molecular structure and function. It also enables the detailed characterization of plant-based resources for industrial, food, and biomedical applications. This review offers a comprehensive and focused survey of the state-of-the-art molecular recognition tools being employed to visualize homogalacturonan in diverse plant samples. We particularly highlight homogalacturonan-specific monoclonal antibodies, which represent the most used and well-established probes. However, we also discuss less common reagents, such as fluorophores, oligosaccharide-based probes, carbohydrate-binding modules, and whole enzymes, as well as emerging chemical biology approaches exemplified by click chemistry. We critically evaluate their strengths, limitations, and suitability for given research objectives and provide the most notable examples of their usage. Lastly, we outline the anticipated future expansion of an advanced, improved range of new molecular tools, which holds the potential to overcome some of the current experimental hurdles.

Cell wall modulation by drought and elevated CO2 in sugarcane leaves

Climate change poses significant challenges to global agriculture, with elevated atmospheric CO2 (eCO2) concentrations and increased frequency of droughts affecting crop productivity. Understanding how economically important crops like sugarcane respond to these combined stresses is essential for developing resilient cultivars. This study explores the effects of eCO2 and drought stress on sugarcane growth and cell wall composition. Sugarcane plants were cultivated under CO2 treatments (390 ppm and 780 ppm) and subjected to drought stress. Leaf biomass, cell wall composition, and global transcriptome sequencing were analyzed. eCO2 (780 ppm) significantly increased leaf biomass by 64%, attributed to enhanced photosynthesis and water-use efficiency. Conversely, drought reduced leaf biomass by 45%, highlighting sugarcane's sensitivity to water scarcity. When both conditions were combined, eCO2 mitigated drought's negative impact, maintaining biomass at levels comparable to ambient conditions. Despite notable changes in biomass, cell wall biomass was only slightly affected. Under drought, a 14% reduction in cell wall biomass was observed alongside compositional changes, including reduced arabinosylation in glucuronoarabinoxylan (GAX). This alteration, supported by decreased xylan arabinosyl transferase (XAT) expression and reduced arabinose content, suggests stronger associations between GAX and cellulose, potentially enhancing drought tolerance by modifying cell wall rigidity and flexibility. Under eCO2, cell wall composition was altered, with reductions in glucose and uronic acid in specific fractions, indicating decreased mixed-linkage glucan (MLG) and pectin. These changes likely increased cell wall flexibility, supporting rapid growth. Combined eCO2 and drought treatments amplified specific modifications, such as enhanced fucosylation of xyloglucan (XG) and potential MLG expansion, both linked to stress adaptation. Overall, the findings underscore the critical role of cell wall plasticity in sugarcane's response to abiotic stress. While eCO2 boosted growth and partially alleviated drought effects, structural changes in cell wall composition under these conditions further contribute to stress resilience, emphasizing the adaptive mechanisms of sugarcane to environmental challenges. This is the first report in which eCO2, and drought are combined to evaluate the response of sugarcane to the impact of climate changes.

A high-resolution model of gene expression during Gossypium hirsutum (cotton) fiber development

BACKGROUND

Cotton fiber development relies on complex and intricate biological processes to transform newly differentiated fiber initials into the mature, extravagantly elongated cellulosic cells that are the foundation of this economically important cash crop. Here we extend previous research into cotton fiber development by employing controlled conditions to minimize variability and utilizing time-series sampling and analyses to capture daily transcriptomic changes from early elongation through the early stages of secondary wall synthesis (6 to 24 days post anthesis; DPA).

RESULTS

A majority of genes are expressed in fiber, largely partitioned into two major coexpression modules that represent genes whose expression generally increases or decreases during development. Differential gene expression reveals a massive transcriptomic shift between 16 and 17 DPA, corresponding to the onset of the transition phase that leads to secondary wall synthesis. Subtle gene expression changes are captured by the daily sampling, which are discussed in the context of fiber development. Coexpression and gene regulatory networks are constructed and associated with phenotypic aspects of fiber development, including turgor and cellulose production. Key genes are considered in the broader context of plant secondary wall synthesis, noting their known and putative roles in cotton fiber development.

CONCLUSIONS

The analyses presented here highlight the importance of fine-scale temporal sampling on understanding developmental processes and offer insight into genes and regulatory networks that may be important in conferring the unique fiber phenotype.

SCPL48 regulates the vessel cell programmed cell death during xylem development in Arabidopsis thaliana

Secondary cell wall (SCW) deposition is tightly coordinated with programmed cell death (PCD) during xylem development and plays a crucial role in plant stress responses. In this study, we characterized a serine carboxypeptidase-like gene, SCPL48, which exhibits xylem cell-specific expression patterns in stem xylem during vascular development. The scpl48 plants exhibited reduced stem xylem cell numbers, particularly vessel cells, accompanied by delayed organelle degradation during PCD and increased secondary wall thickness in xylem vessel cells. In contrast, SCPL48 overexpression resulted in increased vessel cell abundance and accelerated degradation of vessel cell contents, suggesting its critical role in xylem vessel cell differentiation. Notably, SCPL48 expression was significantly up-regulated in response to ABA treatment and drought stress, with SCPL48 overexpression lines demonstrating enhanced drought resistance. Further molecular analyses revealed that SCPL48 was directly targeted and transcriptionally activated by key SCW regulators VND6, and MYB46. Furthermore, the expression of PCD-related protease genes, including XCP1, XSP1, RNS3, MC9, γVPE, and CEP1, showed compensatory changes in both scpl48 mutants and SCPL48 overexpression lines. Collectively, our findings demonstrate that SCPL48 functions as a key regulator in xylem vessel cell differentiation, PCD and drought stress responses.

FERONIA: A Malectin-Domain Receptor Kinase with Intricate Signaling Mechanisms and Profound Importance to Plant Wellness

Plants have evolved elaborate signaling networks, believed to be necessitated by the diversity and complexity of their morphology, developmental and reproductive strategies, and the need to cope with an ever-changing environment from which they are rooted and cannot escape. Their receptor-like kinase superfamilies, with members numbering in the hundreds to more than a thousand, exemplify how plants have evolved their signaling versatility. FERONIA (FER) receptor kinase from model Arabidopsis is a member of the Malectin-domain receptor kinase family conserved among plants. FER has a perplexingly broad functional range, impacting growth to reproduction throughout the plant life cycle, and survival when encountering biotic and abiotic stressors from the environment, such as pathogens and climatic adversity. Efforts to understand FER signaling have brought to light novel signaling strategies at the continuum of the plant cell wall and plasma membrane, and a network of cytoplasmic and nuclear pathways that together support its biological roles. The discussion here focuses on the cell surface mechanisms, including a sugar-peptide interaction-driven liquid-liquid phase separation process along the cell wall-plasma membrane interface and a plasma membrane-linked signaling node comprised of FER, a glycosylphosphatidylinositol-anchored protein, the RHO GTPase molecular switch and a generator for reactive oxygen species (ROS). The emerging recognition of how the broader FER-related receptor kinase family could impact plant wellness and agricultural productivity is also discussed.

Aberrant growth and expansion in Penium margaritaceum triggered by disruption of microtubules and the cell wall

Penium margaritaceum, a unicellular zygnematophyte (Streptophyta), was employed to elucidate changes in cell expansion when cells were challenged with the fungal pectinolytic enzyme, pectate lyase, and/or the microtubule-disrupting agent, amiprophos-methyl (APM). Microtubule disruption by APM resulted in significant swelling at expansion zones. These swollen zones provided an easy marker for the location of expansion zones, particularly in cells with altered cell wall pectin. Short-term treatment with pectate lyase showed pectin degradation primarily at the isthmus expansion zone and two satellite bands, corresponding to the location of future expansion in daughter cells. When the homogalacturonan lattice of the cell wall was removed by treatment with pectate lyase during long treatments, cell division was maintained, but daughter cell products were considerably smaller. Treatment of cells with a mixture of both pectate lyase and APM resulted in a distinct phenotype, consisting of 'dumbbell'-shaped cells, as APM-induced swelling occurs at the novel expansion centers exposed by pectate lyase treatment. These cells also presented other curious alterations, including an extensive, chloroplast-free cytoplasmic zone at the center of the cell, a septum containing β-glycan, arabinogalactan and homogalacturonan epitopes, unique stacks of endoplasmic reticulum, displaced Golgi bodies, and an extensive network of vacuoles. These results provide insight into the importance of cell wall integrity in defining the location of cell growth and division in P. margaritaceum. Understanding these processes in a unicellular zygnematophyte may provide insights into steps involved in the evolution of land plants.

Enhancing maize resistance to Fusarium verticillioides through modulation of cell wall structure and components by ZmXYXT2

INTRODUCTION

Fusarium verticillioides (F. verticillioides) is a prevalent phytopathogen that incites severe diseases in maize, resulting in substantial reductions in grain yield and quality. Despite its widespread impact, the genetic mechanisms underlying resistance to this pathogen remain elusive, with only a limited of resistant genes having been identified to date.

OBJECTIVES

Characterize the function of ZmXYXT2 encoding a putative xylan xylosyltransferase in maize defense against F. verticillioides-induced diseases.

METHODS

Real-time quantitative PCR and transitory transformation of maize protoplasts were conducted to analyze the expression pattern and subcellular localization of ZmXYXT2. The zmxyxt2 mutant, sourced from an ethyl methanesulfonate mutagenesis library, and the ZmXYXT2-overexpressing plants, generated via Agrobacterium tumefaciens-mediated transformation, were utilized for artificial inoculation with F. verticillioides followed by disease severity assessments. Phenotypic assessments, cytological observations, analysis of cell wall components, and histochemical staining were performed to elucidate the regulatory mechanisms of ZmXYXT2.

RESULTS

The absence of ZmXYXT2 renders maize vulnerable to F. verticillioides-caused seedling blight, stalk rot, ear rot and seed rot, along with a notable increase in fumonisin B1 accumulation. Conversely, maize plants overexpressing ZmXYXT2 exhibited significantly heightened immunity to these diseases. Moreover, overexpression of ZmXYXT2 results in notable changes in the composition of maize cell walls, specifically increasing the levels of arabinose, xylose and ferulic acid. These alterations lead to cell wall thickening, effectively barring the intracellular invasion and colonization of F. verticillioides, thereby halting pathogen dissemination between cells. Intriguingly, maize plants overexpressing ZmXYXT2 exhibit enhanced stem strength without compromising yield-related traits.

CONCLUSION

ZmXYXT2 provides maize with resistance to multiple diseases triggered by F. verticillioides and mitigates the accumulation of fumonisin B1. Our study presents a novel approach to bolster maize comprehensive resistance against F. verticillioides-induced diseases by modifying cell wall composition to strengthen its natural defenses.

ZINC FINGER PROTEIN2 suppresses funiculus lignification to ensure seed loading efficiency in Arabidopsis

The plant funiculus anchors the developing seed to the placenta within the inner dorsal pod strands of the silique wall and directly transports nutrients to the seeds. The lignified vasculature critically supports nutrient transport through the funiculus. However, molecular mechanisms underlying lignified secondary cell wall (SCW) biosynthesis in the funiculus remain elusive. Here, we show that the transcription factor ZINC FINGER PROTEIN2 (ZFP2) represses SCW formation in the cortex cells that surround the vasculature. This function is essential for efficient nutrient loading into the seeds. Notably, ZFP2 directly acts on the SCW transcription factor NAC SECONDARY WALL THICKENING PROMOTING FACTOR1 (NST1) to repress cortex cell lignification, providing a mechanism of how SCW biosynthesis is restricted to the vasculature of the funiculus to ensure proper seed loading in Arabidopsis.

In planta ectopic expression of two subtypes of tomato cellulose synthase-like M genes affects cell wall integrity and supports a role in arabinogalactan and/or rhamnogalacturonan-I biosynthesis

Diversification of the cellulose synthase superfamily of glycosyltransferases has provided plants with the ability to synthesize varied cell wall polysaccharides such as xyloglucan, mannans, and the mixed-linkage glucans of cereals. Surprisingly, some but not all members of the cellulose synthase-like M (CslM) gene family have recently been shown to be involved in the glycosylation of the aglycone core of a range of triterpenoid saponins. However, no cell wall activity has yet been attributed to any of the CslM gene family members. Here, evolution of the CslM gene family in eudicots is explored to better understand the differences between the two metabolically distinct classes of CslMs (CslM1 and CslM2) and the very closely related CslGs. To achieve this, a robust tBLASTn approach was developed to identify CslM1, CslM2, and CslG sequences using diagnostic peptides, suitable for complex genomes using unannotated and short-read datasets. To ascertain whether both CslM1 and CslM2 proteins have cell wall functions, in addition to the 'saponin' role of CslM2, tomato CslM1 and CslM2 genes were ectopically expressed in Arabidopsis thaliana by stable transformation and in the transient Nicotiana benthamiana system. Transformed plants were analysed with immunofluorescence, immunogold transmission electron microscopy, and cell wall polysaccharides were extracted for monosaccharide linkage analysis. Our results support a role for both CslM1 and CslM2 in the biosynthesis of type II arabinogalactan linkages, generating new insight into how the diverse functions of CslMs can coexist and providing clear targets for future research.

Multiprotein Complexes of Plant Glycosyltransferases Involved in Their Function and Trafficking

Plant cells utilize protein oligomerization for their functions in numerous important cellular processes. Protein-protein interactions are necessary to stabilize, optimize, and activate enzymes, as well as localize proteins to specific organelles and membranes. Glycosyltransferases-enzymes that attach sugars to polysaccharides, proteins, lipids, and RNA-across multiple plant biosynthetic processes have been demonstrated to interact with one another. The mechanisms behind these interactions are still unknown, but recent research has highlighted extensive examples of protein-protein interactions, specifically in the plant cell wall hemicellulose and pectin biosynthesis that takes place in the Golgi apparatus. In this review, we will discuss what is known so far about the interactions among Golgi-localized glycosyltransferases that are important for their functioning, trafficking, as well as structural aspects.

Cell Wall Microdomains Analysis in the Quadrifids of Utricularia dichotoma

Carnivorous plants have fascinated botanists and ecologists with their various unusual adaptations in organ structure, physiology, and complex interactions with other organisms since the time of Charles Darwin. Species of the genus Utricularia (bladderworts, family Lentibulariaceae) are carnivorous plants that prey mainly on invertebrates using traps (bladders) of leaf origin. In the traps, there are glandular trichomes called quadrifids, which produce digestive enzymes and absorb the products of prey digestion. These quadrifids are unique due to their highly complex glandular cell structure; hence, they are an excellent model for studying the cell wall and its specialization. The main aim of the study was to investigate the presence and distribution of homogalacturonans (HGs) and hemicelluloses in the cell walls of trichome cells and especially in cell wall ingrowths in the quadrifid cells. The following antibodies were used against the wall components: anti-HGs (homogalacturonans) -JIM5 (low methylesterified HGs), JIM7 (highly esterified HGs), LM19 (low methylesterified HGs), CCRC-M38 (a fully de-esterified HG), LM5 (galactan); anti-hemicelluloses-LM25 (galactoxyloglucan; XXLLG, XXLG, XXXG modules of xyloglucans), LM15 (xyloglucan), CCRC-M138 (xylan), LM11 (heteroxylan); and anti-mannans: LM20 (heteromannan) and LM22 (heteromannan). The localization of the examined compounds was determined using immunohistochemistry techniques and immunogold labeling. In quadrifid cells, we found differences in the presence of the epitope detected by the LM5 antibody in the cell walls. In addition, cell wall ingrowths represented distinct microdomains of the cell wall in terms of the occurrence of wall components (they were methylesterified and demethylesterified homogalacturonan-poor). Hemicelluloses (galactoxyloglucan and xyloglucan) and arabinogalactans co-occur in cell wall ingrowths. Also, a part of the cell wall of the pedestal cell, which forms a Casparian strip, represented a distinct microdomain. We did not detect epitopes recognized by LM11, LM20 and LM22 antibodies. Our research shows that several cell wall microdomains occur in the cell walls of quadrifid cells. They differ depending on the presence and distribution of low methylesterified HGs, highly esterified HGs, fully de-esterified HGs, galactan (the epitope detected by the LM5 antibody), xyloglucan, galactoxyloglucan, and xylan (the epitope detected by the CCRC-M138 antibody).

A simple and highly efficient protocol for 13C-labeling of plant cell wall for structural and quantitative analyses via solid-state nuclear magnetic resonance

BACKGROUND

Plant cell walls are made of a complex network of interacting polymers that play a critical role in plant development and responses to environmental changes. Thus, improving plant biomass and fitness requires the elucidation of the structural organization of plant cell walls in their native environment. The 13C-based multi-dimensional solid-state nuclear magnetic resonance (ssNMR) has been instrumental in revealing the structural information of plant cell walls through 2D and 3D correlation spectral analyses. However, the requirement of enriching plants with 13C limits the applicability of this method. To our knowledge, there is only a very limited set of methods currently available that achieve high levels of 13C-labeling of plant materials using 13CO2, and most of them require large amounts of 13CO2 in larger growth chambers.

RESULTS

In this study, a simplified protocol for 13C-labeling of plant materials is introduced that allows ca 60% labeling of the cell walls, as quantified by comparison with commercially labeled samples. This level of 13C-enrichment is sufficient for all conventional 2D and 3D correlation ssNMR experiments for detailed analysis of plant cell wall structure. The protocol is based on a convenient and easy setup to supply both 13C-labeled glucose and 13CO2 using a vacuum-desiccator. The protocol does not require large amounts of 13CO2.

CONCLUSION

This study shows that our 13C-labeling of plant materials can make the accessibility to ssNMR technique easy and affordable. The derived high-resolution 2D and 3D correlation spectra are used to extract structural information of plant cell walls. This helps to better understand the influence of polysaccharide-polysaccharide interaction on plant performance and allows for a more precise parametrization of plant cell wall models.

Understanding pectin cross-linking in plant cell walls

Pectin is a major component of plant cells walls. The extent to which pectin chains crosslink with one another determines crucial properties including cell wall strength, porosity, and the ability of small, biologically significant molecules to access the cell. Despite its importance, significant gaps remain in our comprehension, at the molecular level, of how pectin cross-links influence the mechanical and physical properties of cell walls. This study employs a multidisciplinary approach, combining molecular dynamics simulations, experimental investigations, and mathematical modelling, to elucidate the mechanism of pectin cross-linking and its effect on cell wall porosity. The computational aspects of this work challenge the prevailing egg-box model, favoring instead a zipper model for pectin cross-linking, whilst our experimental work highlights the significant impact of pectin cross-linking on cell wall porosity. This work advances our fundamental understanding of the biochemistry underpinning the structure and function of the plant cell wall. This knowledge has important implications for agricultural biotechnology, informing us about the chemical properties of plant pectins that are best suited for improving crop resilience and amenability to biofuel extraction by modifying the cell wall.

Identifying the role of cellulase gene CsCEL20 upon the infection of Xanthomonas citri subsp. citri in citrus

Citrus canker is a devastating disease caused by Xanthomonas citri subsp. citri (Xcc), which secretes the effector PthA4 into host plants to trigger transcription of the susceptibility gene CsLOB1, resulting in pustule formation. However, the molecular mechanism underlying CsLOB1-mediated susceptibility to Xcc remains elusive. This study identified CsCEL20 as a target gene positively regulated by CsLOB1. Cell expansion and cell wall degradation were observed in sweet orange leaves after Xcc infection. A total of 69 cellulase genes were retrieved within the Citrus sinensis genome, comprising 40 endoglucanase genes and 29 glucosidase genes. Transcriptomic analysis revealed that expression levels of CsCEL8, CsCEL9, CsCEL20, and CsCEL26 were induced by Xcc invasion in sweet orange leaves, but not in the resistant genotype Citron C-05. Among them, CsCEL20 exhibited the highest expression level, with an over 430-fold increase following Xcc infection. Additionally, RT-qPCR analysis confirmed that CsCEL20 expression was induced in susceptible genotypes (Sweet orange, Danna citron, Lemon) upon Xcc invasion, but not in resistant genotypes (Citron C-05, Aiguo citron, American citron). A Single-Nucleotide Polymorphism (SNP) at -423 bp was identified in the CEL20 promoters and exhibits a difference between eight susceptible citrus genotypes and three resistant ones. Moreover, CsCEL20 expression was upregulated in CsLOB1-overexpression transgenic lines compared to the wild type. Dual-luciferase reporter assays indicated that CsLOB1 can target the -505 bp to -168 bp region of CsCEL20 promoter to trans-activate its expression. These findings suggest that CsCEL20 may function as a candidate gene for citrus canker development and may be a promising target for biotechnological breeding of Xcc-resistant citrus genotypes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-024-01531-3.

Cell walls, a comparative view of the composition of cell surfaces of plants, algae and microorganisms

While evolutionary studies indicate that the most ancient groups of organisms on Earth likely descended from a common wall-less ancestor, contemporary organisms lacking a carbohydrate-rich cell surface are exceedingly rare. By developing a cell wall to cover the plasma membrane, cells were able to withstand higher osmotic pressures, colonise new habitats and develop complex multicellular structures. This way, the cells of plants, algae and microorganisms are covered by a cell wall, which can generally be defined as a highly complex structure whose main framework is usually composed of carbohydrates. Rather than static structures, they are highly dynamic and serve a multitude of functions that modulate vital cellular processes, such as growth and interactions with neighbouring cells or the surrounding environment. Thus, despite its vital importance for many groups of life, it is striking that there are few comprehensive documents comparing the cell wall composition of these groups. Thus, the aim of this review was to compare the cell walls of plants with those of algae and microorganisms, paying particular attention to their polysaccharide components. It should be highlighted that, despite the important differences in composition, we have also found numerous common aspects and functionalities.

An alternate route for cellulose microfibril biosynthesis in plants

Similar to cellulose synthases (CESAs), cellulose synthase-like D (CSLD) proteins synthesize β-1,4-glucan in plants. CSLDs are important for tip growth and cytokinesis, but it was unknown whether they form membrane complexes in vivo or produce microfibrillar cellulose. We produced viable CESA-deficient mutants of the moss Physcomitrium patens to investigate CSLD function without interfering CESA activity. Microscopy and spectroscopy showed that CESA-deficient mutants synthesize cellulose microfibrils that are indistinguishable from those in vascular plants. Correspondingly, freeze-fracture electron microscopy revealed rosette-shaped particle assemblies in the plasma membrane that are indistinguishable from CESA-containing rosette cellulose synthesis complexes (CSCs). Our data show that proteins other than CESAs, most likely CSLDs, produce cellulose microfibrils in P. patens protonemal filaments. The data suggest that the specialized roles of CSLDs in cytokinesis and tip growth are based on differential expression and different interactions with microtubules and possibly Ca2+, rather than structural differences in the microfibrils they produce.

Plant cell walls: source of carbohydrate-based signals in plant-pathogen interactions

Plant cell walls are essential elements for disease resistance that pathogens need to overcome to colonise the host. Certain pathogens secrete a large battery of enzymes to hydrolyse plant cell wall polysaccharides, which leads to the release of carbohydrate-based molecules (glycans) that are perceived by plant pattern recognition receptors and activate pattern-triggered immunity and disease resistance. These released glycans are used by colonizing microorganisms as carbon source, chemoattractants to locate entry points at plant surface, and as signals triggering gene expression reprogramming. The release of wall glycans and their perception by plants and microorganisms determines plant-microbial interaction outcome. Here, we summarise and discuss the most recent advances in these less explored aspects of plant-microbe interaction.

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

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

Carbohydrate-active enzymes involved in rice cell wall metabolism

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

How Many Glucan Chains Form Plant Cellulose Microfibrils? A Mini Review

Assessing the number of glucan chains in cellulose microfibrils (CMFs) is crucial for understanding their structure-property relationships and interactions within plant cell walls. This Review examines the conclusions and limitations of the major experimental techniques that have provided insights into this question. Small-angle X-ray and neutron scattering data predominantly support an 18-chain model, although analysis is complicated by factors such as fibril coalescence and matrix polysaccharide associations. Solid-state nuclear magnetic resonance (NMR) spectroscopy allows the estimation of the CMF width from the ratio of interior to surface glucose residues. However, there is uncertainty in the assignment of NMR spectral peaks to surface or interior chains. Freeze-fracture transmission electron microscopy images show cellulose synthase complexes to be "rosettes" of six lobes each consistent with a trimer of cellulose synthase enzymes, consistent with the synthesis of 18 parallel glucan chains in the CMF. Nevertheless, the number of chains in CMFs remains to be conclusively demonstrated.

β-Glucan-binding proteins are key modulators of immunity and symbiosis in mutualistic plant-microbe interactions

In order to discriminate between detrimental, commensal, and beneficial microbes, plants rely on polysaccharides such as β-glucans, which are integral components of microbial and plant cell walls. The conversion of cell wall-associated β-glucan polymers into a specific outcome that affects plant-microbe interactions is mediated by hydrolytic and non-hydrolytic β-glucan-binding proteins. These proteins play crucial roles during microbial colonization: they influence the composition and resilience of host and microbial cell walls, regulate the homeostasis of apoplastic concentrations of β-glucan oligomers, and mediate β-glucan perception and signaling. This review outlines the dual roles of β-glucans and their binding proteins in plant immunity and symbiosis, highlighting recent discoveries on the role of β-glucan-binding proteins as modulators of immunity and as symbiosis receptors involved in the fine-tuning of microbial accommodation.

Mining Candidate Genes for Leaf Angle in Brassica napus L. by Combining QTL Mapping and RNA Sequencing Analysis

Leaf angle (LA) is an important trait of plant architecture, and individuals with narrow LA can better capture canopy light under high-density planting, which is beneficial for increasing the overall yield per unit area. To study the genetic basis and molecular regulation mechanism of leaf angle in rapeseed, we carried out a series of experiments. Quantitative trait loci (QTL) mapping was performed using the RIL population, and seven QTLs were identified. Transcriptome analysis showed that the cell wall formation/biogenesis processes and biosynthesis/metabolism of cell wall components were the most enrichment classes. Most differentially expressed genes (DEGs) involved in the synthesis of lignin, xylan, and cellulose showed down-regulated expression in narrow leaf material. Microscopic analysis suggested that the cell size affected by the cell wall in the junction area of the stem and petiole was the main factor in leaf petiole angle (LPA) differences. Combining QTL mapping and RNA sequencing, five promising candidate genes BnaA01G0125600ZS, BnaA01G0135700ZS, BnaA01G0154600ZS, BnaA10G0154200ZS, and BnaC03G0294200ZS were identified in rapeseed, and most of them were involved in cell wall biogenesis and the synthesis/metabolism of cell wall components. The results of QTL, transcriptome analysis, and cytological analysis were highly consistent, collectively revealing that genes related to cell wall function played a crucial role in regulating the LA trait in rapeseed. The study provides further insights into LA traits, and the discovery of new QTLs and candidate genes is highly beneficial for genetic improvement.

Do Arabinogalactan Proteins Occur in the Transfer Cells of Utricularia dichotoma?

Species in the genus Utricularia are carnivorous plants that prey on invertebrates using traps of leaf origin. The traps are equipped with numerous different glandular trichomes. Trichomes (quadrifids) produce digestive enzymes and absorb the products of prey digestion. The main aim of this study was to determine whether arabinogalactan proteins (AGPs) occur in the cell wall ingrowths in the quadrifid cells. Antibodies (JIM8, JIM13, JIM14, MAC207, and JIM4) that act against various groups of AGPs were used. AGP localization was determined using immunohistochemistry techniques and immunogold labeling. AGPs localized with the JIM13, JIM8, and JIM14 epitopes occurred in wall ingrowths of the pedestal cell, which may be related to the fact that AGPs regulate the formation of wall ingrowths but also, due to the patterning of the cell wall structure, affect symplastic transport. The presence of AGPs in the cell wall of terminal cells may be related to the presence of wall ingrowths, but processes also involve vesicle trafficking and membrane recycling, in which these proteins participate.

Challenges to Increasing Dietary Fiber in White Flour and Bread

Increasing the intake of dietary fiber from staple foods is a key strategy to improve the health of consumers. White bread is an attractive vehicle to deliver increased fiber as it is widely consumed and available to all socio-economic groups. However, fiber only accounts for about 4% of the dry weight of white flour and bread compared to 10-15% in whole grain bread and flour. We therefore discuss the challenges and barriers to developing and exploiting new types of wheat with high fiber content in white flour. These include defining and quantifying individual fiber components and understanding how they are affected by genetic and environmental factors. Rapid high throughput assays suitable for determining fiber content during plant breeding and in grain-utilizing industries are urgently required, while the impact of fiber amount and composition on flour processing quality needs to be understood. Overcoming these challenges should have significant effects on human health.

Leucine rich repeat-malectin receptor kinases IGP1/CORK1, IGP3 and IGP4 are required for arabidopsis immune responses triggered by β-1,4-D-Xylo-oligosaccharides from plant cell walls

Pattern-Triggered Immunity (PTI) in plants is activated upon recognition by Pattern Recognition Receptors (PRRs) of Damage- and Microbe-Associated Molecular Patterns (DAMPs and MAMPs) from plants or microorganisms, respectively. An increasing number of identified DAMPs/MAMPs are carbohydrates from plant cell walls and microbial extracellular layers, which are perceived by plant PRRs, such as LysM and Leucine Rich Repeat-Malectin (LRR-MAL) receptor kinases (RKs). LysM-RKs (e.g. CERK1, LYK4 and LYK5) are needed for recognition of fungal MAMP chitohexaose (β-1,4-D-(GlcNAc)6, CHI6), whereas IGP1/CORK1, IGP3 and IGP4 LRR-MAL RKs are required for perception of β-glucans, like cellotriose (β-1,4-D-(Glc)3, CEL3) and mixed-linked glucans. We have explored the diversity of carbohydrates perceived by Arabidopsis thaliana seedlings by determining PTI responses upon treatment with different oligosaccharides and polysaccharides. These analyses revealed that plant oligosaccharides from xylans [β-1,4-D-(xylose)4 (XYL4)], glucuronoxylans and α-1,4-glucans, and polysaccharides from plants and seaweeds activate PTI. Cross-elicitation experiments of XYL4 with other glycans showed that the mechanism of recognition of XYL4 and the DAMP 33-α-L-arabinofuranosyl-xylotetraose (XA3XX) shares some features with that of CEL3 but differs from that of CHI6. Notably, XYL4 and XA3XX perception is impaired in igp1/cork1, igp3 and igp4 mutants, and almost not affected in cerk1 lyk4 lyk5 triple mutant. XYL4 perception is conserved in different plant species since XYL4 pre-treatment triggers enhanced disease resistance in tomato to Pseudomonas syringae pv tomato DC3000 and PTI responses in wheat. These results expand the number of glycans triggering plant immunity and support IGP1/CORK1, IGP3 and IGP4 relevance in Arabidopsis thaliana glycans perception and PTI activation.

Significance Statement

The characterization of plant immune mechanisms involved in the perception of carbohydrate-based structures recognized as DAMPs/MAMPs is needed to further understand plant disease resistance modulation. We show here that IGP1/CORK1, IGP3 and IGP4 LRR-MAL RKs are required for the perception of carbohydrate-based DAMPs β-1,4-D-(xylose)4 (XYL4) and 33-α-L-arabinofuranosyl-xylotetraose (XA3XX), further expanding the function of these LRR-MAL RKs in plant glycan perception and immune activation.

Plant cell wall-mediated disease resistance: Current understanding and future perspectives

Beyond their function as structural barriers, plant cell walls are essential elements for the adaptation of plants to environmental conditions. Cell walls are dynamic structures whose composition and integrity can be altered in response to environmental challenges and developmental cues. These wall changes are perceived by plant sensors/receptors to trigger adaptative responses during development and upon stress perception. Plant cell wall damage caused by pathogen infection, wounding, or other stresses leads to the release of wall molecules, such as carbohydrates (glycans), that function as damage-associated molecular patterns (DAMPs). DAMPs are perceived by the extracellular ectodomains (ECDs) of pattern recognition receptors (PRRs) to activate pattern-triggered immunity (PTI) and disease resistance. Similarly, glycans released from the walls and extracellular layers of microorganisms interacting with plants are recognized as microbe-associated molecular patterns (MAMPs) by specific ECD-PRRs triggering PTI responses. The number of oligosaccharides DAMPs/MAMPs identified that are perceived by plants has increased in recent years. However, the structural mechanisms underlying glycan recognition by plant PRRs remain limited. Currently, this knowledge is mainly focused on receptors of the LysM-PRR family, which are involved in the perception of various molecules, such as chitooligosaccharides from fungi and lipo-chitooligosaccharides (i.e., Nod/MYC factors from bacteria and mycorrhiza, respectively) that trigger differential physiological responses. Nevertheless, additional families of plant PRRs have recently been implicated in oligosaccharide/polysaccharide recognition. These include receptor kinases (RKs) with leucine-rich repeat and Malectin domains in their ECDs (LRR-MAL RKs), Catharanthus roseus RECEPTOR-LIKE KINASE 1-LIKE group (CrRLK1L) with Malectin-like domains in their ECDs, as well as wall-associated kinases, lectin-RKs, and LRR-extensins. The characterization of structural basis of glycans recognition by these new plant receptors will shed light on their similarities with those of mammalians involved in glycan perception. The gained knowledge holds the potential to facilitate the development of sustainable, glycan-based crop protection solutions.