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

Fungal cell wall biogenesis: structural complexity, regulation and inhibition

The cell wall is the defining organelle of filamentous and yeast-like fungi. It is responsible for morphology, biotic and abiotic interactions and its components confer its unique and variable signature, making it a natural target for antifungal drugs, but a moving target for immune recognition. The wall is however more than the sum of its many parts. The polysaccharides and proteins of the cell wall must be made at the right time and the right place, but also linked together and remodelled throughout the cell cycle and in response to environmental challenges, nutrient availability, damage after predation and to be complaint to the need to establish mutualistic and parasitic associations. This review summarises recent advances in our understanding of the complex and vital process of fungal cell wall biogenesis using the human pathogens Candida albicans and Aspergillus fumigatus as the principal model fungi.

Sunlight-sensitive carbon dots for plant immunity priming and pathogen defence

Global food production faces persistent threats from environmental challenges and pathogenic attacks, leading to significant yield losses. Conventional strategies to combat pathogens, such as fungicides and disease-resistant breeding, are limited by environmental contamination and emergence of pathogen resistance. Herein, we engineered sunlight-sensitive and biodegradable carbon dots (CDs) capable of generating reactive oxygen species (ROS), offering a novel and sustainable approach for plant protection. Our study demonstrates that CDs function as dual-purpose materials: priming plant immune responses and serving as broad-spectrum antifungal agents. Foliar application of CDs generated ROS under light, and the ROS could damage the plant cell wall and trigger cell wall-mediated immunity. Immune activation enhanced plant resistance against pathogens without compromising photosynthetic efficiency or yield. Specifically, spray treatment with CDs at 240 mg/L (2 mL per plant) reduced the incidence of grey mould in N. benthamiana and tomato leaves by 44% and 12%, respectively, and late blight in tomato leaves by 31%. Moreover, CDs (480 mg/L, 1 mL) combined with continuous sunlight irradiation (simulated by xenon lamp, 9.4 × 105 lux) showed a broad-spectrum antifungal activity. The inhibition ratios for mycelium growth were 66.5% for P. capsici, 8% for S. sclerotiorum and 100% for B. cinerea, respectively. Mechanistic studies revealed that CDs effectively inhibited mycelium growth by damaging hyphae and spore structures, thereby disrupting the propagation and vitality of pathogens. These findings suggest that CDs offer a promising, eco-friendly strategy for sustainable crop protection, with potential for practical agricultural applications that maintain crop yields and minimize environmental impact.

A well-annotated genome of Apium graveolens var. dulce cv. Challenger, a celery with resistance to Fusarium oxysporum f. sp. apii race 2

Celery (Apium graveolens var. dulce) production can be limited by the fungal pathogen Fusarium oxysporum f. sp. apii (Foa), particularly at temperatures above 22°C. Because celery has a narrow genetic base, an intraspecific admixture of Apium graveolens was developed into cv. Challenger, which is resistant to Foa race 2, the causal agent of Fusarium yellows, but susceptible to Foa race 4, a relatively unrelated causal agent of Fusarium wilt. We assembled a high-quality, chromosome-level physical map of Challenger with 40 464 RNA-based, protein-coding gene models in 3.3 Gbp and anchored it with a genetic map. Although there is high gene density and higher recombination at the ends of the chromosomes, an average of 56% of the genes/chromosome are in lower recombination zones (<0.025 cM/Mb). We identified Challenger's nucleotide-binding and leucine-rich repeat receptors (NLRs) and pattern recognition receptors (PRRs), the two gene families that encode most resistance (R) genes. In three treatment groups (mock-infested or infested with either Foa race 2 or race 4), 243 NLRs and 445 PRRs were quantified in the celery crowns via Quant-Seq 3' mRNA-Seq (Tag-Seq). We compared the genomes of Challenger with that of the previously published cv. Ventura, which is moderately susceptible to Foa race 2. We present a toolbox for genome-assisted breeding for celery that includes annotated gene models, a protocol for genotype-by-sequencing, documentation of the expression of NLRs and PRRs, and a straightforward strategy for introgressing selected NLR superclusters, 83% of which are in higher recombination regions.

Carposphere microbiota alters grape volatiles and shapes the wine grape typicality

While specific environments are known to shape plant metabolomes and the makeup of their associated microbiome, it is as yet unclear whether carposphere microbiota contribute to the characteristics of grape fruit flavor of a particular wine region. Here, carposphere microbiomes and berry transcriptomes and metabolomes of three grape cultivars growing at six geographic sites were analyzed. The composition of the carposphere microbiome was determined mainly by environmental conditions, rather than grape genotype. Bacterial microbiota likely contributed to grape volatile profiles. Particularly, candidate operational taxonomic units (OTUs) in genus Sphingomonas were highly correlated with grape C6 aldehyde volatiles (also called green leaf volatiles, GLVs), which contribute to a fresh taste. Furthermore, a core set of expressed genes was enriched in lipid metabolism, which is responsible for bacterial colonization and C6 aldehyde volatile synthesis activation. Finally, a similar grape volatile profile was observed after inoculating the berry skin of two grape cultivars with Sphingomonas sp., thus providing evidence for the hypothetical microbe-metabolite relationship. These results provide novel insight into how the environment-microbiome-plant quality (E × Mi × Q) interaction may shape berry flavor and thereby typicality, serving as a foundation for decision-making in vineyard microbial management.

Dynamic transcriptome and GWAS uncover a hydroxyproline-rich glycoprotein that suppresses Agrobacterium-mediated transformation in maize

Genetic transformation is a crucial tool for investigating gene function and advancing molecular breeding in crops, with Agrobacterium tumefaciens-mediated transformation being the primary method for plant genetic modification. However, this approach exhibits significant genotypic dependence in maize. Therefore, to overcome these limitations, we combined dynamic transcriptome analysis and genome-wide association study (GWAS) to identify the key genes controlling Agrobacterium infection frequency (AIF) in immature maize embryos. Transcriptome analysis of Agrobacterium-infected embryos uncovered 8483 and 1580 genotype-specific response genes in the maize line 18-599R with low AIF and A188 with high AIF, respectively. A weighted gene co-expression network analysis (WGCNA) revealed five and seven stage-specific co-expression modules in each corresponding line. Based on a self-developed AIF quantitation method, the GWAS revealed 30 AIF-associated single-nucleotide polymorphisms and 315 candidate genes under multiple environments. Integration of GWAS and WGCNA further identified 12 key genes associated with high AIF in A188. ZmHRGP, encoding a hydroxyproline-rich glycoprotein, was functionally validated as a key factor of AIF in immature embryos. Knockout of ZmHRGP enabled us to establish a high-efficiency genetic transformation system for the 18-599R line, with the transformation frequency being approximately 80%. Moreover, the transient reduction of ZmHRGP expression significantly enhanced the AIF of maize calluses and leaves. Collectively, these findings advance our understanding of plant factors controlling Agrobacterium infection and contribute to developing more efficient Agrobacterium-mediated transformation systems in crops.

Between Host and Invaders: The Subcellular Cell Wall Dynamics at the Plant-Pathogen Interface

Plant-pathogen interactions have profound ecological implications and are crucial for food security. Usually studied at the two extreme scales of plant organ symptomatology and host-microbe molecules, they are a cell-cell event mainly occurring at the subcellular level of the plant apoplast. Here, the cell walls of both organisms suffer an intense alteration as a consequence of active degradation by the opponent and self-protection mechanisms to survive and continue growing. The plant cell wall modifications and their role in defense as danger signals and activators of signaling cascades have been studied for a few decades, mainly at the organ plane. Still, much remains unknown about this process, including cellular and subcellular minority decorations, proteins, and mechanical cues. Comparatively, the microbial cell wall changes in planta are virtually unexplored. By investigating the interface between plant and microbial cell walls biochemically, structurally, and mechanically, we aim to highlight the dynamic interplay in these subcellular areas and its significance for the host-invader interaction.

New insights into plant cell wall functions

The plant cell wall is an extremely complicated natural nanoscale structure composed of cellulose microfibrils embedded in a matrix of noncellulosic polysaccharides, further reinforced by the phenolic compound lignins in some cell types. Such network formed by the interactions of multiscale polymers actually reflects functional form of cell wall to meet the requirements of plant cell functionalization. Therefore, how plants assemble cell wall functional structure is fundamental in plant biology and critical for crop trait formation and domestication as well. Due to the lack of effective analytical techniques to characterize this fundamental but complex network, it remains difficult to establish direct links between cell-wall genes and phenotypes. The roles of plant cell walls are often underestimated as indirect. Over the past decades, many genes involved in cell wall biosynthesis, modification, and remodeling have been identified. The application of a variety of state-of-the-art techniques has made it possible to reveal the fine cell wall networks and polymer interactions. Hence, many exciting advances in cell wall biology have been achieved in recent years. This review provides an updated overview of the mechanistic and conceptual insights in cell wall functionality, and prospects the opportunities and challenges in this field.

The GCN4-Swi6B module mediates low nitrogen-induced cell wall remodeling in Ganoderma lucidum

In natural habitats, microorganisms encounter various unfavorable environmental stresses, including nitrogen deficiency. As the outermost barrier, the cell wall plays a crucial role in the interaction between the cell and the external environment. However, the effect of low nitrogen on cell wall thickness, especially the underlying molecular mechanism, is unclear. Here, we found that compared with those under normal nitrogen conditions, both the cell wall thickness and polysaccharide content of Ganoderma lucidum are increased under low nitrogen conditions. Furthermore, the abundance of SWI6B, a transcription factor that participates in cell wall remodeling, is also increased in low-nitrogen environments. The thickness and polysaccharide content of the cell wall increased in SWI6B-overexpression strains (SWI6B-OEs) but decreased in SWI6-knockdown strains (swi6-kds). Moreover, although the cell wall thickness of all the genotypes increased under nitrogen-limited conditions, the percentage of upregulated swi6-kds was significantly lower than that of the WT, and the percentage of increased SWI6B-OEs was the highest. Moreover, GCN4, a key transcription factor of the low-nitrogen signaling pathway, was found to directly bind to the promoter of SWI6. The transcriptional and translational levels of SWI6B were reduced in GCN4-knockdown strains (gcn4-kds), indicating a positive regulation of SWI6B by GCN4. Consistently, the cell wall thickness of gcn4-kds was also lower than that of the wild type. Taken together, our results revealed that the GCN4-Swi6B module regulates cell wall remodeling in G. lucidum under nitrogen deficiency conditions.

IMPORTANCE

To survive in stressful environments, fungi initiate cell wall remodeling pathways to adaptively modify the cell wall composition and structure. Here, we found that nitrogen deficiency upregulated the cell wall polysaccharide content and cell wall thickness through the GCN4-SWI6B signaling pathway. Our findings provide valuable insights into the environmental adaptation of fungal cell walls, contributing to a deeper understanding of fungal responses to environmental stress.

Berberine bridge enzyme-like oxidases orchestrate homeostasis and signaling of oligogalacturonides in defense and upon mechanical damage

Plant immunity is triggered by endogenous elicitors known as damage-associated molecular patterns (DAMPs). Oligogalacturonides (OGs) are DAMPs released from the cell wall (CW) demethylated homogalacturonan during microbial colonization, mechanical or pest-provoked mechanical damage, and physiological CW remodeling. Berberine bridge enzyme-like (BBE-l) proteins named OG oxidases (OGOXs) oxidize and inactivate OGs to avoid deleterious growth-affecting hyper-immunity and possible cell death. Using OGOX1 over-expressing lines and ogox1/2 double mutants, we show that these enzymes determine the levels of active OGs vs. inactive oxidized products (ox-OGs). The ogox1/2-deficient plants have elevated levels of OGs, while plants overexpressing OGOX1 accumulate ox-OGs. The balance between OGs and ox-OGs affects disease resistance against Pseudomonas syringae pv. tomato, Pectobacterium carotovorum, and Botrytis cinerea depending on the microbial capacity to respond to OGs and metabolize ox-OGs. Gene expression upon plant infiltration with OGs reveals that OGOXs orchestrate OG signaling in defense as well as upon mechanical damage, pointing to these enzymes as apoplastic players in immunity and tissue repair.

Cell wall bricks of defence: the case study of oligogalacturonides

The plant cell wall (CW) is more than a structural barrier; it serves as the first line of defence against pathogens and environmental stresses. During pathogen attacks or physical damage, fragments of the CW, known as CW-derived Damage-Associated Molecular Patterns (CW-DAMPs), are released. These molecular signals play a critical role in activating the plant's immune responses. Among CW-DAMPs, oligogalacturonides (OGs), fragments derived from the breakdown of pectin, are some of the most well-studied. This review highlights recent advances in understanding the functional and signalling roles of OGs, beginning with their formation through enzymatic CW degradation during pathogen invasion or mechanical injury. We discuss how OGs perception triggers intracellular signalling pathways that enhance plant defence and regulate interactions with microbes. Given that excessive OG levels can negatively impact growth and development, we also examine the regulatory mechanisms plants use to fine-tune their responses, avoiding immune overactivation or hyper- immunity. As natural immune modulators, OGs (and more generally CW-DAMPs), offer a promising, sustainable alternative to chemical pesticides by enhancing crop resilience without harming the environment. By strengthening plant defences and supporting eco-friendly agricultural practices, OGs hold great potential for advancing resilient and sustainable farming systems.

Protein Phosphatases MoPtc5, MoPtc1, and MoPtc2 Contribute to the Vegetative Growth, Stress Adaptation, and Virulence of Magnaporthe oryzae

Protein phosphatases are crucial enzymes that regulate key cellular processes such as the cell cycle, gene transcription, and translation in eukaryotes. Seven PP2C protein phosphatases have been identified in Magnaporthe oryzae. However, their synergistic roles in the pathology and physiology of M. oryzae remain poorly investigated. By qRT-PCR analysis, we found that PTC1 and PTC2 are significantly upregulated in the PTC5 deletion mutant. The double deletion of the MoPTC5/MoPTC1 and MoPTC5/MoPTC2 genes significantly reduced hyphal growth, conidiophore formation, sporulation, and virulence in M. oryzae. In addition, the double-knockout mutants were increasingly sensitive to different osmotic, oxidative, and cell wall stresses. Western blot analysis revealed that MoPtc5 plays a synergistic function with MoPtc1 and MoPtc2 in the regulation of MoMps1 and MoOsm1 phosphorylation levels. Lastly, appressorium formation and turgor generation were remarkably affected in the ΔMoptc5ΔMoptc1 and ΔMoptc5ΔMoptc2 double-deletion mutants. These findings demonstrate the overlapping roles of PP2c protein phosphatase in the fungal development and pathogenesis of M. oryzae.

Study on the damage and variation of Agropyron mongolicum induced by the combined action of discharge plasma and plasma-activated water

To investigate the effect of combined action of discharge plasma (DP) and plasma-activated water (PAW) in mutagenesis breeding, this study focuses on Agropyron mongolicum. We utilized high-voltage DC pulsed dielectric barrier discharge for seed treatment, alone and in combination with PAW. The research focused on germination rates, evolution of physicochemical properties of imbibition residual solution, reactive oxygen species (ROS), malondialdehyde (MDA), and volatile organic compounds (VOCs) to assess DP-induced damage and variability in Agropyron mongolicum. Results indicated that after 18 h of combined treatment, the germination rate of Agropyron mongolicum dropped to 29.67%, below the LD50 threshold. Treated seedlings exhibited elevated ROS and MDA levels compared to controls. The concentration of reactive nitrogen and oxygen species (RONS) in the imbibition residual solution of the combined treatment group was lower than in freshly prepared PAW, indicating RONS penetration into the seed embryo via water, leading to oxidative damage. Enhanced lateral root differentiation, early tillering, increased biomass, and albino variant plants were observed in the surviving seedlings post-treatment. Transmission electron microscope (TEM) and Gas Chromatography-Ion Mobility Spectrometry (GC-IMS) analysis confirmed that plasma treatment induced oxidative damage in Agropyron mongolicum. In conclusion, high-power, long-duration direct DP treatment caused oxidative damage and reduced germination rates in Agropyron mongolicum, with PAW intensifying these effects. PAW was identified as the main driver of variation and lethality, while DP played a supportive role. Combined DP and PAW treatment induced variations in Agropyron mongolicum, providing experimental evidence and theoretical insights for applying DP treatment in plant mutagenesis breeding.

Enzymes that catalyze cyclization of β-1,2-glucans

β-1,2-Glucans are physiologically important polymers for interactions such as symbiosis and pathogenesis between organisms and adaptation to environmental changes. However, rarity of β-1,2-glucans in nature limits exploration of related enzymes. Recently, many β-1,2-glucan-degrading enzymes have been found after identification of a novel phosphorylase acting on β-1,2-glucooligosaccharides. The expansion of the repertoire has reached revelation of the cyclization mechanism of cyclic β-1,2-glucan synthase and led to finding of new enzymes catalyzing cyclization of β-1,2-glucans in a manner different from cyclic β-1,2-glucan synthase. In this review, we mainly focus on newly found enzymes that catalyze cyclization of β-1,2-glucans along with existence of β-1,2-glucan-associated carbohydrates in nature and introduction of the repertoire of β-1,2-glucan-degrading enzymes. KEY POINTS: • Newly found domain which cyclizes β-1,2-glucan created a new glycoside hydrolase family. • Cyclization is performed with a unique mechanism. • α-1,6-Cyclized β-1,2-glucan is produced by an enzyme in another newly found family.

Plant cell wall structure and dynamics in plant-pathogen interactions and pathogen defence

Plant cell walls delimit cells from their environment and provide mechanical stability to withstand internal turgor pressure as well as external influences. Environmental factors can be beneficial or harmful for plants and vary substantially depending on prevailing combinations of climate conditions and stress exposure. Consequently, the physicochemical properties of plant cell walls need to be adaptive, and their functional integrity needs to be monitored by the plant. One major threat to plants is posed by phytopathogens, which employ a diversity of infection strategies and lifestyles to colonize host tissues. During these interactions, the plant cell wall represents a barrier that impedes the colonization of host tissues and pathogen spread. In a competition for maintenance and breakdown, plant cell walls can be rapidly and efficiently remodelled by enzymatic activities of plant and pathogen origin, heavily influencing the outcome of plant-pathogen interactions. We review the role of locally and systemically induced cell wall remodelling and the importance of tissue-dependent cell wall properties for the interaction with pathogens. Furthermore, we discuss the importance of cell wall-dependent signalling for defence response induction and the influence of abiotic factors on cell wall integrity and cell wall-associated pathogen resistance mechanisms.

Microscopy and spatial-metabolomics identify tissue-specific metabolic pathways uncovering salinity and drought tolerance mechanisms in Avicennia marina and Phoenix dactylifera roots

In arid and semi-arid climates, native plants have developed unique strategies to survive challenging conditions. These adaptations often rely on molecular pathways that shape plant architecture to enhance their resilience. Date palms (Phoenix dactylifera) and mangroves (Avicennia marina) endure extreme heat and high salinity, yet the metabolic pathways underlying this resilience remain underexplored. Here, we integrate tissue imaging with spatial metabolomics to uncover shared and distinct adaptive features in these species. We found that mangrove roots accumulate suberin and lignin in meristematic tissues, this is unlike other plant species, where only the differentiation zones contain these compounds. Our metabolomic analysis shows that date palm roots are enriched in metabolites involved in amino acid biosynthesis, whereas compounds involved in lignin and suberin production were more abundant in mangrove roots. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) revealed tissue- and species-specific metabolite distributions in root tissues. We identified common osmoprotectants accumulating in the exodermis/epidermis of date palm and mangrove root meristems, along with a unique metabolite highly abundant in the inner cortex of date palm roots. These findings provide valuable insights into stress adaptation pathways and highlight key tissue types involved in root stress response.

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.

Linear β-1,2-glucans trigger immune hallmarks and enhance disease resistance in plants

Immune responses in plants are triggered by molecular patterns or elicitors, recognized by plant pattern recognition receptors. Such molecular patterns are the consequence of host-pathogen interactions, and the response cascade activated after their perception is known as pattern-triggered immunity (PTI). Glucans have emerged as key players in PTI, but the ability of certain glucans to stimulate defensive responses in plants remains understudied. This work focused on identifying novel glucan oligosaccharides as molecular patterns. The ability of various microorganism-derived glucans to trigger PTI responses was tested, revealing that specific microbial-derived molecules, such as short linear β-1,2-glucans, trigger this response in plants by increasing the production of reactive oxygen species (ROS), mitogen-activated protein kinase phosphorylation, and differential expression of defence-related genes in Arabidopsis thaliana. Pre-treatments with β-1,2-glucan trisaccharide (B2G3) improved Arabidopsis defence against bacterial and fungal infections in a hypersusceptible genotype. The knowledge generated was then transferred to the monocotyledonous model species maize and wheat, demonstrating that these plants also respond to β-1,2-glucans, with increased ROS production and improved protection against fungal infections following B2G3 pre-treatments. In summary, as with other β-glucans, plants perceive β-1,2-glucans as warning signals which stimulate defence responses against phytopathogens.

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.

Transcriptomic and sugar metabolic analysis reveals molecular mechanisms of peach gummosis in response to Neofusicoccum parvum infection

Peach gummosis, a devastating disease caused by Neofusicoccum parvum, significantly shortens peach tree lifespan and reduces the yield of peach trees. Despite its impact, the molecular mechanism underlying this disease remains largely unexplored. In this study, we used RNA-seq, sugar metabolism measurements, and an integrated transcriptional and metabolomic analysis to uncover the molecular events driving peach gummosis. Our results revealed that N. parvum infection drastically altered the transcripts of cell wall degradation-related genes, the log2Fold change in the transcript level of Prupe.1G088900 encoding xyloglucan endotransglycosylase decreased 2.6-fold, while Prupe.6G075100 encoding expansin increased by 2.58-fold at 12 hpi under N. parvum stress. Additionally, sugar content analysis revealed an increase in maltose, sucrose, L-rhamnose, and inositol levels in the early stages of infection, while D-galactose, D-glucose, D-fructose consistently declined as gummosis progressed. Key genes related to cell wall degradation and starch degradation, as well as UDP-sugar biosynthesis, were significantly upregulated in response to N. parvum. These findings suggest that N. parvum manipulates cell wall degradation and UDP-sugar-related genes to invade peach shoot cells, ultimately triggering gum secretion. Furthermore, weighted gene co-expression network analysis (WGCNA) identified two transcription factors, ERF027 and bZIP9, as central regulators in the downregulated and upregulated modules, respectively. Overall, this study enhances our understanding of the physiological and molecular responses of peach trees to N. parvum infection and provide valuable insights into the mechanisms of peach defense against biotic stresses.

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.

AlphaFold-guided redesign of a plant pectin methylesterase inhibitor for broad-spectrum disease resistance

Plant cell walls are a critical site where plants and pathogens continuously struggle for physiological dominance. Here we show that dynamic remodeling of pectin methylesterification of plant cell walls is a component of the physiological and co-evolutionary struggles between hosts and pathogens. A pectin methylesterase (PsPME1) secreted by Phytophthora sojae decreases the degree of pectin methylesterification, thus synergizing with an endo-polygalacturonase (PsPG1) to weaken plant cell walls. To counter PsPME1-mediated susceptibility, a plant-derived pectin methylesterase inhibitor protein, GmPMI1, protects pectin to maintain a high methylesterification status. GmPMI1 protects plant cell walls from enzymatic degradation by inhibiting both soybean and P. sojae pectin methylesterases during infection. However, constitutive expression of GmPMI1 disrupted the trade-off between host growth and defense responses. We therefore used AlphaFold structure tools to design a modified form of GmPMI1 (GmPMI1R) that specifically targets and inhibits pectin methylesterases secreted from pathogens but not from plants. Transient expression of GmPMI1R enhanced plant resistance to oomycete and fungal pathogens. In summary, our work highlights the biochemical modification of the cell wall as an important focal point in the physiological and co-evolutionary conflict between hosts and microbes, providing an important proof of concept that AI-driven structure-based tools can accelerate the development of new strategies for plant protection.