Biology subjects

Melida, H.

Publications and source records attributed to Melida, H..

7 recordsLinked to original sources

bioRxiv2026

A pathogen α-L-arabinofuranosidase degrades host-derived immunogenic oligosaccharides to suppress plant immunity

Plant cell wall fragments released during pathogen attack can act as signalling molecules that trigger immune responses. Successful pathogens have potentially evolved diverse strategies to evade host recognition, including minimizing the accumulation of cell wall-derived elicitors. However, the mechanisms underlying this process remain largely unknown. Here, we characterized ZtGH54, an -L-arabinofuranosidase from the wheat pathogen Zymoseptoria tritici, that is essential for the acquisition of sugar nutrients from arabinan and arabinoxylan wall polysaccharides. ZtGH54 also hydrolyzes immunogenic oligosaccharides derived from arabinoxylan to prevent host recognition. Remarkably, this strategy is effective only in a subset of wheat cultivars, as the contribution of ZtGH54 to virulence is cultivar-dependent. While a ZtGH54 substrate is broadly recognized in wheat, one of the products generated by ZtGH54, xylotetraose, is recognized only by specific wheat cultivars, revealing natural variation in the perception of xylan-derived oligosaccharides. These findings establish ZtGH54 as a key virulence factor that simultaneously exploits cell wall host resources and suppresses wheat immunity through the precise hydrolysis of plant cell wall-derived signals.

plant biology↗

bioRxiv2025

Enhancing Plant Immune Training and Protection through Damage- and Microbe-Associated Molecular Patterns from Anaerobic Digestate

Olive oil production is a major global agricultural industry that generates significant waste, particularly olive pomace, which poses environmental and economic challenges. Anaerobic digestion has emerged as a promising solution for its valorization into biogas and reducing its environmental impact. However, the resulting digestate remains underutilized and its long-term environmental impact is uncertain. Traditional disposal methods are costly and inefficient, underscoring the need for more sustainable approaches. In this study, olive pomace digestate was biorefined and its components were upcycled into soil amendments and plant immunostimulants. Metagenomic analysis revealed a diverse microbial community in the liquid fraction, including Luteimonas, Pseudomonas, and Caldicoprobacter. We obtained a MIcrobial Protein Extract (MIPE) from this biomass, containing precursors of microbe- and damage-associated molecular patterns including Flagellin, Elongation Factor Tu, and the phytocytokine Golven. Treatment with MIPE triggered a rapid plant immune response, characterized by increased hydrogen peroxide production, phosphorylation of mitogen-activated protein kinases, and the upregulation of defense-related genes such as CYP81F2, FRK1, and WRKY53. MIPE-induced priming enhanced Arabidopsis and tomato resistance to Botrytis cinerea and Pseudomonas syringae. Our findings highlight digestate as a source of bioelicitors, offering a sustainable alternative to chemical pesticides while enhancing plant immunity, valorizing olive mill waste and promoting sustainable agriculture.

plant biology↗

bioRxiv2024

Zymoseptoria tritici stealth infection is facilitated by stage-specific down-regulation of a β-glucanase

Plant cell walls constitute a major defence barrier against pathogens, although it is unclear how specific cell wall components impact pathogen colonisation. Pathogens secrete cell wall degrading enzymes (CWDEs) to facilitate plant colonisation, but damaged, infected cells are often a source of cell wall-derived oligosaccharides that trigger host immunity. The mechanisms by which pathogens minimize the release of cell wall-derived oligosaccharides while colonizing the host remain to be elucidated. We combined biochemical, molecular genetics and transcriptomic analyses to functionally characterize a glycoside hydrolase (ZtGH45) from the wheat pathogen Zymoseptoria tritici. ZtGH45 gene is expressed during the necrotrophic phase of the fungus, coinciding with an accumulation of wheat {beta}-1,3/1,4-mixed-linked glucan (MLG)-derived oligosaccharides. We show that overexpression of ZtGH45 enhances {beta}-1,3/1,4-glucan hydrolysis and the derived oligosaccharides trigger an immune response in wheat, which hinders Z. tritici virulence. The results demonstrate that tight regulation of ZtGH45 is critical for the infection process to prevent early accumulation of MLG oligosaccharides that would prematurely induce host immunity counterbalancing fungal virulence. We suggest that the balance between plant cell wall degradation by fungal CWDE and the release of immunogenic wall-derived oligosaccharides governs the outcome of host invasion by pathogens.

plant biology↗

bioRxiv2024

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

Immune responses in plants are triggered by molecular patterns or elicitors, recognized by plant pattern recognition receptors (PRRs). Such molecular patterns arise from 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 certain glucans ability to stimulate defensive responses in plants remains understudied. This work focused on identifying novel glucan oligosaccharides acting as molecular patterns. The ability of various microorganism-derived glucans to prompt PTI responses was tested, revealing that specific microbial-derived glucans, such as short linear {beta}-1,2-glucans, trigger this response in plants by increasing reactive oxygen species (ROS) production, MAP kinase phosphorylation, and differential expression of defence-related genes in Arabidopsis thaliana. Pretreatments with {beta}-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, confirming that these plants also respond to {beta}-1,2-glucans, with increased ROS production and improved protection against fungal infections following B2G3 pretreatments. In summary, as with other {beta}-glucans, plants perceive {beta}-1,2-glucans as warning signals and stimulate defence responses against phytopathogens. HighlightsWe describe a new group of glycans present in the extracellular matrices of some plant-interacting microorganisms that are sensed by host surveillance systems and enhance the plants natural resistance to disease.

plant biology↗

bioRxiv2022

Interplay of EXO70 and MLO proteins modulates trichome cell wall composition and powdery mildew susceptibility

EXO70 proteins are essential constituents of the octameric exocyst complex implicated in vesicle tethering during exocytosis, while MLO proteins are plant-specific calcium channels of which some isoforms play a key role during fungal powdery mildew pathogenesis. We here detected by a variety of histochemical staining procedures an unexpected phenotypic overlap of A. thaliana exo70H4 and mlo2 mlo6 mlo12 triple mutant plants regarding the biogenesis of leaf trichome secondary cell walls. Biochemical and Fourier transform infrared spectroscopic analyses of isolated trichomes corroborated deficiencies in the composition of trichome cell walls in exo70H4 and mlo2 mlo6 mlo12 mutants. Transgenic lines expressing fluorophore- tagged EXO70H4 and MLO variants exhibited extensive co-localization of these proteins at the trichome plasma membrane and cell wall. Furthermore, mCherry- EXO70H4 mislocalized in trichomes of the mlo triple mutant and, vice versa, MLO6- GFP exhibited aberrant subcellular localization in trichomes of the exo70H4 mutant. Transgenic expression of GFP-marked PMR4 callose synthase, a previously identified cargo of EXO70H4 dependent exocytosis, revealed reduced cell wall delivery of GFP- PMR4 in mlo triple mutant plants. In vivo protein-protein interaction assays uncovered isoform-preferential physical interaction between EXO70 and MLO proteins. Finally, exo70H4 and mlo mutants, when combined, showed synergistically enhanced resistance to powdery mildew attack. Taken together, our data point to an isoform- specific interplay of EXO70 and MLO proteins in the modulation of trichome cell wall biogenesis and powdery mildew susceptibility, possibly by (co-)regulating focal secretion of cell wall-related cargo.

plant biology↗

bioRxiv2022

A group of Arabidopsis thaliana Leucine Rich Repeat-Malectin Receptor Kinases are required for the activation of immune responses triggered by cellulose and mixed-linked glucan oligosaccharides

Plant immune system perceives through the extracellular ectodomains (ECDs) of Pattern Recognition Receptors (PRRs) a diversity of carbohydrate ligands from plant and microbial cell walls, which activate Pattern-Triggered Immunity (PTI). Among these ligands are oligosaccharides derived from mixed-linked {beta}-1,3/{beta}-1,4-glucans (MLGs, e.g., {beta}-1,4-D-(Glc)2-{beta}-1,3-D-Glc, MLG43) and cellulose (e.g., {beta}-1,4-D-(Glc)3, CEL3). The mechanisms of perception of carbohydrates by plants are poorly characterized, with the exception of that determining recognition of fungal chitin oligosaccharides (e.g., {beta}-1,4-D(GlcNAc)6, CHI6) that involves several PRRs with LysM-ECDs that function as receptor or co-receptors. Here, we describe the isolation and characterization of Arabidopsis thaliana mutants impaired in glycan perception (igp), which are defective in PTI activation mediated by MLG43 and CEL3, but not CHI6. igp1-igp4 are altered in receptor-like kinases [RLKs: AT1G56145 (IGP1), AT1G56130 (IGP2/3), and AT1G56140 (IGP4)] with Leucine-Rich-Repeat (LRR) and Malectin (MAL) domains in their ECDs. igp4 is a T-DNA insertional, loss of function mutant whereas igp1 and the allelic igp2/igp3 harbour point mutations (E906K and G773E, respectively) in their kinase domains, which impact their structure and surface electrostatic potential as revealed by in silico structural analyses. Notably, Isothermal Titration Calorimetry assays with purified ECD-RLKs showed that AT1G56145 binds with high affinity CEL3 (Kd = 1.19 {+/-} 0.03 M) and cellopentaose (Kd = 1.40 {+/-} 0.01 M), but not MLG43, supporting AT1G56145 function as a plant PRR for cellulose oligosaccharides. Our data suggest that these LRR-MAL RLKs are receptor/co-receptors of a novel mechanism of perception of cellulose and MLG-derived oligosaccharides and PTI activation in Arabidopsis thaliana. Significance StatementNew oligosaccharides that trigger plant immunity have been described recently, but the mechanisms of perception of these glycans are unknown. We describe here three Arabidopsis thaliana receptor kinases (AT1G56130, AT1G56140, and AT1G56145) with Leucine Rich Repeat (LRR) and Malectin (MAL) domains in their extracellular ectodomains (ECDs), which function as Pattern Recognition Receptors (PRRs) triggering immune response mediated by oligosaccharides from cellulose ({beta}-1,4-glucan) and mixed-linked {beta}-1,3/1,4-glucans (MLGs) of plant and microbial cell walls. The ECD-AT1G56145 binds cellulose oligosaccharides, but not MLGs, supporting its function as a novel receptor of carbohydrate ligands in plants. Our data indicate that these LRR-MAL-PRRs control a complex mechanism of oligosaccharides perception and immune activation that differs from that of fungal chitin oligosaccharides recognition which involves LysM-PRRs.

plant biology↗

bioRxiv2020

Arabidopsis cell wall composition determines disease resistance specificity and fitness

Plant cell walls are complex structures subject to dynamic remodeling in response to developmental and environmental cues, and play essential functions in disease resistance responses. We tested the specific contribution of plant cell walls to immunity by determining the susceptibility of a set of Arabidopsis cell wall mutants (cwm) to pathogens with different parasitic styles: a vascular bacterium, a necrotrophic fungus and a biotrophic oomycete. Remarkably, most cwm mutants tested (31/38; 81.6%) showed alterations in their resistance responses to at least one of these pathogens, in comparison to wild-type plants, illustrating the relevance of wall composition in determining disease resistance phenotypes. We found that the enhanced resistance of cwm plants to the necrotrophic and vascular pathogens negatively impacted on cwm fitness traits, like biomass and seed yield. Enhanced resistance of cwm plants is not only mediated by canonical immune pathways, like those modulated by phytohormones or Microbe-Associated Molecular Patterns, which are not de-regulated in all cwm tested. Pectin-enriched wall fractions isolated from cwm plants triggered immune responses in other plants, suggesting that wall-mediated defensive pathways might contribute to cwm resistance. Cell walls of cwm plants show a high diversity of composition alterations as revealed by glycome profiling that detect specific wall carbohydrate moieties. Mathematical analysis of glycome profiling data identified correlations between the amounts of specific wall carbohydrate moieties and disease resistance phenotypes of cwm plants. These data support the relevant and specific function of plant wall composition in plant immune response modulation and in balancing disease resistance/development trade-offs.

plant biology↗