Biology subjects

Sanchez-Vallet, A.

Publications and source records attributed to Sanchez-Vallet, A..

13 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

From omics to enhanced fungal virulence: Overexpression of a putative secreted protein improves Beauveria bassiana biocontrol potential against the insect pests Piezodorus guildinii and Tenebrio molitor

The entomopathogenic fungus Beauveria bassiana is widely used as a biocontrol agent, but its efficacy varies depending on the target insect species. Piezodorus guildinii, a major soybean pest, exhibits low susceptibility to B. bassiana. Thus, biocontrol of this pest requires improving virulence of B. bassiana. Here, we used genomic and transcriptomic analyses to identify novel genes associated with the enhanced virulence of B. bassiana strain ILB308 when exposed to the insect epicuticular hydrocarbon n-pentadecane. Comparative analysis with the lower-virulence strain ILB205 revealed differentially expressed genes (DEGs) linked to genetic information process pathways and immune evasion. Among these DEGs, we identified BbCBM9_1, a secreted carbohydrate-binding protein, as a candidate virulence factor. Overexpression of BbCBM9_1 in ILB205 led to enhanced virulence against P. guildinii and Tenebrio molitor, as well as improved conidial germination, tolerance to oxidative and cell wall stress, and increased growth in nutrient-rich and glycerol-supplemented media. This demonstrates that the enhanced virulence observed in ILB308 grown on n-pentadecane can be replicated by overexpressing an associated gene in a low-virulence strain. Our study, highlights the potential of integrating transcriptomics and targeted genetic modifications to optimize fungal biocontrol agents for improved pest management.

microbiology↗

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

Novel genomic features in entomopathogenic fungus Beauveria bassiana: supernumerary chromosomes and putative virulence genes involved in the infection process of soybean pest Piezodorus guildinii.

Biological control methods involving entomopathogenic fungi like Beauveria bassiana have shown to be a valuable approach in integrated pest management as an environmentally friendly alternative to control pests and pathogens. Identifying genetic determinants of pathogenicity in B. bassiana is instrumental for enhancing its virulence against insects like the resistant soybean pest Piezodorus guildinii. This study focused on comparative genomics of different B. bassiana strains and gene expression analyses to identify virulence genes in the hypervirulent strain ILB308, especially in response to infection of P. guildniii and growth on hydrocarbon HC15, a known virulence enhancer. Strain ILB308 showed the highest number of virulence-related features, such as candidate virulence proteins, effectors, small secreted proteins, and biosynthetic gene clusters. ILB308 also had a high percentage of unique DNA sequences, including six putative supernumerary scaffolds. Gene expression analysis at 4 days post-inoculation revealed upregulation of known virulence factors, including Tudor domain proteins, LysM motif-containing proteins, and subtilisin-like proteases, and novel genes like secreted effectors and heat-labile enterotoxins. Growth on HC15 led to the upregulation of genes associated with oxidoreductase activity related to cuticular alkane degradation and fermentation metabolism/antioxidant responses in the hemolymph. The presence of supernumerary chromosomes and unique virulence genes in ILB308 may contribute to its higher virulence and could be considered as potential targets for enhancing fungal virulence through genetic manipulation. Author SummaryUnderstanding mechanisms of virulence and virulence enhancement in Beauveria bassiana can lay the basis for the development of improved biocontrol agents. Here we used genomic and transcriptomic approaches to study the infection process of ILB308 -an hypervirulent strain- against insect pest Piezodorus guildinii. We found that this strain has putative supernumerary chromosomes and an enriched set of presumed virulence proteins like secreted effectors. We infer that the particular assortment of strain specific genes and supernumerary chromosome/s play a role in the degree of virulence exhibited by ILB308 and could be used for future strain improvement strategies.

genomics↗

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↗

bioRxiv2024

The Zymoseptoria tritici avirulence factor AvrStb6 accumulates in hyphae close to stomata and triggers a wheat defense response hindering fungal penetration

Zymoseptoria tritici, the causal agent of septoria tritici blotch, is one of Europes most damaging wheat pathogens, causing significant economic losses. Genetic resistance is a common strategy to control the disease, Stb6 being a resistance gene used for over 100 years in Europe. This study investigates the molecular mechanisms underlying Stb6-mediated resistance. Utilizing confocal microscopy imaging, we identified that Z. tritici epiphytic hyphae mainly accumulates the corresponding avirulence factor AvrStb6 in close proximity to stomata. Consequently, the progression of AvrStb6-expressing avirulent strains is hampered during penetration. The fungal growth inhibition co-occurs with a transcriptional reprogramming in wheat characterized by an induction of immune responses, genes involved in stomata regulation, and cell wall-related genes. Overall, we shed light on the gene-for-gene resistance mechanisms in the wheat - Z. tritici pathosystem at the cytological and transcriptomic level, and our results highlight that stomata penetration is a critical process for pathogenicity and resistance.

plant biology↗

bioRxiv2023

Zymoseptoria tritici suppresses the host immune response and facilitates the success of avirulent strains in mixed infections

Plants interact with a plethora of pathogenic microorganisms in nature. Pathogen-plant interaction experiments focus mainly on single-strain infections, typically ignoring the complexity of multi-strain infections even though mixed infections are common and critical for the infection outcome. The wheat pathogen Zymoseptoria tritici forms highly diverse fungal populations in which several pathogen strains often colonize the same leaf. Despite the importance of mixed infections, the mechanisms governing interactions between a mixture of pathogen strains within a plant host remain largely unexplored. Here we demonstrate that avirulent pathogen strains benefit from being in mixed infections with virulent strains. We show that virulent strains suppress the wheat immune response, allowing the avirulent strain to colonize the apoplast and to reproduce. Our experiments indicate that virulent strains in mixed infections can challenge the plant immune system both locally and systemically, providing a mechanistic explanation for the persistence of avirulent pathogen strains in fields planted to resistant host plants.

plant biology↗

bioRxiv2023

Sas3-mediated histone acetylation regulates effector gene activation in a fungal plant pathogen

Effector proteins are secreted by plant pathogens to enable host colonization. Typically, effector genes are tightly regulated, have very low expression levels in axenic conditions, and are strongly induced during host colonization. Chromatin remodeling contributes to the activation of effector genes in planta by still poorly known mechanisms. In this work we investigated the role of histone acetylation in effector gene derepression in plant pathogens. We used Zymoseptoria tritici, a major pathogen of wheat, as a model to determine the role of lysine acetyltransferases (KATs) in plant infection. We showed that effector gene activation is associated with chromatin remodeling, featuring increased acetylation levels of histone H3 lysine 9 (H3K9) and 14 (H3K14) in effector loci. We functionally characterized the role of Z. tritici KATs and demonstrated their distinct contributions to growth, development, and infection. Sas3 is required for host colonization and pycnidia production, while Gcn5 has a major role in pycnidia production. Furthermore, we demonstrated that Sas3 is involved in acetylation of H3K9 and H3K14 in effector loci and in effector gene activation during plant infection. We propose that Sas3-mediated histone acetylation is required for spatiotemporal activation of effector genes and virulence of Z. tritici. IMPORTANCEPathogen infections require the production of effectors that enable host colonization. Effectors have diverse functions and are only expressed at certain stages of the infection cycle. Thus, effector genes are tightly regulated by several mechanisms, including chromatin remodeling. Here, we investigate the role of histone acetylation in effector gene activation in the fungal wheat pathogen Zymoseptoria tritici. We demonstrated that lysine acetyltransferases (KATs) are essential for the spatiotemporal regulation of effector genes. We show that two KATs, Sas3 and Gcn5, are involved in leaf symptom development and pycnidia formation. Importantly, our results indicated that Sas3 controls histone acetylation of effector loci and is a regulator of effector gene activation during stomatal penetration. Overall, our work demonstrates the key role of histone acetylation in regulating gene expression associated with plant infection.

plant biology↗

bioRxiv2021

Soil composition and plant genotype determine benzoxazinoid-mediated plant-soil feedbacks in cereals

Plant-soil feedbacks refer to effects on plants that are mediated by soil modifications caused by the previous plant generation. Maize conditions the surrounding soil by secretion of root exudates including benzoxazinoids (BXs), a class of bioactive secondary metabolites. Previous work found that a BX- conditioned soil microbiota enhances insect resistance while reducing biomass in the next generation of maize plants. Whether these BX-mediated and microbially driven feedbacks are conserved across different soils and response species is unknown. We found the BX-feedbacks on maize growth and insect resistance conserved between two arable soils, but absent in a more fertile grassland soil, suggesting a soil-type dependence of BX feedbacks. We demonstrated that wheat also responded to BX-feedbacks. While the negative growth response to BX-conditioning was conserved in both cereals, insect resistance showed opposite patterns, with an increase in maize and a decrease in wheat. Wheat pathogen resistance was not affected. Finally and consistent with maize, we found the BX-feedbacks to be cultivar specific. Taken together, BX- feedbacks affected cereal growth and resistance in a soil and genotype dependent manner. Cultivar-specificity of BX-feedbacks is a key finding, as it hides the potential to optimize crops that avoid negative plant-soil feedbacks in rotations.

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↗

bioRxiv2019

A secreted LysM effector protects fungal hyphae through chitin-dependent homodimer polymerization

Plants trigger immune responses upon recognition of fungal cell wall chitin, followed by the release of various antimicrobials, including chitinase enzymes that hydrolyze chitin. In turn, many fungal pathogens secrete LysM effectors that prevent chitin recognition by the host through scavenging of chitin oligomers. We previously showed that intrachain LysM dimerization of the Cladosporium fulvum effector Ecp6 confers an ultrahigh-affinity binding groove that competitively sequesters chitin oligomers from host immune receptors. Additionally, particular LysM effectors are found to protect fungal hyphae against chitinase hydrolysis during host colonization. However, the molecular basis for the protection of fungal cell walls against hydrolysis remained unclear. Here, we determined a crystal structure of the single LysM domain-containing effector Mg1LysM of the wheat pathogen Zymoseptoria tritici and reveal that Mg1LysM is involved in the formation of two kinds of dimers; a chitin-dependent dimer as well as a chitin-independent homodimer. In this manner, Mg1LysM gains the capacity to form a supramolecular structure by chitin-induced oligomerization of chitin-independent Mg1LysM homodimers, a property that confers protection to fungal cell walls against host chitinases.

microbiology↗

bioRxiv2018

A fungal avirulence factor encoded in a highly plastic genomic region triggers partial resistance to septoria tritici blotch

O_LICultivar-strain specificity in the wheat-Zymoseptoria tritici pathosystem determines the infection outcome and is controlled by resistance genes on the host side, of which many have been identified. However, on the pathogen side, the molecular determinants of specificity are largely unknown.\nC_LIO_LIWe used genetic mapping, targeted gene disruption and allele swapping to characterize the recognition of the new avirulence factor Avr3D1. We then combined population genetic and comparative genomic analyses to estimate the evolutionary trajectory of Avr3D1.\nC_LIO_LIAvr3D1 is specifically recognized by cultivars harboring the resistance gene Stb7 and triggers a strong defence response without preventing pathogen infection and reproduction. Avr3D1 resides in a cluster of putative effector genes located in a region populated by independent transposable element insertions. The gene is present in all 132 investigated strains and is highly polymorphic, with a total of 30 different protein variants. We demonstrated that certain amino acid mutations in Avr3D1 led to evasion of recognition.\nC_LIO_LIThese results demonstrate that quantitative resistance and gene-for-gene interactions are not mutually exclusive per se. Location of avirulence genes in highly plastic genomic regions likely facilitates accelerated evolution that enables escape from recognition by resistance proteins.\nC_LI

plant biology↗

bioRxiv2016

Verticillium dahliae LysM effectors differentially contribute to virulence on plant hosts

Chitin-binding LysM effectors contribute to virulence of various plant pathogenic fungi that are causal agents of foliar diseases. Here, we report on LysM effectors of the soil-borne fungal vascular wilt pathogen Verticillium dahliae. Comparative genomics revealed three core LysM effectors that are conserved in a collection of V. dahliae strains. Remarkably, and in contrast to the previously studied LysM effectors of other plant pathogens, no expression of core LysM effectors was monitored in planta in a taxonomically diverse panel of host plants. Moreover, targeted deletion of the individual LysM effector genes in V. dahliae strain JR2 did not compromise virulence in infections on Arabidopsis, tomato or Nicotiana benthamiana. Interestingly, an additional lineage-specific LysM effector is encoded in the genome of V. dahliae strain VdLs17 but not in any other V. dahliae strain sequenced to date. Remarkably, this lineage-specific effector is expressed in planta and contributes to virulence of V. dahliae strain VdLs17 on tomato, but not on Arabidopsis or on N. benthamiana. Functional analysis revealed that this LysM effector binds chitin, is able to suppress chitin-induced immune responses, and protects fungal hyphae against hydrolysis by plant hydrolytic enzymes. Thus, in contrast to the core LysM effectors of V. dahliae, this lineage-specific LysM effector of strain VdLs17 contributes to virulence in planta.

plant biology↗