Biology subjects

Pouzet, C.

Publications and source records attributed to Pouzet, C..

8 recordsLinked to original sources

bioRxiv2026

Leaf hydraulics is a core component of plant immunity

Hydathodes at leaf margins mediate guttation of xylem-derived fluids and serve as primary entry sites for adapted vascular bacterial pathogens such as Xanthomonas campestris. Infection of Arabidopsis mutants with fewer hydathodes resulted in spontaneous mesophyll water-soaking and revealed unexpectedly-large pathogen populations explained by direct infection of the mesophyll niche through stomata and subsequent proliferation. Physical blockage of hydathodes also induced mesophyll water-soaking and enhanced bacterial growth in both Arabidopsis and cauliflower leaves. These findings reveal a dual role for hydathodes as primary sites of infection while being essential to restrict pathogen proliferation in nonvascular tissues. More broadly, our study identifies leaf hydraulics and guttation as central components of water immunity in vascular plants.

plant biology↗

bioRxiv2023

Medicago truncatula SOBIR1 controls specificity in the Rhizobium-legume symbiosis

Medicago truncatula Nod Factor Perception (MtNFP) is a lysin-domain Receptor-Like Kinase (LysM-RLK) that plays a key role in the Rhizobium-legume symbiosis, and is involved in plant immunity. MtNFP also has an inactive kinase domain, suggesting that the protein is involved in different receptor complexes. Using the MtNFP pseudo-kinase domain as a bait in a Yeast two Hybrid screen, we identified M. truncatula SUPPRESSOR OF BIR1 (MtSOBIR1) as a new interactor of MtNFP. We showed that an interaction between the two RLKs can occur in planta and that the kinase domain of MtSOBIR1 is active and can transphosphorylate the pseudo-kinase domain of MtNFP. Like in other plants, our data suggest a positive role of MtSOBIR1 in immunity; MtSOBIR1 could functionally complement an Atsobir1 mutant for defence activation, and a Mtsobir1 mutant was defective in pathogen-induced defence gene expression. We also showed that MtSOBIR1 has a symbiotic role with Mtsobir1 mutants showing a strong symbiotic phenotype in a plant genotype- and rhizobial strain-specific manner. The symbiotic role was apparent both at an early stage of rhizobial infection and in nodules. Together, these data suggest that, like MtNFP, MtSOBIR1 has a dual role, and can control immunity in both pathogenic and beneficial situations, with positive or negative roles, respectively.

plant biology↗

bioRxiv2022

The neighboring genes AvrLm10A and AvrLm10B are part of a large multigene family of cooperating effector genes conserved in Dothideomycetes and Sordariomycetes

With only a few exceptions, fungal effectors (small secreted proteins) have long been considered as species- or even isolate-specific. With the increasing availability of high-quality fungal genomes and annotations, trans-species or trans-genera families of effectors are being uncovered. Two avirulence effectors, AvrLm10A and AvrLm10B, of Leptosphaeria maculans, the fungus responsible for stem canker of oilseed rape, are members of such a large family of effectors. AvrLm10A and AvrLm10B are neighboring genes, organized in divergent transcriptional orientation. Sequence searches within the L. maculans genome show that AvrLm10A/AvrLm10B belong to a multigene family comprising five pairs of genes with a similar tail-to-tail organization. The two genes in a pair always had the same expression pattern and two expression profiles were distinguished, associated with the biotrophic colonization of cotyledons and / or petioles and stems. Of the two protein pairs further investigated Lmb_jn3_08094/Lmb_jn3_08095 and Lmb_jn3_09745 / Lmb_jn3_09746, one (Lmb_jn3_09745 / Lmb_jn3_09746) had the ability to physically interact, similarly to what was previously described for the AvrLm10A/AvrLm10B pair. AvrLm10A homologues are present in more than 30 Dothideomycete and Sordariomycete plant-pathogenic fungi whereas fewer AvrLm10B homologues were identified. One of the AvrLm10A homologues, SIX5, is an effector from Fusarium oxysporum f.sp. lycopersici physically interacting with the avirulence effector Avr2. We found that AvrLm10A homologues were associated with at least eight distinct putative effector families, suggesting an ability of AvrLm10A/SIX5 to cooperate with diverse effectors. These results point to a general role of the AvrLm10A/SIX5 protein as a cooperator protein, able to interact with diverse families of effectors whose encoding gene is co-regulated with the neighboring AvrLm10A homologue.

plant biology↗

bioRxiv2021

A newly-evolved chimeric lysin motif receptor-like kinase in Medicago truncatula spp. tricycla R108 extends its Rhizobia symbiotic partnership

O_LIRhizobial lipochitooligosaccharidic Nod factors (NFs), specified by nod genes, are the primary determinants of host specificity in the legume-Rhizobia symbiosis. C_LIO_LIWe examined the nodulation ability of Medicago truncatula cv Jemalong A17 and M. truncatula ssp. tricycla R108 with the Sinorhizobium meliloti nodF/nodL mutant, which produces modified NFs. We then applied genetic and functional approaches to study the genetic basis and mechanism of nodulation of R108 by this mutant. C_LIO_LIWe show that the nodF/nodL mutant can nodulate R108 but not A17. Using genomics and reverse genetics, we identified a newly-evolved, chimeric LysM receptor-like kinase gene in R108, LYK2bis, which is responsible for the phenotype and can allow A17 to gain nodulation with the nodF/nodL mutant. We found that LYK2bis is involved in nodulation by mutants producing non-O-acetylated NFs and interacts with the key receptor protein NFP. Many, but not all natural S. meliloti and S. medicae strains tested require LYK2bis for efficient nodulation of R108. C_LIO_LIOur findings reveal that a newly-evolved gene in R108, LYK2bis, extends nodulation specificity to mutants producing non-O-acetylated NFs and is important for nodulation by many natural Sinorhizobia. Evolution of this gene may present an adaptive advantage to allow nodulation by a greater variety of strains. C_LI

plant biology↗

bioRxiv2021

An NLR Integrated Decoy toolkit to identify plant pathogen effector targets

Plant resistance genes (or NLR "Nod-like Receptors") are known to contain atypical domains procuring them with a decoy capacity. Some of these integrated domains (or ID) allow the plant to lure the virulence determinants ("effectors") of pathogens and triggering a specific NLR immune reaction. In this work, our goal was to generate a library of known IDs that could be screened with plant pathogen effectors in order to identify putative new effector virulence targets and NLR-effector pairs. We curated the IDs contained in NLRs from seven model and crop plant species. We cloned 52 IDs representing 31 distinct Pfam domains. This library was screened for interaction by yeast-two-hybrid with a set of 31 conserved Ralstonia solanacearum type III effectors. This screening and the further in planta interaction assay allowed us to identify three interactions, involving different IDs (kinase, DUF3542, WRKY) and two type III effectors (RipAE and PopP2). PopP2 was found to physically interact with ID#85, an atypical WRKY domain integrated in the GmNLR-ID85 NLR protein from Soybean. Using a imaging method in living plant cells, we showed that PopP2 associates with ID#85 in the nucleus. But unlike the known WRKY-containing Arabidopsis RRS1-R NLR receptor, this newly identified soybean WRKY domain could not be acetylated by PopP2 and its atypical sequence (WRKYGKR) also probably renders it inefficient in plant immunity triggering. This ID toolkit is available for screening with other plant pathogen effectors and should prove useful to discover new effectors targets and potentially engineer new plant resistance genes.

plant biology↗

bioRxiv2020

A DEAD BOX RNA helicase from Medicago truncatula is hijacked by an RNA-binding effector from the root pathogen Aphanomyces euteiches to facilitate host infection

Microbial effectors from plant pathogens are molecules that target host components to facilitate colonization. While eukaryotic pathogens are virtually able to produce hundreds of effectors, the molecular mechanisms allowing effectors to promote infection are still largely unexplored. Here we show that the effector AeSSP1256 from the soilborne oomycete pathogen Aphanomyces euteiches is able to interact with plant RNA. Heterologous expression of AeSSP1256 delays Medicago truncatula host roots development and facilitate pathogen colonization. Transcriptomic analyses of AeSSP1256-expressing roots show a downregulation of genes implicated in ribosome biogenesis pathway. A yeast-two hybrid approach reveals that AeSSP1256 associates with a nucleolar L7 ribosomal protein and a M. truncatula RNA helicase (MtRH10) orthologous to the Arabidopsis RNA helicase RH10. Association of AeSSP1256 with MtRH10 impaired the capacity of MtRH10 to bind nucleic acids. Promoter:GUS composite plants revealed that MtRH10 is expressed preferentially in the meristematic root cells. Missense MtRH10 plants displayed shorter roots with developmental delay and are more susceptible to A. euteiches infection. These results show that the effector AeSSP1256 facilitates pathogen infection by causing stress on plant ribosome biogenesis and by hijacking a host RNA helicase involved in root development and resistance to root pathogens.

plant biology↗

bioRxiv2020

Reconstitution of intestinal stem cell niche in vitro with pharmacological inhibitors or L-WRN conditioned medium differentially regulates epithelial proliferation, differentiation and barrier function in rabbit caecum organoids

Intestinal organoids are self-organized 3-dimensional (3D) structures formed by a single layer of polarized epithelial cells. This innovative in vitro model is highly relevant to study physiology of the intestinal epithelium and its role in nutrition and barrier function. However, this model has never been developed in rabbits, while it would have potential applications for biomedical and veterinary research. Here, we cultured rabbit caecum organoids with either pharmacological inhibitors (2Ki medium) or L-WRN cells conditioned medium (L-WRN CM) to reconstitute the intestinal stem cell niche in vitro. Large spherical organoids were obtained with the 2Ki medium and this morphology was associated with a high level of proliferation and stem cells markers gene expression. In contrast, organoids cultured with L-WRN CM had a smaller diameter; a greater cell height and part of them were not spherical. When the L-WRN CM was used at low concentration (5%) for two days, the gene expression of stem cells and proliferation markers were very low, while absorptive and secretory cells markers and antimicrobial peptides were elevated. Epithelial cells within organoids were polarized in 3D cultures with 2Ki medium or L-WRN CM (apical side towards the lumen). We cultured dissociated organoid cells in 2D monolayers, which allowed accessibility to the apical compartment. Under these conditions, actin stress fibers were observed with the 2Ki medium, while perijonctionnal localization of actin was observed with the L-WRN CM suggesting, in 2D cultures as well, a higher differentiation level in the presence of L-WRN CM. In conclusion, rabbit caecum organoids cultured with the 2Ki medium were more proliferative and less differentiated than organoids cultured with L-WRN CM. We propose that organoids cultured with the 2Ki medium could be used to rapidly generate in vitro a large number of rabbit intestinal epithelial stem cells while organoids cultured with the L-WRN CM represent a suitable model to study differentiated rabbit epithelium.

cell biology↗

bioRxiv2017

A bacterial GW-effector targets Arabidopsis AGO1 to promote pathogenicity and induces Effector-triggered immunity by disrupting AGO1 homeostasis

Pseudomonas syringae type III effectors were previously shown to suppress the Arabidopsis microRNA (miRNA) pathway through unknown mechanisms. Here, we first show that the HopT1-1 effector promotes bacterial growth by suppressing the Arabidopsis Argonaute 1 (AGO1)-dependent miRNA pathway. We further demonstrate that HopT1-1 interacts with Arabidopsis AGO1 through conserved glycine/tryptophan (GW) motifs, and in turn suppresses miRNA function. This process is not associated with a general decrease in miRNA accumulation. Instead, HopT1-1 reduces the level of AGO1-associated miRNAs in a GW-dependent manner. Therefore, HopT1-1 alters AGO1-miRISC activity, rather than miRNA biogenesis or stability. In addition, we show that the AGO1-binding platform of HopT1-1 is essential to suppress the production of reactive oxygen species (ROS) and of callose deposits during Pattern-triggered immunity (PTI). These data imply that the RNA silencing suppression activity of HopT1-1 is intimately coupled with its virulence function. Overall, these findings provide sound evidence that a bacterial effector has evolved to directly target a plant AGO protein to suppress PTI and cause disease.

plant biology↗