Biology subjects

Castel, B.

Publications and source records attributed to Castel, B..

9 recordsLinked to original sources

bioRxiv2026

A novel pathosystem between Aeschynomene evenia and Aphanomyces euteiches reveals new immune components in quantitative legume root-rot resistance.

Legumes are pivotal for sustainable agriculture, yet their productivity is hindered by soilborne pathogens such as Aphanomyces euteiches. This study introduces Aeschynomene evenia as a novel model to investigate legume immunity and its interplay with Nod factor-independent symbiosis (NFIS). Inoculation of A. evenia accessions with A. euteiches strains revealed a range of quantitative resistance levels. Phenotypic and cytological analyses showed a compatible interaction, including root browning, intracellular colonisation, and oospore production; along with partial resistance traits such as phenolic accumulation at the endodermal barrier. Transcriptomic analyses at 1 and 3 dpi identified 3,403 differentially expressed genes (DEGs), with upregulated genes associated with pathogen perception, immune signalling and specialised metabolite biosynthesis. Kinase-mediated signalling, ROS homeostasis, and WRKY transcription factors were among the most enriched functional categories. Comparative transcriptomics with Medicago truncatula confirmed conserved immune responses, while A. evenia displayed broader transcriptional repression. Integration with symbiotic transcriptomic data revealed overlapping gene signatures, including AeRLCK2 and AeCRK, previously found to be NFIS-specific, as putative dual-function kinases. Aerlck2 and Aecrk mutants exhibited enhanced resistance to A. euteiches, supporting their roles in immune regulation. This work positions A. evenia-A. euteiches as a valuable system to dissect legume quantitative resistance and its intersection with symbiosis.

plant biology↗

bioRxiv2025

EPP1 is an ancestral component of the plant Common SymbiosisPathway

The success of plants on land has been enabled by mutualistic intracellular associations with microbes for 450 million years (Delaux and Schornack 2021). Because of their intracellular nature, the establishment of these interactions requires tight regulation by the host plants. In particular, three genes - SYMRK, CCaMK and CYCLOPS - form the core of an ancestral common symbiosis pathway (CSP) for intracellular symbioses, and are conserved since the most recent common ancestor of land plants (Radhakrishnan et al. 2020; Delaux et al. 2015; Wang et al. 2010; Parniske 2008). Here, we describe EPP1 as a fourth gene committed to the CSP. Among land plants, EPP1 is conserved only in species able to associate with at least one type of intracellular symbiont. We found that loss-of-function epp1 mutants or EPP1 knock-down lines in four clades of land plants - legumes, Solanaceae, monocots and bryophytes - are all impaired in their ability to associate with arbuscular mycorrhizal fungi. We discovered that the plasma membrane-localized receptor-like SYMRK phosphorylates EPP1 on a conserved serine residue and that this phosphorylation is essential for symbiosis. Using a gain-of-function approach, we demonstrate that EPP1 is upstream of the nuclear kinase CCaMK. We propose that EPP1 is an ancestral component of the essential pathway that has regulated plant symbiosis for half a billion years.

plant biology↗

bioRxiv2025

Exploring fern pathosystems and immune receptors to bridge gaps in plant immunity

Land plants include angiosperms, bryophytes, lycophytes and ferns, each of which may deploy distinct strategies to resist pathogens. Here, we investigate fern-pathogen interactions by characterizing novel pathosystems and analysing the diversity of fern immune receptors. A collection of fern species was inoculated with a diverse set of microbes, and disease symptoms were assessed. We further leveraged published genome mining tools to analyse the diversity of RECEPTOR-LIKE KINASES, RECEPTOR-LIKE PROTEINS (RLKs/RLPs) and NUCLEOTIDE-BINDING AND LEUCINE-RICH REPEATS (NLRs), along with key immune signalling components, in ferns. Our results reveal that ferns exhibit a range of responses to pathogens, including non-host resistance and specific resistance mechanisms. Among ten ferns tested, Pteris vittata displays the broadest spectrum of pathogen compatibility. Genome mining indicates that ferns encode a diverse repertoire of putative immune receptors, antimicrobial peptides and mediators of systemic acquired resistance. Ferns possess numerous RLKs/RLPs, resembling those required for cell-surface immunity in angiosperms. They also encode diverse NLRs, including a previously undescribed class with a disordered N-terminal domain, termed disN-NLR. These findings provide insights into disease resistance evolution and open promising perspectives for crop protection strategies.

plant biology↗

bioRxiv2024

A helper NLR targets organellar membranes to trigger immunity

Upon activation, plant NLR immune receptors are known to assemble into oligomeric resistosomes that insert into the plasma membrane, forming Ca2+-permeable channels and triggering immunity. Here, we show that the RPW8-like coiled-coil (CCR-) NLR NRG1 primarily targets organelles instead of the plasma membrane. Unlike canonical CC-NLRs, activated NRG1 accumulates at the chloroplast envelope and channels stromal Ca2+ into the cytosol. AlphaFold modeling of the NRG1 resistosome reveals an unusually long N-terminal membrane-insertion structure that would span the double chloroplast membranes. Nanobody-mediated relocalization shows functional membrane specificity: chloroplast trapping abolishes activity of the canonical helper CC-NLR NRC4 but not NRG1. NRG1 orthologs, from non-flowering lineages to angiosperms, target chloroplasts, suggesting that organelle-centered defense dates back to at least [~]360 million years. We propose that coiled-coil NLR diversification has enabled compartment-specific immune signaling to capture diverse Ca2+ stores.

plant biology↗

bioRxiv2024

Berberine Bridge enzyme-like oxidases orchestrate homeostatic control and signaling of oligogalacturonides in defense and wounding

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 tissue damage, and physiological CW remodeling. Berberine Bridge Enzyme-like (BBE-l) proteins named OG oxidases (OGOXs) have been proposed to govern OGs homeostasis, which is necessary 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 (oxOGs). The ogox1/2-deficient plants have elevated levels of OGs, while plants overexpressing OGOX1 accumulate oxOGs. The balance between OGs and oxOGs affect disease resistance against Pseudomonas syringae pv tomato, Pectobacterium carotovorum, and Botrytis cinerea depending on the microbial capacity to respond to OGs and metabolize oxOGs. Gene expression upon plant infiltration with OGs reveals that OGOXs orchestrate OG signaling in defense as well as upon tissue damage, pointing to these enzymes as apoplastic players in immunity and tissue repair. TeaserOxidases control the homeostasis of oligogalacturonides in the cell wall and play a pivotal role in the plant immunity.

plant biology↗

bioRxiv2022

Generation of inheritable A-to-G transitions using adenine base editing and NG-PAM Cas9 in Arabidopsis thaliana

CRISPR/Cas9 technology is an important tool for functional genomics and crop improvement. It can be used to generate mutations at precise positions in the genome. Base editors consist of deaminase components and Cas9 to specify the type of mutation, such as C-to-T (cytosine base editors) or A-to-G (adenine base editors) transition. Available adenine base editor vectors usually make use of canonical Cas9, which limits their use to 5-NGG-3 containing targets. We combined a relaxed variant of SpCas9 that uses 5-NG-3 containing targets with the adenine base editor containing TadA7.10 or TadA8e to make a set of vectors. By using a phenotype-based screen, we found that our vectors efficiently induce A-to-G somatic mutations in a 5-NGG-3 PAM context in Arabidopsis thaliana up to 81% efficiency. Such mutations are inheritable at the homozygous stage in T2. Among tested vectors, pECNUS4 (Addgene #184887), which carries TadA8e, showed highest efficiency at generating a stable A-to-G transition in a 5-NGH-3 PAM context in the gene DM3. Using this vector, we were able to recreate a naturally occurring allele of DM3 in two generations without the transgene. pECNUS4 is a new component of the CRISPR toolbox to be used for introducing desired adenine base transitions with an expanded target window for functional genomic research and trait improvement.

plant biology↗

bioRxiv2021

Evolutionary trade-offs at the Arabidopsis WRR4A resistance locus underpin alternate Albugo candida recognition specificities

The oomycete Albugo candida causes white rust of Brassicaceae, including vegetable and oilseed crops, and wild relatives such as Arabidopsis thaliana. Novel White Rust Resistance (WRR)-genes from Arabidopsis enable new insights into plant/parasite co-evolution. WRR4A from Arabidopsis accession Col-0 provides resistance to many but not all white rust races, and encodes a nucleotide-binding (NB), leucine-rich repeat (LRR) (NLR) immune receptor protein. Col-0 WRR4A resistance is broken by a Col-0-virulent isolate of A. candida race 4 (AcEx1). We identified an allele of WRR4A in Arabidopsis accession Oy-0 and other accessions that confers full resistance to AcEx1. WRR4AOy-0 carries a C-terminal extension required for recognition of AcEx1, but reduces recognition of several effectors recognized by the WRR4ACol-0 allele. WRR4AOy-0 confers full resistance to AcEx1 when expressed as a transgene in the oilseed crop Camelina sativa. SignificanceA C-terminal extension in an allele of the Arabidopsis resistance-protein WRR4A changes effector recognition specificity, enabling the WRR4AOy-0 allele to confer immunity to Albugo candida races that overcome the WRR4ACol-0 allele. This resistance can be transferred to the oil-producing crop Camelina sativa. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=137 SRC="FIGDIR/small/437434v1_ufig1.gif" ALT="Figure 1"> View larger version (29K): org.highwire.dtl.DTLVardef@a68de6org.highwire.dtl.DTLVardef@ae0addorg.highwire.dtl.DTLVardef@4b3384org.highwire.dtl.DTLVardef@12330b2_HPS_FORMAT_FIGEXP M_FIG C_FIG

plant biology↗

bioRxiv2019

An rpw8 quadruple mutant of Arabidopsis Col-0 is partially compromised in bacterial and fungal resistance

The plant immune system relies on both cell-surface and intracellular NLR (nucleotide-binding, leucine-rich repeat) receptors. NLRs respond to pathogen effectors and activate effector-triggered immunity: a cocktail of responses, often accompanied by cell death, resulting in resistance. RPW8 encodes an unusual non-NLR Resistance (R) protein and confers broad-spectrum powdery mildew resistance. It requires genetic components also required by some NLRs, resembles the HeLo-containing protein MLKL (necroptosis executor in animals) and HET-S (cell death executor in fungi) and is targeted to the extra-haustorial membrane during powdery mildew infection by its N-terminal non-cleaved signal anchor domain. RPW8 displays extensive recent duplication events in Arabidopsis and certain alleles can induce oligomerisation-dependent activation of the NLR RPP7. All these features enabled us to formulate hypotheses for RPW8 function: (1) RPW8 could be a cell death executor for defence against pathogens. (2) RPW8 could be a decoy for effector targets. To test these hypotheses, we generated a quadruple knock-out mutant of the four RPW8-homologous copies in Arabidopsis Col-0, using CRISPR. The mutant still displays cell death upon activation of four well-characterised NLRs. However, it is partially impaired in powdery mildew resistance and also in bacterial resistance. Interestingly Col-0_rpw8 is delayed in flowering transition. In conclusion, RPW8 plays a broad role in immunity and plant development, beyond resistance to powdery mildew. There is no evidence that it is involved in executing ETI-associated cell death.

plant biology↗

bioRxiv2018

Optimization of T-DNA architecture for Cas9-mediated mutagenesis in Arabidopsis

Bacterial CRISPR systems have been widely adopted to create operator-specified site-specific nucleases. Such nuclease action commonly results in loss-of-function alleles, facilitating functional analysis of genes and gene families We conducted a systematic comparison of components and T-DNA architectures for CRISPR-mediated gene editing in Arabidopsis, testing multiple promoters, terminators, sgRNA backbones and Cas9 alleles. We identified a T-DNA architecture that usually results in stable (i.e. homozygous) mutations in the first generation after transformation. Notably, the transcription of sgRNA and Cas9 in head-to-head divergent orientation usually resulted in highly active lines. Our Arabidopsis data may prove useful for optimization of CRISPR methods in other plants.

plant biology↗