Biology subjects

Choi, J.

Publications and source records attributed to Choi, J..

At least 73 records · Page 4Linked to original sources

bioRxiv2025

Cross-Species Transcriptomic Integration Reveals a Conserved, MIRO1-Mediated Macrophage-to-T Cell Signaling Axis Driving Immunosuppression in Glioma

Mitochondrial regulators are increasingly recognized for their influence on immune signaling within the tumor microenvironment (TME). In glioma, where immunosuppression limits therapeutic efficacy, we investigate how targeting the mitochondrial protein MIRO1 alters the TME. We combine single-nucleus RNA sequencing of murine gliomas treated in vivo with a MIRO1-binding compound and bulk RNA sequencing of human glioma resections treated with the same compound ex vivo. Cross-species transcriptomic integration reveals a MIRO1-responsive program in the TME. Among shared targets, we identify PARP11/Parp11 as a consistently upregulated gene in glioma that is downregulated following MIRO1-binding compound treatment in both human and mouse gliomas. Cell-cell communication analysis shows that a specific cluster of macrophages (MAC1), which exhibits robust Parp11 and Pdl1 (encoding PD-L1) expression, sends immunosuppressive signals to CD8+ cytotoxic T cells, and may receive prostaglandin E{square} signals from another cluster of macrophages (MAC4). Targeting MIRO1 eliminates this cell circuitry and reduces the tumor cell population. Our study provides a transcriptomic framework for understanding mitochondria-immune crosstalk and nominates MIRO1-PARP11 as a potential effector axis of brain immune dysfunction. Summary BlurbTranscriptomic integration of single-nucleus RNA sequencing of murine gliomas and bulk RNA sequencing of human gliomas reveals an immunosuppressive signaling axis in the glioma TME, mediated by MIRO1.

cancer biology↗

bioRxiv2025

Fast-conducting mechanonociceptors uniquely engage reflexive and affective pain circuitry to drive protective responses

Nociceptors detect damaging stimuli and evoke pain in healthy animals. We conducted an optogenetic activation screen to identify genetically defined nociceptor populations that elicit place aversion and nocifensive behaviors in response to stimulation. Smr2Cre- and Bmpr1bCre-labeled A{delta} high-threshold mechanoreceptors (HTMRs) emerged as two of the few nociceptor populations, and we focused on investigating their physiological, morphological, functional, and synaptic properties. These neurons densely innervate skin and other organs, are activated only by intense, potentially damaging stimuli, and are necessary for protective responses to sharp mechanical stimuli. Centrally, A{delta}-HTMRs projections span multiple spinal segments and terminate across spinal cord laminae, forming strong, monosynaptic connections onto anterolateral tract projection neurons, including antenna cells of the deep dorsal horn. A{delta}-HTMRs also engage a local spinal reflex circuit enabling a remarkably rapid limb withdrawal. Thus, A{delta}-HTMRs are myelinated nociceptors with unique properties that can be exploited for development of new analgesics.

neuroscience↗

bioRxiv2025

Neo-sex chromosomes are not correlated with ecology or environment in eutherian mammals

The XX/XY chromosome system is highly conserved in therian mammals. Despite this evolutionary persistence, multiple variant sex chromosome systems exist in mammals. The potential contribution of genomic conflict to the evolution of neo-sex chromosomes has been studied extensively, while the influence of climate and ecology on the emergence and persistence of neo-sex chromosomes is less well understood. Building on previous literature that suggests that ecoclimatic factors can influence intralocus sexual conflict and other forms of genome evolution, we tested whether neo-sex chromosomes in mammals are associated with these factors. We conducted a phylogenetic logistic regression in three representative mammal families using a dataset of variant mammalian sex chromosomes and a database of tetrapod traits and environmental associations. We also incorporated a dataset of mammal karyotypes to test for potential signatures of meiotic drive. When using a single phylogeny, none of the seven ecoclimatic variables tested nor chromosome morphology were significantly correlated with neo-sex chromosomes. However, correlations between neo-sex chromosomes and both range size and mean annual temperature were data-dependent and sensitive to differences in tree topology, demonstrating the importance of accounting for alternative evolutionary hypotheses in comparative methods.

evolutionary biology↗

bioRxiv2025

CRISPR-Induced NUT Suppression Promotes Differentiation and Enhances Trop2-Targeted Immunocytokine Response in NUT Carcinoma

NUT carcinoma (NC) is an aggressive malignancy driven by NUTM1 gene rearrangements with limited therapeutic options. Here, we show that direct suppression of NUTM1 using CRISPR/Cas9 induces squamous-like differentiation and upregulates TROP2 expression in NC cells. Building on this finding, we developed a TROP2-interferon beta (IFN-{beta}) mutein immunocytokine that selectively targets TROP2-expressing tumors. Combined NUTM1 suppression and TROP2-targeted immunotherapy synergistically enhanced cytotoxic and immune-mediated responses in vitro. Transcriptomic and spatial analyses of NC patient tumors revealed that differentiation status correlates with TROP2 expression, upregulated immune pathways, and favorable clinical outcomes. Our results suggest that overcoming differentiation blockade not only alters tumor phenotype but also creates a more immune-permissive microenvironment. These findings highlight the therapeutic potential of sequential tumor reprogramming followed by targeted immunotherapy in treating NC and propose a broader strategy for overcoming differentiation blockade in fusion-driven cancers.

cancer biology↗

bioRxiv2025

Parallel Evolution of Bacteroidota as Long-Term Endosymbionts of Insects

Symbiotic relationships transform diverse aspects of both symbiont and host biology. The most visible changes include a massive reduction of the endosymbiont genome and the development of novel host organs, cells, and compartments specialized for harboring the symbionts. However, many insect symbiosis studies have previously focused either on Proteo-bacteria or only on a particular symbiosis stage, limiting our broad understanding of how and why symbiont diversity arises from specific microbial clades, how the symbiont genomes erode over evolutionary time, and what the consequences of symbiosis are for diverse host-symbiont pairs. Thanks to the repeated gains and losses of nutritional symbionts, scale insects provide an ideal evolutionary playground for tracking the parallel transitions of insect symbionts that originated as independent evolutionary replicates from the same bacterial phylum. Using extensive genome sampling across the scale insect phylogeny, we recapitulated the path of Bacteroidota transitioning from recently established host-associated bacteria to highly specialized insect endosymbionts with minimal gene sets. Their genomes exhibit strikingly parallel patterns of gene loss and pseudogenization across all gene categories, with some stochastic differences in essential genes for genetic processing and amino acid biosynthesis. In addition to the genetic transition, we show with imaging methods that the symbiotic cells and organs exhibit a trend from more dispersed bacteriocytes to highly compact (and likely more specialized) bacteriomes, which are closely localized to the hosts digestive system. Our results outline at both genomic and cellular levels a recurrent path by which insect symbioses independently arise, are temporarily maintained for up to several hundred million years, and then are replaced by new symbionts that repeat the process. The gradual nature of the process implies that the outcomes of symbiosis initially depend on how professional vs. naive the host and symbiont are. Over evolutionary time, compatible host-symbiont lineages emerge from these interactions and become preferred.

evolutionary biology↗

bioRxiv2025

Unraveling diel regulation of cuticle biosynthesis

The plant cuticle is vital for growth and adaptation to environmental stresses. Although cuticle biosynthesis is dynamically regulated by environmental cues, the molecular mechanisms integrating these external signals with intracellular responses remain largely unknown. Here, we discovered that cuticle biosynthesis is precisely orchestrated by two distinct regulatory modules acting in synchrony with the diel cycle. Daylight is perceived by phytochrome B (phyB), which suppresses cuticular wax biosynthesis by degradation of PIF4, a phytochrome-interacting bHLH factor that activates wax biosynthetic genes. This suppression is alleviated when phyB itself is degraded by the E3 ubiquitin ligase LRB, leading to diurnal activation of PIF4. In contrast, loss-of-function and transcriptional assays of CFLAP1 demonstrated its direct negative role in cutin biosynthesis. At night, the E3 ubiquitin ligase COP1 mediates proteasomal degradation of CFLAP1, thereby promoting cutin accumulation via activation of BDG1. Together, these results reveal that two regulatory modules, LRB-phyB-PIF4 and COP1-CFLAP1 coordinate the diel regulation of cuticle formation, ensuring timely assembly of the protective barrier.

plant biology↗

bioRxiv2025

Genomic diversity and functional potential of facultative bacterial symbionts across scale insects

Microbial symbionts play pivotal roles in the physiology, ecology, and evolution of insects. While obligate symbionts have been extensively characterized in insects feeding on nutritionally poor diets, the diversity and functional roles of facultative bacterial symbionts remain largely unexplored in many insect lineages, including scale insects (Hemiptera: Coccomorpha). Here, we present a genome-resolved metagenomic and comparative genomic analysis of facultative bacterial symbionts across 120 scale insect metagenomes from 20 different families. Our analyses reveal rich and taxonomically diverse facultative symbiont communities, dominated by the Pseudomonadota, such as Wolbachia, Rickettsia, Arsenophonus, and Sodalis. Genomic features reveal substantial variation in genome sizes, coding densities, metabolic potentials, and hostinteraction genes among symbiont clades, indicating lineage-specific lifestyles and host interactions. Interestingly, alphaproteobacterial and gammaproteobacterial symbionts mostly co-occur within their respective hosts. Gammaproteobacterial symbionts exhibit broader metabolic repertoires and potential defense capabilities via the APSE phage toxin cassettes, while alphaproteobacterial symbionts retain reduced metabolic capabilities, Type IV secretion systems, and reproductive manipulation genes (cifAB and wmk). We propose how the symbiont genes related to nutritional provisioning, defensive symbiosis, and reproductive manipulation may influence the biology and evolution of scale insects. Our results provide the first comprehensive genomic overview of facultative bacterial symbionts in scale insects, revealing their evolutionary dynamics and putative functions.

genomics↗

bioRxiv2025

Splicing of HPV16 E6 promotes aggressive invasion in oropharyngeal cancer via endocytosis of E-cadherin

Human papillomavirus-positive oropharyngeal squamous cell carcinoma (HPV+ OPSCC) has become the most common HPV-associated cancer in developed countries, yet a significant subset of patients develops recurrence despite favorable treatment responses. Biomarkers that identify aggressive tumors at diagnosis are therefore needed. In HPV+ cancers, the viral E6 transcript can be expressed as two main variants, the full-length isoform (E6FL) and the spliced E6*I isoform. Here, we investigated the functional and clinical impact of E6FL and E6*I in HPV+OPSCC. Across multiple preclinical models, E6*I promoted migration and aggressive invasion relative to E6FL and was associated with redistribution of E-cadherin away from the cell membrane. In multi-institutional patient cohorts, a previously developed E6FL:E6ALL influence score, which captures E6 splicing-associated host transcriptional biology, was associated with clinical outcomes. Lower scores, reflecting greater E6*I impact, were associated with worse overall survival and recurrence-free survival. Multiplexed immunofluorescence of 75 primary pretreatment biopsies further showed that a lower influence score was linked to reduced membrane and increased cytoplasmic localization of E-cadherin, while a tissue-based E-cadherin localization score was associated with recurrence. Mechanistically, E6*I overexpression promotes E-cadherin internalization, likely through the Rab11-associated trafficking pathway. Splice-switching oligonucleotides that shifted endogenous E6 splicing toward E6FL reduced invasion in two HPV+ OPSCC models. Together, these findings position HPV E6 splicing as a regulatory axis underlying aggressive HPV+ OPSCC biology and support E6 splicing and membrane-to-cytoplasmic ECAD localization as candidate risk-stratification biomarkers.

cancer biology↗

bioRxiv2025

Preselection CD4+CD8+ thymocytes modulate TCR responsiveness following TCRβ selection

Modulation of TCR sensitivity during positive selection is critical to avoid negative selection and direct thymocytes into their appropriate lineage. Thymocytes just prior to positive selection (preselection) are highly responsive to low affinity self-ligands and are also actively rearranging their TCR locus as they await a positive selection signal. Preselection DP thymocytes were thought to be relatively homogeneous and TCR modulation during this stage had not been previously described. Here we provide evidence for progressive gene expression changes within the preselection DP thymocyte population that correlates with a gradual loss of TCR responsiveness and a defect in upregulating TCR target genes associated with the CD4 fate. We relate these observations to the link between positive selection and T cell lineage commitment.

immunology↗

bioRxiv2025

Isolation of Pure Disease Specific Aging Trajectories in Spatial Transcriptomics via the Delta Delta Method

Disentangling normal aging from disease driven transcriptional change remains a major obstacle for spatial genomics. We introduce the Delta-Delta ({Delta}{Delta}) Method, a contrastive trajectory framework that resolves a four-dimensional progression (genes x cell types x brain regions x time) by subtracting the wild type (WT) aging trajectory from the transgenic (TG) trajectory to yield a pure disease trajectory ({Delta}{Delta}log2FC). The method is platform agnostic, integrates with common spatial transcriptomics workflows, and outputs direction and speed of change summaries, enriched pathways, and region and cell type specific maps. In a demonstration using G2-3 -synuclein TG mice and age matched WT controls at 6 and 10 months across hippocampus and midbrain, {Delta}{Delta} uncovered opposite regional dynamics in glutamatergic neurons and a convergent enrichment of RNA splicing pathways, corroborated by alternative splicing analyses. By explicitly modeling time while controlling for aging within each region and cell type, the {Delta}{Delta} Method isolates disease specific molecular programs that are obscured in conventional bulk or single cell analyses, and provides a generalizable framework for trajectory aware mechanistic target prioritization in neurodegeneration and other progressive conditions.

bioinformatics↗

bioRxiv2025

Proteolytic cleavage of G3BP1 by calpain 1 couples NMDAR activation to mTOR-dependent local translation

Ribonucleoprotein (RNP) granules are dynamic, membraneless organelles that sequester translationally repressed mRNAs and RNA-binding proteins, playing a pivotal role in the regulation of localized protein synthesis. While disassembly of RNP granules is essential for reactivating translation, the mechanisms by which neuronal activity regulates this process remain poorly understood. In this study, we show that stimulation of N-methyl-D-aspartate (NMDA) receptor (NMDAR) triggers calcium influx, leading to activation of calpain 1 and subsequent proteolytic cleavage of Ras-GTPase-activating protein binding protein 1 (G3BP1), a core component of stress granules. This cleavage results in the disassembly of G3BP1 granules in the neurites and promotes mTOR-dependent local translation, thereby linking synaptic activity to spatially restricted protein synthesis. Finally, we demonstrate that the NMDAR-calpain 1-G3BP1-mTOR signaling axis contributes to axonal regeneration, establishing proteolytic remodeling of RNP granules as a key mechanism of activity-dependent neural repair, with potential implications for therapeutic intervention in brain injury.

neuroscience↗

bioRxiv2025

Dual checkpoint blockade of glioblastoma with Anti-PD-1 and Anti-LAG-3 promotes expansion of tumor-reactive T cell clones along a unique pathway of differentiation

IDH-wildtype grade IV glioblastoma is the most aggressive adult primary brain tumor and remains refractory to anti-PD-1 monotherapy despite evidence of limited tumor-specific T cell induction. To determine the impact of immune checkpoint inhibitors (ICIs) on glioblastoma T cell transcriptional landscape and repertoire, we conducted paired single-cell RNA sequencing (scRNA-seq) and T cell receptor sequencing (TCR-seq) of tumor-infiltrating lymphocytes (TILs) from patients with untreated, newly diagnosed glioblastoma and from recurrent glioblastoma treated with dual checkpoint blockade targeting PD-1 and LAG-3. Using a validated transcriptional signature, we found that predicted tumor-reactive T cells (TRC) in untreated glioblastomas reside almost exclusively in a clonally expanded GZMKhi population with developmental plasticity, affording them the potential to differentiate into both tissue-resident and terminal effector T cells. Dual ICI therapy induced substantial clonal remodeling, characterized by the recruitment of new TRC from the periphery into the tumor microenvironment (TME) and differentiation into transitional effectors and ultimately terminal effectors along a gradient characterized by simultaneous acquisition of cytotoxic and exhaustion genes, regulated by specific transcriptional, metabolic, and epigenetic programs. Longitudinal clonal tracking in peripheral blood confirmed that with ICI treatment, most TRC expand transiently in circulation prior to tumor infiltration, with peripherally derived clones becoming the major contributor to the GZMKhi TRC that further expand in the tumor. Our study provides the first comprehensive map of T cell clonal dynamics and differentiation in glioblastoma following dual ICIs and highlights a potential mechanism of immune activation and peripheral recruitment of TRC in glioblastoma not previously described. Our results suggest that therapeutic strategies to sustain these GZMKhi early effector and transitional effector T cells may further enhance ICI therapeutic efficacy in glioblastoma.

immunology↗

bioRxiv2025

Versatile HIV Rev-dependent reporter cell system for stringent and sensitive quantification of viral reservoirs, neutralizing antibodies, and restriction factors

Detecting and measuring HIV reservoirs, neutralizing antibodies, and restriction factors are important for HIV cure research and the development of new therapeutics and vaccines. Here we describe the development and validation of several HIV Rev-dependent indicator cell lines for these purposes. These reporter cells come from different T-lymphoblast cell lines, including MOLT-4-R5, SupT1-R5, CEM-SS, A3R5, and from the adherent TZM cell platform based on HeLa clone JC53. These cells express CD4, CXCR4, and various levels of CCR5. We compared these cell lines for responsiveness to both X4 and R5-tropic viruses, and confirmed that reporter expression in these cells is not affected by stimulation from mitogens but is responsive to HIV Tat and Rev, reducing non-specific reporter induction from the leaky LTR promoter. To validate the sensitivity of the Rev-dependent reporter cell systems, we conducted a viral dilution assay with three primary HIV-1 clade C swarms from an adult in Malawi. We also validated the systems for quantifying antibody neutralization and screening restriction factors; these systems are also sensitive for viral outgrowth assays for quantifying viral reservoirs in clinical and basic research settings. Given that the systems can measure HIV accurately in complex environments with mitogens or other substances, they can be used for versatile applications, such as quantifying latent reservoirs, testing inhibitory compounds, conducting neutralizing antibody assays, and identifying new restriction factors.

microbiology↗

bioRxiv2025

PHO2 suppresses arbuscular mycorrhizal symbiosis in high phosphate conditions

Arbuscular mycorrhizal (AM) symbiosis is an ancient relationship formed between most plants and Glomeromycotina fungi, typically in response to phosphate (Pi) limitation in soils. By hosting these fungi in their roots, plants extend their access to essential mineral nutrients and water beyond the rhizosphere, while providing the fungus with carbon in return. This mutualistic symbiosis presents a promising tool for enhancing sustainability in agriculture, as it not only supports plant nutrition but also immunity and wider soil health. However, achieving high crop yields currently relies on supplementing plants with excess Pi, which suppresses AM symbiosis. We found that this suppression is mediated by a key negative regulator of the Pi starvation response (PSR) in rice (Oryza sativa), Phosphate overaccumulator 2 (PHO2). PHO2 encodes an E2 ubiquitin-conjugating enzyme which targets various proteins involved in the PSR in Pi-sufficient conditions for protein degradation. Here we report that pho2 mutants of rice and Nicotiana benthamiana retained high AM fungal colonisation even in high Pi conditions. Our transcriptomic analysis of uninoculated rice roots revealed that pho2 mutants are less sensitive to Pi treatment and retain susceptibility to AM symbiosis by maintaining expression of a core set of AM-related genes gating the early stage AM fungal entry, such as genes involved in strigolactone biosynthesis, LysM-containing plant receptors for fungal molecules, and components of the common symbiosis signalling pathway (CSSP). Furthermore, isotope tracing using 33P and phosphate transporter (PHT1) gene expression patterns collectively suggest enhanced direct and symbiotic Pi overaccumulation in pho2 mutant leaves. Together, our data reveal a new role for PHO2, as a negative regulator of AM colonisation and symbiotic Pi accumulation in shoots.

plant biology↗

bioRxiv2025

Deep learning-based classification of complex intracellular calcium concentration patterns

Intracellular calcium ion (Ca2+) exhibits diverse dynamical behaviors, including complex oscillations such as bursting and chaos. The distinction of diverse dynamical patterns in time series data holds significant biochemical and biophysical implications, as these patterns are intimately related to physiological cellular states associated with health and disease. In this work, we introduce a deep learning framework based on a large kernel convolutional neural network (LKCNN) for the classification of dynamical states of intracellular Ca2+ dynamics. We use a chemical Langevin equation to generate synthetic data for training the LKCNN, simulating intracellular Ca2+ concentration patterns mimicking real experimental traces. We show that the LKCNN framework reliably classifies diverse intracellular Ca2+ dynamical regimes, achieving near 90% accuracy across all dynamical states. To this end, we propose an optimized kernel size for the LKCNN classifier, which captures both short-lived fluctuations and long-range correlations. While steady states, bursting, and simple oscillations are robustly distinguished with near-perfect accuracy, the performance slightly degrades for chaotic and multiple periodicity states under realistic levels of intrinsic fluctuations, reflecting genuine overlap in their temporal signatures. We validate our classifier with experimental Ca2+ concentration data, showing strong agreement with manual labeling and confirming generalizability beyond synthetic datasets. These results establish LKCNNs as flexible and scalable tools for systematic classification of cellular dynamics, with broad potential applications to other oscillatory biological processes.

biophysics↗

bioRxiv2025

Frataxin deficiency drives cardiac dysfunction and transcriptional dysregulation in Friedreich ataxia iPSC model

Friedreich ataxia (FRDA) is a progressive neuromuscular degenerative disorder caused by GAA repeat expansions in the FXN gene, leading to frataxin deficiency and multisystem pathology. Cardiomyopathy is the leading cause of mortality in individuals with FRDA. To investigate the cellular and molecular mechanisms underlying FRDA-associated cardiac dysfunction, we employed induced pluripotent stem cell (iPSC) lines derived from three individuals with FRDA, each paired with an isogenic control line generated through CRISPR/Cas9-mediated excision of the pathogenic GAA repeat expansion. Correction of the mutation restored FXN expression to levels comparable to healthy donor iPSCs, and all lines differentiated efficiently into cardiomyocytes. Functional analysis revealed significant contractile abnormalities in FRDA cardiomyocytes and multicellular cardiac microtissues, including prolonged contraction and relaxation times and faster beating rates, consistent with clinical observations of cardiac contractile dysfunction. FRDA cardiomyocytes also exhibited pathological features such as increased cell size, irregular calcium transients, elevated mitochondrial reactive oxygen species levels, increased mitochondrial fission and increased cell death. These phenotypes were exacerbated by pathological levels of iron supplementation in culture media, highlighting the heightened sensitivity of frataxin-deficient cardiomyocytes to iron-induced metabolic stress. RNA sequencing revealed a distinct transcriptional profile associated with frataxin deficiency. MEG3 and PCDHGA10 were consistently dysregulated across all three FRDA-iPSC lines and may represent early molecular markers of FRDA cardiomyopathy. Together, these findings establish a robust human iPSC model of FRDA cardiomyopathy that captures early disease phenotypes and reveals novel molecular targets. This preclinical human model provides valuable insight into the pathogenesis of FRDA and provides a platform for developing early-stage therapeutic interventions.

pathology↗

bioRxiv2025

Pentilludin reduces rat amphetamine and remifentail self-administration with good pharmacologic and toxicologic profiles

Pentilludin is a novel, potent (690 nM) irreversible inhibitor of actions of the receptor type protein tyrosine phosphatase D (PTPRD). Pentilludin displays no in vitro activities in Ames or micronucleus tests, at hERG channels or at targets for currently-licensed drugs. Rats treated with pentilludin doses up to 100 mg/kg/day for two weeks have not been found to display behavioral, hematologic or serum chemistry abnormalities. Treatment with 20 mg/kg sc pentilludin prior to every other M-W-F self-administration session substantially reduces self-administration of amphetamine and more modestly reduces self-administration of remifentanil. Pentilludin provides a novel means for reducing self-administration of psychostimulant and, modestly, opiate drugs in ways that could enhance abstinence in humans.

pharmacology and toxicology↗

bioRxiv2025

The Ralstonia solanacearum E3 ligase effector RipV1 targets subfamily IXb receptor-like cytoplasmic kinases that negatively regulate immunity in Nicotiana benthamiana.

Plants detect microbe-associated molecular patterns from pathogens via plasma membrane- localized receptors which activate multiple signaling cascades that lead to pattern-triggered immunity (PTI). Receptor-like cytoplasmic kinases (RLCKs) are essential hubs of plant immune signaling, associating with receptors and intracellular proteins through phosphorylation events. As a consequence, RLCKs have emerged as common targets of pathogen effectors. To improve our knowledge on Solanaceae responses to the bacterial wilt pathogen Ralstonia solanacearum, we conducted a yeast two-hybrid screen between tomato RLCKs and effectors conserved in R. solanacearum Korean isolates. Several members of RLCK subfamily IXb, which contain a ubiquitin-ligase plant U-box domain in addition to the kinase domain, interacted with RipV1, an effector containing a novel E3 ligase domain (NEL). In vitro assays revealed that RLCK-IXb-1 displayed ubiquitin-ligase activity but no detectable kinase activity. RipV1 could trans- ubiquitinate RLCK-IXb-1 in vitro and promote its stability in planta. Using virus-induced gene silencing of RLCK-IXb homologs in Nicotiana benthamiana, we could further show that several RLCK-IXb proteins act as negative regulators of early PTI signaling. RipV1 was previously reported to contribute to R. solanacearum virulence in potato and to elicit cell death in an E3 ligase activity-dependent manner in N. benthamiana. Here we show that RipV1-induced cell death occurred in plants impaired for effector recognition but could be suppressed by over-expression of RLCK-IXb-1, suggesting that this response is related to the virulence function of RipV1. Altogether, our work identifies possible substrates of an NEL effector and underlines the complex roles of RLCKs in plant immune signaling.

plant biology↗