Biology subjects

Locci, F.

Publications and source records attributed to Locci, F..

10 recordsLinked to original sources

bioRxiv2026

Arabidopsis cysteine protease RD19 limits RBOHD-generated ROS production in pattern triggered immunity

Plants perceive pathogenic threats through receptors localized at the plasma membrane and inside cells to initiate pattern-triggered immunity (PTI) and effector-triggered immunity (ETI), respectively. PTI and ETI pathways are interconnected and partially converge on the EDS1-PAD4-ADR1 branch which stimulates anti-pathogen defence. Besides these canonical immune pathways, proteolysis plays a pivotal role in immunity by regulating the abundance and activities of diverse components. We previously identified Arabidopsis papain-like cysteine protease RD19 as a PAD4 interactor and showed that RD19 promotes resistance to host-adapted pathogens. Here, we investigated the contribution of RD19 to bacterial flg22 and nlp20 elicited PTI responses which exhibit, respectively, partial and high PAD4 dependence. We show that although PAD4 and RD19 both promote PTI, they have separate functions. In resting (non-triggered) and nlp20-triggered tissues, RD19 limits RBOHD protein accumulation and consequently ROS production. Using N-terminomic enrichment and protease cleavage site identification methods we identify candidate RD19 substrates in resting and nlp20-responding tissues. Our analysis shows that two immune-related aspartyl proteases AED3 and AED2/ASPG1 are likely direct RD19 targets. This study reveals a role of RD19 in ROS regulation and advances our understanding of proteolysis and dynamic RD19 substrate targeting in plant immunity.

plant biology↗

bioRxiv2026

Plant pathogens cleave 2′cADPR to suppress TIR immune signaling

Small molecules produced by TIR (Toll-interleukin-1 receptor) domains are essential for plant immune signaling. A central TIR-derived signal is 2'cADPR, a cyclic ADP-ribose (ADPR) molecule that is generated by plant TIR-domain proteins upon sensing pathogen infection. Here we show that XopQ, a virulence protein widespread in plant pathogenic bacteria, cleaves 2'cADPR and converts it into an inactive, linear ADPR molecule. Steady-state kinetic analyses revealed that XopQ is a highly efficient enzyme that hydrolyzes 2'cADPR with near diffusion-limited catalytic efficiency, while displaying high specificity and no detectable activity toward closely related molecules such as 3'cADPR. We show that XopQ eliminates 2'cADPR in planta and prevents accumulation of pRib-AMP, a derivative of 2'cADPR that activates the downstream immune complex EDS1-PAD4. Our data demonstrate that XopQ inhibits PAD4-dependent plant immunity and can promote pathogen virulence even when the pathogen carries an avirulence effector that triggers TIR-mediated immune signaling. Finally, we show that XopQ can also inhibit type VI Thoeris, a bacterial anti-phage defense system that relies on 2'cADPR signaling, possibly explaining why XopQ and type VI Thoeris are not observed co-occurring in bacterial genomes. Our findings uncover a widespread and conserved strategy used by plant pathogens to directly target host TIR signaling.

Plant Biology↗

bioRxiv2026

Conserved TIR-only proteins drive transcriptional defense and basal immunity in dicot and monocot plants

Toll/interleukin-1/resistance (TIR) domain NADase enzymes signal in plant immunity by producing ribosylated nucleotide second messengers which activate EDS1 dimer-helper NLR pathways to restrict pathogen growth. Members of a small, distinctive group of TIR-only proteins are conserved between dicots and monocots, yet their functions remain poorly understood. Here, we show that conserved TIR-only proteins in Arabidopsis and barley share a fundamental enzymatic role in promoting basal defense against virulent filamentous pathogens, independently of NLR mediated effector-triggered immunity. Metabolite analysis of transiently expressed Arabidopsis and barley TIR-only proteins revealed their capacity to produce ribosylated cyclic nucleotides in vivo. By comparing phenotypes of tir-only and eds1 pad4 CRISPR mutants in the two species, as well as adr1 mutants in barley, we established that the TIR-only proteins promote PAMP-triggered transcriptional defenses associated with pathogen restriction. Barley possesses just one essential TIR-only enzyme and mutations of the two conserved TIR-only members in Arabidopsis were not compensated for by numerous other TIR-domain genes in the basal immune response. These findings suggest that conserved TIR-only proteins make a crucial contribution to TIR basal defense signaling networks of Arabidopsis and barley. We propose that a shared function in transcriptional defense regulation could explain the evolutionary retention of this discrete TIR-only group across monocot and dicot lineages.

plant biology↗

bioRxiv2025

Small Molecule Binding to EDS1/PAD4 in LRR-RP-Mediated Pattern-Triggered Immunity

Pattern-triggered immunity (PTI) is a key defense mechanism initiated when pathogen-associated molecular patterns are recognized by receptors, including leucine-rich repeat receptor proteins (LRR-RPs)1,2. EDS1 and PAD4 are crucial for LRR-RP-mediated PTI activation3. Small molecule (SM) phosphoribosyl-AMP/ADP, generated by TIR-domain NADase activity, promote the recruitment of helper NLRs into EDS1-PAD4 complex4,5. Here, we show that BAK1 recruitment to LRR-RP complexes is unaffected in eds1-2 or pad4-1 mutants, but is abolished in the sobir1-12 mutant, highlighting the essential role of SOBIR1 in surface immune receptor complex formation. Furthermore, SM-binding to EDS1 and PAD4 is critical for LRR-RP-mediated PTI, as SM-binding-deficient mutants fail to restore immune responses. De novo SM synthesis is required for late PTI responses, including PR1 expression and bacterial resistance, but not for early responses such as ROS and ethylene production. The TNL SADR1 functions only in late PTI responses, suggesting distinct roles of multiple TIR-domain proteins in PTI signaling.

plant biology↗

bioRxiv2024

The Arabidopsis amino acid transporter UmamiT20 confers susceptibility to B. cinerea

O_LIInduction of SWEET sugar transporters by bacterial pathogens via transcription activator-like (TAL) effectors is necessary for successful blight infection of rice, cassava and cotton, - likely providing sugars for bacterial propagation. C_LIO_LIHere, we show that infection of Arabidopsis by the necrotrophic fungus Botrytis cinerea causes increased accumulation of amino acid transporter UmamiT20 mRNA in leaves. UmamiT20 protein accumulates in leaf veins surrounding the lesions after infection. Consistent with a role during infection, umamiT20 knock-out mutants were less susceptible to B. cinerea. C_LIO_LIFunctional assays demonstrate that UmamiT20 mediates amino acid transport of a wide range of amino acid substrates. C_LIO_LIPathogen-induced UmamiT20 mRNA and protein accumulation support the hypothesis that transporter-mediated pathogen susceptibility is not unique to SWEETs in bacterial blight of rice but also for a necrotrophic fungus and implicate nutrients other than sucrose, i.e., amino acids, in nutrition or nutrient signaling related to immunity. We hypothesize that stacking of mutations in different types of susceptibility-related nutrient carriers to interfere with access to several nutrients may enable engineering robust pathogen resistance in a wide range of plant-pathogen systems. C_LI Lay AbstractPathogens infect plants to gain access to their nutrient resources, enabling the pathogens to cause disease and reproduce efficiently. Here we find that an amino acid transporter constitutes a susceptibility factor for the fungal pathogen B. cinerea.

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↗

bioRxiv2021

Differential EDS1 requirement for cell death activities of plant TIR-domain proteins

Toll/interleukin-1 Receptor (TIR) domains are integral to immune systems across all domains of life. TIRs exist as single-domain and as larger receptor or adaptor proteins. In plants, TIRs constitute N-terminal domains of nucleotide-binding leucine-rich repeat (NLR) immune receptors. Although TIR-NLR and TIR signaling requires the Enhanced disease susceptibility 1 (EDS1) protein family, TIR domains persist in species that have incomplete or no EDS1 members. To assess whether particular TIR groups appear with EDS1, we searched for TIR-EDS1 co-occurrence patterns. Using a large-scale phylogenetic analysis of TIR domains from 39 algae and land plant species, we identify four conserved TIR groups, two of which are TIR-NLRs present in eudicots and two are more widespread. Presence of one TIR-only protein group is highly correlated with EDS1 and members of this group elicit EDS1-dependent cell death. By contrast, a more widely represented TIR group of TIR-NB-WD40/TPR (TNP) proteins (formerly called XTNX) has at least one member which can induce EDS1-independent cell death. Our data provide a new phylogeny-based plant TIR classification and identify TIR groups that appear to have evolved with and are dependent on EDS1, while others have EDS1-independent activity. One sentence summaryLand plants have evolved four conserved TIR groups

plant biology↗

bioRxiv2021

Arabidopsis Topless-related 1 mitigates physiological damage and growth penalties of induced immunity

Transcriptional corepressors of the Topless family are important regulators of plant hormone and immunity signaling. The lack of a genome-wide profile of their chromatin associations limits understanding of transcriptional regulation in plant immune responses. Chromatin immunoprecipitation with sequencing (ChIP-seq) was performed on GFP-tagged Topless-related 1 (TPR1) expressed in Arabidopsis thaliana lines with and without constitutive immunity dependent on Enhanced Disease Susceptibility 1 (EDS1). RNA-seq profiling of pathogen-infected tpl/tpr mutants and assessments of growth and physiological parameters were employed to determine TPL/TPR roles in transcriptional immunity and defense homeostasis. TPR1 bound to promoter regions of ~1,400 genes and ~10% of the detected binding required EDS1 immunity signaling. A tpr1 tpl tpr4 (t3) mutant displayed mildly enhanced defense-related transcriptional reprogramming upon bacterial infection but not increased bacterial resistance. Bacteria or pep1 phytocytokine-challenged t3 plants exhibited, respectively, photosystem II dysfunction and exacerbated root growth inhibition. Transgenic expression of TPR1 restored the t3 physiological defects. We propose that TPR1 and TPL-family proteins function in Arabidopsis to reduce detrimental effects associated with activated transcriptional immunity.

plant biology↗

bioRxiv2020

Arabidopsis cell surface LRR immune receptor signaling through the EDS1-PAD4-ADR1 node

Plants use both cell surface and intracellular immune receptors with leucine rich-repeat (LRRs) to detect pathogens. LRR receptor kinases (LRR-RKs) and LRR receptor-like proteins (LRR-RPs) recognize extracellular microbe-derived molecules to confer pattern-triggered immunity (PTI), while nucleotide-binding LRR (NLR) proteins detect microbial effectors inside the cell to confer effector-triggered immunity (ETI). Despite PTI and ETI signaling being initiated in different compartments, both rely on the transcriptional activation of similar sets of genes, suggesting convergence in signaling upstream of nuclear events. Here we report that two sets of molecules, helper NLRs from the ADR1 (ACTIVATED DISEASE RESISTANCE 1) family as well as lipase-like proteins EDS1 (ENHANCED DISEASE SUSCEPTIBILITY 1) and PAD4 (PHYTOALEXIN DEFICIENT 4), are required not only for ETI, but also for PTI. A further similarity is seen in the evolutionary patterns of some PTI and ETI receptor genes, with both often being highly polymorphic, and with nevertheless distinct roles of LRR-RK and LRR-RP receptors in immunity. We find that the LRR-RK SOBIR1 directly links LRR-RPs with the ADR1 helper NLR as well as EDS1 and PAD4, suggesting the formation of constitutive supramolecular signalosome complexes at the inner side of the plasma membrane. We propose that the EDS1-PAD4-ADR1 node is an essential component and convergence point for immune signaling cascades activated by both surface-resident LRR-RP receptors and intracellular NLR receptors.

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↗