Nucleotide-binding Leucine-rich Repeat Receptors Research Articles

A trade-off between investment in molecular defense repertoires and growth in plants.

Given the negative fitness effects that pathogens impose on their hosts, the benefits of resistance should be universal. However, there is marked variation across plant species in the number of nucleotide-binding leucine-rich repeat receptors, which form a cornerstone of defense. The growth-defense trade-off hypothesis predicts costs associated with defense investment to generate variation in these traits. Our analysis comparing features of the intracellular immune-receptor repertoires with trait data of 187 species shows that in wild plants, the size of the molecular defense repertoire correlates negatively with growth. By contrast, we do not find evidence for a growth-defense trade-off in agricultural plants. Our cross-species approach highlights the central role of defense investment in shaping ecological trait variation and its sensitivity to domestication.

Activation of a helper NLR by plant and bacterial TIR immune signaling.

Plant intracellular nucleotide-binding leucine-rich repeat (NLR) receptors with an N-terminal Toll/interleukin-1 receptor (TIR) domain sense pathogen effectors to initiate immune signaling. TIR domains across different kingdoms possess NADase activities and can produce phosphoribosyl adenosine monophosphate/diphosphate (pRib-AMP/ADP) or cyclic ADPR (cADPR) isomers. Lipase-like proteins, EDS1 and PAD4, transduce immune signals from sensor TIR-NLRs to a helper NLR called ADR1, which executes immune function. We report the structure and function of Arabidopsis EDS1-PAD4-ADR1 (EPA) heterotrimer in complex with pRib-AMP/ADP activated by plant or bacterial TIR signaling. 2'cADPR can be hydrolyzed into pRib-AMP and thus activates EPA signaling. Bacterial TIR domains producing 2'cADPR also activate EPA function. Our findings suggest that 2'cADPR may be the storage form of the unstable signaling molecule pRib-AMP.

Recognition of a salivary effector by the TNL protein RCSP promotes effector-triggered immunity and systemic resistance in Nicotiana benthamiana.

Insects secret chemosensory proteins (CSPs) into plant cells as potential effector proteins during feeding. The molecular mechanisms underlying how CSPs activate plant immunity remain largely unknown. We show that CSPs from six distinct insect orders induce dwarfism when overexpressed in Nicotiana benthamiana. Agrobacterium-mediated transient expression of Nilaparvata lugens CSP11 (NlCSP11) triggered cell death and plant dwarfism, both of which were dependent on ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1), neuregulin 1 (NRG1) and SENESCENCE-ASSOCIATED GENE 101 (SAG101), indicating the activation of effector-triggered immunity (ETI) in N. benthamiana. Overexpression of NlCSP11 led to stronger systemic resistance against Pseudomonas syringae DC3000 lacking effector HopQ1-1 and tobacco mosaic virus, and induced higher accumulation of salicylic acid (SA) in uninfiltrated leaves compared to another effector XopQ that is recognized by a Toll-interleukin-1 receptor (TIR) domain nucleotide-binding leucine-rich repeat receptor (TNL) called ROQ1 in N. benthamiana. Consistently, NlCSP11-induced dwarfism and systemic resistance, but not cell death, were abolished in N. benthamiana transgenic line expressing the SA-degrading enzyme NahG. Through large-scale virus-induced gene silencing screening, we identified a TNL protein that mediates the recognition of CSPs (RCSP), including aphid effector MP10 that triggers resistance against aphids in N. benthamiana. Co-immunoprecipitation, bimolecular fluorescence complementation and AlphaFold2 prediction unveiled an interaction between NlCSP11 and RCSP. Interestingly, RCSP does not contain the conserved catalytic glutamic acid in the TIR domain, which is required for TNL function. Our findings point to enhanced ETI and systemic resistance by a TNL protein via hyperactivation of the SA pathway. Moreover, RCSP is the first TNL identified to recognize an insect effector.

Identifying nucleotide-binding leucine-rich repeat receptor and pathogen effector pairing using transfer-learning and bilinear attention network.

Nucleotide-binding leucine-rich repeat (NLR) family is a class of immune receptors capable of detecting and defending against pathogen invasion. They have been widely used in crop breeding. Notably, the correspondence between NLRs and effectors (CNE) determines the applicability and effectiveness of NLRs. Unfortunately, CNE data is very scarce. In fact, we've found a substantial 91291 NLRs confirmed via wet experiments and bioinformatics methods but only 387 CNEs are recognized, which greatly restricts the potential application of NLRs. We propose a deep learning algorithm called ProNEP to identify NLR-effector pairs in a high-throughput manner. Specifically, we conceptualized the CNE prediction task as a protein-protein interaction (PPI) prediction task. Then, ProNEP predicts the interaction between NLRs and effectors by combining the transfer learning with a bilinear attention network. ProNEP achieves superior performance against state-of-the-art models designed for PPI predictions. Based on ProNEP, we conduct extensive identification of potential CNEs for 91291 NLRs. With the rapid accumulation of genomic data, we expect that this tool will be widely used to predict CNEs in new species, advancing biology, immunology, and breeding. The ProNEP is available at http://nerrd.cn/#/prediction. The project code is available at https://github.com/QiaoYJYJ/ProNEP.

RIN4 immunity regulators mediate recognition of the core effector RipE1 of Ralstonia solanacearum by the receptor Ptr1.

Ralstonia solanacearum causes lethal bacterial wilt diseases in numerous crops, resulting in considerable yield losses. Harnessing genetic resistance is desirable for safeguarding plants against phytopathogens. However, genetic resources resistant to bacterial wilt are limited in crops. RipE1, a conserved type Ⅲ effector with cysteine protease activity, is recognized in Nicotiana benthamiana and Arabidopsis (Arabidopsis thaliana). Here, using a virus-induced gene silencing approach, we identified the gene encoding N. benthamiana homologue of Ptr1 (NbPtr1a), a coiled-coil nucleotide-binding leucine-rich repeat receptor (NLR) recognizing RipE1. Silencing or editing NbPtr1a completely abolished RipE1-induced cell death, indicating recognition of RipE1 by NbPtr1a. Genetic complementation confirmed this recognition, which is conserved across multiple solanaceous plants. Expression of RipE1 in planta or within pathogenic bacteria promoted pathogen colonization of Nbptr1a mutant plants, demonstrating its virulence function independent of NLR recognition. Silencing NbRIN4 enhanced RipE1-induced cell death, while expressing NbRIN4 inhibited it, suggesting that NbRIN4 is involved in recognition of NbPtr1a-RipE1. Furthermore, RipE1 associated with and cleaved NbRIN4, AtRIN4, and tomato (Solanum lycopersicum) SlRIN4 proteins through its cysteine protease activity. Silencing NbRIN4 in Nbptr1a mutants did not prevent RipE1 from promoting pathogen colonization, suggesting that NbRIN4 is not the primary target for RipE1-mediated virulence. Additionally, NbRIN4 suppressed self-association of the coiled-coil domain of NbPtr1a, which is critical for NbPtr1a-mediated cell death and resistance. Finally, we demonstrated that activation of NbPtr1a requires RipE1-mediated elimination of NbRIN4. Given the conserved nature of RipE1, Ptr1 holds great potential for protecting crops from diverse R. solanacearum strains and other distinct pathogens.

Phylogenomic insights into the diversity and evolution of RPW8-NLRs and their partners in plants.

Plants use nucleotide-binding leucine-rich repeat receptors (NLRs) to sense pathogen effectors, initiating effector-triggered immunity (ETI). NLRs containing RESISTANCE TO POWDERY MILDEW 8 domain (RNLs) function as "helper" NLRs in flowering plants and support the immune responses mediated by "sensor" NLRs in cooperation with lipase-EP domain fused proteins (EP proteins). Despite their crucial roles in ETI, much remains unclear about the evolutionary trajectories of RNLs and their functional partners EP proteins. Here, we perform phylogenomic analyses of RNLs in 90 plants, covering the major diversity of plants, and identify the presence of RNLs in land plants and green algae, expanding the distribution of RNLs. We uncover a neglected major RNL group in gymnosperms, besides the canonical major group with NRG1s and ADR1s, and observe a drastic increase in RNL repertoire size in conifers. Phylogenetic analyses indicate that RNLs originated multiple times through domain shuffling, and the evolution of RNLs underwent a birth-and-death process. Moreover, we trace the origin of EP proteins back to the last common ancestor of vascular plants. We find that both RNLs and EP proteins evolve mainly under negative selection, revealing strong constraints on their function. Concerted losses and positive correlation in copy number are observed between RNL and EP sublineages, suggesting their cooperation in function. Together, our findings provide insights into the origin and evolution of plant helper NLRs, with implications for predicting novel innate immune signaling modules.

Activation of an atypical plant NLR with an N-terminal deletion initiates cell death at the vacuole

Plants evolve nucleotide-binding leucine-rich repeat receptors (NLRs) to induce immunity. Activated coiled-coil (CC) domain containing NLRs (CNLs) oligomerize and form apparent cation channels promoting calcium influx and cell death, with the alpha-1 helix of the individual CC domains penetrating the plasma membranes. Some CNLs are characterized by putative N-myristoylation and S-acylation sites in their CC domain, potentially mediating permanent membrane association. Whether activated Potentially Membrane Localized NLRs (PMLs) mediate cell death and calcium influx in a similar way is unknown. We uncovered the cell-death function at the vacuole of an atypical but conserved Arabidopsis PML, PML5, which has a significant deletion in its CCG10/GA domain. Active PML5 oligomers localize in Golgi membranes and the tonoplast, alter vacuolar morphology, and induce cell death, with the short N-terminus being sufficient. Mutant analysis supports a potential role of PMLs in plant immunity. PML5-like deletions are found in several Brassicales paralogs, pointing to the evolutionary importance of this innovation. PML5, with its minimal CC domain, represents the first identified CNL utilizing vacuolar-stored calcium for cell death induction.

Protein disulfide isomerase A4 binds to Brucella BtpB and mediates intracellular NAD+/NADH metabolism in RAW264.7 cells

The Toll/interleukin-1 receptor (TIR) signaling domain is distributed widely in mammalian Toll-like receptors and adaptors, plant nucleotide-binding leucine-rich repeat receptors, and specific bacterial virulence proteins. Proteins that possess TIR domain exhibit NADase activity which is distinct from the canonical signaling function of these domains. However, the effects of bacterial TIR domain proteins on host metabolic switches and the underlying mechanism of NADase activity in these proteins remain unclear. Here, we utilized Brucella TIR domain-containing type IV secretion system effector protein, BtpB, to explore the mechanism of NADase activity in host cells. We showed that using ectopic expression BtpB not only generates depletion of NAD+ but also loss of NADH and ATP in RAW264.7 macrophage cells. Moreover, immunoprecipitation-mass spectrometry, co-immunoprecipitation, and confocal microscope assays revealed that BtpB interacted with host protein disulfide isomerase A4 (PDIA4). The Brucella mutant strain deleted the gene for BtpB, significantly decreased PDIA4 expression. Furthermore, our data revealed that PDIA4 played an important role in regulating intracellular NAD+/NADH levels in macrophages, and PDIA4 overexpression restored the decline of intracellular NAD+ and NADH levels induced by Brucella BtpB. The results provide new insights into the metabolic regulatory activity of TIR domain proteins in the critical human and animal pathogen Brucella.

Effect of Suan Zao Ren (Semen Ziziphi Spinosae) Extract on the TXNIP/NLRP3 Pathway in Insomniac Rats

Abstract Objectives This study aimed to investigate the therapeutic effects of Suan Zao Ren (Semen Ziziphi Spinosae, SZS) extract on insomnia induced by p-chlorophenylalanine (PCPA) in rats and its influence on the thioredoxin-interacting protein (TXNIP)/nucleotide-binding domain Leucine-rich repeat and pyrin domain-containing receptor 3 (NLRP3) inflammasome pathway, and to preliminarily explore the mechanism by which SZS extract improves insomnia. Methods Fifty male Sprague–Dawley (SD) rats were used, with 8 rats in the blank group and 42 rats in the modeling group. The modeling group was induced by intraperitoneal injection of PCPA at a dose of 500 mg·kg−1 for six consecutive days, with daily cage exchange. After 6 days, 40 successfully modeled rats were randomly divided into five groups: the model group (equal volume of distilled water), the positive group (0.75 mg·kg−1), and low-, medium-, and high-dose SZS extract groups (1.5, 3, and 6 g·kg−1, respectively), with 8 rats in each group. Treatments were administered for seven consecutive days. Enzyme-linked immunosorbent assay was used to measure levels of 5-hydroxytryptamine (5-HT) and gamma-aminobutyric acid (GABA) in the rat cerebral cortex. The thiobarbituric acid (TBA) method was used to determine malondialdehyde (MDA) levels, and the hydroxylamine method was used to determine superoxide dismutase (SOD) levels. The 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) method was used to measure total antioxidant capacity (TAOC) in the cerebral cortex. Pathological changes in the cerebral cortex were observed, and Western blot was used to detect the protein expressions of TXNIP, NLRP3, apoptosis-associated speck-like protein containing a Caspase activation and recruitment domain (CARD), and cysteine–aspartate-specific protease 1 (Caspase-1) in the cerebral cortex. Results Compared with the blank group, the model group showed a significantly prolonged sleep latency (p < 0.001) and a significantly shortened sleep duration (p < 0.001). There were no changes in serum MDA and SOD levels. MDA levels in the cerebral cortex were significantly increased (p < 0.001), while SOD and TAOC levels were significantly decreased (p < 0.001). The 5-HT level was increased (p < 0.05), and the GABA level was significantly decreased (p < 0.001). SZS extract improved these conditions to varying degrees. Light microscopy showed no significant changes in cortical neurons but transmission electron microscopy revealed intact mitochondrial structures in the blank group, while the model group showed swollen and unclear mitochondria with reduced organelles. After 7 days of treatment, these conditions improved in the SZS extract groups. Compared with the blank group, the expressions of the four proteins in the model group were increased, and the expressions of these proteins were decreased in the SZS extract groups compared with the model group. Conclusion SZS extract may exert an antioxidant effect to treat insomnia by downregulating the expression of TXNIP/NLRP3 proteins and regulating oxidative stress levels in the cerebral cortex.

Engineering the plant intracellular immune receptor Sr50 to restore recognition of the AvrSr50 escape mutant.

Sr50, an intracellular nucleotide-binding leucine-rich repeat receptor (NLR), confers resistance of wheat against stem rust caused by the fungal pathogen Puccinia graminis f. sp. tritici. The receptor recognizes the pathogen effector AvrSr50 through its C-terminal leucine-rich repeat domain, initiating a localized cell death immune response. However, this immunity is compromised by mutations in the effector, as in the escape mutant AvrSr50QCMJC, which evades Sr50 detection. In this study, we employed iterative computational structural analyses and site-directed mutagenesis for rational engineering of Sr50 to gain recognition of AvrSr50QCMJC. Following an initial structural hypothesis driven by molecular docking, we identified the Sr50K711D single mutant, which induces an intermediate immune response against AvrSr50QCMJC without losing recognition against AvrSr50. Increasing gene expression with a stronger promoter enabled the mutant to elicit a robust response, indicating weak effector recognition can be complemented by enhanced receptor expression. Further structural refinements led to the creation of five double mutants and two triple mutants with dual recognition of AvrSr50 and AvrSr50QCMJC with greater immune response intensities than Sr50K711D against the escape mutant. All effective mutations against AvrSr50QCMJC required the K711D substitution, indicating that multiple solutions exist for gain of recognition, but the path to reach these mutations may be confined. Furthermore, this single substitution alters the prediction of AlphaFold 2, allowing it to model the complex structure of Sr50K711D and AvrSr50 that match our final structural hypothesis. Collectively, our study outlines a framework for rational engineering of NLR systems to overcome pathogen escape mutations and provides datasets for future computational models for NLR resurrection.

Activation of the helper NRC4 immune receptor forms a hexameric resistosome

Innate immune responses to microbial pathogens are regulated by intracellular receptors known as nucleotide-binding leucine-rich repeat receptors (NLRs) in both the plant and animal kingdoms. Across plant innate immune systems, "helper" NLRs (hNLRs) work in coordination with "sensor" NLRs (sNLRs) to modulate disease resistance signaling pathways. Activation mechanisms of hNLRs based on structures are unknown. Our research reveals that the hNLR, known as NLR required for cell death 4 (NRC4), assembles into a hexameric resistosome upon activation by the sNLR Bs2 and the pathogenic effector AvrBs2. This conformational change triggers immune responses by facilitating the influx of calcium ions (Ca2+) into the cytosol. The activation mimic alleles of NRC2, NRC3, or NRC4 alone did not induce Ca2+ influx and cell death in animal cells, suggesting that unknown plant-specific factors regulate NRCs' activation in plants. These findings significantly advance our understanding of the regulatory mechanisms governing plant immune responses.

Alternative splicing of a potato disease resistance gene maintains homeostasis between growth and immunity.

Plants possess a robust and sophisticated innate immune system against pathogens and must balance growth with rapid pathogen detection and defense. The intracellular receptors with nucleotide-binding leucine-rich repeat (NLR) motifs recognize pathogen-derived effector proteins and thereby trigger the immune response. The expression of genes encoding NLR receptors is precisely controlled in multifaceted ways. The alternative splicing (AS) of introns in response to infection is recurrently observed but poorly understood. Here we report that the potato (Solanum tuberosum) NLR gene RB undergoes AS of its intron, resulting in 2 transcriptional isoforms, which coordinately regulate plant immunity and growth homeostasis. During normal growth, RB predominantly exists as an intron-retained isoform RB_IR, encoding a truncated protein containing only the N-terminus of the NLR. Upon late blight infection, the pathogen induces intron splicing of RB, increasing the abundance of RB_CDS, which encodes a full-length and active R protein. By deploying the RB splicing isoforms fused with a luciferase reporter system, we identified IPI-O1 (also known as Avrblb1), the RB cognate effector, as a facilitator of RB AS. IPI-O1 directly interacts with potato splicing factor StCWC15, resulting in altered localization of StCWC15 from the nucleoplasm to the nucleolus and nuclear speckles. Mutations in IPI-O1 that eliminate StCWC15 binding also disrupt StCWC15 re-localization and RB intron splicing. Thus, our study reveals that StCWC15 serves as a surveillance facilitator that senses the pathogen-secreted effector and regulates the trade-off between RB-mediated plant immunity and growth, expanding our understanding of molecular plant-microbe interactions.

NbPTR1 confers resistance against Pseudomonas syringae pv. actinidiae in kiwifruit.

Pseudomonas syringae pv. actinidiae biovar 3 (Psa3) causes a devastating canker disease in yellow-fleshed kiwifruit (Actinidia chinensis). The effector HopZ5, which is present in all isolates of Psa3 causing global outbreaks of pandemic kiwifruit canker disease, triggers immunity in Nicotiana benthamiana and is not recognised in susceptible A. chinensis cultivars. In a search for N. benthamiana nonhost resistance genes against HopZ5, we found that the nucleotide-binding leucine-rich repeat receptor NbPTR1 recognised HopZ5. RPM1-interacting protein 4orthologues from N. benthamiana and A. chinensis formed a complex with NbPTR1 and HopZ5 activity was able to disrupt this interaction. No functional orthologues of NbPTR1 were found in A. chinensis. NbPTR1 transformed into Psa3-susceptible A. chinensis var. chinensis 'Hort16A' plants introduced HopZ5-specific resistance against Psa3. Altogether, this study suggested that expressing NbPTR1 in Psa3-susceptible kiwifruit is a viable approach to acquiring resistance to Psa3 and it provides valuable information for engineering resistance in otherwise susceptible kiwifruit genotypes.

The soybean plasma membrane GmDR1 protein conferring broad-spectrum disease and pest resistance regulates several receptor kinases and NLR proteins

Overexpression of Glycine max disease resistant 1 (GmDR1) exhibits broad-spectrum resistance against Fusarium virguliforme, Heterodera glycines (soybean cyst nematode), Tetranychus urticae (Koch) (spider mites), and Aphis glycines Matsumura (soybean aphids) in soybean. To understand the mechanisms of broad-spectrum immunity mediated by GmDR1, the transcriptomes of a strong and a weak GmDR1-overexpressor following treatment with chitin, a pathogen- and pest-associated molecular pattern (PAMP) common to these organisms, were investigated. The strong and weak GmDR1-overexpressors exhibited altered expression of 6098 and 992 genes, respectively, as compared to the nontransgenic control following chitin treatment. However, only 192 chitin- and 115 buffer-responsive genes exhibited over two-fold changes in expression levels in both strong and weak GmDR1-overexpressors as compared to the control. MapMan analysis of the 192 chitin-responsive genes revealed 64 biotic stress-related genes, of which 53 were induced and 11 repressed as compared to the control. The 53 chitin-induced genes include nine genes that encode receptor kinases, 13 encode nucleotide-binding leucine-rich repeat (NLR) receptor proteins, seven encode WRKY transcription factors, four ethylene response factors, and three MYB-like transcription factors. Investigation of a subset of these genes revealed three receptor protein kinases, seven NLR proteins, and one WRKY transcription factor genes that are induced following F. virguliforme and H. glycines infection. The integral plasma membrane GmDR1 protein most likely recognizes PAMPs including chitin and activates transcription of genes encoding receptor kinases, NLR proteins and defense-related genes. GmDR1 could be a pattern recognition receptor that regulates the expression of several NLRs for expression of PAMP-triggered immunity and/or priming the effector triggered immunity.

Plant Immunity: At the Crossroads of Pathogen Perception and Defense Response.

Plants are challenged by different microbial pathogens that affect their growth and productivity. However, to defend pathogen attack, plants use diverse immune responses, such as pattern-triggered immunity (PTI), effector-triggered immunity (ETI), RNA silencing and autophagy, which are intricate and regulated by diverse signaling cascades. Pattern-recognition receptors (PRRs) and nucleotide-binding leucine-rich repeat (NLR) receptors are the hallmarks of plant innate immunity because they can detect pathogen or related immunogenic signals and trigger series of immune signaling cascades at different cellular compartments. In plants, most commonly, PRRs are receptor-like kinases (RLKs) and receptor-like proteins (RLPs) that function as a first layer of inducible defense. In this review, we provide an update on how plants sense pathogens, microbe-associated molecular patterns (PAMPs or MAMPs), and effectors as a danger signals and activate different immune responses like PTI and ETI. Further, we discuss the role RNA silencing, autophagy, and systemic acquired resistance as a versatile host defense response against pathogens. We also discuss early biochemical signaling events such as calcium (Ca2+), reactive oxygen species (ROS), and hormones that trigger the activation of different plant immune responses. This review also highlights the impact of climate-driven environmental factors on host-pathogen interactions.

Proteolysis in plant immunity.

Compared with transcription and translation, protein degradation machineries can act faster and be targeted to different subcellular compartments, enabling immediate regulation of signaling events. It is therefore not surprising that proteolysis has been used extensively to control homeostasis of key regulators in different biological processes and pathways. Over the past decades, numerous studies have shown that proteolysis, where proteins are broken down to peptides or amino acids through ubiquitin-mediated degradation systems and proteases, is a key regulatory mechanism to control plant immunity output. Here, we briefly summarize the roles various proteases play during defence activation, focusing on recent findings. We also update the latest progress of ubiquitin-mediated degradation systems in modulating immunity by targeting plant membrane-localized pattern recognition receptors, intracellular nucleotide-binding domain leucine-rich repeat receptors, and downstream signaling components. Additionally, we highlight recent studies showcasing the importance of proteolysis in maintaining broad-spectrum resistance without obvious yield reduction, opening new directions for engineering elite crops that are resistant to a wide range of pathogens with high yield.

Powdery mildew effectors AVRA1 and BEC1016 target the ER J-domain protein HvERdj3B required for immunity in barley.

The barley powdery mildew fungus, Blumeria hordei (Bh), secretes hundreds of candidate secreted effector proteins (CSEPs) to facilitate pathogen infection and colonization. One of these, CSEP0008, is directly recognized by the barley nucleotide-binding leucine-rich-repeat (NLR) receptor MLA1 and therefore is designated AVRA1. Here, we show that AVRA1 and the sequence-unrelated Bh effector BEC1016 (CSEP0491) suppress immunity in barley. We used yeast two-hybrid next-generation interaction screens (Y2H-NGIS), followed by binary Y2H and in planta protein-protein interactions studies, and identified a common barley target of AVRA1 and BEC1016, the endoplasmic reticulum (ER)-localized J-domain protein HvERdj3B. Silencing of this ER quality control (ERQC) protein increased Bh penetration. HvERdj3B is ER luminal, and we showed using split GFP that AVRA1 and BEC1016 translocate into the ER signal peptide-independently. Overexpression of the two effectors impeded trafficking of a vacuolar marker through the ER; silencing of HvERdj3B also exhibited this same cellular phenotype, coinciding with the effectors targeting this ERQC component. Together, these results suggest that the barley innate immunity, preventing Bh entry into epidermal cells, requires ERQC. Here, the J-domain protein HvERdj3B appears to be essential and can be regulated by AVRA1 and BEC1016. Plant disease resistance often occurs upon direct or indirect recognition of pathogen effectors by host NLR receptors. Previous work has shown that AVRA1 is directly recognized in the cytosol by the immune receptor MLA1. We speculate that the AVRA1 J-domain target being inside the ER, where it is inapproachable by NLRs, has forced the plant to evolve this challenging direct recognition.

Nucleotide-binding leucine-rich repeat receptor homologs Pib and PibH8 interact and contribute to immunity in rice.

Plant nucleotide-binding leucine-rich repeat receptors (NLRs) sense pathogen effectors and activate effector-triggered immunity (ETI). Many plant NLRs form pairs with other NLRs to recognize effectors and initiate ETI. PIRICULARIA ORYZAE RESISTANCE IN BL1 (Pib), an NLR protein in rice (Oryza sativa), activates resistance by recognizing the rice blast effector AvrPib. The activation of Pib is suppressed by SH3 DOMAIN-CONTAINING PROTEIN 2 (OsSH3P2) in the absence of AvrPib. However, how Pib triggers defense responses and whether Pib pairs with another NLR are not clear. In this study, we identified Pib by map-based cloning and showed that a homolog of Pib, PIB HOMOLOGUE 8 (PibH8), interacts with Pib. Pib and PibH8 mediate resistance to the Magnaporthe oryzae isolate Guy11, a rice blast strain carrying AvrPib. Interestingly, the pib/pibh8 double mutant exhibited enhanced susceptibility to Guy11 compared to the single mutant. Furthermore, PibH8 can oligomerize through its coiled-coil (CC) domain, which also contributes to the Pib-PibH8 interaction, suggesting that Pib and PibH8 may form a complex to recognize AvrPib. OsSH3P2 inhibited the interaction of Pib and PibH8 through association with the CC domain of PibH8. Taken together, these results indicate that both Pib and PibH8 are required for rice blast resistance to M. oryzae carrying AvrPib, which is negatively regulated by OsSH3P2. This study not only identifies an NLR that functions in rice blast resistance but also reveals a possible complex immune strategy in which homologous NLR proteins may regulate the complete activation of plant immunity.

Pattern-Triggered Immunity and Effector-Triggered Immunity: crosstalk and cooperation of PRR and NLR-mediated plant defense pathways during host-pathogen interactions.

The elucidation of the molecular basis underlying plant-pathogen interactions is imperative for the development of sustainable resistance strategies against pathogens. Plants employ a dual-layered immunological detection and response system wherein cell surface-localized Pattern Recognition Receptors (PRRs) and intracellular Nucleotide-Binding Leucine-Rich Repeat Receptors (NLRs) play pivotal roles in initiating downstream signalling cascades in response to pathogen-derived chemicals. Pattern-Triggered Immunity (PTI) is associated with PRRs and is activated by the recognition of conserved molecular structures, known as Pathogen-Associated Molecular Patterns. When PTI proves ineffective due to pathogenic effectors, Effector-Triggered Immunity (ETI) frequently confers resistance. In ETI, host plants utilize NLRs to detect pathogen effectors directly or indirectly, prompting a rapid and more robust defense response. Additionally epigenetic mechanisms are participating in plant immune memory. Recently developed technologies like CRISPR/Cas9 helps in exposing novel prospects in plant pathogen interactions. In this review we explore the fascinating crosstalk and cooperation between PRRs and NLRs. We discuss epigenomic processes and CRISPR/Cas9 regulating immune response in plants andrecent findings that shed light on the coordination of these defense layers. Furthermore, we alsohave discussed the intricate interactions between the salicylic acid and jasmonic acid signalling pathways in plants, offering insights into potential synergistic interactions that would be harnessed for the development of novel and sustainable resistance strategies against diverse group of pathogens.

Natural Compounds Oridonin and Shikonin Exhibit Potentially Beneficial Regulatory Effects on Select Functions of Microglia.

Accumulating evidence indicates that the adverse neuroimmune activation of microglia, brain immunocytes that support neurons, contributes to a range of neuroinflammatory disorders, including Alzheimer's disease. Correcting the abnormal functions of microglia is a potential therapeutic strategy for these diseases. Nucleotide-binding domain leucine-rich repeat and pyrin domain-containing receptor (NLRP) 3 inflammasomes are implicated in adverse microglial activation and their inhibitors, such as the natural compounds oridonin and shikonin, reduce microglial immune responses. We hypothesized that some of the beneficial effects of oridonin and shikonin on microglia are independent of their suppression of NLRP3 inflammasomes. Murine and human microglia-like cells were stimulated with bacterial lipopolysaccharide (LPS) only, which did not induce NLRP3 inflammasome activation or the resulting secretion of interleukin (IL)-1β, allowing for the identification of other anti-inflammatory effects. Under these experimental conditions, both oridonin and shikonin reduced nitric oxide (NO) secretion and the cytotoxicity of BV-2 murine microglia towards HT-22 murine neuronal cells, but upregulated BV-2 cell phagocytic activity. Only oridonin inhibited the secretion of tumor necrosis factor (TNF) by stimulated BV-2 microglia, while only shikonin suppressed the respiratory burst response of human HL-60 microglia-like cells. This observed discrepancy indicates that these natural compounds may have different molecular targets in microglia. Overall, our results suggest that oridonin and shikonin should be further investigated as pharmacological agents capable of correcting dysfunctional microglia, supporting their potential use in neuroinflammatory disorders.