Effector triggered immunity

Melon CmRLCK VII-8 kinase genes CmRLCK27, CmRLCK30 and CmRLCK34 modulate resistance against bacterial and fungal diseases in Arabidopsis

Receptor-like cytoplasmic kinases (RLCKs) represent a distinct class of receptor-like kinases crucial for various aspects of plant biology, including growth, development, and stress responses. This study delves into the characterization of RLCK VII-8 members within cucurbits, particularly in melon, examining both structural features and the phylogenetic relationships of these genes/proteins. The investigation extends to their potential involvement in disease resistance by employing ectopic overexpression in Arabidopsis. The promoters of CmRLCK VII-8 genes harbor multiple phytohormone- and stress-responsive cis-acting elements, with the majority (excluding CmRLCK39) displaying upregulated expression in response to defense hormones and fungal infection. Subcellular localization studies reveal that CmRLCK VII-8 proteins predominantly reside on the plasma membrane, with CmRLCK29 and CmRLCK30 exhibiting additional nuclear distribution. Notably, Arabidopsis plants overexpressing CmRLCK30 manifest dwarfing and delayed flowering phenotypes. Overexpression of CmRLCK27, CmRLCK30, and CmRLCK34 in Arabidopsis imparts enhanced resistance against Botrytis cinerea and Pseudomonas syringae pv. tomato DC3000, concomitant with the strengthened expression of defense genes and reactive oxygen species accumulation. The CmRLCK VII-8 members actively participate in chitin- and flg22-triggered immune responses. Furthermore, CmRLCK30 interacts with CmMAPKKK1 and CmARFGAP, adding a layer of complexity to the regulatory network. In summary, this functional characterization underscores the regulatory roles of CmRLCK27, CmRLCK30, and CmRLCK34 in immune responses by influencing pathogen-induced defense gene expression and ROS accumulation.

Identification of an SCF Ubiquitin Ligase Complex that Contributes to Resistance Against Valsa Canker in Apple

E3 ubiquitin ligases play a critical role in plant disease resistance. Among them, the Skp1-Cullin-F-box protein (SCF) ubiquitin ligase complex is the largest family and regulates the ubiquitination of a wide range of proteins. Apple Valsa canker (AVC) is a fungal disease of apple trees caused by the fungus Valsa mali, which can lead to significant economic losses. However, the function of the SCF complex in apple resistance to this disease is still largely unknown. In this study, we identified an SCF ubiquitin ligase complex that can enhance resistance to Valsa canker in apple. Disease evaluation experiments demonstrated that MdSkp1 increased apple resistance to AVC. Furthermore, MdSkp1 interacted with an F-box protein, MdSKIP14, and interacted with a cullin-1 protein, MdCUL1, to form an SCF ubiquitin ligase complex. Additionally, we revealed both MdSKIP14 and MdCUL1 as positive regulators of AVC resistance. In conclusion, our results identified an SCF complex capable of contributing to apple resistance against AVC, providing a theoretical basis for apple disease resistance and the sustainable development of the industry. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Plant-Fungi Interactions: Where It Goes?

Fungi live different lifestyles-including pathogenic and symbiotic-by interacting with living plants. Recently, there has been a substantial increase in the study of phytopathogenic fungi and their interactions with plants. Symbiotic relationships with plants appear to be lagging behind, although progressive. Phytopathogenic fungi cause diseases in plants and put pressure on survival. Plants fight back against such pathogens through complicated self-defense mechanisms. However, phytopathogenic fungi develop virulent responses to overcome plant defense reactions, thus continuing their deteriorative impacts. Symbiotic relationships positively influence both plants and fungi. More interestingly, they also help plants protect themselves from pathogens. In light of the nonstop discovery of novel fungi and their strains, it is imperative to pay more attention to plant-fungi interactions. Both plants and fungi are responsive to environmental changes, therefore construction of their interaction effects has emerged as a new field of study. In this review, we first attempt to highlight the evolutionary aspect of plant-fungi interactions, then the mechanism of plants to avoid the negative impact of pathogenic fungi, and fungal strategies to overcome the plant defensive responses once they have been invaded, and finally the changes of such interactions under the different environmental conditions.

Molecular insights into the responses of barley to yellow mosaic disease through transcriptome analysis

BACKGROUND

Barley (Hordeum vulgare L.) represents the fourth most essential cereal crop in the world, vulnerable to barley yellow mosaic virus (BaYMV) and/or barley mild mosaic virus (BaMMV), leading to the significant yield reduction. To gain a better understanding of the mechanisms regarding barley crop tolerance to virus infection, we employed a transcriptome sequencing approach and investigated global gene expression among three barley varieties under both infected and control conditions.

RESULTS

High-throughput sequencing outputs revealed massive genetic responses, reflected by the barley transcriptome after BaYMV and/or BaMMV infection. Significant enrichments in peptidase complex and protein processing in endoplasmic reticulum were clustered through Gene ontology and KEGG analysis. Many genes were identified as transcription factors, antioxidants, disease resistance genes and plant hormones and differentially expressed between infected and uninfected barley varieties. Importantly, general response genes, variety-specific and infection-specific genes were also discovered. Our results provide useful information for future barley breeding to resist BaYMV and BaMMV.

CONCLUSIONS

Our study elucidates transcriptomic adaptations in barley response to BaYMV/BaMMV infection through high-throughput sequencing technique. The analysis outcome from GO and KEGG pathways suggests that BaYMV disease induced regulations in multiple molecular-biology processes and signalling pathways. Moreover, critical DEGs involved in defence and stress tolerance mechanisms were displayed. Further functional investigations focusing on these DEGs contributes to understanding the molecular mechanisms of plant response to BaYMV disease infection, thereby offering precious genetic resources for breeding barley varieties resistant to BaYMV disease.

Enhanced resistance to Bacillus thuringiensis Cry1Ac toxin mediated by the activation of prophenoloxidase in a cosmopolitan pest

Plutella xylostella has evolved resistance to Bacillus thuringiensis Cry1Ac toxin over a long evolutionary period. Enhanced immune response is an important factor in insect resistance to a variety of insecticides, and whether phenoloxidase (PO), an immune protein, is involved in resistance to Cry1Ac toxin in P. xylostella remains unclear. Here, spatial and temporal expression patterns showed that prophenoloxidase (PxPPO1 and PxPPO2) in the Cry1S1000-resistant strain was more highly expressed in eggs, 4th instar, head, and hemolymph than those in G88-susceptible strain. The results of PO activity analysis showed that after treatment with Cry1Ac toxin PO activity was about 3 times higher than that before treatment. Furthermore, knockout of PxPPO1 and PxPPO2 significantly increased the susceptibility to Cry1Ac toxin. These findings were further supported by the knockdown of Clip-SPH2, a negative regulator of PO, which resulted in increased PxPPO1 and PxPPO2 expression and Cry1Ac susceptibility in the Cry1S1000-resistant strain. Finally, the synergistic effect of quercetin showed that larval survival decreased from 100 % to <20 % compared to the control group. This study will provide a theoretical basis for the analysis of immune-related genes (PO) genes involved in the resistance mechanism and pest control of P. xylostella.

Insights to Gossypium defense response against Verticillium dahliae: the Cotton Cancer

The soil-borne pathogen Verticillium dahliae, also referred as "The Cotton Cancer," is responsible for causing Verticillium wilt in cotton crops, a destructive disease with a global impact. To infect cotton plants, the pathogen employs multiple virulence mechanisms such as releasing enzymes that degrade cell walls, activating genes that contribute to virulence, and using protein effectors. Conversely, cotton plants have developed numerous defense mechanisms to combat the impact of V. dahliae. These include strengthening the cell wall by producing lignin and depositing callose, discharging reactive oxygen species, and amassing hormones related to defense. Despite the efforts to develop resistant cultivars, there is still no permanent solution to Verticillium wilt due to a limited understanding of the underlying molecular mechanisms that drive both resistance and pathogenesis is currently prevalent. To address this challenge, cutting-edge technologies such as clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9), host-induced gene silencing (HIGS), and gene delivery via nano-carriers could be employed as effective alternatives to control the disease. This article intends to present an overview of V. dahliae virulence mechanisms and discuss the different cotton defense mechanisms against Verticillium wilt, including morphophysiological and biochemical responses and signaling pathways including jasmonic acid (JA), salicylic acid (SA), ethylene (ET), and strigolactones (SLs). Additionally, the article highlights the significance of microRNAs (miRNAs), circular RNAs (circRNAs), and long non-coding RNAs (lncRNAs) in gene expression regulation, as well as the different methods employed to identify and functionally validate genes to achieve resistance against this disease. Gaining a more profound understanding of these mechanisms could potentially result in the creation of more efficient strategies for combating Verticillium wilt in cotton crops.

Legumes Regulate Symbiosis with Rhizobia via Their Innate Immune System

Plant roots are constantly exposed to a diverse microbiota of pathogens and mutualistic partners. The host's immune system is an essential component for its survival, enabling it to monitor nearby microbes for potential threats and respond with a defence response when required. Current research suggests that the plant immune system has also been employed in the legume-rhizobia symbiosis as a means of monitoring different rhizobia strains and that successful rhizobia have evolved to overcome this system to infect the roots and initiate nodulation. With clear implications for host-specificity, the immune system has the potential to be an important target for engineering versatile crops for effective nodulation in the field. However, current knowledge of the interacting components governing this pathway is limited, and further research is required to build on what is currently known to improve our understanding. This review provides a general overview of the plant immune system's role in nodulation. With a focus on the cycles of microbe-associated molecular pattern-triggered immunity (MTI) and effector-triggered immunity (ETI), we highlight key molecular players and recent findings while addressing the current knowledge gaps in this area.

Effector-Triggered Trained Immunity: An Innate Immune Memory to Microbial Virulence Factors?

In the last decade, a major dogma in the field of immunology has been called into question by the identification of a cell autonomous innate immune memory. This innate immune memory (also named trained immunity) was found to be mostly carried by innate immune cells and to be characterized by an exacerbated inflammatory response with a heightened expression of proinflammatory cytokines, including TNF-α, IL-6 and IL-1β. Unlike the vast majority of cytokines, IL-1β is produced as a proform (pro-IL-1β) and requires a proteolytic cleavage to exert its biological action. This cleavage takes place mainly within complex molecular platforms named inflammasomes. These platforms are assembled upon both the infectious or sterile activation of NOD-like receptors (NLRs), thereby allowing for the recruitment and activation of caspases and the subsequent maturation of pro-IL-1β into IL-1β. The NLRP3 inflammasome has recently been implicated both in western diet-induced trained immunity, and in the detection of microbial virulence factors (effector-triggered immunity (ETI)). Here, we will attempt to link these two immune processes and provide arguments to hypothesize the existence of trained immunity triggered by microbial virulence factors (effector-triggered trained immunity (ETTI)).

Antimicrobial peptide expression in the cockroach gut during enterobacterial infection is specific and influenced by type III secretion

Omnivorous synanthropic cockroaches, such as the German cockroach (Blattella germanica), are reservoirs and vectors of enteric bacterial pathogens. A lifestyle conducive to frequent encounters with high loads of diverse bacteria may have led to the evolution of unique innate immune systems in these insects. The innate immune response of insects relies largely on generalized mechanisms to sense and eliminate foreign microbes. However, analyses of the genomes of common synanthropic cockroaches previously revealed a repertoire of pathogen associated molecular pattern (PAMP) receptors and antimicrobial peptides (AMPs) that is significantly expanded relative to most holometabolous insect models and vectors, supporting the intriguing possibility that cockroaches may encode enhanced recognition within their immune system and may possess an enhanced capacity to fine tune innate immune responses. Investigating how cockroaches respond to infection with enterobacteria provides the opportunity to expand our fundamental knowledge of the regulation of insect innate immunity in a context that is biologically and medically relevant. German cockroaches can harbor both Salmonella enterica serovar Typhimurium and Escherichia coli in their gut without experiencing pathogenesis. The former colonizes the gut and replicates while the latter persists only transiently. We hypothesized that differences in the innate immune response may contribute to or result from the difference in infection dynamics between the two enterobacteria. To test this hypothesis, we used qRT-PCR to analyze expression of five genes encoding representative AMPs (Attacins, Blattellicin, Defensins) in the gut of German cockroaches 1 and 24 h after ingestion of live or heat-killed enterobacteria. We found that robust AMP expression was induced in response to ingestion of a live wild-type strain of S. Typhimurium, but not in response to live E. coli, heat-killed S. Typhimurium, or a live mutant strain of S. Typhimurium lacking type III secretion systems. These results indicate that the cockroach immune system does not respond to stimulation with high levels of ingested bacterial PAMPs such as peptidoglycan. Rather, AMP expression in the gut appears to be induced by active bacterial colonization involving type III secretion. We speculate that this form of regulation may have evolved to prevent over activation of the immune system from frequent ingestion of innocuous, non-colonizing, or non-viable bacteria. While additional work is needed to delineate the molecular mechanisms underlying our observations, our findings provide significant novel insight into the immunological adaptation of cockroaches to life in septic environments as well as the factors that regulate bacterial pathogen transmission by these insects.

p38-MAPK recruits the proteolytic pathways in Caenorhabditis elegans during bacterial infection

In eukaryotic organisms, cell-signalling completely relies on Post Translational Modifications (PTMs) that can function as regulatory switches. Phosphorylation is a fundamental and frequently occurring PTM in almost all eukaryotes. Herein, we have studied the importance of protein phosphorylation using classical proteomic techniques in C. elegans upon bacterial infection. The differentially regulated proteins during bacterial infection were excised from SDS-PAGE (One-Dimensional) gel (TiO₂ column elutes) and subjected to MALDI-TOF-MS which ended up in identifying 220 proteins kinetically. KEGG pathway analysis of those proteins suggested that MAPK pathway was part of the innate immunity. Thus, we have characterized p38-MAPK (one of the crucial downstream MAPKs) using immunoblotting, subcellular fractionation, coimmunoprecipitation, LC-MS/MS, bioinformatics studies and qPCR. Meanwhile, KU25 strain (pmk-1 mutant) exhibited an earlier mortality during infection suggesting the crucial role of p38-MAPK during host-pathogen interaction. Interestingly, Reactome pathway analysis of p38 interactors (CoIP coupled to LC-MS/MS) revealed the involvement of various proteolytic pathway players (ubiquitination, SUMOylation and Neddylation) during bacterial infection. Further, the regulation of SUMOylation and Neddylation was identified and validated using immunoblotting and qPCR analyses, respectively. Concisely, our study indicated that bacterial infection triggers the MAPK cascade to elicit innate immunity which in turn recruits proteolytic pathways to counteract the invading pathogen.

Analysis of Bacteria-Triggered Inflammasome: Activation in Neutrophils by Immunoblot

Detection of microbes relies on the expression of germline-encoded pattern recognition receptors (PRRs). While PRRs can directly sense conserved pattern expressed by various microbes, they can also induce effector-triggered immunity (ETI) by sensing pathogenic alterations of cellular homeostasis. One consequence of ETI is the death of the infected cell through the induction of inflammasome-dependent cell death, namely, pyroptosis. Such process can be easily studied in macrophages and epithelial cells, yet neutrophils encode an arsenal of proteolytic enzymes that imped easy and reliable study of ETI-triggered inflammasome response. Here, we describe an immunoblotting methodology to study both ETI- and PRR-driven inflammasome responses in neutrophils upon bacterial infections. This method is also transposable to other microbial pathogen- and toxin-induced inflammasome response in neutrophils.

Verticillium dahliae effector VDAL protects MYB6 from degradation by interacting with PUB25 and PUB26 E3 ligases to enhance Verticillium wilt resistance

Verticillium wilt is a severe plant disease that causes massive losses in multiple crops. Increasing the plant resistance to Verticillium wilt is a critical challenge worldwide. Here, we report that the hemibiotrophic Verticillium dahliae-secreted Asp f2-like protein VDAL causes leaf wilting when applied to cotton leaves in vitro but enhances the resistance to V. dahliae when overexpressed in Arabidopsis or cotton without affecting the plant growth and development. VDAL protein interacts with Arabidopsis E3 ligases plant U-box 25 (PUB25) and PUB26 and is ubiquitinated by PUBs in vitro. However, VDAL is not degraded by PUB25 or PUB26 in planta. Besides, the pub25 pub26 double mutant shows higher resistance to V. dahliae than the wild-type. PUBs interact with the transcription factor MYB6 in a yeast two-hybrid screen. MYB6 promotes plant resistance to Verticillium wilt while PUBs ubiquitinate MYB6 and mediate its degradation. VDAL competes with MYB6 for binding to PUBs, and the role of VDAL in increasing Verticillium wilt resistance depends on MYB6. Taken together, these results suggest that plants evolute a strategy to utilize the invaded effector protein VDAL to resist the V. dahliae infection without causing a hypersensitive response (HR); alternatively, hemibiotrophic pathogens may use some effectors to keep plant cells alive during its infection in order to take nutrients from host cells. This study provides the molecular mechanism for plants increasing disease resistance when overexpressing some effector proteins without inducing HR, and may promote searching for more genes from pathogenic fungi or bacteria to engineer plant disease resistance.

The rise, fall and resurrection of chemical-induced resistance agents

Since the discovery that the plant immune system could be augmented for improved deployment against biotic stressors through the exogenous application of chemicals that lead to induced resistance (IR), many such IR-eliciting agents have been identified. Initially it was hoped that these chemical IR agents would be a benign alternative to traditional chemical biocides. However, owing to low efficacy and/or a realization that their benefits sometimes come at the cost of growth and yield penalties, chemical IR agents fell out of favour and were seldom used as crop protection products. Despite the lack of interest in agricultural use, researchers have continued to explore the efficacy and mechanisms of chemical IR. Moreover, as we move away from the approach of 'zero tolerance' toward plant pests and pathogens toward integrated pest management, chemical IR agents could have a place in the plant protection product list. In this review, we chart the rise and fall of chemical IR agents, and then explore a variety of strategies used to improve their efficacy and remediate their negative adverse effects. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Over-expression of SlWRKY46 in tomato plants increases susceptibility to Botrytis cinerea by modulating ROS homeostasis and SA and JA signaling pathways

WRKY, as one of the largest families of transcription factors (TFs), binds to cis-acting elements of downstream genes to regulate biotic and abiotic stress. However, the role of SlWRKY46 in fungal disease response induced by Botrytis cinerea (B.cinerea) and potential mechanism remains obscure. To ascertain the role of SlWRKY46 in response to B.cinerea, we constructed SlWRKY46-overexpression plants, which were then inoculated with B.cinerea. SlWRKY46-overexpression plants were more susceptible to B.cinerea and accompanied by the inhibited activities of phenylalanine ammonialyase (PAL), polyphenol oxidase (PPO), chitinase (CHI), and β-1,3-glucanase (GLU). Additionally, SlWRKY46-overexpression plants showed the decreased activities of ascorbate peroxidase (APX), superoxide dismutase (SOD) and the content of H₂O₂, and the increased content of O₂^•-. Moreover, over-expression of SlWRKY46 suppressed the salicylic acid (SA) and jasmonic acid (JA) marker genes, pathogenesis related protein (PR1), and proteinase inhibitors (PI Ⅰ and PI Ⅱ) and consequently aggravated the disease symptoms. Therefore, we speculated that SlWRKY46 played negative regulatory roles in B. cinerea infection probably by inhibiting the activities of antioxidants and disease resistance enzymes, regulating SA and JA signaling pathways and modulating reactive oxygen (ROS) homeostasis.

Mechanisms of Effector-Mediated Immunity Revealed by the Accidental Human Pathogen Legionella pneumophila

Many Gram-negative bacterial pathogens employ translocated virulence factors, termed effector proteins, to facilitate their parasitism of host cells and evade host anti-microbial defenses. However, eukaryotes have evolved to detect effector-mediated virulence strategies through a phenomenon termed effector-triggered immunity (ETI). Although ETI was discovered in plants, a growing body of literature demonstrates that metazoans also utilize effector-mediated immunity to detect and clear bacterial pathogens. This mini review is focused on mechanisms of effector-mediated immune responses by the accidental human pathogen Legionella pneumophila. We highlight recent advancements in the field and discuss the future prospects of harnessing effectors for the development of novel therapeutics, a critical need due to the prevalence and rapid spread of antibiotic resistance.

Keeping in Touch with Type-III Secretion System Effectors: Mass Spectrometry-Based Proteomics to Study Effector-Host Protein-Protein Interactions

Manipulation of host cellular processes by translocated bacterial effectors is key to the success of bacterial pathogens and some symbionts. Therefore, a comprehensive understanding of effectors is of critical importance to understand infection biology. It has become increasingly clear that the identification of host protein targets contributes invaluable knowledge to the characterization of effector function during pathogenesis. Recent advances in mapping protein-protein interaction networks by means of mass spectrometry-based interactomics have enabled the identification of host targets at large-scale. In this review, we highlight mass spectrometry-driven proteomics strategies and recent advances to elucidate type-III secretion system effector-host protein-protein interactions. Furthermore, we highlight approaches for defining spatial and temporal effector-host interactions, and discuss possible avenues for studying natively delivered effectors in the context of infection. Overall, the knowledge gained when unravelling effector complexation with host factors will provide novel opportunities to control infectious disease outcomes.

Key Genes and Genetic Interactions of Plant-Pathogen Functional Modules in Poplar Infected by Marssonina brunnea

Marssonina brunnea, the causative pathogen of Marssonina leaf spot of poplars (MLSP), devastates poplar plantations by forming black spots on leaves and defoliating trees. Although MLSP has been studied for over 30 years, the key genes that function during M. brunnea infection and their effects on plant growth are poorly understood. Here, we used multigene association studies to investigate the effects of key genes in the plant-pathogen interaction pathway, as revealed by transcriptome analysis, on photosynthesis and growth in a natural population of 435 Populus tomentosa individuals. By analyzing transcriptomic changes during three stages of infection, we detected 628 transcription factor genes among the 7,611 differentially expressed genes that might be associated with basal defense responses. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses revealed that transcriptomic changes across different stages of infection lead to the reprogramming of metabolic processes possibly related to defense activation. We identified 29,399 common single-nucleotide polymorphisms (SNPs) within 221 full-length genes in plant-pathogen interaction pathways that were significantly associated with photosynthetic and growth traits. We also detected 4,460 significant epistatic pairs associated with stomatal conductance, tree diameter, and tree height. Epistasis analysis uncovered significant interactions between 2,561 SNP-SNP pairs from different functional modules in the plant-pathogen interaction pathway, revealing possible genetic interactions. This analysis revealed many key genes that function during M. brunnea infection and their potential roles in mediating photosynthesis and plant growth, shedding light on genetic interactions between functional modules in the plant-pathogen interaction pathway.

[Plant resistance to pathogens: A review describing the vertical and horizontal resistance concepts]

Understanding plant resistance requires an interdisciplinary effort between biological and agricultural sciences. In this setting, phytopathology has experienced an upsurge of interest from researchers and scholars in the disciplines of ecology, evolution and molecular biology. This encounter did neither avoid misunderstandings among scholars nor the use of similar concepts with different meanings. The purpose of this paper is to offer a modern comprehensive view of plant resistance against pathogens using a classical phytopathology concept as framework: Van der Plank s concept of horizontal and vertical resistance. This concept is used in other agricultural science disciplines (plant breeding and genetics), supporting why it is a proper framework for explaining plant resistance. Within this frame, other classical phytopathologycal concepts are explained in combination with modern model descriptions of plant-pathogen interactions and how all these concepts are related with quantitative and field resistance. This review is written in Spanish because it serves an additional purpose. In the Spanish-speaking America, besides interdisciplinarity, phytopathology as an academic discipline faces another challenge: the students' low-English language proficiency. In this regard, this review intends to become a companion guide for plant-pathology teachers in the region interested in providing an insight into the modern concepts of plant resistance.

The pyrin inflammasome in host-microbe interactions

Pyrin is an inflammasome sensor in phagocytes that is activated in response to bacterial toxins and effectors that modify RhoA. Pathogen effector-triggered pyrin activation is analogous to an indirect guard mechanism in plants. Pyrin activation appears to be triggered when RhoA GTPases in a host cell are prevented from binding downstream signaling proteins (transducers). RhoA transducers that control this response include PRK kinases, which negatively regulate pyrin by phosphorylation and binding of 14-3-3 proteins. Microtubules regulate pyrin at different levels and may serve as a platform for inflammasome nucleation. Pyrin increases inflammation in the lung, gut or systemically during infection or intoxication in mouse models and protects against systemic infection by decreasing bacterial loads. Pathogenic Yersinia spp. overcome this protective response using effectors that inhibit the pyrin inflammasome. Gain of function mutations in MEFV, the gene encoding pyrin, cause the autoinflammatory disease Familial Mediterranean Fever. Yersinia pestis may have selected for gain of function MEFV mutations in the human population.

The Role of a Glucosinolate-Derived Nitrile in Plant Immune Responses

Glucosinolates are defense-related secondary metabolites found in Brassicaceae. When Brassicaceae come under attack, glucosinolates are hydrolyzed into different forms of glucosinolate hydrolysis products (GHPs). Among the GHPs, isothiocyanates are the most comprehensively characterized defensive compounds, whereas the functional study of nitriles, another group of GHP, is still limited. Therefore, this study investigates whether 3-butenenitrile (3BN), a nitrile, can trigger the signaling pathways involved in the regulation of defense responses in Arabidopsis thaliana against biotic stresses. Briefly, the methodology is divided into three stages, (i) evaluate the physiological and biochemical effects of exogenous 3BN treatment on Arabidopsis, (ii) determine the metabolites involved in 3BN-mediated defense responses in Arabidopsis, and (iii) assess whether a 3BN treatment can enhance the disease tolerance of Arabidopsis against necrotrophic pathogens. As a result, a 2.5 mM 3BN treatment caused lesion formation in Arabidopsis Columbia (Col-0) plants, a process found to be modulated by nitric oxide (NO). Metabolite profiling revealed an increased production of soluble sugars, Krebs cycle associated carboxylic acids and amino acids in Arabidopsis upon a 2.5 mM 3BN treatment, presumably via NO action. Primary metabolites such as sugars and amino acids are known to be crucial components in modulating plant defense responses. Furthermore, exposure to 2.0 mM 3BN treatment began to increase the production of salicylic acid (SA) and jasmonic acid (JA) phytohormones in Arabidopsis Col-0 plants in the absence of lesion formation. The production of SA and JA in nitrate reductase loss-of function mutant (nia1nia2) plants was also induced by the 3BN treatments, with a greater induction for JA. The SA concentration in nia1nia2 plants was lower than in Col-0 plants, confirming the previously reported role of NO in controlling SA production in Arabidopsis. A 2.0 mM 3BN treatment prior to pathogen assays effectively alleviated the leaf lesion symptom of Arabidopsis Col-0 plants caused by Pectobacterium carotovorum ssp. carotovorum and Botrytis cinerea and reduced the pathogen growth on leaves. The findings of this study demonstrate that 3BN can elicit defense response pathways in Arabidopsis, which potentially involves a coordinated crosstalk between NO and phytohormone signaling.

Interleukin-32 in Infection, Inflammation and Cancer Biology

Cytokines are small pleiotropic polypeptids secreted dominantly by the cells of the immune system. These polypeptids are main mediators of innate and acquired immunity, responsible for clonal expansion and differentiation of immune cells, initiation of immune response and enhancing of effector functions of leukocytes. Cytokine-related effects are most studied in the fields of inflammation, immunology, and cancer biology. In this review we discuss one of the most intriguing, recently discovered proinflammatory cytokine, interleukin 32.

Transcriptome profiling reveals the response process of tomato carrying Cf-19 and Cladosporium fulvum interaction

BACKGROUND

During tomato cultivation, tomato leaf mould is a common disease caused by Cladosporium fulvum (C. fulvum). By encoding Cf proteins, which can recognize corresponding AVR proteins produced by C. fulvum, Cf genes provide resistance to C. fulvum, and the resistance response patterns mediated by different Cf genes are not identical. Plants carrying the Cf-19 gene show effective resistance to C. fulvum in the field and can be used as new resistant materials in breeding. In this study, to identify key regulatory genes related to resistance and to understand the resistance response process in tomato plants carrying Cf-19, RNA sequencing (RNA-seq) was used to analyse the differences between the response of resistant plants (CGN18423, carrying the Cf-19 gene) and susceptible plants (Moneymaker (MM), carrying the Cf-0 gene) at 0, 7 and 20 days after inoculation (dai).

RESULTS

A total of 418 differentially expressed genes (DEGs) were identified specifically in the CGN18423 response process. Gene Ontology (GO) analysis revealed that GO terms including "plasma membrane (GO_Component)", "histidine decarboxylase activity (GO_Function)", and "carboxylic acid metabolic process (GO_Process)", as well as other 10 GO terms, were significantly enriched. The "plant hormone signal transduction" pathway, which was unique to CGN18423 in the 0-7 dai comparison, was identified. Moreover, ten key regulatory points were screened from the "plant hormone signal transduction" pathway and the "plant pathogen interaction" pathway. Hormone content measurements revealed that the salicylic acid (SA) contents increased and peaked at 7 dai, after which the contents deceased and reached minimum values in both CGN18423 and MM plants at 20 dai. The jasmonic acid (JA) content increased to a very high level at 7 dai but then decreased to nearly the initial level at 20 dai in CGN18423, while it continued to increase slightly during the whole process from 0 to 20 dai in MM.

CONCLUSIONS

The initial responses are very different between the resistant and susceptible plants. The "plant hormone signal transduction" pathway is important for the formation of Cf-19-mediated immunity. In addition, both JA and SA play roles in regulating the Cf-19-dependent resistance response.

BTB-BACK Domain E3 Ligase MdPOB1 Suppresses Plant Pathogen Defense against Botryosphaeria dothidea by Ubiquitinating and Degrading MdPUB29 Protein in Apple

Apple ring rot is a severe disease that affects the yield and quality of apple fruits worldwide. However, the underlying molecular mechanism that involved in this process still remains largely unexplored. Here, we report that apple POZ/BTB CONTAINING-PROTEIN 1 (MdPOB1), a BTB-BACK domain E3 ligase protein, functions to suppress apple pathogen defense against Botryosphaeria dothidea (B. dothidea). Both in vitro and in vivo assays indicated that MdPOB1 interacted directly with and degraded apple U-box E3 ligase MdPUB29, a well-established positive regulator of plant innate immunity, through the ubiquitin/26S proteasome pathway. A series of transgenic analyses in apple fruits demonstrated that MdPOB1 affected apple pathogen defense against B. dothidea at least partially, if not completely, via regulating MdPUB29. Additionally, it was found that the apple pathogen defense against B. dothidea was correlated with the H2O2 contents and the relative expression of salicylic acid (SA) synthesis- and SA signaling-related genes, which might be regulated via degradation of MdPUB29 by MdPOB1. Overall, our findings provide new insights into the mechanism of the MdPOB1 modulation of apple ring rot resistance, which occur by directly regulating potential downstream target protein MdPUB29 for proteasomal degradation in apple.

The evolutionary history of LysM-RLKs (LYKs/LYRs) in wild tomatoes

Background

The LysM receptor-like kinases (LysM-RLKs) are important to both plant defense and symbiosis. Previous studies described three clades of LysM-RLKs: LysM-I/LYKs (10+ exons per gene and containing conserved kinase residues), LysM-II/LYRs (1–5 exons per gene, lacking conserved kinase residues), and LysM-III (two exons per gene, with a kinase unlike other LysM-RLK kinases and restricted to legumes). LysM-II gene products are presumably not functional as conventional receptor kinases, but several are known to operate in complexes with other LysM-RLKs. One aim of our study was to take advantage of recently mapped wild tomato transcriptomes to evaluate the evolutionary history of LysM-RLKs within and between species. The second aim was to place these results into a broader phylogenetic context by integrating them into a sequence analysis of LysM-RLKs from other functionally well-characterized model plant species. Furthermore, we sought to assess whether the Group III LysM-RLKs were restricted to the legumes or found more broadly across Angiosperms.

Results

Purifying selection was found to be the prevailing form of natural selection within species at LysM-RLKs. No signatures of balancing selection were found in species-wide samples of two wild tomato species. Most genes showed a greater extent of purifying selection in their intracellular domains, with the exception of SlLYK3 which showed strong purifying selection in both the extracellular and intracellular domains in wild tomato species. The phylogenetic analysis did not reveal a clustering of microbe/functional specificity to groups of closely related proteins. We also discovered new putative LysM-III genes in a range of Rosid species, including Eucalyptus grandis.

Conclusions

The LysM-III genes likely originated before the divergence of E. grandis from other Rosids via a fusion of a Group II LysM triplet and a kinase from another RLK family. SlLYK3 emerges as an especially interesting candidate for further study due to the high protein sequence conservation within species, its position in a clade of LysM-RLKs with distinct LysM domains, and its close evolutionary relationship with LYK3 from Arabidopsis thaliana.

Electronic supplementary material

The online version of this article (10.1186/s12862-019-1467-3) contains supplementary material, which is available to authorized users.

WRKY7, -11 and -17 transcription factors are modulators of the bZIP28 branch of the unfolded protein response during PAMP-triggered immunity in Arabidopsis thaliana

Plants must defend themselves against pathogens. The defense response requires greater protein synthesis, which generates endoplasmic reticulum (ER) stress, yet failure to attenuate this stress has detrimental effects. WRKY7/11/17 transcription factors (TFs) are negative regulators of immunity since mutants are more resistant to Pseudomonas syringae pv tomato (Pst) infection. Here, we reveal a connection between ER-stress and the molecular mechanisms underlying the wrky mutant phenotype. The bZIP28 TF upregulates ER-chaperone expression (BiP1/2, ERdj3B, and SDF2) upon exposure of Arabidopsis to a bacterial defense elicitor, flagellin 22 (Flg22). Also, the activation of ER-chaperones is more sustained in double and triple wrky mutants treated with Flg22, suggesting that WRKY7/11/17 TFs downregulate these genes. Moreover, wrky mutants accumulate more bZIP28 transcripts in response to Flg22, indicating that WRKY7/11/17 transcriptionally repress this TF. Using Arabidopsis protoplasts, we also demonstrate that WRKYs bind to the bZIP28 promoter via W-box elements. Additionally, triple wrky mutants are more resistant, whilst bzip28 mutants are more susceptible, to Pst infection. Finally, we postulate a model of PAMP-Triggered Immunity regulation, where Flg22 activates bZIP28-signaling inducing the expression of ER-stress genes, as well as WRKY7/11/17 expression, which in turn inhibits PTI by downregulating bZIP28, controlling physiological responses in the Arabidopsis-Pst interaction.

NRG1 functions downstream of EDS1 to regulate TIR-NLR-mediated plant immunity in Nicotiana benthamiana

Effector-triggered immunity (ETI) in plants involves a large family of nucleotide-binding leucine-rich repeat (NLR) immune receptors, including Toll/IL-1 receptor-NLRs (TNLs) and coiled-coil NLRs (CNLs). Although various NLR immune receptors are known, a mechanistic understanding of NLR function in ETI remains unclear. The TNL Recognition of XopQ 1 (Roq1) recognizes the effectors XopQ and HopQ1 from Xanthomonas and Pseudomonas, respectively, which activates resistance to Xanthomonas euvesicatoria and Xanthomonas gardneri in an Enhanced Disease Susceptibility 1 (EDS1)-dependent way in Nicotiana benthamiana In this study, we found that the N. benthamiana N requirement gene 1 (NRG1), a CNL protein required for the tobacco TNL protein N-mediated resistance to tobacco mosaic virus, is also essential for immune signaling [including hypersensitive response (HR)] triggered by the TNLs Roq1 and Recognition of Peronospora parasitica 1 (RPP1), but not by the CNLs Bs2 and Rps2, suggesting that NRG1 may be a conserved key component in TNL signaling pathways. Besides EDS1, Roq1 and NRG1 are necessary for resistance to Xanthomonas and Pseudomonas in N. benthamiana NRG1 functions downstream of Roq1 and EDS1 and physically associates with EDS1 in mediating XopQ-Roq1-triggered immunity. Moreover, RNA sequencing analysis showed that XopQ-triggered gene-expression profile changes in N. benthamiana were almost entirely mediated by Roq1 and EDS1 and were largely regulated by NRG1. Overall, our study demonstrates that NRG1 is a key component that acts downstream of EDS1 to mediate various TNL signaling pathways, including Roq1 and RPP1-mediated HR, resistance to Xanthomonas and Pseudomonas, and XopQ-regulated transcriptional changes in N. benthamiana.

Nucleolar fibrillarin is an evolutionarily conserved regulator of bacterial pathogen resistance

Innate immunity is the first line of defense against infections. Pathways regulating innate responses can also modulate other processes, including stress resistance and longevity. Increasing evidence suggests a role for the nucleolus in regulating cellular processes implicated in health and disease. Here we show the highly conserved nucleolar protein, fibrillarin, is a vital factor regulating pathogen resistance. Fibrillarin knockdown enhances resistance in C. elegans against bacterial pathogens, higher levels of fibrillarin induce susceptibility to infection. Pathogenic infection reduces nucleolar size, ribsosomal RNA, and fibrillarin levels. Genetic epistasis reveals fibrillarin functions independently of the major innate immunity mediators, suggesting novel mechanisms of pathogen resistance. Bacterial infection also reduces nucleolar size and fibrillarin levels in mammalian cells. Fibrillarin knockdown prior to infection increases intracellular bacterial clearance, reduces inflammation, and enhances cell survival. Collectively, these findings reveal an evolutionarily conserved role of fibrillarin in infection resistance and suggest the nucleolus as a focal point in innate immune responses.

Knockout of SlMAPK3 Reduced Disease Resistance to Botrytis cinerea in Tomato Plants

Mitogen-activated protein kinases (MAPKs) play an important role in defense responses to biotic and abiotic stresses. In order to investigate the role of SlMAPK3 in tomato plant resistance to Botrytis cinerea, two lines of slmapk3 mutants and wild-type (WT) tomato plants were used. The results showed that slmapk3 mutants were more susceptible to B. cinerea and that knockout of SlMAPK3 reduced the activities of defense enzymes and enhanced the accumulation of reactive oxygen species (ROS). Furthermore, we detected the expressions of salicylic acid (SA) and jasmonic acid (JA) signaling-related genes and found that knockout of SlMAPK3 enhanced the expressions of SlPR1, SlPAD4 and SlEDS1, whereas reduced the expressions of SlLoxC, SlPI I and SlPI II and enhanced the expressions of SlJAZ1 and SlMYC2. We postulate that SlMAPK3 plays a positive role in tomato plant resistance to B. cinerea through regulating ROS accumulation and SA and JA defense signaling pathways.

Interaction between Insects, Toxins, and Bacteria: Have We Been Wrong So Far?

Toxins are a major virulence factor produced by many pathogenic bacteria. In vertebrates, the response of hosts to the bacteria is inseparable from the response to the toxins, allowing a comprehensive understanding of this tripartite host-pathogen-toxin interaction. However, in invertebrates, this interaction has been investigated by two complementary but historically distinct fields of research: toxinology and immunology. In this article, I highlight how such dichotomy between these two fields led to a biased, or even erroneous view of the ecology and evolution of the interaction between insects, toxins, and bacteria. I focus on the reason behind such a dichotomy, on how to bridge the fields together, and on confounding effects that could bias the outcome of the experiments. Finally, I raise four questions at the border of the two fields on the cross-effects between toxins, bacteria, and spores that have been largely underexplored to promote a more comprehensive view of this interaction.

Comparative Transcriptomics Reveals How Wheat Responds to Infection by Zymoseptoria tritici

The fungus Zymoseptoria tritici causes septoria tritici blotch (STB) on wheat, an important disease globally and the most damaging wheat disease in Europe. Despite the global significance of STB, the molecular basis of wheat defense against Z. tritici is poorly understood. Here, we use a comparative transcriptomic study to investigate how wheat responds to infection by four distinct strains of Z. tritici. We examined the response of wheat across the entire infection cycle, identifying both shared responses to the four strains and strain-specific responses. We found that the early asymptomatic phase is characterized by strong upregulation of genes encoding receptor-like kinases and pathogenesis-related proteins, indicating the onset of a defense response. We also identified genes that were differentially expressed among the four fungal strains, including genes related to defense. Genes involved in senescence were induced during both the asymptomatic phase and at late stages of infection, suggesting manipulation of senescence processes by both the plant and the pathogen. Our findings illustrate the need, when identifying important genes affecting disease resistance in plants, to include multiple pathogen strains.

The early response during the interaction of fungal phytopathogen and host plant

Plants can be infected by a variety of pathogens, most of which can cause severe economic losses. The plants resist the invasion of pathogens via the innate or acquired immune system for surviving biotic stress. The associations between plants and pathogens are sophisticated beyond imaging and the interactions between them can occur at a very early stage after their touching each other. A number of researchers in the past decade have shown that many biochemical events appeared even as early as 5 min after their touching for plant disease resistance response. The early molecular interactions of plants and pathogens are likely to involve protein phosphorylation, ion fluxes, reactive oxygen species (ROS) and other signalling transduction. Here, we reviewed the recent progress in the study for molecular interaction response of fungal pathogens and host plant at the early infection stage, which included many economically important crop fungal pathogens such as cereal rust fungi, tomato Cladosporium fulvum, rice blast and so on. By dissecting the earlier infection stage of the diseases, the avirulent/virulent genes of pathogen or resistance genes of plant could be defined more clearly and accurately, which would undoubtedly facilitate fungal pathogenesis study and resistant crop breeding.

The Microbial Zoo in the C. elegans Intestine: Bacteria, Fungi and Viruses

C. elegans is an invaluable model organism that has been a driving force in many fundamental biological discoveries. However, it is only in the past two decades that it has been applied to host–pathogen interaction studies. These studies have been facilitated by the discoveries of natural microbes that infect C. elegans, including bacteria, fungi and viruses. Notably, many of these microbes share a common site of infection, the C. elegans intestine. Furthermore, the recent descriptions of a natural gut microbiota in C. elegans raise the possibility that this could be a novel model system for microbiome and trans-kingdom interaction studies. Here we review studies of C. elegans host–microbe interactions with a particular focus on the intestine.

Deletion of NADH oxidase in Listeria monocytogenes promotes the bacterial infection of brain

NADH oxidase (NOX) plays important roles in respiration and reactive oxygen species (ROS) generation in cells. In this study, we explored the function of NOX in Listeria monocytogenes by gene deletion. From our results, nox mutant strain (∆nox) had lower H₂O₂ level and showed no significant alteration in bacteria growth activity. But it had enhanced invasiveness during the invasion of glial cells and mice brain compared to wildtype strain. Furthermore, several virulence genes involved in invasion, such as inlA, inlB, vip and sigB, were upregulated in ∆nox, and the alterations could be restored by complementation. To explore if nox was involved in the interaction of pathogen and host, we examined the generation of host ROS including superoxide and H₂O₂ during infection, and found ∆nox invasion leading to less superoxide and H₂O₂ generation. Besides, the upregulation of pro-inflammatory factors in glial cells was restrained when invaded by ∆nox compared to wildtype and complementary strain. In conclusion, our study evaluated the function of nox in L. monocytogenes and indicated that nox could regulate the invasion of L. monocytogenes by regulating virulence genes expression and the interaction of host-and- pathogens.

Par3 integrates Tiam1 and phosphatidylinositol 3-kinase signaling to change apical membrane identity

Pathogens can alter epithelial polarity by recruiting polarity proteins to the apical membrane, but how a change in protein localization is linked to polarity disruption is not clear. In this study, we used chemically induced dimerization to rapidly relocalize proteins from the cytosol to the apical surface. We demonstrate that forced apical localization of Par3, which is normally restricted to tight junctions, is sufficient to alter apical membrane identity through its interactions with phosphatidylinositol 3-kinase (PI3K) and the Rac1 guanine nucleotide exchange factor Tiam1. We further show that PI3K activity is required upstream of Rac1, and that simultaneously targeting PI3K and Tiam1 to the apical membrane has a synergistic effect on membrane remodeling. Thus, Par3 coordinates the action of PI3K and Tiam1 to define membrane identity, revealing a signaling mechanism that can be exploited by human mucosal pathogens.

Cold-inducible proteins CIRP and RBM3, a unique couple with activities far beyond the cold

Cold-inducible RNA-binding protein (CIRP) and RNA-binding motif protein 3 (RBM3) are two evolutionarily conserved RNA-binding proteins that are transcriptionally upregulated in response to low temperature. Featuring an RNA-recognition motif (RRM) and an arginine-glycine-rich (RGG) domain, these proteins display many similarities and specific disparities in the regulation of numerous molecular and cellular events. The resistance to serum withdrawal, endoplasmic reticulum stress, or other harsh conditions conferred by RBM3 has led to its reputation as a survival gene. Once CIRP protein is released from cells, it appears to bolster inflammation, contributing to poor prognosis in septic patients. A variety of human tumor specimens have been analyzed for CIRP and RBM3 expression. Surprisingly, RBM3 expression was primarily found to be positively associated with the survival of chemotherapy-treated patients, while CIRP expression was inversely linked to patient survival. In this comprehensive review, we summarize the evolutionary conservation of CIRP and RBM3 across species as well as their molecular interactions, cellular functions, and roles in diverse physiological and pathological processes, including circadian rhythm, inflammation, neural plasticity, stem cell properties, and cancer development.

The Enterobacterial Genotoxins: Cytolethal Distending Toxin and Colibactin

While the DNA damage induced by ionizing radiation and by many chemical compounds and drugs is well characterized, the genotoxic insults inflicted by bacteria are only scarcely documented. However, accumulating evidence indicates that we are exposed to bacterial genotoxins. The prototypes of such bacterial genotoxins are the Cytolethal Distending Toxins (CDTs) produced by Escherichia coli and Salmonella enterica serovar Typhi. CDTs display the DNase structure fold and activity, and induce DNA strand breaks in the intoxicated host cell nuclei. E. coli and certain other Enterobacteriaceae species synthesize another genotoxin, colibactin. Colibactin is a secondary metabolite, a hybrid polyketide/nonribosomal peptide compound synthesized by a complex biosynthetic machinery. In this review, we summarize the current knowledge on CDT and colibactin produced by E. coli and/or Salmonella Typhi. We describe their prevalence, genetic determinants, modes of action, and impact in infectious diseases or gut colonization, and discuss the possible involvement of these genotoxigenic bacteria in cancer.

The C. elegans CCAAT-Enhancer-Binding Protein Gamma Is Required for Surveillance Immunity

Pathogens attack host cells by deploying toxins that perturb core host processes. Recent findings from the nematode C. elegans and other metazoans indicate that surveillance or "effector-triggered" pathways monitor functioning of these core processes and mount protective responses when they are perturbed. Despite a growing number of examples of surveillance immunity, the signaling components remain poorly defined. Here, we show that CEBP-2, the C. elegans ortholog of mammalian CCAAT-enhancer-binding protein gamma, is a key player in surveillance immunity. We show that CEBP-2 acts together with the bZIP transcription factor ZIP-2 in the protective response to translational block by P. aeruginosa Exotoxin A as well as perturbations of other processes. CEBP-2 serves to limit pathogen burden, promote survival upon P. aeruginosa infection, and also promote survival upon Exotoxin A exposure. These findings may have broad implications for the mechanisms by which animals sense pathogenic attack and mount protective responses.

Mimicking microbial strategies for the design of mucus-permeating nanoparticles for oral immunization

Dealing with mucosal delivery systems means dealing with mucus. The name mucosa comes from mucus, a dense fluid enriched in glycoproteins, such as mucin, which main function is to protect the delicate mucosal epithelium. Mucus provides a barrier against physiological chemical and physical aggressors (i.e., host secreted digestive products such as bile acids and enzymes, food particles) but also against the potentially noxious microbiota and their products. Intestinal mucosa covers 400m(2) in the human host, and, as a consequence, is the major portal of entry of the majority of known pathogens. But, in turn, some microorganisms have evolved many different approaches to circumvent this barrier, a direct consequence of natural co-evolution. The understanding of these mechanisms (known as virulence factors) used to interact and/or disrupt mucosal barriers should instruct us to a rational design of nanoparticulate delivery systems intended for oral vaccination and immunotherapy. This review deals with this mimetic approach to obtain nanocarriers capable to reach the epithelial cells after oral delivery and, in parallel, induce strong and long-lasting immune and protective responses.

Repurposing salicylanilide anthelmintic drugs to combat drug resistant Staphylococcus aureus

Staphylococcus aureus is a Gram-positive bacterium that has become the leading cause of hospital acquired infections in the US. Repurposing Food and Drug Administration (FDA) approved drugs for antimicrobial therapy involves lower risks and costs compared to de novo development of novel antimicrobial agents. In this study, we examined the antimicrobial properties of two commercially available anthelmintic drugs. The FDA approved drug niclosamide and the veterinary drug oxyclozanide displayed strong in vivo and in vitro activity against methicillin resistant S. aureus (minimum inhibitory concentration (MIC): 0.125 and 0.5 μg/ml respectively; minimum effective concentration: ≤ 0.78 μg/ml for both drugs). The two drugs were also effective against another Gram-positive bacteria Enterococcus faecium (MIC 0.25 and 2 μg/ml respectively), but not against the Gram-negative species Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter aerogenes. The in vitro antimicrobial activity of niclosamide and oxyclozanide were determined against methicillin, vancomycin, linezolid or daptomycin resistant S. aureus clinical isolates, with MICs at 0.0625-0.5 and 0.125-2 μg/ml for niclosamide and oxyclozanide respectively. A time-kill study demonstrated that niclosamide is bacteriostatic, whereas oxyclozanide is bactericidal. Interestingly, oxyclozanide permeabilized the bacterial membrane but neither of the anthelmintic drugs exhibited demonstrable toxicity to sheep erythrocytes. Oxyclozanide was non-toxic to HepG2 human liver carcinoma cells within the range of its in vitro MICs but niclosamide displayed toxicity even at low concentrations. These data show that the salicylanilide anthelmintic drugs niclosamide and oxyclozanide are suitable candidates for mechanism of action studies and further clinical evaluation for treatment of staphylococcal infections.

Microbial pathogenesis and host defense in the nematode C. elegans

Epithelial cells line the surfaces of the body, and are on the front lines of defense against microbial infection. Like many other metazoans, the nematode Caenorhabditis elegans lacks known professional immune cells and relies heavily on defense mediated by epithelial cells. New results indicate that epithelial defense in C. elegans can be triggered through detection of pathogen-induced perturbation of core physiology within host cells and through autophagic defense against intracellular and extracellular pathogens. Recent studies have also illuminated a diverse array of pathogenic attack strategies used against C. elegans. These findings are providing insight into the underpinnings of host/pathogen interactions in a simple animal host that can inform studies of infectious diseases in humans.

Insect-derived cecropins display activity against Acinetobacter baumannii in a whole-animal high-throughput Caenorhabditis elegans model

The rise of multidrug-resistant Acinetobacter baumannii and a concomitant decrease in antibiotic treatment options warrants a search for new classes of antibacterial agents. We have found that A. baumannii is pathogenic and lethal to the model host organism Caenorhabditis elegans and have exploited this phenomenon to develop an automated, high-throughput, high-content screening assay in liquid culture that can be used to identify novel antibiotics effective against A. baumannii. The screening assay involves coincubating C. elegans with A. baumannii in 384-well plates containing potential antibacterial compounds. At the end of the incubation period, worms are stained with a dye that stains only dead animals, and images are acquired using automated microscopy and then analyzed using an automated image analysis program. This robust assay yields a Z' factor consistently greater than 0.7. In a pilot experiment to test the efficacy of the assay, we screened a small custom library of synthetic antimicrobial peptides (AMPs) that were synthesized using publicly available sequence data and/or transcriptomic data from immune-challenged insects. We identified cecropin A and 14 other cecropin or cecropin-like peptides that were able to enhance C. elegans survival in the presence of A. baumannii. Interestingly, one particular hit, BR003-cecropin A, a cationic peptide synthesized by the mosquito Aedes aegypti, showed antibiotic activity against a panel of Gram-negative bacteria and exhibited a low MIC (5 μg/ml) against A. baumannii. BR003-cecropin A causes membrane permeability in A. baumannii, which could be the underlying mechanism of its lethality.

Plant pathogenic bacteria target the actin microfilament network involved in the trafficking of disease defense components

Cells of infected organisms transport disease defense-related molecules along actin filaments to deliver them to their sites of action to combat the pathogen. To accommodate higher demand for intracellular traffic, plant F-actin density increases transiently during infection or treatment of Arabidopsis with pathogen-associated molecules. Many animal and plant pathogens interfere with actin polymerization and depolymerization to avoid immune responses. Pseudomonas syringae, a plant extracellular pathogen, injects HopW1 effector into host cells to disrupt the actin cytoskeleton and reduce vesicle movement in order to elude defense responses. In some Arabidopsis accessions, however, HopW1 is recognized and causes resistance via an actin-independent mechanism. HopW1 targets isoform 7 of vegetative actin (ACT7) that is regulated by phytohormones and environmental factors. We hypothesize that dynamic changes of ACT7 filaments are involved in plant immunity.