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PubMed2025

Proteomic snapshot of pattern triggered immunity in the Arabidopsis leaf apoplast.

The apoplast is a critical interface in plant-pathogen interactions, particularly in the context of pattern-triggered immunity (PTI), which is initiated by recognition of microbe-associated molecular patterns. Our study characterizes the proteomic profile of the Arabidopsis apoplast during PTI induced by flg22, a 22-amino-acid bacterial flagellin epitope, to elucidate the output of PTI. Apoplastic washing fluid was extracted with minimal cytoplasmic contamination for liquid chromatography-tandem mass spectrometry analysis. By comparing our data to publicly available transcriptome profiles of flg22 treatment from 1 to 18 h, we observed that several highly abundant proteins exhibit relatively unchanged gene expression across all time points. We also observed topological bias in peptide recovery of 19 enriched receptor-like kinases with peptides predominantly recovered from their ectodomains. Notably, tetraspanin 8, an exosome marker, was enriched in PTI samples. We additionally confirmed increased concentrations of exosomes during PTI. This study enhances our understanding of the proteomic changes in the apoplast during plant immune responses and lays the groundwork for future investigations into the molecular mechanisms of plant defense under recognition of pathogen molecular patterns.

Arabidopsis↗

PubMed2000

Effector proteins of phytopathogenic bacteria: bifunctional signals in virulence and host recognition.

Phytopathogenic bacteria deliver effectors of disease into plant hosts via a Type III secretion system. These Type III effectors have genetically determined roles in virulence. They also are among the components recognized by the putative receptors of the plant innate immune system. Recent breakthroughs include localization of some of these Type III effectors to specific host cell compartments, and the first dissection of pathogenicity islands that carry them.

Bacteria↗

PubMed2005

Involvement of PPS3 phosphorylated by elicitor-responsive mitogen-activated protein kinases in the regulation of plant cell death.

Mitogen-activated protein kinase (MAPK) cascades play pivotal roles in plant innate immunity. Overexpression of StMEK1(DD), a constitutively active MAPK kinase that activates salicylic acid-induced protein kinase (SIPK) and wound-induced protein kinase (WIPK), provokes hypersensitive response-like cell death in Nicotiana benthamiana. Here we purified a 51-kD MAPK, which was activated in potato (Solanum tuberosum) tubers treated with hyphal wall elicitor of a plant pathogen, and isolated the cDNA designated StMPK1. The deduced amino acid sequence of the StMPK1 showed strong similarity to stress-responsive MAPKs, such as tobacco (Nicotiana tabacum) SIPK and Arabidopsis (Arabidopsis thaliana) AtMPK6. To investigate the downstream signaling of StMPK1, we identified several proteins phosphorylated by StMPK1 (PPSs) using an in vitro expression cloning method. To dissect the biological function of PPSs in the plant defense, we employed virus-induced gene silencing (VIGS) in N. benthamiana. VIGS of NbPPS3 significantly delayed cell death induced by the transient expression of StMEK1(DD) and treatment with hyphal wall elicitor. Furthermore, the mobility shift of NbPPS3 on SDS-polyacrylamide gel was induced by transient expression of StMEK1(DD). The mobility shift of NbPPS3 induced by StMEK1(DD) was not compromised by VIGS of WIPK or SIPK alone, but drastically reduced by the silencing of both WIPK and SIPK. This work strongly supports the idea that PPS3 is a physiological substrate of StMPK1 and is involved in cell death activated by a MAPK cascade.

Amino Acid Sequence↗

PubMed2006

Defoliating insect immune defense interacts with induced plant defense during a population outbreak.

During population outbreaks, top-down and bottom-up factors are unable to control defoliator numbers. To our knowledge, details of biotic interactions leading to increased population density have not been studied during real population outbreaks. We experimentally assessed the strength of plant defenses and of insect immunocompetence, assumed to contribute to active insect resistance against parasitoids and pathogens, in the geometrid Epirrita autumnata during a steep increase in population density. We demonstrated rapid (same-season) induced resistance in the foliage of its host, mountain birch. The response was systemic, spreading throughout the tree, and retarded larval growth rate by approximately 10%. On the other hand, no direct delayed carry-over effects were found in the next season in larval growth rate, mortality, or pupal mass. Larval damage to a tree during the previous year, however, significantly (by approximately 13%) accelerated the advance of the immune response (measured as melanization of an implant inserted into the pupal hemocoel). The encapsulation rate correlated positively with larval mortality in trees in which larvae had been introduced the previous year, but not in control trees. Both of these observations suggest that induced plant defense was associated with an increased insect immunocompetence during the population increase.

Animals↗

PubMed2004

Identification of MAPKs and their possible MAPK kinase activators involved in the Pto-mediated defense response of tomato.

The Pto kinase mediates resistance to bacterial speck disease in tomato by activating host defenses upon recognition of Pseudomonas syringae pv. tomato strains expressing the AvrPto or AvrPtoB proteins. Previous gene-silencing experiments have indicated that mitogen activated protein kinase (MAPK) cascades play a key role downstream of the Pto kinase to activate host defense responses. Here we use biochemical methods to demonstrate that two tomato MAPKs, LeMPK2 and LeMPK3, are activated in leaves in a Pto-specific manner upon expression of AvrPto and AvrPtoB. We show that these same MAPKs are activated upon overexpression of LeMAPKKKalpha, a protein previously demonstrated to be involved in Pto-mediated immunity. We identified two phylogenetically unrelated MAPK kinases (LeMKK2 and LeMKK4) that when overexpressed in leaves elicit cell death and activate LeMPK2 and LeMPK3. In vitro analysis demonstrated that LeMKK2 and LeMKK4 each phosphorylate the same subset of three MAPKs. Together these data provide biochemical evidence for the involvement of MAPK cascades in Pto-mediated resistance.

Arabidopsis Proteins↗

PubMed2003

Naip5 affects host susceptibility to the intracellular pathogen Legionella pneumophila.

BACKGROUND: Legionella pneumophila is a gram-negative bacterial pathogen that is the cause of Legionnaires' Disease. Legionella produces disease because it can replicate inside a specialized compartment of host macrophages. Macrophages isolated from various inbred mice exhibit large differences in permissiveness for intracellular replication of Legionella. A locus affecting this host-resistance phenotype, Lgn1, has been mapped to chromosome 13, but the responsible gene has not been identified. RESULTS: Here, we report that Naip5 (also known as Birc1e) influences susceptibility to Legionella. Naip5 encodes a protein that is homologous to plant innate immunity (so-called "resistance") proteins and has been implicated in signaling pathways related to apoptosis regulation. Detailed recombination mapping and analysis of expression implicates Naip5 in the Legionella permissiveness differences among mouse strains. A bacterial artificial chromosome (BAC) transgenic line expressing a nonpermissive allele of Naip5 exhibits a reduction in macrophage Legionella permissiveness. In addition, morpholino-based antisense inhibition of Naip5 causes an increase in the Legionella permissiveness of macrophages. CONCLUSIONS: We conclude that polymorphisms in Naip5 are involved in the permissiveness differences of mouse macrophages for intracellular Legionella replication. We speculate that Naip5 is a functional mammalian homolog of plant "resistance" proteins that monitor for, and initiate host response to, the presence of secreted bacterial virulence proteins.

Animals↗

PubMed2003

Defensins: antimicrobial peptides of innate immunity.

The production of natural antibiotic peptides has emerged as an important mechanism of innate immunity in plants and animals. Defensins are diverse members of a large family of antimicrobial peptides, contributing to the antimicrobial action of granulocytes, mucosal host defence in the small intestine and epithelial host defence in the skin and elsewhere. This review, inspired by a spate of recent studies of defensins in human diseases and animal models, focuses on the biological function of defensins.

Amino Acid Sequence↗

PubMed2006

Does R gene resistance allow wheat to prevent plant growth effects associated with Hessian fly (Diptera: Cecidomyiidae) attack?

Resistance genes (R genes) are an important part of the plant's immune system. Among insects, the Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae), larva is the target of the greatest number of characterized R genes (H1-H32). The biochemical/molecular mechanism of R gene resistance to Hessian fly is not well understood. In the absence of an effective R gene, larvae caused extensive growth deficits (> 30 cm) in wheat seedlings. In the presence of one of three effective R genes, H6, H9, or H13, larvae caused small growth deficits (approximately 3-4 cm) in two leaves (third and fourth) that were actively growing during the first days of larval attack. After larvae died on R gene plants, the fifth leaf and tiller leaves exhibited small increases in growth (2-4 cm). Growth responses of susceptible and resistant plants diverged at a time when Hessian fly larvae were establishing a nutritive gall tissue at feeding sites. The results of this study support the hypothesis that R gene resistance cannot prevent initial larval attack, but, by stopping the formation of the larval gall, it prevents the most serious consequences of larval attack.

Animals↗

PubMed2003

An ancient enzyme domain hidden in the putative beta-glucan elicitor receptor of soybean may play an active part in the perception of pathogen-associated molecular patterns during broad host resistance.

A successful defense against potential pathogens requires that a host organism is able to discriminate between self and nonself structures. Soybean (Glycine max L.) exploits a specific molecular pattern, a 1,6-beta-linked and 1,3-beta-branched heptaglucoside (HG), present in cell walls of the oomycetal pathogen Phytophthora sojae, as a signal compound eliciting the onset of defense reactions. The specific and high affinity HG-binding site is contained in the beta-glucan-binding protein (GBP), which in turn is part of a proposed receptor complex. The ability to perceive and respond to Phytophthora cell wall-derived beta-glucan elicitors is exclusive to plants that belong to the Fabaceae. However, we propose that the presence of the GBP is essential, but not sufficient for beta-glucan elicitor-dependent disease resistance because genes encoding GBP-related proteins can be retrieved from many plant species. Furthermore, we show that the GBP is composed of two different carbohydrateactive protein domains, one containing the beta-glucan-binding site, and the other related to glucan endoglucosidases of fungal origin. The glucan hydrolase displays most likely an endo-specific mode of action, cleaving only 1,3-beta-d-glucosidic linkages of oligoglucosides consisting of at least four moieties. Thus, the intrinsic endo-1,3-beta-glucanase activity of the GBP is perfectly suited during initial contact with Phytophthora to release oligoglucoside fragments enriched in motifs that constitute ligands for the high affinity binding site present in the same protein. The concept of innate immunity in plants receives substantial support by this highly sophisticated system using ancient enzyme modules as an active part of the recognition mechanism.

Amino Acid Motifs↗

PubMed2004

Genetic analysis and mapping of resistance to lettuce dieback: a soilborne disease caused by tombusviruses.

A diverse collection of modern, heirloom and specialty cultivars, plant introduction (PI) accessions, and breeding lines of lettuce were screened for susceptibility to lettuce dieback, which is a disease caused by soilborne viruses of the family Tombusviridae. Susceptibility was evaluated by visual symptom assessment in fields that had been previously shown to be infested with Lettuce necrotic stunt virus. Of the 241 genotypes tested in multiple field experiments, 76 remained symptom-free in infested fields and were therefore classified as resistant to dieback. Overall, resistant genotypes were as prevalent among modern cultivars as in heirloom cultivars or primitive germplasm. Within modern germplasm, however, all crisphead (iceberg) cultivars were resistant, while all romaine cultivars were susceptible. Using enzyme-linked immunosorbent assay, tombusviruses were detected in leaves of some plants of resistant genotypes that were grown in infested fields, suggesting that symptom-free plants are not immune to viral infection. The inheritance of resistance was studied for 'Salinas', a modern iceberg cultivar, and PI 491224, the progenitor of recently released romaine germplasm with resistance to lettuce dieback. Resistance was conferred by a dominant allele at a single locus in both genotypes. The tombusvirus resistance locus from 'Salinas', Tvr1, was mapped in an intraspecific Lactuca sativa population to a location that corresponds to linkage group 2 on the consensus map of Lactuca. The largest cluster of resistance genes in lettuce, the Dm1/Dm3 cluster, is found on this linkage group; however, the precise position of Tvr1 relative to this cluster has not yet been determined. To our knowledge, Tvr1 is the first tombusvirus resistance gene identified for any plant host.

Chromosome Mapping↗

PubMed2002

Immune system and antioxidants, especially those derived from Indian medicinal plants.

During the functioning of the immune system, such as in phagocytosis, reactive oxygen and nitrogen species are generated. If they are left unchecked they can affect the components of the immune system by inducing oxidative damage. This is more so in the elderly or during inflammation where there is excess generation of these reactive species than can be taken care of by the defenses in the form of antioxidants. Dietary supplementation with antioxidants may greatly help in such conditions. There are some indications of possible benefits of antioxidant supplementation. Natural compounds from medicinal plants having antioxidant and immunomodulatory activities have potential as therapeutic agents in this regard. Indian medicinal plants with these activities have been identified and their antioxidant and immunomodulatory effects reviewed. The possible future prospects in this regard are also outlined.

Adjuvants, Immunologic↗

PubMed1999

Plant pathogenesis-related proteins: molecular mechanisms of gene expression and protein function.

Higher plants accumulate several kinds of "pathogenesis-related (PR)" proteins in response to infection by pathogens such as fungi or viruses. Gene expression of one group of PR proteins is known to be mediated by phytohormone ethylene. Here we describe the signal transduction system from the ethylene receptor ETR to transcription factors, ERFs. Ethylene-inducible PR genes are expressed constitutively in roots and cultured cells even when are not infected. We discuss the mechanisms of this pathogen-independent expression of PR genes and describe recent findings in the study of molecular mechanisms of antifungal activities of the PR proteins. Genes of PR-1 and -5 proteins have now been identified in the genomes of various species of organisms, including humans and nematodes. PR proteins may contribute to the innate immunity of plants as well as to that of other organisms.

Amino Acid Sequence↗

PubMed1999

Human gamma delta T cells recognize alkylamines derived from microbes, edible plants, and tea: implications for innate immunity.

Approximately 4% of peripheral blood T cells in humans express a T cell receptor with markedly restricted germline gene segment usage (V gamma 2 V delta 2). Remarkably, these T cells expand 2- to 10-fold (8%-60% of all circulating T cells) during many microbial infections. We show here that these T cells recognize a family of naturally occurring primary alkylamines in a TCR-dependent manner. These antigenic alkylamines are secreted to millimolar concentrations in bacterial supernatants and are found in certain edible plants. Given the large numbers of memory V gamma 2 V delta 2 T cells in adult humans, recognition of alkylamine antigens offers the immune system a response of the magnitude of major superantigens for alpha beta T cells and may bridge the gap between innate and adaptive immunity.

Amines↗

PubMed2000

Prevalence of hepatitis A virus infection in sewage plant workers of Central Italy: is indication for vaccination justified?

Prevalence of antibodies to hepatitis A virus (HAV) was studied in a group of 65 sewage plant workers living in Tuscany, Central Italy. In order to evaluate the effect of several confounders (age, place of birth, income, educational degree, sea-food consumption, etc.), subjects under study were matched with 160 other workers residing in the same area. Anti-HAV was detected in about 51% of sewage workers and 44% of other employees. The difference was not statistically significant. Both univariate and multivariate analysis showed that the main variables related to previous HAV infection were increasing age (P<0.001), birth in Southern Italy (P<0.01) and lower educational degree (P<0.001). Although other studies in Northern and Central Europe showed a slightly higher risk of infection in sewage workers versus general population, lack of evidence of occupational risk in Italy might be explained by the relative importance of a higher degree of viral circulation in the past. The changing epidemiology of HAV infection in Italy with increasing numbers of susceptibles in adults and the potential occupational risk suggest that the present indication to immunize sewage plant workers against hepatitis A should be maintained.

Adult↗

PubMed2026

Biocontrol effect of a solid-state fermentation-derived extract mixture of Trichoderma asperellum on sunflower Sclerotinia rot and associated host defense responses.

Sclerotinia disease is a destructive fungal disease of sunflowers, soybeans, and other economically important crops, causing substantial yield loss and quality deterioration. Long-term reliance on dose-dependent broad-spectrum fungicides is constrained by resistance risks and potential environmental burdens, creating tension with the sustainability goal of "reducing pesticide use while improving efficacy." Here, we explore a Trichoderma spp.-based microbial disease management strategy. Whole-genome sequencing of Trichoderma asperellum TCS007 isolated from Antarctic marine sediments, coupled with genome mining, predicted diverse biosynthetic gene clusters putatively associated with siderophores, polyketides, nonribosomal peptides, and terpenoids; the corresponding metabolites are not chemically confirmed and require further validation. Using a solid-state fermentation workflow, we prepared a fermentation-derived extract mixture (TCS007-SSF-Ex). In vitro assays showed dose-dependent inhibition of Sclerotinia sclerotiorum by TCS007-SSF-Ex (EC50 = 1.252 mg/L), and microscopy revealed cellular damage-consistent changes, including organelle disruption and plasmolysis. Pathogen transcriptomic and metabolism-related analyses indicated broad perturbations in organelle biogenesis and metabolic processes, with significant alterations in pathways associated with succinate, D-glucose, and phenylacetate; these results are consistent with growth inhibition and reduced pathogenicity, but specific molecular targets and causal links remain to be validated. In vivo, under certain application conditions, triple applications increased APX activity (+492.5%) and β-1,3-glucanase activity (+419.6%). Collectively, this work supports a "pathogen suppression-host defense induction" framework and facilitates subsequent identification of active components and mechanistic validation.IMPORTANCESclerotinia diseases cause recurrent and economically important losses in oilseed crops, while long-term fungicide use is constrained by resistance risks and environmental burdens. Trichoderma-based biocontrol is a promising complementary strategy, yet evidence supporting metabolite-containing Trichoderma-derived preparations as immune elicitors remains less consolidated than that for living inoculants, and scalable production routes are still needed. Here, we examine an Antarctic marine sediment-derived strain, Trichoderma asperellum TCS007, and a solid-state fermentation (SSF)-derived extract mixture (TCS007-SSF-Ex) produced via solid-state fermentation. We combine in vitro antifungal assays, pathogen ultrastructural observations, and correlative omics analyses with in vivo measurements of sunflower defense enzymes (APX and β-1,3-glucanase) to evaluate a "pathogen suppression-host defense induction" framework. Our findings support the potential of SSF-derived Trichoderma metabolite mixtures for greener management of Sclerotinia disease and provide a foundation for future chemical identification of active components and mechanistic validation.

Ascomycota↗

PubMed2002

Plant disease resistance: commonality and novelty in multicellular innate immunity.

Pathogen avirulence genes encode for effector molecules that play a crucial role in the process of pathogen colonization of plant tissue. Successful host defense requires rapid and efficient detection of the pathogen avirulence factors. In the last few years, much progress has been made in delineating the plant molecular sentinels that participate in pathogen identification. Because this ability is genetic information that is 'hard-wired' into the genome, it is called 'innate immunity' and it draws its origins from a phylogenetically ancient form of immunity common to plants and animals. Conservation is shown in many of the functional molecular motifs of innate genes such as the Toll/interleukin 1 receptor domains, nucleotide binding domains and structures that contain leucine rich repeats. Novel plant molecular surveillance domains also include pathogen pattern recognition by coiled-coil domains and specialized kinases. The rapid evolution of plant innate immunity genes is readily detected in their sequence polymorphism, by their massive amplification and appearance in the genome in a clustered organization. By comparative biology of highly diverged innate immunity systems we can enhance our appreciation of the truly basic forces that have shaped its evolution in mutlicellular organisms.

Amino Acid Sequence↗

PubMed2006

Resistance proteins: molecular switches of plant defence.

Specificity of the plant innate immune system is often conferred by resistance (R) proteins. Most R proteins contain leucine-rich repeats (LRRs), a central nucleotide-binding site (NBS) and a variable amino-terminal domain. The LRRs are mainly involved in recognition, whereas the amino-terminal domain determines signalling specificity. The NBS forms part of a nucleotide binding (NB)-ARC domain that presumably functions as a molecular switch. The conserved nature of NB-ARC proteins makes it possible to map mutations of R protein residues onto the crystal structures of related NB-ARC proteins, providing hypotheses for the functional roles of these residues. A functional model emerges in which the LRRs control the molecular state of the NB-ARC domain. Pathogen recognition triggers nucleotide-dependent conformational changes that might induce oligomerisation, thereby providing a scaffold for activation of downstream signalling components.

Molecular Biology↗

PubMed2001

The effects of chromosomes 3A and 3B on resistance to Fusarium head blight in tetraploid wheat.

Fusarium head blight (FHB) caused by Fusarium graminearum is one of the most destructive diseases of wheat in areas where the weather is warm and humid after heading. Previous studies indicate that the level of resistance to FHB varies not only among wheat cultivars but also among some of their wild relatives. No accession, however, has yet been identified to be completely immune to FHB among the Gramineae. It is known that durum wheat (Triticum turgidum L. conv. durum) is consistently more susceptible to FHB than common wheat (T. aestivum L.). The importance of the D genome in conferring resistance to FHB has been emphasized. Meanwhile, recent studies using molecular markers report effective QTLs on chromosome 3BS in a hexaploid population and on 3A in tetraploid recombinant inbred chromosome lines. In this study, we performed an evaluation of the effects of homoeologous group 3 chromosomes of T. turgidum ssp. dicoccoides on resistance to FHB using a set of chromosome substitution lines of a durum wheat cultivar 'Langdon'. The accession of T. turgidum ssp. dicoccoides examined in this study was more susceptible for Type II resistance (resistance to spread of FHB in the head) than 'Langdon'. Both of the chromosome substitution lines of 3A and 3B showed the same level of resistance with 'Langdon', but bleaching of the heads was completely prevented in the substitution lines of chromosome 3A without relationship to rachis fragility. It was concluded that the chromosome 3A of T. turgidum ssp. dicoccoides carries resistance gene(s) to head bleaching caused by FHB.

Chromosomes↗