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Results for “Plant Immunity”

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At least 55 records · Page 3Linked to original sources
PubMed2001

RNA silencing as a plant immune system against viruses.

"RNA silencing" refers to related processes of post-trancriptional control of gene expression found in plants, animals and fungi. A unifying feature of RNA silencing is that it mediates sequence-specific degradation of target transcripts, recruiting RNA molecules of 21-23 nucleotides as specificity determinants. In higher plants, RNA silencing serves as an adaptive, antiviral defence system, which is transmitted systemically in response to localized virus challenge. Plant viruses have elaborated a variety of counter-defensive measures to overcome the host silencing response. One of these strategies is to produce proteins that target the cell autonomous or signalling steps of RNA silencing. It is not known whether a similar antiviral mechanism also operates in animal cells.

Animals↗
PubMed2006

A pathogen-inducible endogenous siRNA in plant immunity.

RNA interference, mediated by small interfering RNAs (siRNAs), is a conserved regulatory process that has evolved as an antiviral defense mechanism in plants and animals. It is not known whether host cells also use siRNAs as an antibacterial defense mechanism in eukaryotes. Here, we report the discovery of an endogenous siRNA, nat-siRNAATGB2, that is specifically induced by the bacterial pathogen Pseudomonas syringae carrying effector avrRpt2. We demonstrate that the biogenesis of this siRNA requires DCL1, HYL1, HEN1, RDR6, NRPD1A, and SGS3. Its induction also depends on the cognate host disease resistance gene RPS2 and the NDR1 gene that is required for RPS2-specified resistance. This siRNA contributes to RPS2-mediated race-specific disease resistance by repressing PPRL, a putative negative regulator of the RPS2 resistance pathway.

Animals↗
PubMed2006

Molecular evolution of plant immune system genes.

Molecular population genetic studies are providing new perspectives on the evolution of genes that confer resistance to pathogens and herbivores. Here, we compare the evolutionary history of different components of the defense response (detection, signaling and response) and of genes with parallel function in plants and Drosophila. A review of the literature indicates that the dominant form of selection acting on defense genes (balancing, positive and purifying) differs among components of defense. Sampling of particular classes of genes and genes from non-model organisms, however, remains limited. Future studies combining molecular evolutionary analyses with ecological genetic and functional analyses should better reveal how natural selection has shaped defense gene evolution.

Animals↗
PubMed1998

Reactive oxygen intermediates mediate a systemic signal network in the establishment of plant immunity.

Recognition of an avirulent pathogen stimulates an oxidative burst generating O2- and H2O2, and these reactive oxygen intermediates (ROIs) cue the induction of defense genes and cell death in the development of a restricted lesion. This localized hypersensitive response (HR) is accompanied by the development of systemic acquired resistance to virulent pathogens. Here we show that inoculation of Arabidopsis leaves with avirulent Pseudomonas syringae induces secondary oxidative bursts in discrete cells in distant tissues, leading to low-frequency systemic micro-HRs. The primary oxidative burst induces these systemic responses, and both the primary burst and the secondary microbursts are required for systemic immunity. Hence, ROIs mediate a reiterative signal network underlying systemic as well as local resistance responses.

Arabidopsis↗
PubMed2005

Plant immunity: the EDS1 regulatory node.

ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) and its interacting partner, PHYTOALEXIN DEFICIENT 4 (PAD4), constitute a regulatory hub that is essential for basal resistance to invasive biotrophic and hemi-biotrophic pathogens. EDS1 and PAD4 are also recruited by Toll-Interleukin-1 receptor (TIR)-type nucleotide binding-leucine rich repeat (NB-LRR) proteins to signal isolate-specific pathogen recognition. Recent work points to a fundamental role of EDS1 and PAD4 in transducing redox signals in response to certain biotic and abiotic stresses. These intracellular proteins are important activators of salicylic acid (SA) signaling and also mediate antagonism between the jasmonic acid (JA) and ethylene (ET) defense response pathways. EDS1 forms several molecularly and spatially distinct complexes with PAD4 and a newly discovered in vivo signaling partner, SENESCENCE ASSOCIATED GENE 101 (SAG101). Together, EDS1, PAD4 and SAG101 provide a major barrier to infection by both host-adapted and non-host pathogens.

Arabidopsis↗
PubMed2006

The tomato NBARC-LRR protein Prf interacts with Pto kinase in vivo to regulate specific plant immunity.

Immunity in tomato (Solanum lycopersicum) to Pseudomonas syringae bacteria expressing the effector proteins AvrPto and AvrPtoB requires both Pto kinase and the NBARC-LRR (for nucleotide binding domain shared by Apaf-1, certain R gene products, and CED-4 fused to C-terminal leucine-rich repeats) protein Prf. Pto plays a direct role in effector recognition within the host cytoplasm, but the role of Prf is unknown. We show that Pto and Prf are coincident in the signal transduction pathway that controls ligand-independent signaling. Pto and Prf associate in a coregulatory interaction that requires Pto kinase activity and N-myristoylation for signaling. Pto interacts with a unique Prf N-terminal domain outside of the NBARC-LRR domain and resides in a high molecular weight recognition complex dependent on the presence of Prf. In this complex, both Pto and Prf contribute to specific recognition of AvrPtoB. The data suggest that the role of Pto is confined to the regulation of Prf and that the bacterial effectors have evolved to target this coregulatory molecular switch.

Base Sequence↗
PubMed2006

The Pto kinase of tomato, which regulates plant immunity, is repressed by its myristoylated N terminus.

Specific recognition of the Pseudomonas syringae effector proteins AvrPto and AvrPtoB in tomato is mediated by Pto kinase resulting in induction of defense responses, including hypersensitive cell death via a signaling pathway requiring the nucleotide-binding leucine-rich repeats protein Prf. Pto is a myristoylated protein, and N-myristoylation is required for signaling. Here we demonstrated a role for N-myristoylation in controlling Pto kinase activity. A myristoylated peptide corresponding to Pto residues 2-10 significantly impaired the kinase activity of N-truncated Pto. We show that kinase inhibition was specific to the myristoylated form of the peptide and that free myristate supplied in trans was a potent suppressor of Pto kinase activity. Thus, myristate, but not Pto residues 2-10, contributes to suppression of kinase activity in vitro. Accordingly, elimination of the in vivo myristoylation potential of Pto de-repressed kinase activity. The increased potency of free myristate relative to the myristoylated N-peptide inhibitor suggested that the peptide moiety is antagonistic to repression by myristate. Suppression of related protein kinases by myristate declined with similarity to Pto, and the inhibitory activity could be attributed to hydrophobicity. We present evidence that inhibition of Pto by the myristoylated N-peptide is mediated through a previously identified surface regulatory patch. The data show a role for negative regulation of Pto by N-myristoylation, in addition to the previously demonstrated positive role, and are consistent with a model in which the acylated N terminus is sequestered in the catalytic cleft prior to release by Pto activation.

Enzyme Activation↗
PubMed2026

A CsWRKY46-CsPBL9-CsARI1 tripartite regulatory module coordinates H2O2 production and callose deposition in citrus fruit immunity.

Plant immunity against pathogens involves multiple immune responses and intricate regulatory networks. However, how immune networks are deployed in fruit remains poorly understood. Here, we show that citrus fruit immune responses, including hydrogen peroxide (H2O2) production and callose deposition, are multiply regulated by transcriptional activation, phosphorylation, and ubiquitination. Citrus sinensis genes encoding nicotinamide adenine dinucleotide phosphate (NADPH) oxidase CsRBOHG and callose synthase CsCalS5, responsible for H2O2 production and callose deposition, respectively, are transcriptionally activated by CsWRKY46. Phosphorylation-enhanced activity of CsRBOHG by CsPBL9 enhances immunity. RING1-IBR-RING2 (RBR)-type E3 ligase CsARI1, acting as an immune brake, ubiquitinates CsRBOHG and CsCalS5 for degradation. Interestingly, CsARI1 also shows a moonlight function wherein it interacts with CsPBL9 in a non-ubiquitination manner, disrupting CsPBL9's interaction with CsRBOHG. This CsARI1-CsPBL9 interaction is stimulated by H2O2 as feedback. Moreover, H2O2 contributes to callose deposition, indicating an interplay between two immune responses. Our study reveals a tripartite regulatory hub orchestrating self-linked immunity in citrus fruit.

CP: plants↗
PubMed2006

Innate immunity in plants: a continuum of layered defenses.

Plant responses to pathogenic invaders result from recognition of nonself elicitors. Host surveillance proteins activate distinct signaling pathways that induce partially overlapping defensive responses. Pathogen virulence is promoted by inhibition of these pathways. This evolutionary struggle has produced plant immune systems that rely on a continuum of layered defenses.

Bacteria↗
PubMed2003

High-affinity salicylic acid-binding protein 2 is required for plant innate immunity and has salicylic acid-stimulated lipase activity.

Salicylic acid (SA) is a critical hormone for signaling innate immunity in plants. Here we present the purification and characterization of SA-binding protein 2 (SABP2), a tobacco protein that is present in low abundance and specifically binds SA with high affinity. Sequence analysis predicted that SABP2 is a lipase belonging to the alpha/beta fold hydrolase super family. Confirming this prediction, recombinant SABP2 exhibited lipase activity against several synthetic substrates. Moreover, this lipase activity was stimulated by SA binding and may generate a lipid-derived signal. Silencing of SABP2 expression suppressed local resistance to tobacco mosaic virus, induction of pathogenesis-related 1 (PR-1) gene expression by SA, and development of systemic acquired resistance. Together, these results suggest that SABP2 is an SA receptor that is required for the plant immune response. We further propose that SABP2 belongs to a large class of ligand-stimulated hydrolases involved in stress hormone-mediated signal transduction.

Amino Acid Sequence↗
PubMed2005

Autophagy regulates programmed cell death during the plant innate immune response.

The plant innate immune response includes the hypersensitive response (HR), a form of programmed cell death (PCD). PCD must be restricted to infection sites to prevent the HR from playing a pathologic rather than protective role. Here we show that plant BECLIN 1, an ortholog of the yeast and mammalian autophagy gene ATG6/VPS30/beclin 1, functions to restrict HR PCD to infection sites. Initiation of HR PCD is normal in BECLIN 1-deficient plants, but remarkably, healthy uninfected tissue adjacent to HR lesions and leaves distal to the inoculated leaf undergo unrestricted PCD. In the HR PCD response, autophagy is induced in both pathogen-infected cells and distal uninfected cells; this is reduced in BECLIN 1-deficient plants. The restriction of HR PCD also requires orthologs of other autophagy-related genes including PI3K/VPS34, ATG3, and ATG7. Thus, the evolutionarily conserved autophagy pathway plays an essential role in plant innate immunity and negatively regulates PCD.

Amino Acid Sequence↗
PubMed2006

Specific bacterial suppressors of MAMP signaling upstream of MAPKKK in Arabidopsis innate immunity.

Plants and animals possess innate immune systems to prevent infections and are effectively "nonhosts" for most potential pathogens. The molecular mechanisms underlying nonhost immunity in plants remain obscure. In Arabidopsis, nonhost/nonpathogenic Pseudomonas syringae sustains but pathogenic P. syringae suppresses early MAMP (microbe-associated molecular pattern) marker-gene activation. We performed a cell-based genetic screen of virulence factors and identified AvrPto and AvrPtoB as potent and unique suppressors of early-defense gene transcription and MAP kinase (MAPK) signaling. Unlike effectors of mammalian pathogens, AvrPto and AvrPtoB intercept multiple MAMP-mediated signaling upstream of MAPKKK at the plasma membrane linked to the receptor. In transgenic Arabidopsis, AvrPto blocks early MAMP signaling and enables nonhost P. syringae growth. Deletions of avrPto and avrPtoB from pathogenic P. syringae reduce its virulence. The studies reveal a fundamental role of MAMP signaling in nonhost immunity, and a novel action of type III effectors from pathogenic bacteria.

Arabidopsis↗
PubMed2006

MAMPs and MIMPs: proposed classifications for inducers of innate immunity.

Plants encode a sophisticated innate immune system. Resistance against potential pathogens often relies on active responses. Prerequisite to the induction of defences is recognition of the pathogenic threat. Significant advances have been made in our understanding of the non-self molecules that are recognized by plants and the means by which plants perceive them. Established terms describing these recognition events, including microbe-associated molecular pattern (MAMP), MAMP-receptor, effector, and resistance (R) protein, need clarification to represent our current knowledge adequately. In this review we propose criteria to classify inducers of plant defence as either MAMPs or microbe-induced molecular patterns (MIMPs). We refine the definition of MAMP to mean a molecular sequence or structure in ANY pathogen-derived molecule that is perceived via direct interaction with a host defence receptor. MIMPs are modifications of host-derived molecules that are induced by an intrinsic activity of a pathogen-derived effector and are perceived by a host defence receptor. MAMP-receptors have previously been classified separately from R-proteins as a discrete class of surveillance molecules. However, MAMP-receptors and R-proteins cannot be distinguished on the basis of their protein structures or their induced responses. We propose that MAMP-receptors and MIMP-receptors are each a subset of R-proteins. Although our review is based on examples from plant pathogens and plants, the principles discussed might prove applicable to other organisms.

Immunity, Innate↗
PubMed2006

Bacterial elicitation and evasion of plant innate immunity.

Recent research on plant responses to bacterial attack has identified extracellular and intracellular host receptors that recognize conserved pathogen-associated molecular patterns and more specialized virulence proteins, respectively. These findings have shed light on our understanding of the molecular mechanisms by which bacteria elicit host defences and how pathogens have evolved to evade or suppress these defences.

Animals↗