1,720,988 research outputs found
The Pseudomonas syringae effector protein, AvrRPS4, requires in planta processing and the KRVY domain to function
No full textA Pseudomonas syringae pv. pisi effector protein, AvrRPS4, triggers RPS4-dependent immunity in Arabidopsis. We characterized biochemical and genetic aspects of AvrRPS4 function. Secretion of AvrRPS4 from Pst DC3000 is type III secretion-dependent, and AvrRPS4 is processed into a smaller form in plant cells but not in bacteria or yeast. Agrobacterium-mediated transient expression analysis of N-terminally truncated AvrRPS4 mutants revealed that the C-terminal 88 amino acids are sufficient to trigger the hypersensitive response in turnip. N-terminal sequencing of the processed AvrRPS4 showed that processing occurs between G133 and G134. The processing-deficient mutant, R112L, still triggers RPS4-dependent immunity, suggesting that the processing is not required for the AvrRPS4 avirulence function. AvrRPS4 enhances bacterial growth when delivered by Pta 6606 into Nicotiana benthamiana in which AvrRPS4 is not recognized. Transgenic expression of AvrRPS4 in the Arabidopsis rps4 mutant enhances the growth of Pst DC3000 and suppresses PTI (PAMP-triggered immunity), showing that AvrRPS4 promotes virulence in two distinct host plants. Furthermore, full virulence activity of AvrRPS4 requires both proteolytic processing and the KRVY motif at the N-terminus of processed AvrRPS4. XopO, an Xcv effector, shares the amino acids required for AvrRPS4 processing and the KRVY motif. XopO is also processed into a smaller form in N. benthamiana, similar to AvrRPS4, suggesting that a common mechanism is involved in activation of the virulence activities of both AvrRPS4 and XopO.112825sciescopu
Expression and functional roles of the pepper pathogen-induced transcription factor RAV1 in bacterial disease resistance, and drought and salt stress tolerance
No full textA novel pathogen-induced gene encoding the RAV (Related to ABI3/VP1) transcription factor, CARAV1, was isolated from pepper leaves infected with Xanthomonas campestris pv. vesicatoria. CARAV1 contains two distinct DNA-binding domains AP2 and B3 uniquely found in higher plants. Transient expression analysis of the smGFP:CARAV1 fusion construct in Arabidopsis protoplasts and pepper epidermal cells revealed the CARAV1 protein to be localized in the nucleus. The N-terminal region of CARAV1 fused to the GAL4 DNA-binding domain was required to activate transcription of reporter genes in yeast. In yeast one-hybrid, the recognition of CAACA and CACCTG motifs also were essential for the CARAV1 protein to bind to a specific target gene and activate the reporter gene. The expression of the CARAV1 gene was strongly induced early in pepper leaves during the pathogen infection, abiotic elicitors and environmental stresses. CARAV1 transcripts were localized in the phloem cells of leaf tissues during pathogen infection and ethylene treatment. Ectopic expression of the CARAV1 gene in transgenic Arabidopsis plants induced some PR genes and enhanced resistance against infection by Pseudomonas syringae pv. tomato DC3000 and osmotic stresses by high salinity and dehydration. The CARAV1 promoter activation was induced by P. syringae pv. tabaci, salicylic acid and abscisic acid. These data suggest that pathogen- and abiotic stress-inducible CARAV1 functions as a transcriptional activator triggering resistance to bacterial infection and tolerance to osmotic stresses.11114119sciescopu
The Downy Mildew Effector Proteins ATR1 and ATR13 Promote Disease Susceptibility in Arabidopsis thaliana W
Get PDFThe downy mildew (Hyaloperonospora parasitica) effector proteins ATR1 and ATR13 trigger RPP1-Nd/WsB- and RPP13-Nd-dependent resistance, respectively, in Arabidopsis thaliana. To better understand the functions of these effectors during compatible and incompatible interactions of H. parasitica isolates on Arabidopsis accessions, we developed a novel delivery system using Pseudomonas syringae type III secretion via fusions of ATRs to the N terminus of the P. syringae effector protein, AvrRPS4. ATR1 and ATR13 both triggered the hypersensitive response (HR) and resistance to bacterial pathogens in Arabidopsis carrying RPP1-Nd/WsB or RPP13-Nd, respectively, when delivered from P. syringae pv tomato (Pst) DC3000. In addition, multiple alleles of ATR1 and ATR13 confer enhanced virulence to Pst DC3000 on susceptible Arabidopsis accessions. We conclude that ATR1 and ATR13 positively contribute to pathogen virulence inside host cells. Two ATR13 alleles suppressed bacterial PAMP ( for Pathogen-Associated Molecular Patterns)-triggered callose deposition in susceptible Arabidopsis when delivered by DC3000 Delta CEL mutants. Furthermore, expression of another allele of ATR13 in plant cells suppressed PAMP-triggered reactive oxygen species production in addition to callose deposition. Intriguingly, although Wassilewskija (Ws-0) is highly susceptible to H. parasitica isolate Emco5, ATR13(Emco5) when delivered by Pst DC3000 triggered localized immunity, including HR, on Ws-0. We suggest that an additional H. parasitica Emco5 effector might suppress ATR13-triggered immunity.11140137sciescopu
Differential expression and in situ localization of a pepper defensin (CADEF1) gene in response to pathogen infection, abiotic elicitors and environmental stresses in Capsicum annuum
No full textPepper defensin (CADEF1) clone was isolated from cDNA library constructed from pepper leaves infected with avirulent strain Bv5-4a of Xanthomonas campestris pv. vesicatoria. Putative protein encoded by CADEF1 gene consists of 78 amino acids including eight conserved cysteine residues to form four structure-stabilizing, disulfide bridges. Transcription of the CADEF1 gene was earlier and more strongly induced by X. campestris pv. vesicatoria infection in the incompatible than in the compatible interaction. CADEF1 mRNA was constitutively expressed in stem, root and green fruit of pepper. Transcripts of CADEF1 gene drastically accumulated in pepper leaf tissues treated with salicylic acid (SA), methyl jasmonate (MeJA), abscisic acid (ABA), hydrogen peroxide (H2O2), benzothiadiazole (BTH) and D,L-beta-amino-n-butyric acid (BABA). In situ hybridization results revealed that CADEF1 mRNA was localized in the phloem areas of vascular bundles in leaf tissues treated with exogenous SA, MeJA and ABA. Strong accumulation of CADEF1 mRNA occurred in pepper leaves in response to wounding, high salinity and drought stress. These results suggest that bacterial pathogen infection, abiotic elicitors and some environmental stresses may play a significant role in signal transduction pathway for CADEF1 gene expression. (C) 2004 Elsevier Ireland Ltd. All rights reserved.115566sciescopu
Effector-assisted breeding for bacterial wilt resistance in horticultural crops
No full textRalstonia solanacearum (Rso) is a causal agent of bacterial wilt disease in a wide range of horticultural crops. Rso strains are heterogeneous in nature and are therefore difficult in terms of both classification and developmentof disease resistance. Rso pathogen-associated molecular patterns (PAMPs) and effector proteins are secreted into plant cells, where they respectively activate and suppress plant immunity, thereby affecting Rso virulence. We review the current knowledge of Rso disease resistance and efforts to generate Rso-resistant crop plants. Further, we propose the introduction into plants of known pattern recognition receptors (PRRs) that recognize Rso PAMPs in order to confer resistance to a large number of strains. Additionally, the conserved ‘core’ effectors from Rso phylotypes could be used to identify and deploy nucleotide-binding leucine-rich repeat (NLR) resistance genes in a desired crop cultivar. We suggest that a phylotype-specific effector-assisted breeding program be instituted to rapidly identify disease resistance genes in available plant germplasm collections. Furthermore, stacking multiple NLRs that recognize Rso effectors would provide durable disease resistance by minimizing the chance for Rso to evade the implemented resistance. Finally, we propose that this strategy would most efficiently be achieved through development of transgenic crop lines.1120Nsciescopuskc
HopAS1 recognition significantly contributes to Arabidopsis nonhost resistance to Pseudomonas syringae pathogens
No full textPlant immunity is activated by sensing either conserved microbial signatures, called pathogen/microbe-associated molecular patterns (P/MAMPs), or specific effectors secreted by pathogens. However, it is not known why most microbes are nonpathogenic in most plant species. Nonhost resistance (NHR) consists of multiple layers of innate immunity and protects plants from the vast majority of potentially pathogenic microbes. Effector-triggered immunity (ETI) has been implicated in race-specific disease resistance. However, the role of ETI in NHR is unclear. Pseudomonas syringae pv. tomato (Pto) T1 is pathogenic in tomato (Solanum lycopersicum) yet nonpathogenic in Arabidopsis. Here, we show that, in addition to the type III secretion system (T3SS)-dependent effector (T3SE) avrRpt2, a second T3SE of Pto T1, hopAS1, triggers ETI in nonhost Arabidopsis. hopAS1 is broadly present in P.similar to syringae strains, contributes to virulence in tomato, and is quantitatively required for Arabidopsis NHR to Pto T1. Strikingly, all tested P.similar to syringae strains that are pathogenic in Arabidopsis carry truncated hopAS1 variants of forms, demonstrating that HopAS1-triggered immunity plays an important role in Arabidopsis NHR to a broad-range of P.similar to syringae strains.111615sciescopu
CAZFP1, CYS2/HiS(2)-type zinc-finger transcription factor gene functions as a pathogen-induced early-defense gene in Capsicum annuum
No full textA pepper zinc-finger protein gene, CAZFP1, encoding the Cys(2)/His(2)-type zinc-finger transcription factor was isolated from pepper leaves inoculated with an avirulent strain Bv5-4a of Xanthomonas campestris pv. vesicatoria. The CAZFP1 protein is a nuclear targeting protein, which functions as a transcriptional regulator. The full-length CAZFP1 had no transcriptional activation activity, whereas the C-terminal region of CAZFP1 had transactivation activity. The CAZFP1 transcripts were constitutively expressed in the pepper stem, root, flower and red fruit, but were not detectable in the leaf and green fruit. The CAZFP1 transcripts accumulated earlier than the CABPR1 (PR-1) gene in the incompatible interaction of the pepper leaves with X. campestris pv. vesicatoria. The CAZFP1 transcripts were significantly induced in the systemic, uninoculated leaf tissues early after inoculation with bacterial pathogens, but gradually declined thereafter. The CAZFP1 transcripts were localized, and confined to the phloem cells of the vascular bundle in the pepper leaf midrib in response to Colletotrichum. coccodes infection, ethylene and abscisic acid. The CAZFP1 gene was also induced much earlier by abiotic elicitors and environmental stresses, compared with the CABPR1 gene. Overexpression of the CAZFP1 gene in the transgenic Arabidopsis plants enhanced not only the resistance against infection by Pseudomonas syringae pv. tomato, but also the drought tolerance. These results suggest that the CAZFP1 gene functions as an early-defense gene to enhance disease resistance and drought tolerance.1157sciescopu
Two linked pairs of Arabidopsis TNL resistance genes independently confer recognition of bacterial effector AvrRps4
No full textPlant immunity requires recognition of pathogen effectors by intracellular NB-LRR immune receptors encoded by Resistance (R) genes. Most R proteins recognize a specific effector, but some function in pairs that recognize multiple effectors. Arabidopsis thaliana TIR-NB-LRR proteins RRS1-R and RPS4 together recognize two bacterial effectors, AvrRps4 from Pseudomonas syringae and PopP2 from Ralstonia solanacearum. However, AvrRps4, but not PopP2, is recognized in rrs1/rps4 mutants. We reveal an R gene pair that resembles and is linked to RRS1/RPS4, designated as RRS1B/RPS4B, which confers recognition of AvrRps4 but not PopP2. Like RRS1/RPS4, RRS1B/RPS4B proteins associate and activate defence genes upon AvrRps4 recognition. Inappropriate combinations (RRS1/RPS4B or RRS1B/RPS4) are non-functional and this specificity is not TIR domain dependent. Distinct putative orthologues of both pairs are maintained in the genomes of Arabidopsis thaliana relatives and are likely derived from a common ancestor pair. Our results provide novel insights into paired R gene function and evolution.113425sciescopu
Draft genome sequence of Pseudomonas syringae pathovar syringae strain FF5, causal agent of stem tip dieback disease on ornamental pear
No full textPseudomonas syringae FF5 causes stem tip dieback disease on ornamental pear (Pyrus calleryana). Its genome encodes a complete type III secretion system (T3SS) and HopAC1, HopM1, AvrE1, HopI1, HopAA1, HopJ1, HopAH2, HopAH1, HopAG1, and HopAZ1. Lacking detectable homologues of other T3SS effectors, it may encode novel, undiscovered effectors
Distinct regions of the Pseudomonas syringae coiled-coil effector AvrRps4 are required for activation of immunity
No full textGram-negative phytopathogenic bacteria translocate effector proteins into plant cells to subvert host defenses. These effectors can be recognized by plant nucleotide-binding-leucine-rich repeat immune receptors, triggering defense responses that restrict pathogen growth. AvrRps4, an effector protein from Pseudomonas syringae pv. pisi, triggers RPS4-dependent immunity in resistant accessions of Arabidopsis. To better understand the molecular basis of AvrRps4-triggered immunity, we determined the crystal structure of processed AvrRps4 (AvrRps4C, residues 134-221), revealing that it forms an antiparallel a-helical coiled coil. Structure-informedmutagenesis reveals an electronegative surface patch in AvrRps4C required for recognition by RPS4; mutations in this region can also uncouple triggering of the hypersensitive response from disease resistance. This uncoupling may result from a lower level of defense activation, sufficient for avirulence but not for triggering a hypersensitive response. Natural variation in AvrRps4 reveals distinct recognition specificities that involve a surface-exposed residue. Recently, a direct interaction between AvrRps4 and Enhanced Disease Susceptibility 1 has been implicated in activation of immunity. However, we were unable to detect direct interaction between AvrRps4 and Enhanced Disease Susceptibility 1 after coexpression in Nicotiana benthamiana or in yeast cells. How intracellular plant immune receptors activate defense upon effector perception remains an unsolved problem. The structure of AvrRps4C, and identification of functionally important residues for its activation of plant immunity, advances our understanding of these processes in a well-defined model pathosystem.113229sciescopu
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