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Hotson A, Chosed R, Shu H, Orth K, Mudgett MB. Xanthomonas type III effector XopD targets SUMO-conjugated proteins in planta. Mol Microbiol 2004; 50:377-89. [PMID: 14617166 DOI: 10.1046/j.1365-2958.2003.03730.x] [Citation(s) in RCA: 217] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Xanthomonas campestris pathovar vesicatoria (Xcv) uses the type III secretion system (TTSS) to inject effector proteins into cells of Solanaceous plants during pathogenesis. A number of Xcv TTSS effectors have been identified; however, their function in planta remains elusive. Here, we provide direct evidence for a functional role for a phytopathogenic bacterial TTSS effector in planta by demonstrating that the Xcv effector XopD encodes an active cysteine protease with plant-specific SUMO substrate specificity. XopD is injected into plant cells by the TTSS during Xcv pathogenesis, translocated to subnuclear foci and hydrolyses SUMO-conjugated proteins in vivo. Our studies suggest that XopD mimics endogenous plant SUMO isopeptidases to interfere with the regulation of host proteins during Xcv infection.
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Affiliation(s)
- Andrew Hotson
- Department of Biological Sciences, Stanford University, Stanford, CA 94305-5020, USA
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52
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Hotson A, Mudgett MB. Cysteine proteases in phytopathogenic bacteria: identification of plant targets and activation of innate immunity. CURRENT OPINION IN PLANT BIOLOGY 2004; 7:384-90. [PMID: 15231260 DOI: 10.1016/j.pbi.2004.05.003] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Phytopathogenic bacteria use the type-III secretion system (TTSS) to inject effector proteins into plant cells, presumably to colonize their hosts. The function of these proteins inside plant cells has remained a mystery for years. The recent discovery that the effectors XopD, AvrXv4, AvrPphB, and AvrRpt2 have cysteine protease functions reveals that the proteolysis of host substrates is an important strategy employed by pathogens to alter plant physiology. Moreover, the characterization of these proteases and their targets provides new insight to mechanisms of bacterial virulence and the activation of plant immunity.
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Affiliation(s)
- Andrew Hotson
- Department of Biological Sciences, Stanford University, Stanford, California 94305-5020, USA
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53
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Abramovitch RB, Martin GB. Strategies used by bacterial pathogens to suppress plant defenses. CURRENT OPINION IN PLANT BIOLOGY 2004; 7:356-364. [PMID: 15231256 DOI: 10.1016/j.pbi.2004.05.002] [Citation(s) in RCA: 123] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Plant immune systems effectively prevent infections caused by the majority of microbial pathogens that are encountered by plants. However, successful pathogens have evolved specialized strategies to suppress plant defense responses and induce disease susceptibility in otherwise resistant hosts. Recent advances reveal that phytopathogenic bacteria use type III effector proteins, toxins, and other factors to inhibit host defenses. Host processes that are targeted by bacteria include programmed cell death, cell wall-based defense, hormone signaling, the expression of defense genes, and other basal defenses. The discovery of plant defenses that are vulnerable to pathogen attack has provided new insights into mechanisms that are essential for both bacterial pathogenesis and plant disease resistance.
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Affiliation(s)
- Robert B Abramovitch
- Boyce Thompson Institute for Plant Research and Department of Plant Pathology, Cornell University, Ithaca, New York 14853, USA
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54
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Innes RW. Guarding the goods. New insights into the central alarm system of plants. PLANT PHYSIOLOGY 2004; 135:695-701. [PMID: 15208416 PMCID: PMC514106 DOI: 10.1104/pp.104.040410] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2004] [Revised: 02/14/2004] [Accepted: 02/16/2004] [Indexed: 05/18/2023]
Affiliation(s)
- Roger W Innes
- Department of Biology, Indiana University, Bloomington, Indiana 47405-7107, USA.
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55
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Tans-Kersten J, Brown D, Allen C. Swimming motility, a virulence trait of Ralstonia solanacearum, is regulated by FlhDC and the plant host environment. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2004; 17:686-95. [PMID: 15195951 DOI: 10.1094/mpmi.2004.17.6.686] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Swimming motility allows the bacterial wilt pathogen Ralstonia solanacearum to efficiently invade and colonize host plants. However, the bacteria are essentially nonmotile once inside plant xylem vessels. To determine how and when motility genes are expressed, we cloned and mutated flhDC, which encodes a major regulator of flagellar biosynthesis and bacterial motility. An flhDC mutant was nonmotile and less virulent than its wild-type parent on both tomato and Arabidopsis; on Arabidopsis, the flhDC mutant also was less virulent than a nonmotile fliC flagellin mutant. Genes in the R. solanacearum motility regulon had strikingly different expression patterns in culture and in the plant. In culture, as expected, flhDC expression depended on PehSR, a regulator of early virulence factors; and, in turn, FlhDC was required for fliC (flagellin) expression. However, when bacteria grew in tomato plants, flhDC was expressed in both wild-type and pehR mutant backgrounds, although PehSR is necessary for motility both in culture and in planta. Both flhDC and pehSR were significantly induced in planta relative to expression levels in culture. Unexpectedly, the fliC gene was expressed in planta at cell densities where motile bacteria were not observed, as well as in a nonmotile flhDC mutant. Thus, expression of flhDC and flagellin itself are uncoupled from bacterial motility in the host environment, indicating that additional signals and regulatory circuits repress motility during plant pathogenesis.
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Affiliation(s)
- Julie Tans-Kersten
- Department of Plant Pathology, University of Wisconsin-Madison, 1630 Linden Drive, Madison 53706, USA
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56
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Losada L, Sussan T, Pak K, Zeyad S, Rozenbaum I, Hutcheson SW. Identification of a novel Pseudomonas syringae Psy61 effector with virulence and avirulence functions by a HrpL-dependent promoter-trap assay. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2004; 17:254-262. [PMID: 15000392 DOI: 10.1094/mpmi.2004.17.3.254] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The hrp pathogenicity island of Pseudomonas syringae encodes a type III secretion system (TTSS) that translocates effectors into plant cells. Most genes encoding effectors are dispersed in the P. syringae genome. Regardless of location, all are regulated coordinately by the alternative sigma factor HrpL. An HrpL-dependent promoter-trap assay was developed to screen genomic libraries of P. syringae strains for promoters whose activity in Escherichia coli is dependent on an inducible hrpL construct. Twenty-two HrpL-dependent promoter fragments were isolated from P. syringae Psy61 that included promoters for known HrpL-dependent genes. One fragment also was isolated that shared no similarity with known genes but retained a near consensus HrpL-dependent promoter. The sequence of the region revealed a 375-amino acid open reading frame encoding a 40.5-kDa product that was designated HopPsyL. HopPsyL was structurally similar to other secreted effectors and carried a putative chloroplast-targeting signal and two predicted transmembrane domains. HopPsyL':'AvrRpt2 fusions were translocated into host cells via the P. syringae pv. tomato DC3000 hrp TTSS. A hopPsyL::kan mutant of Psy61 exhibited strongly reduced virulence in Phaseolus vulgaris cv. Kentucky Wonder, but did not appear to act as a defense response suppressor. The ectopically expressed gene reduced the virulence of Pseudomonas syringae DC3000 transformants in Arabidopsis thaliana Col-0. The gene was shown to be conserved in 6 of 10 P. syringae pv. syringae strains but was not detected in 35 strains of other pathovars. HopPsyL appears to be a novel TTSS-dependent effector that functions as a host-species-specific virulence factor in Psy61.
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Affiliation(s)
- L Losada
- Department of Cell Biology and Molecular Genetics, Microbiology Bldg, University of Maryland, College Park 20742, USA
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57
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Lim MTS, Kunkel BN. Mutations in the Pseudomonas syringae avrRpt2 gene that dissociate its virulence and avirulence activities lead to decreased efficiency in AvrRpt2-induced disappearance of RIN4. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2004; 17:313-321. [PMID: 15000398 DOI: 10.1094/mpmi.2004.17.3.313] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The avrRpt2 gene from Pseudomonas syringae pv. tomato exhibits avirulence activity on Arabidopsis expressing the resistance gene RPS2 but promotes bacterial virulence on susceptible rps2 Arabidopsis. To understand the functional relationship between the avirulence and virulence activities of avrRpt2, we analyzed a series of six avrRpt2 mutants deficient in eliciting the RPS2-dependent hypersensitive response. We show that the mutants are also severely impaired in triggering RSP2-dependent resistance. Four of these mutants are severely impaired in their virulence activity, whereas two alleles, encoding C-terminal deletions of AvrRpt2, retain significant but slightly reduced virulence activity. Thus, the avirulence and virulence activities of avrRpt2 can be genetically uncoupled. We tested the ability of the two C-terminal deletion mutants to trigger AvrRpt2-induced elimination of the Arabidopsis RIN4 protein and show that they retain this activity but are less efficient than wild-type AvrRpt2. Thus, reduced AvrRpt2 virulence activity is correlated with reduced efficiency in the induction of RIN4 disappearance. This suggests that an alteration in kinetics of RIN4 disappearance triggered by the C-terminal deletion mutants may provide the mechanistic basis for the uncoupling of the avirulence and virulence activities of avrRpt2.
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Affiliation(s)
- Melisa T S Lim
- Department of Biology, Washington University in St. Louis, St. Louis, MO 63130, USA
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58
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He P, Chintamanani S, Chen Z, Zhu L, Kunkel BN, Alfano JR, Tang X, Zhou JM. Activation of a COI1-dependent pathway in Arabidopsis by Pseudomonas syringae type III effectors and coronatine. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2004; 37:589-602. [PMID: 14756769 DOI: 10.1111/j.1365-313x.2003.01986.x] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Gram-negative bacteria use a variety of virulence factors including phytotoxins, exopolysaccharides, effectors secreted by the type III secretion system, and cell-wall-degrading enzymes to promote parasitism in plants. However, little is known about how these virulence factors alter plant cellular responses to promote disease. In this study, we show that virulent Pseudomonas syringae strains activate the transcription of an Arabidopsis ethylene response factor (ERF) gene, RAP2.6, in a coronatine insensitive 1 (COI1)-dependent manner. A highly sensitive RAP2.6 promoter-firefly luciferase (RAP2.6-LUC) reporter line was developed to monitor activities of various bacterial virulence genes. Analyses of P. syringae pv. tomato DC3000 mutants indicated that both type III secretion system and the phytotoxin coronatine are required for RAP2.6 induction. We show that at least five individual type III effectors, avirulence B (AvrB), AvrRpt2, AvrPphB, HopPtoK, and AvrPphEPto, contributed to RAP2.6 induction. Gene-for-gene recognition was not involved in RAP2.6 induction because plants lacking RPM1 and RPS2 responded normally to AvrB and AvrRpt2 in RAP2.6 expression. Interestingly, the role of coronatine in RAP2.6 induction can be partially substituted by the addition of avrB in DC3000, suggesting that AvrB may mimic coronatine. These results suggest that P. syringae type III effectors and coronatine act by augmenting a COI1-dependent pathway to promote parasitism.
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Affiliation(s)
- Ping He
- Department of Plant Pathology, Kansas State University, Manhattan, KS 66506, USA
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59
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Chen Z, Kloek AP, Cuzick A, Moeder W, Tang D, Innes RW, Klessig DF, McDowell JM, Kunkel BN. The Pseudomonas syringae type III effector AvrRpt2 functions downstream or independently of SA to promote virulence on Arabidopsis thaliana. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2004; 37:494-504. [PMID: 14756766 DOI: 10.1111/j.1365-313x.2003.01984.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
AvrRpt2, a Pseudomonas syringae type III effector protein, functions from inside plant cells to promote the virulence of P. syringae pv. tomato strain DC3000 (PstDC3000) on Arabidopsis thaliana plants lacking a functional copy of the corresponding RPS2 resistance gene. In this study, we extended our understanding of AvrRpt2 virulence activity by exploring the hypothesis that AvrRpt2 promotes PstDC3000 virulence by suppressing plant defenses. When delivered by PstDC3000, AvrRpt2 suppresses pathogen-related (PR) gene expression during infection, suggesting that AvrRpt2 suppresses defenses mediated by salicylic acid (SA). However, AvrRpt2 promotes PstDC3000 growth on transgenic plants expressing the SA-degrading enzyme NahG, indicating that AvrRpt2 does not promote bacterial virulence by modulating SA levels during infection. AvrRpt2 general virulence activity does not depend on the RPM1 resistance gene, as mutations in RPM1 had no effect on AvrRpt2-induced phenotypes. Transgenic plants expressing AvrRpt2 displayed enhanced susceptibility to PstDC3000 strains defective in type III secretion, indicating that enhanced susceptibility of these plants is not because of suppression of defense responses elicited by other type III effectors. Additionally, avrRpt2 transgenic plants did not exhibit increased susceptibility to Peronospora parasitica and Erysiphe cichoracearum, suggesting that AvrRpt2 virulence activity is specific to P. syringae.
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Affiliation(s)
- Zhongying Chen
- Department of Biology, Washington University in St Louis, St Louis, MO 63130, USA
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60
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Jin P, Wood MD, Wu Y, Xie Z, Katagiri F. Cleavage of the Pseudomonas syringae type III effector AvrRpt2 requires a host factor(s) common among eukaryotes and is important for AvrRpt2 localization in the host cell. PLANT PHYSIOLOGY 2003; 133:1072-82. [PMID: 14526114 PMCID: PMC281603 DOI: 10.1104/pp.103.025999] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2003] [Revised: 06/01/2003] [Accepted: 08/04/2003] [Indexed: 05/17/2023]
Abstract
Many phytopathogenic bacteria use a type III secretion system to deliver type III effector proteins into the host plant cell. The Pseudomonas syringae type III effector AvrRpt2 is cleaved at a specific site when translocated into the host cell. In this study, we first demonstrate that the factor(s) required for AvrRpt2 cleavage is present in extracts from animal and yeast cells, as well as plant cells. The cleavage factor in animal and plant cell extracts was heat labile but relatively insensitive to protease inhibitors. Second, mutational analysis of AvrRpt2 was applied to identify features important for its cleavage. In addition to two of the amino acid residues in the immediate vicinity of the cleavage site, a large part of the region C-terminal to the cleavage site was required when AvrRpt2 was cleaved in animal cell extract. Most of these features were also important when AvrRpt2 was cleaved in plant cells. Third, we investigated the effect of cleavage in interactions of AvrRpt2 with plant cells. Cleavage of AvrRpt2 appeared to be important for proper interactions with Arabidopsis cells that lack the resistance gene product corresponding to AvrRpt2, RPS2. In addition, removal of the region N-terminal to the cleavage site was important for the correct localization of the C-terminal effector region of the protein in the host cell. We speculate that the virulence function of AvrRpt2 requires removal of the N-terminal region to redirect the effector protein to a specific subcellular location in the host cell after translocation of the protein.
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Affiliation(s)
- Ping Jin
- Diversa Corp, San Diegeo, CA 92121, USA
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61
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Ponciano G, Ishihara H, Tsuyumu S, Leach JE. Bacterial Effectors in Plant Disease and Defense: Keys to Durable Resistance? PLANT DISEASE 2003; 87:1272-1282. [PMID: 30812540 DOI: 10.1094/pdis.2003.87.11.1272] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
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62
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Quirino BF, Bent AF. Deciphering host resistance and pathogen virulence: the Arabidopsis/Pseudomonas interaction as a model. MOLECULAR PLANT PATHOLOGY 2003; 4:517-30. [PMID: 20569411 DOI: 10.1046/j.1364-3703.2003.00198.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
SUMMARY The last decade has witnessed steady progress in deciphering the molecular basis of plant disease resistance and pathogen virulence. Although contributions have been made using many different plant and pathogen species, studies of the interactions between Arabidopsis thaliana and Pseudomonas syringae have yielded a particularly significant body of information. The present review focuses on recent findings regarding R gene products and the guard hypothesis, RAR1/SGT1 and other examples where protein processing activity is implicated in disease resistance or susceptibility, the use of microarray expression profiling to generate information and experimental leads, and important molecular- and genome-level discoveries regarding P. syringae effectors that mediate bacterial virulence. The development of the Arabidopsis-Pseudomonas model system is also reviewed briefly, and we close with a discussion of characteristics to consider when selecting other pathosystems as experimentally tractable models for future research.
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Affiliation(s)
- Betania F Quirino
- Genomics and Biotecnology Program, Universidade Católica de Brasília, Brasília, DF, Brazil
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63
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Badel JL, Nomura K, Bandyopadhyay S, Shimizu R, Collmer A, He SY. Pseudomonas syringae pv. tomato DC3000 HopPtoM (CEL ORF3) is important for lesion formation but not growth in tomato and is secreted and translocated by the Hrp type III secretion system in a chaperone-dependent manner. Mol Microbiol 2003; 49:1239-51. [PMID: 12940984 DOI: 10.1046/j.1365-2958.2003.03647.x] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Pseudomonas syringae pv. tomato DC3000 is a pathogen of tomato and Arabidopsis that injects virulence effector proteins into host cells via a type III secretion system (TTSS). TTSS-deficient mutants have a Hrp- phenotype, that is, they cannot elicit the hypersensitive response (HR) in non-host plants or pathogenesis in host plants. Mutations in effector genes typically have weak virulence phenotypes (apparently due to redundancy), but deletion of six open reading frames (ORF) in the DC3000 conserved effector locus (CEL) reduces parasitic growth and abolishes disease symptoms without affecting function of the TTSS. The inability of the DeltaCEL mutant to cause disease symptoms in tomato was restored by a clone expressing two of the six ORF that had been deleted: CEL ORF3 (HopPtoM) and ORF4 (ShcM). A DeltahopPtoM::nptII mutant was constructed and found to grow like the wild type in tomato but to be strongly reduced in its production of necrotic lesion symptoms. HopPtoM expression in DC3000 was activated by the HrpL alternative sigma factor, and the protein was secreted by the Hrp TTSS in culture and translocated into Arabidopsis cells by the Hrp TTSS during infection. Secretion and translocation were dependent on ShcM, which was neither secreted nor translocated but, like typical TTSS chaperones, could be shown to interact with HopPtoM, its cognate effector, in yeast two-hybrid experiments. Thus, HopPtoM is a type III effector that, among known plant pathogen effectors, is unusual in making a major contribution to the elicitation of lesion symptoms but not growth in host tomato leaves.
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Affiliation(s)
- Jorge L Badel
- Department of Plant Pathology, Cornell University, Ithaca, NY 14853, USA
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64
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Arnold DL, Pitman A, Jackson RW. Pathogenicity and other genomic islands in plant pathogenic bacteria. MOLECULAR PLANT PATHOLOGY 2003; 4:407-20. [PMID: 20569400 DOI: 10.1046/j.1364-3703.2003.00187.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
SUMMARY Pathogenicity islands (PAIs) were first described in uropathogenic E. coli. They are now defined as regions of DNA that contain virulence genes and are present in the genome of pathogenic strains, but absent from or only rarely present in non-pathogenic variants of the same or related strains. Other features include a variable G+C content, distinct boundaries from the rest of the genome and the presence of genes related to mobile elements such as insertion sequences, integrases and transposases. Although PAIs have now been described in a wide range of both plant and animal pathogens it has become evident that the general features of PAIs are displayed by a number of regions of DNA with functions other than pathogenicity, such as symbiosis and antibiotic resistance, and the general term genomic islands has been adopted. This review will describe a range of genomic islands in plant pathogenic bacteria including those that carry effector genes, phytotoxins and the type III protein secretion cluster. The review will also consider some medically important bacteria in order to discuss the range, acquisition and stabilization of genomic islands.
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Affiliation(s)
- Dawn L Arnold
- Centre for Research in Plant Science, Faculty of Applied Sciences, University of the West of England, Coldharbour Lane, Bristol, BS16 1QY, UK
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65
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Rathjen JP, Moffett P. Early signal transduction events in specific plant disease resistance. CURRENT OPINION IN PLANT BIOLOGY 2003; 6:300-306. [PMID: 12873522 DOI: 10.1016/s1369-5266(03)00057-8] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Gene-for-gene disease resistance in plants is initiated by highly specific molecular recognition processes, which often lead to a cell-death phenotype termed the hypersensitive response (HR). Recent studies have yielded insight into recognition events, and have begun to explain why the virulence and avirulence activities of pathogen effector molecules often appear to be linked. The nucleotide-binding (NB)-leucine-rich repeat (LRR) proteins appear to be central to both recognition and the activation of defence responses. New structure-function studies suggest that intramolecular interactions are important in the regulation of these proteins.
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Affiliation(s)
- John P Rathjen
- The Sainsbury Laboratory, Norwich Research Park, Colney, NR4 7UH, Norwich, UK. john.
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66
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Hauck P, Thilmony R, He SY. A Pseudomonas syringae type III effector suppresses cell wall-based extracellular defense in susceptible Arabidopsis plants. Proc Natl Acad Sci U S A 2003; 100:8577-82. [PMID: 12817082 PMCID: PMC166271 DOI: 10.1073/pnas.1431173100] [Citation(s) in RCA: 368] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Bacterial effector proteins secreted through the type III secretion system (TTSS) play a crucial role in causing plant and human diseases. Although the ability of type III effectors to trigger defense responses in resistant plants is well understood, the disease-promoting functions of type III effectors in susceptible plants are largely enigmatic. Previous microscopic studies suggest that in susceptible plants the TTSS of plant-pathogenic bacteria transports suppressors of a cell wall-based plant defense activated by the TTSS-defective hrp mutant bacteria. However, the identity of such suppressors has remained elusive. We discovered that the Pseudomonas syringae TTSS down-regulated the expression of a set of Arabidopsis genes encoding putatively secreted cell wall and defense proteins in a salicylic acid-independent manner. Transgenic expression of AvrPto repressed a similar set of host genes, compromised defense-related callose deposition in the host cell wall, and permitted substantial multiplication of an hrp mutant. AvrPto is therefore one of the long postulated suppressors of an salicylic acid-independent, cell wall-based defense that is aimed at hrp mutant bacteria.
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67
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Espinosa A, Guo M, Tam VC, Fu ZQ, Alfano JR. The Pseudomonas syringae type III-secreted protein HopPtoD2 possesses protein tyrosine phosphatase activity and suppresses programmed cell death in plants. Mol Microbiol 2003; 49:377-87. [PMID: 12828636 DOI: 10.1046/j.1365-2958.2003.03588.x] [Citation(s) in RCA: 161] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The bacterial plant pathogen Pseudomonas syringae possesses a type III protein secretion system that delivers many virulence proteins into plant cells. A subset of these proteins (called Avr proteins) is recognized by the plant's innate immune system and triggers defences. One defence-associated response is the hypersensitive response (HR), a programmed cell death (PCD) of plant tissue. We have previously identified HopPtoD2 as a type III secreted protein from P. s. pv. tomato DC3000. Sequence analysis revealed that an N-terminal domain shared homology with AvrPphD and a C-terminal domain was similar to protein tyrosine phosphatases (PTPs). We demonstrated that purified HopPtoD2 possessed PTP activity and this activity required a conserved catalytic Cys residue (Cys(378)). Interestingly, HopPtoD2 was capable of suppressing the HR elicited by an avirulent P. syringae strain on Nicotiana benthamiana. HopPtoD2 derivatives that lacked Cys(378) no longer suppressed the HR indicating that HR suppression required PTP activity. A constitutively active MAPK kinase, called NtMEK2DD, is capable of eliciting an HR-like cell death when transiently expressed in tobacco. When NtMEK2DD and HopPtoD2 were co-delivered into plant cells, the HR was suppressed indicating that HopPtoD2 acts downstream of NtMEK2DD. DC3000 hopPtoD2 mutants were slightly reduced in their ability to multiply in planta and displayed an enhanced ability to elicit an HR. The identification of HopPtoD2 as a PTP and a PCD suppressor suggests that the inactivation of MAPK pathways is a virulence strategy utilized by bacterial plant pathogens.
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Affiliation(s)
- Avelina Espinosa
- Plant Science Initiative, University of Nebraska--Lincoln, NE 68588-0660, USA
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68
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Bretz JR, Mock NM, Charity JC, Zeyad S, Baker CJ, Hutcheson SW. A translocated protein tyrosine phosphatase of Pseudomonas syringae pv. tomato DC3000 modulates plant defence response to infection. Mol Microbiol 2003; 49:389-400. [PMID: 12828637 DOI: 10.1046/j.1365-2958.2003.03616.x] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Pseudomonas syringae strains translocate effector proteins into host cells via the hrp-encoded type III protein secretion system (TTSS) to facilitate pathogenesis in susceptible plants. However, the mechanisms by which pathogenesis is favoured by these effectors are not well understood. Individual strains express multiple effectors with apparently distinct activities that are co-ordinately regulated by the alternative sigma factor HrpL. Genes for several effectors were identified in the P. syringae pv. tomato DC3000 genome using a promoter trap assay to identify HrpL-dependent promoters. In addition to orthologues of avrPphE and hrpW, an unusual allele of avrPphD was detected that carried an IS52 insertion. Using this avrPphD::IS52 allele as a probe, a wild-type allele of avrPphD, hopPtoD1, and a chimeric homologue were identified in the DC3000 genome. This chimeric homologue, identified as HopPtoD2 in the annotated DC3000 genome, consisted of an amino terminal secretion domain similar to that of AvrPphD fused to a potential protein tyrosine phosphatase domain. Culture filtrates of strains expressing HopPtoD2 were able to dephosphorylate pNPP and two phosphotyrosine peptides. HopPtoD2 was shown to be translocated into Arabidopsis thaliana cells via the hrp-encoded TTSS. A DeltahopPtoD2 mutant of DC3000 exhibited strongly reduced virulence in Arabidopsis thaliana. Ectopic expression of hopPtoD2 in P. syringae Psy61 that lacks a native hopPtoD2 orthologue delayed the development of several defence-associated responses including programmed cell death, active oxygen production and transcription of the pathogenesis-related gene PR1. The results indicate that HopPtoD2 is a translocated effector with protein tyrosine phosphatase activity that modulates plant defence responses.
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Affiliation(s)
- James R Bretz
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA
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69
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Charity JC, Pak K, Delwiche CF, Hutcheson SW. Novel exchangeable effector loci associated with the Pseudomonas syringae hrp pathogenicity island: evidence for integron-like assembly from transposed gene cassettes. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2003; 16:495-507. [PMID: 12795376 DOI: 10.1094/mpmi.2003.16.6.495] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Pseudomonas syringae strains use a type III secretion system (TTSS) to translocate effector proteins that assist in the parasitism of host plant cells. Some genes for effector proteins are clustered in the exchangeable effector locus (EEL) associated with the hrp pathogenicity island. A polymerase chain reaction-based screen was developed to amplify the EEL from P. syringae strains. Of the 86 strains screened, the EEL was successfully amplified from 30 predominately North American P. syringae pv. syringae strains using hrpK and queA-derived primers and from an additional three strains using hrpL and queA-derived primers. Among the amplified EEL, ten distinct types of EEL were identified that could be classified into six families distinguishable by genetic composition, but other types of EEL may be present in strains isolated in other geographical regions. No linkage with the host range of the source strain was apparent. Gene cassettes carrying conserved flanking, coding, and intergenic sequences, present in different combinations, were identified in the characterized EEL. Six new alleles of known effectors were identified that differed from the homolog in sequence, size, or both of the gene. One of these apparently novel effector proteins, HopPsyB, retained a strongly conserved amino terminus similar to that of HopPsyA, but other regions of the two polypeptides were only weakly similar. hopPsyB was expressed from an apparent operon that included hrpK and a shcA homolog, shcB. Escherichia coli MC4100 expressing the hrp TTSS, ShcB, and HopPsyB elicited the hypersensitive response (HR) in tobacco, consistent with effector production. Indicative of translocation as an effector, P. syringae pv. tomato DC3000 expressing a HopPsyB':'AvrRpt2 fusion elicited the HR in RPS2+ Arabidopsis thaliana. P. syringae pv. tomato DC3000 carrying HopPsyB exhibited slightly enhanced virulence in several Brassica spp. These results are consistent with the hypotheses that the EEL is a source of disparate effectors functioning in pathogenicity of P. syringae strains and that it evolved independently of the hrp pathogenicity island central conserved region, most likely through integron-like assembly of transposed gene cassettes.
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Affiliation(s)
- James C Charity
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA
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70
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Abstract
A plant protein RIN4 is targeted and modified by bacterial pathogens as part of the disease process. At least two host resistance proteins monitor this pathogen interference and trigger the plant's defence responses.
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Affiliation(s)
- Jeff Ellis
- CSIRO Plant Industry, GPO BOX 1600 Canberra ACT 2601, Australia.
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71
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Deng WL, Rehm AH, Charkowski AO, Rojas CM, Collmer A. Pseudomonas syringae exchangeable effector loci: sequence diversity in representative pathovars and virulence function in P. syringae pv. syringae B728a. J Bacteriol 2003; 185:2592-602. [PMID: 12670984 PMCID: PMC152607 DOI: 10.1128/jb.185.8.2592-2602.2003] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Pseudomonas syringae is a plant pathogen whose pathogenicity and host specificity are thought to be determined by Hop/Avr effector proteins injected into plant cells by a type III secretion system. P. syringae pv. syringae B728a, which causes brown spot of bean, is a particularly well-studied strain. The type III secretion system in P. syringae is encoded by hrp (hypersensitive response and pathogenicity) and hrc (hrp conserved) genes, which are clustered in a pathogenicity island with a tripartite structure such that the hrp/hrc genes are flanked by a conserved effector locus and an exchangeable effector locus (EEL). The EELs of P. syringae pv. syringae B728a, P. syringae strain 61, and P. syringae pv. tomato DC3000 differ in size and effector gene composition; the EEL of P. syringae pv. syringae B728a is the largest and most complex. The three putative effector proteins encoded by the P. syringae pv. syringae B728a EEL--HopPsyC, HopPsyE, and HopPsyV--were demonstrated to be secreted in an Hrp-dependent manner in culture. Heterologous expression of hopPsyC, hopPsyE, and hopPsyV in P. syringae pv. tabaci induced the hypersensitive response in tobacco leaves, demonstrating avirulence activity in a nonhost plant. Deletion of the P. syringae pv. syringae B728a EEL strongly reduced virulence in host bean leaves. EELs from nine additional strains representing nine P. syringae pathovars were isolated and sequenced. Homologs of avrPphE (e.g., hopPsyE) and hopPsyA were particularly common. Comparative analyses of these effector genes and hrpK (which flanks the EEL) suggest that the EEL effector genes were acquired by horizontal transfer after the acquisition of the hrp/hrc gene cluster but before the divergence of modern pathovars and that some EELs underwent transpositions yielding effector exchanges or point mutations producing effector pseudogenes after their acquisition.
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Affiliation(s)
- Wen-Ling Deng
- Department of Plant Pathology, Cornell University, Ithaca, New York 14853, USA
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72
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Abstract
The type III secretion system is an essential virulence system used by many Gram-negative bacterial pathogens to deliver effector proteins into host cells. This review summarizes recent advancements in the understanding of the type III secretion system of Pseudomonas syringae, including regulation of the type III secretion genes, assembly of the Hrp pilus, secretion signals, the putative type III effectors identified to date, and their virulence action after translocation into plant cells.
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Affiliation(s)
- Qiaoling Jin
- Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, USA
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73
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Kang L, Li J, Zhao T, Xiao F, Tang X, Thilmony R, He S, Zhou JM. Interplay of the Arabidopsis nonhost resistance gene NHO1 with bacterial virulence. Proc Natl Acad Sci U S A 2003; 100:3519-24. [PMID: 12626746 PMCID: PMC152325 DOI: 10.1073/pnas.0637377100] [Citation(s) in RCA: 130] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
It is poorly understood why a particular plant species is resistant to the vast majority of potential pathogens that infect other plant species, a phenomenon referred to as "nonhost" resistance. Here, we show that Arabidopsis NHO1, encoding a glycerol kinase, is required for resistance to and induced by Pseudomonas syringae isolates from bean and tobacco. NHO1 is also required for resistance to the fungal pathogen Botrytis cinerea, indicating that NHO1 is not limited to bacterial resistance. Strikingly, P. s. pv. tomato DC3000, an isolate fully virulent on Arabidopsis, actively suppressed the NHO1 expression. This suppression is abolished in coi1 plants, indicating that DC3000 required an intact jasmonic acid signaling pathway in the plant to suppress NHO1 expression. Constitutive overexpression of NHO1 led to enhanced resistance to this otherwise virulent bacterium. The presence of avrB in DC3000, which activates a cultivar-specific "gene-for-gene" resistance in Arabidopsis, restored the induction of NHO1 expression. Thus, NHO1 is deployed for both general and specific resistance in Arabidopsis and targeted by the bacterium for parasitism.
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Affiliation(s)
- Li Kang
- Department of Plant Pathology, Kansas State University, Manhattan, KS 66506, USA
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74
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Kim H, Snesrud EC, Haas B, Cheung F, Town CD, Quackenbush J. Gene expression analyses of Arabidopsis chromosome 2 using a genomic DNA amplicon microarray. Genome Res 2003; 13:327-40. [PMID: 12618363 PMCID: PMC430289 DOI: 10.1101/gr.552003] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2002] [Accepted: 12/20/2002] [Indexed: 11/24/2022]
Abstract
The gene predictions and accompanying functional assignments resulting from the sequencing and annotation of a genome represent hypotheses that can be tested and used to develop a more complete understanding of the organism and its biology. In the model plant Arabidopsis thaliana, we developed a novel approach to constructing whole-genome microarrays based on PCR amplification of the 3' ends of each predicted gene from genomic DNA, and constructed an array representing more than 94% of the predicted genes and pseudogenes on chromosome 2. With this array, we examined various tissues and physiological conditions, providing expression-based validation for 84% of the gene predictions and providing clues as to the functions of many predicted genes. Further, by examining the distribution of expression along the physical chromosome, we were able to identify a region of repressed transcription that may represent a previously undescribed heterochromatic region.
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Affiliation(s)
- Heenam Kim
- The Institute for Genomic Research, Rockville, MD 20850, USA
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75
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Mackey D, Belkhadir Y, Alonso JM, Ecker JR, Dangl JL. Arabidopsis RIN4 is a target of the type III virulence effector AvrRpt2 and modulates RPS2-mediated resistance. Cell 2003; 112:379-89. [PMID: 12581527 DOI: 10.1016/s0092-8674(03)00040-0] [Citation(s) in RCA: 640] [Impact Index Per Article: 30.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Type III pili deliver effector proteins (virulence factors) from bacterial pathogens to host cells. Plants express disease resistance (R) proteins that respond specifically to a particular type III effector by activating immune responses. We demonstrated previously that two unrelated type III effectors from Pseudomonas syringae target and modify the Arabidopsis RIN4 protein. Here, we show that AvrRpt2, a third, unrelated type III effector, also targets RIN4 and induces its posttranscriptional disappearance. This effect is independent of the presence of RPS2, the Arabidopsis R protein that senses AvrRpt2. RIN4 overexpression inhibits multiple phenotypes associated with AvrRpt2 function. Conversely, disruption of RIN4 results in RPS2-dependent lethality. RPS2 and RIN4 physically associate in the plant. We suggest that RIN4 is the target of the AvrRpt2 virulence function, and that perturbation of RIN4 activates RPS2. Thus, RIN4 is a point of convergence for the activity of at least three unrelated P. syringae type III effectors.
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MESH Headings
- Arabidopsis/genetics
- Arabidopsis/immunology
- Arabidopsis Proteins/genetics
- Arabidopsis Proteins/immunology
- Bacterial Infections/genetics
- Bacterial Infections/immunology
- Bacterial Proteins/genetics
- Bacterial Proteins/immunology
- Carrier Proteins/genetics
- Carrier Proteins/immunology
- Cell Membrane/genetics
- Cell Membrane/immunology
- Cell Membrane/metabolism
- Gene Expression Regulation, Plant/genetics
- Gene Expression Regulation, Plant/immunology
- Genes, Lethal/genetics
- Genes, Lethal/immunology
- Immunity, Innate/genetics
- Immunity, Innate/immunology
- Immunologic Surveillance/genetics
- Immunologic Surveillance/immunology
- Intracellular Signaling Peptides and Proteins
- Models, Biological
- Mutation/genetics
- Mutation/immunology
- Plants, Genetically Modified/genetics
- Plants, Genetically Modified/immunology
- Transcription, Genetic/genetics
- Transcription, Genetic/immunology
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Affiliation(s)
- David Mackey
- Department of Horticulture and Crop Science, The Ohio State University, Room 306C Kottman Hall, Columbus, OH 43210, USA
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76
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Axtell MJ, Staskawicz BJ. Initiation of RPS2-specified disease resistance in Arabidopsis is coupled to the AvrRpt2-directed elimination of RIN4. Cell 2003; 112:369-77. [PMID: 12581526 DOI: 10.1016/s0092-8674(03)00036-9] [Citation(s) in RCA: 556] [Impact Index Per Article: 26.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Plants have evolved a sophisticated innate immune system to recognize invading pathogens and to induce a set of host defense mechanisms resulting in disease resistance. Pathogen recognition is often mediated by plant disease resistance (R) proteins that respond specifically to one or a few pathogen-derived molecules. This specificity has led to suggestions of a receptor-ligand mode of R protein function. Delivery of the bacterial effector protein AvrRpt2 by Pseudomonas syringae specifically induces disease resistance in Arabidopsis plants expressing the RPS2 R protein. We demonstrate that RPS2 physically interacts with Arabidopsis RIN4 and that AvrRpt2 causes the elimination of RIN4 during activation of the RPS2 pathway. AvrRpt2-mediated RIN4 elimination also occurs in the rps2, ndr1, and Atrar1 mutant backgrounds, demonstrating that this activity can be achieved independent of an RPS2-mediated signaling pathway. Therefore, we suggest that RPS2 initiates signaling based upon perception of RIN4 disappearance rather than direct recognition of AvrRpt2.
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Affiliation(s)
- Michael J Axtell
- Department of Plant and Microbial Biology, University of California, Berkeley, Berkeley, CA 94720, USA
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77
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Tao Y, Xie Z, Chen W, Glazebrook J, Chang HS, Han B, Zhu T, Zou G, Katagiri F. Quantitative nature of Arabidopsis responses during compatible and incompatible interactions with the bacterial pathogen Pseudomonas syringae. THE PLANT CELL 2003; 15:317-30. [PMID: 12566575 PMCID: PMC141204 DOI: 10.1105/tpc.007591] [Citation(s) in RCA: 491] [Impact Index Per Article: 23.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2002] [Accepted: 12/02/2002] [Indexed: 05/17/2023]
Abstract
We performed large-scale mRNA expression profiling using an Affymetrix GeneChip to study Arabidopsis responses to the bacterial pathogen Pseudomonas syringae. The interactions were compatible (virulent bacteria) or incompatible (avirulent bacteria), including a nonhost interaction and interactions mediated by two different avirulence gene-resistance (R) gene combinations. Approximately 2000 of the approximately 8000 genes monitored showed reproducible significant expression level changes in at least one of the interactions. Analysis of biological variation suggested that the system behavior of the plant response in an incompatible interaction was robust but that of a compatible interaction was not. A large part of the difference between incompatible and compatible interactions can be explained quantitatively. Despite high similarity between responses mediated by the R genes RPS2 and RPM1 in wild-type plants, RPS2-mediated responses were strongly suppressed by the ndr1 mutation and the NahG transgene, whereas RPM1-mediated responses were not. This finding is consistent with the resistance phenotypes of these plants. We propose a simple quantitative model with a saturating response curve that approximates the overall behavior of this plant-pathogen system.
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Affiliation(s)
- Yi Tao
- Torrey Mesa Research Institute, Syngenta Research and Technology, San Diego, California 92121, USA
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78
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Abramovitch RB, Kim YJ, Chen S, Dickman MB, Martin GB. Pseudomonas type III effector AvrPtoB induces plant disease susceptibility by inhibition of host programmed cell death. EMBO J 2003; 22:60-9. [PMID: 12505984 PMCID: PMC140047 DOI: 10.1093/emboj/cdg006] [Citation(s) in RCA: 326] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2002] [Revised: 11/04/2002] [Accepted: 11/04/2002] [Indexed: 12/23/2022] Open
Abstract
The AvrPtoB type III effector protein is conserved among diverse genera of plant pathogens suggesting it plays an important role in pathogenesis. Here we report that Pseudomonas AvrPtoB acts inside the plant cell to inhibit programmed cell death (PCD) initiated by the Pto and Cf9 disease resistance proteins and, remarkably, the pro-apoptotic mouse protein Bax. AvrPtoB also suppressed PCD in yeast, demonstrating that AvrPtoB functions as a cell death inhibitor across kingdoms. Using truncated AvrPtoB proteins, we identified distinct N- and C-terminal domains of AvrPtoB that are sufficient for host recognition and PCD inhibition, respectively. We also identified a novel resistance phenotype, Rsb, that is triggered by an AvrPtoB truncation disrupted in the anti-PCD domain. A Pseudomonas syringae pv. tomato DC3000 strain with a chromosomal mutation in the AvrPtoB C-terminus elicited Rsb-mediated immunity in previously susceptible tomato plants and disease was restored when full-length AvrPtoB was expressed in trans. Thus, our results indicate that a type III effector can induce plant susceptibility to bacterial infection by inhibiting host PCD.
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Affiliation(s)
- Robert B. Abramovitch
- Boyce Thompson Institute for Plant Research, Department of Plant Pathology, Cornell University, Ithaca, NY 14853 and Department of Plant Pathology, University of Nebraska, Lincoln, NE 68583, USA Corresponding author e-mail:
| | - Young-Jin Kim
- Boyce Thompson Institute for Plant Research, Department of Plant Pathology, Cornell University, Ithaca, NY 14853 and Department of Plant Pathology, University of Nebraska, Lincoln, NE 68583, USA Corresponding author e-mail:
| | - Shaorong Chen
- Boyce Thompson Institute for Plant Research, Department of Plant Pathology, Cornell University, Ithaca, NY 14853 and Department of Plant Pathology, University of Nebraska, Lincoln, NE 68583, USA Corresponding author e-mail:
| | - Martin B. Dickman
- Boyce Thompson Institute for Plant Research, Department of Plant Pathology, Cornell University, Ithaca, NY 14853 and Department of Plant Pathology, University of Nebraska, Lincoln, NE 68583, USA Corresponding author e-mail:
| | - Gregory B. Martin
- Boyce Thompson Institute for Plant Research, Department of Plant Pathology, Cornell University, Ithaca, NY 14853 and Department of Plant Pathology, University of Nebraska, Lincoln, NE 68583, USA Corresponding author e-mail:
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79
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Martin GB, Bogdanove AJ, Sessa G. Understanding the functions of plant disease resistance proteins. ANNUAL REVIEW OF PLANT BIOLOGY 2003; 54:23-61. [PMID: 14502984 DOI: 10.1146/annurev.arplant.54.031902.135035] [Citation(s) in RCA: 523] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Many disease resistance (R) proteins of plants detect the presence of disease-causing bacteria, viruses, or fungi by recognizing specific pathogen effector molecules that are produced during the infection process. Effectors are often pathogen proteins that probably evolved to subvert various host processes for promotion of the pathogen life cycle. Five classes of effector-specific R proteins are known, and their sequences suggest roles in both effector recognition and signal transduction. Although some R proteins may act as primary receptors of pathogen effector proteins, most appear to play indirect roles in this process. The functions of various R proteins require phosphorylation, protein degradation, or specific localization within the host cell. Some signaling components are shared by many R gene pathways whereas others appear to be pathway specific. New technologies arising from the genomics and proteomics revolution will greatly expand our ability to investigate the role of R proteins in plant disease resistance.
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Affiliation(s)
- Gregory B Martin
- Boyce Thompson Institute for Plant Research and Department of Plant Pathology, Cornell University, Ithaca, New York 14853, USA.
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80
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Badel JL, Charkowski AO, Deng WL, Collmer A. A gene in the Pseudomonas syringae pv. tomato Hrp pathogenicity island conserved effector locus, hopPtoA1, contributes to efficient formation of bacterial colonies in planta and is duplicated elsewhere in the genome. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2002; 15:1014-1024. [PMID: 12437299 DOI: 10.1094/mpmi.2002.15.10.1014] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The ability of Pseudomonas syringae to grow in planta is thought to be dependent upon the Hrp (type III secretion) system and multiple effector proteins that this system injects into plant cells. ORF5 in the conserved effector locus of the P. syringae pv. tomato DC3000 Hrp pathogenicity island was shown to encode a Hrp-secreted protein and to have a similarly secreted homolog encoded in an effector-rich pathogenicity island located elsewhere in the genome. These putative effector genes were designated hopPtoA1 and hopPtoA2, respectively. DNA gel blot analysis revealed that sequences hybridizing with hopPtoA1 were widespread among P. syringae pathovars, and some strains, like DC3000, appear to have two copies of the gene. uidA transcriptional fusions revealed that expression of hopPtoA1 and hopPtoA2 can be activated by the HrpL alternative sigma factor. hopPtoA1 and hopPtoA1/hopPtoA2 double mutants were not obviously different from wild-type P. syringae pv. tomato DC3000 in their ability to produce symptoms or to increase their total population size in host tomato and Arabidopsis leaves. However, confocal laser-scanning microscopy of GFP (green fluorescent protein)-labeled bacteria in Arabidopsis leaves 2 days after inoculation revealed that the frequency of undeveloped individual colonies was higher in the hopPtoA1 mutant and even higher in the hopPtoA1/hopPtoA2 double mutant. These results suggest that hopPtoA1 and hopPtoA2 contribute redundantly to the formation of P. syringae pv. tomato DC3000 colonies in Arabidopsis leaves.
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Affiliation(s)
- J L Badel
- Department of Plant Pathology, Cornell University, Ithaca, NY 14853, USA
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81
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Jackson RW, Mansfield JW, Ammouneh H, Dutton LC, Wharton B, Ortiz-Barredo A, Arnold DL, Tsiamis G, Sesma A, Butcher D, Boch J, Kim YJ, Martin GB, Tegli S, Murillo J, Vivian A. Location and activity of members of a family of virPphA homologues in pathovars of Pseudomonas syringae and P. savastanoi. MOLECULAR PLANT PATHOLOGY 2002; 3:205-216. [PMID: 20569328 DOI: 10.1046/j.1364-3703.2002.00121.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Summary virPphA is a major determinant of the pathogenicity of Pseudomonas savastanoi pv. phaseolicola to Phaseolus bean. A family of homologues of virPphA was detected in pathovars of P. savastanoi and P. syringae. We examined the structure and activity of alleles designated virPphA, virPphA(Pgy), and virPphA(Psv) from P. savastanoi pathovars phaseolicola, glycinea, and savastanoi, respectively, and avrPtoB from P. syringae pv. tomato. Sequencing showed that the virPphA(Pgy) homologue had a 48-bp central deletion in the open reading frame (ORF) compared with virPphA and virPphA(Psv), but otherwise all three P. savastanoi alleles had > 98% identity at the DNA level. By contrast, AvrPtoB from P. syringae pv. tomato strain DC3000 was predicted to have only 51% amino acid similarity with VirPphA. All ORFs have an upstream hrp-box promoter indicating potential regulation by HrpL. Each cloned homologue was introduced into the P. savastanoi pv. phaseolicola strain RW60, which lacks a native plasmid carrying virPphA as part of a pathogenicity island (PAI), and which is not pathogenic on bean. The homologues all restored virulence, as measured by the development of water-soaked lesions in bean pods, and increased bacterial populations in leaves compared with RW60 alone. RW60 harbouring virPphA or virPphA(Psv) elicited a strong hypersensitive reaction (HR) in soybean cv. Osumi; the presence of avrPtoB caused a weak HR, but virPphA(Pgy) did not affect the null reaction observed in soybean with RW60 alone. A second effector gene, avrPphD, was detected on the genomic clones carrying virPphA(Pgy) and virPphA(Psv). avrPphD was also present in both P. savastanoi pv. phaseolicola and P. syringae pv. tomato, but elsewhere in their genomes. Comparison of the genomic locations of virPphA and other effectors found in the P. savastanoi pv. phaseolicola PAI revealed the greatest divergence of the sequences surrounding virPphA to be in P. syringae pv. tomato.
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Affiliation(s)
- Robert W Jackson
- Centre for Research in Plant Science, Faculty of Applied Sciences, University of the West of England, Coldharbour Lane, Bristol BS16 1QY, UK
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82
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Marois E, Van den Ackerveken G, Bonas U. The xanthomonas type III effector protein AvrBs3 modulates plant gene expression and induces cell hypertrophy in the susceptible host. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2002; 15:637-646. [PMID: 12118879 DOI: 10.1094/mpmi.2002.15.7.637] [Citation(s) in RCA: 147] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Xanthomonas campestris pv. vesicatoria bacteria expressing the type III effector protein AvrBs3 induce a hypersensitive response in pepper plants carrying the resistance gene Bs3. Here, we report that infection of susceptible pepper and tomato plants leads to an AvrBs3-dependent hypertrophy of the mesophyll tissue. Agrobacterium-mediated transient expression of the avrBs3 gene in tobacco and potato plants resulted in a similar phenotype. Induction of hypertrophy was shown to depend on the repeat region, nuclear localization signals, and acidic transcription activation domain (AAD) of AvrBs3, suggesting that the effector modulates the host's transcriptome. To search for host genes regulated by AvrBs3 in an AAD-dependent manner, we performed a cDNA-amplified fragment length polymorphism analysis of pepper mRNA populations. Thirteen AvrBs3-induced transcripts were identified and confirmed by reverse transcriptase-polymerase chain reaction. Sequence analysis revealed homologies to auxin-induced and expansinlike genes, which play a role in cell enlargement. These results suggest that some of the AvrBs3-induced genes may be involved in hypertrophy development and that xanthomonads possess type III effectors that steer host gene expression.
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Affiliation(s)
- Eric Marois
- Institut für Genetik, Martin-Luther-Universität Halle-Wittenberg, Halle, Germany
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83
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Boch J, Joardar V, Gao L, Robertson TL, Lim M, Kunkel BN. Identification of Pseudomonas syringae pv. tomato genes induced during infection of Arabidopsis thaliana. Mol Microbiol 2002; 44:73-88. [PMID: 11967070 DOI: 10.1046/j.1365-2958.2002.02877.x] [Citation(s) in RCA: 160] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Phytopathogenic bacteria possess a large number of genes that allow them to grow and cause disease on plants. Many of these genes should be induced when the bacteria come in contact with plant tissue. We used a modified in vivo expression technology (IVET) approach to identify genes from the plant pathogen Pseudomonas syringae pv. tomato that are induced upon infection of Arabidopsis thaliana and isolated over 500 in planta-expressed (ipx) promoter fusions. Sequence analysis of 79 fusions revealed several known and potential virulence genes, including hrp/hrc, avr and coronatine biosynthetic genes. In addition, we identified metabolic genes presumably important for adaptation to growth in plant tissue, as well as several genes with unknown function that may encode novel virulence factors. Many ipx fusions, including several corresponding to novel genes, are dependent on HrpL, an alternative RNA polymerase sigma factor that regulates the expression of virulence genes. Expression analysis indicated that several ipx fusions are strongly induced upon inoculation into plant tissue. Disruption of one ipx gene, conserved effector locus (CEL) orf1, encoding a putative lytic murein transglycosylase, resulted in decreased virulence of P. syringae. Our results demonstrate that this screen can be used successfully to isolate genes that are induced in planta, including many novel genes potentially involved in pathogenesis.
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Affiliation(s)
- Jens Boch
- Department of Biology, Campus Box 1137, Washington University, 1 Brookings Drive, St Louis, MO 63130, USA
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84
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Mackey D, Holt BF, Wiig A, Dangl JL. RIN4 interacts with Pseudomonas syringae type III effector molecules and is required for RPM1-mediated resistance in Arabidopsis. Cell 2002; 108:743-54. [PMID: 11955429 DOI: 10.1016/s0092-8674(02)00661-x] [Citation(s) in RCA: 767] [Impact Index Per Article: 34.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
In Arabidopsis, RPM1 confers resistance against Pseudomonas syringae expressing either of two sequence unrelated type III effectors, AvrRpm1 or AvrB. An RPM1-interacting protein (RIN4) coimmunoprecipitates from plant cell extracts with AvrB, AvrRpm1, or RPM1. Reduction of RIN4 protein levels inhibits both the hypersensitive response and the restriction of pathogen growth controlled by RPM1. RIN4 reduction causes diminution of RPM1. RIN4 reduction results in heightened resistance to virulent Peronospora parasitica and P. syringae, and ectopic defense gene expression. Thus, RIN4 positively regulates RPM1-mediated resistance yet is, formally, a negative regulator of basal defense responses. AvrRpm1 and AvrB induce RIN4 phosphorylation. This may enhance RIN4 activity as a negative regulator of plant defense, facilitating pathogen growth. RPM1 may "guard" against pathogens that use AvrRpm1 and AvrB to manipulate RIN4 activity.
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Affiliation(s)
- David Mackey
- Department of Biology, University of North Carolina, Chapel Hill, NC 27599, USA
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85
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Katagiri F, Thilmony R, He SY. The Arabidopsis thaliana-pseudomonas syringae interaction. THE ARABIDOPSIS BOOK 2002; 1:e0039. [PMID: 22303207 PMCID: PMC3243347 DOI: 10.1199/tab.0039] [Citation(s) in RCA: 308] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Affiliation(s)
- Fumiaki Katagiri
- Plant Health Department, Torrey Mesa Research Institute, 3115 Merryfield Row, San Diego, CA 92121, USA
| | - Roger Thilmony
- Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, USA
| | - Sheng Yang He
- Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, USA
- Corresponding Author: Sheng Yang He, 206 Plant Biology Bldg., Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, USA, Tel: (517) 353-9181, Fax: (517) 353 –9168,
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86
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Luderer R, Joosten MH. Avirulence proteins of plant pathogens: determinants of victory and defeat. MOLECULAR PLANT PATHOLOGY 2001; 2:355-364. [PMID: 20573025 DOI: 10.1046/j.1464-6722.2001.00086.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
summary The simplest way to explain the biochemical basis of the gene-for-gene concept is by direct interaction between a pathogen-derived avirulence (Avr) gene product and a receptor protein, which is encoded by the matching resistance (R) gene of the host plant. The number of R genes for which the matching Avr gene has been cloned is increasing. The number of host-pathogen relationships, however, for which a direct interaction between R and Avr gene products could be proven is still very limited. This observation suggests that in various host-pathogen relationships no physical interaction between R and Avr proteins occurs, and that perception of AVR proteins by their matching R gene products is indirect. Indirect perception implies that at least a third component is required. The 'Guard hypothesis' proposes that this third component could be the virulence target of an AVR protein. Binding of the AVR protein to its virulence target is perceived by the matching R protein, which is 'guarding' the virulence target. An intriguing aspect of the 'Guard hypothesis' is that the Avr gene product causes avirulence of the pathogen through interaction with its virulence target in the plant. This would mean that, although AVR proteins are generally thought to be bifunctional (avirulence as well as virulence factors), this dual function might be based on a single biochemical event. This review focuses on the way AVR proteins are perceived by their matching R gene products. The various components that determine the outcome of the interaction will be discussed, with an emphasis on the dual function of AVR proteins.
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Affiliation(s)
- R Luderer
- Laboratory of Phytopathology, Wageningen University, Marijkeweg 22, 6709 PG Wageningen, the Netherlands
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87
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Shapiro AD, Zhang C. The role of NDR1 in avirulence gene-directed signaling and control of programmed cell death in Arabidopsis. PLANT PHYSIOLOGY 2001; 127:1089-1101. [PMID: 11706189 DOI: 10.1104/pp.010096] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Arabidopsis plants containing the ndr1-1 mutation are incapable of mounting a hypersensitive response to bacteria carrying avrRpt2, but show an exaggerated cell death response to bacteria carrying avrB (Century et al., 1995). We show here that ndr1-1 plants are severely impaired in induction of systemic acquired resistance and PR1-driven transcription of a reporter gene in response to Pseudomonas syringae strains carrying avrRpt2 but not in response to P. syringae carrying avrB. The ndr1-1 mutation also impaired salicylic acid (SA) accumulation in response to treatments that produced reactive oxygen species (ROS) and impaired induction of systemic acquired resistance in response to in situ production of ROS. Hydrogen peroxide accumulated in wild-type Arabidopsis leaves beginning 4 to 7 h postinoculation with P. syringae carrying either avrRpt2 or avrB. In ndr1-1 plants, P. syringae carrying avrRpt2 elicited no detectable hydrogen peroxide production. Hydrogen peroxide production in response to bacteria carrying avrB was similar to that of Columbia in kinetics but of lesser intensity at early time points. These data are interpreted to indicate that NDR1 links ROS generation to SA production and that the phenotypic consequences of the ndr1-1 mutation are caused by a reduced ability to accumulate SA upon pathogen infection.
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Affiliation(s)
- A D Shapiro
- Delaware Agricultural Experiment Station, Department of Plant and Soil Sciences, College of Agriculture and Natural Resources, University of Delaware, Newark, DE 19717-1303, USA.
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88
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Frederick RD, Ahmad M, Majerczak DR, Arroyo-Rodríguez AS, Manulis S, Coplin DL. Genetic organization of the Pantoea stewartii subsp. stewartii hrp gene cluster and sequence analysis of the hrpA, hrpC, hrpN, and wtsE operons. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2001; 14:1213-22. [PMID: 11605961 DOI: 10.1094/mpmi.2001.14.10.1213] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The hrp/wts gene cluster of Pantoea stewartii subsp. stewartii is required for pathogenicity on sweet corn and the ability to elicit a hypersensitive response (HR) in tobacco. Site-directed transposon mutagenesis and nucleotide sequencing were used to identify hrp/wts genes within the left 20 kb of this cluster. Seventeen open reading frames (ORFs) comprise seven genetic complementation groups. These ORFs share homology with hrp and dsp genes from Erwinia amylovora, Erwinia chrysanthemi, and Pseudomonas syringae pathovars and have been designated, in map order, wtsF, wtsE, hrpN, hrpV, hrpT, hrcC, hrpG, hrpF, hrpE, hrpD, hrcJ, hrpB, hrpA, hrpS, hrpY, hrpX, and hrpL. Putative hrp consensus promoter sequences were identified upstream of hrpA, hrpF, hrpN, and wtsE. Expression of the hrpA, hrpC, and wtsE operons was regulated by HrpS. Transposon mutations in all of the hrp operons abolished pathogenicity and HR elicitation, except for the hrpN and hrpV mutants, which were still pathogenic. hrpS, hrpXY, and hrpL regulatory mutations abolished HrpN synthesis, whereas secretory mutations in the hrpC, hrpA, and hrpJ operons permitted intracellular HrpN synthesis. wtsEF mutants were not pathogenic but still produced HrpN and elicited the HR. wtsE encodes a 201-kDa protein that is similar to DspE in E. amylovora and AvrE in P. syringae pv. tomato, suggesting that this protein is a major virulence factor involved in the elicitation of water-soaked lesions.
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Affiliation(s)
- R D Frederick
- Department of Plant Pathology, The Ohio State University, Columbus 43210-1087, USA
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89
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Hutcheson SW, Bretz J, Sussan T, Jin S, Pak K. Enhancer-binding proteins HrpR and HrpS interact to regulate hrp-encoded type III protein secretion in Pseudomonas syringae strains. J Bacteriol 2001; 183:5589-98. [PMID: 11544221 PMCID: PMC95450 DOI: 10.1128/jb.183.19.5589-5598.2001] [Citation(s) in RCA: 119] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In Pseudomonas syringae strains, the hrp-hrc pathogenicity island consists of an HrpL-dependent regulon that encodes a type III protein translocation complex and translocated effector proteins required for pathogenesis. HrpR and HrpS function as positive regulatory factors for the hrpL promoter, but their mechanism of action has not been established. Both HrpR and HrpS are structurally related to enhancer-binding proteins, but they lack receiver domains and do not appear to require a cognate protein kinase for activity. hrpR and hrpS were shown to be expressed as an operon: a promoter was identified 5' to hrpR, and reverse transcriptase PCR detected the presence of an hrpRS transcript. The hrpR promoter and coding sequence were conserved among P. syringae strains. The coding sequences for hrpR and hrpS were cloned into compatible expression vectors, and their activities were monitored in Escherichia coli transformants carrying an hrpL'-lacZ fusion. HrpS could function as a weak activator of the hrpL promoter, but the activity was only 2.5% of the activity detected when both HrpR and HrpS were expressed in the reporter strain. This finding is consistent with a requirement for both HrpR and HrpS in the activation of the hrpL promoter. By using a yeast two-hybrid assay, an interaction between HrpR and HrpS was detected, suggestive of the formation of a heteromeric complex. Physical interaction of HrpR and HrpS was confirmed by column-binding experiments. The results show that HrpR and HrpS physically interact to regulate the sigma(54)-dependent hrpL promoter in P. syringae strains.
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Affiliation(s)
- S W Hutcheson
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, Maryland 20742, USA.
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90
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Staskawicz BJ, Mudgett MB, Dangl JL, Galan JE. Common and contrasting themes of plant and animal diseases. Science 2001; 292:2285-9. [PMID: 11423652 DOI: 10.1126/science.1062013] [Citation(s) in RCA: 272] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Recent studies in bacterial pathogenesis reveal common and contrasting mechanisms of pathogen virulence and host resistance in plant and animal diseases. This review presents recent developments in the study of plant and animal pathogenesis, with respect to bacterial colonization and the delivery of effector proteins to the host. Furthermore, host defense responses in both plants and animals are discussed in relation to mechanisms of pathogen recognition and defense signaling. Future studies will greatly add to our understanding of the molecular events defining host-pathogen interactions.
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Affiliation(s)
- B J Staskawicz
- Department of Plant and Microbial Biology, University of California at Berkeley, Berkeley, CA 94720, USA.
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91
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Banerjee D, Zhang X, Bent AF. The leucine-rich repeat domain can determine effective interaction between RPS2 and other host factors in arabidopsis RPS2-mediated disease resistance. Genetics 2001; 158:439-50. [PMID: 11333251 PMCID: PMC1461633 DOI: 10.1093/genetics/158.1.439] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Like many other plant disease resistance genes, Arabidopsis thaliana RPS2 encodes a product with nucleotide-binding site (NBS) and leucine-rich repeat (LRR) domains. This study explored the hypothesized interaction of RPS2 with other host factors that may be required for perception of Pseudomonas syringae pathogens that express avrRpt2 and/or for the subsequent induction of plant defense responses. Crosses between Arabidopsis ecotypes Col-0 (resistant) and Po-1 (susceptible) revealed segregation of more than one gene that controls resistance to P. syringae that express avrRpt2. Many F(2) and F(3) progeny exhibited intermediate resistance phenotypes. In addition to RPS2, at least one additional genetic interval associated with this defense response was identified and mapped using quantitative genetic methods. Further genetic and molecular genetic complementation experiments with cloned RPS2 alleles revealed that the Po-1 allele of RPS2 can function in a Col-0 genetic background, but not in a Po-1 background. The other resistance-determining genes of Po-1 can function, however, as they successfully conferred resistance in combination with the Col-0 allele of RPS2. Domain-swap experiments revealed that in RPS2, a polymorphism at six amino acids in the LRR region is responsible for this allele-specific ability to function with other host factors.
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Affiliation(s)
- D Banerjee
- Department of Plant Pathology, University of Wisconsin, 1630 Linden Dr., Madison, WI 53706m USA
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92
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Chang JH, Tobias CM, Staskawicz BJ, Michelmore RW. Functional studies of the bacterial avirulence protein AvrPto by mutational analysis. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2001; 14:451-459. [PMID: 11310732 DOI: 10.1094/mpmi.2001.14.4.451] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Pseudomonas syringae pathovars expressing avrPto are avirulent on plants expressing the resistance gene Pto. Over 85 mutants of avrPto were generated with multiple strategies, and several assays were used to characterize AvrPto function. Only a core of 95 amino acids of the 164 residues was sufficient for binding Pto in the yeast two-hybrid system. Only nine of 65 mutant proteins of AvrPto with amino acid substitutions, created in planta and in vitro, did not interact with Pto in the Gal4 yeast two-hybrid system, suggesting that AvrPto can tolerate many nonconservative substitutions and still interact with Pto. These nine and 12 additional substitution mutants of AvrPto were characterized further. The ability to elicit a hypersensitive response and the effect on pathogenesis in planta for these 21 mutants of AvrPto were strongly correlated with recognition by Pto in the yeast two-hybrid system. Analyses of two proteins with substitutions H54P or D52G/L65P indicated that these residues may be required for delivery into the host cell and protein stability in the bacterial cytoplasm, respectively. The mutants that no longer interacted with Pto and had modified activities in planta were predicted to have changes in their secondary structure.
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Affiliation(s)
- J H Chang
- NSF Center for Engineering Plants for Resistance Against Pathogens, University of California-Davis, 95616, USA.
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93
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Innes RW. Targeting the targets of Type III effector proteins secreted by phytopathogenic bacteria. MOLECULAR PLANT PATHOLOGY 2001; 2:109-115. [PMID: 20572998 DOI: 10.1046/j.1364-3703.2001.00057.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Affiliation(s)
- R W Innes
- Department of Biology, Indiana University, Bloomington, IN 47405-3700, USA
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94
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Guttman DS, Greenberg JT. Functional analysis of the type III effectors AvrRpt2 and AvrRpm1 of Pseudomonas syringae with the use of a single-copy genomic integration system. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2001; 14:145-55. [PMID: 11204777 DOI: 10.1094/mpmi.2001.14.2.145] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Gram-negative phytopathogenic bacteria require a type III secretion apparatus for pathogenesis, presumably to deliver Avr effector proteins directly into plant cells. To extend previous studies of Avr effectors that employed plasmids encoding Avr proteins, we developed a system that permits the integration of any gene into the Pseudomonas syringae genome in single copy. With this system, we confirmed earlier findings showing that P. syringae pv. maculicola strain PsmES4326 expressing the AvrRpt2 effector induces a resistance response in plants with the cognate R gene, RPS2. Chromosomally located avrRpt2, however, provoked a stronger resistance response than that observed with plasmid-expressed AvrRpt2 in RPS2+ plants. Additionally, chromosomal expression of AvrRpt2 conferred a fitness advantage on P. syringae grown in rps2- plants, aiding in growth within leaves and escape to leaf surfaces that was difficult to detect with plasmid-borne avrRpt2. Finally, with the use of the genomic integration system, we found that a chimeric protein composed of the N terminus of the heterologous AvrRpml effector and the C-terminal effector region of AvrRpt2 was delivered to plant cells. Because the C terminus of AvrRpt2 cannot translocate into plant cells on its own, this indicates that the N-terminal region can direct secretion and translocation during an infection, which supports the view that Avr proteins have a modular design. This work establishes a readily manipulatable system to study type III effectors in a biologically realistic context.
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Affiliation(s)
- D S Guttman
- Department of Molecular Genetics and Cell Biology, The University of Chicago, 60637, USA.
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95
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Axtell MJ, McNellis TW, Mudgett MB, Hsu CS, Staskawicz BJ. Mutational analysis of the Arabidopsis RPS2 disease resistance gene and the corresponding pseudomonas syringae avrRpt2 avirulence gene. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2001; 14:181-188. [PMID: 11204781 DOI: 10.1094/mpmi.2001.14.2.181] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Plants have evolved a large number of disease resistance genes that encode proteins containing conserved structural motifs that function to recognize pathogen signals and to initiate defense responses. The Arabidopsis RPS2 gene encodes a protein representative of the nucleotide-binding site-leucine-rich repeat (NBS-LRR) class of plant resistance proteins. RPS2 specifically recognizes Pseudomonas syringae pv. tomato strains expressing the avrRpt2 gene and initiates defense responses to bacteria carrying avrRpt2, including a hypersensitive cell death response (HR). We present an in planta mutagenesis experiment that resulted in the isolation of a series of rps2 and avrRpt2 alleles that disrupt the RPS2-avrRpt2 gene-for-gene interaction. Seven novel avrRpt2 alleles incapable of eliciting an RPS2-dependent HR all encode proteins with lesions in the C-terminal portion of AvrRpt2 previously shown to be sufficient for RPS2 recognition. Ten novel rps2 alleles were characterized with mutations in the NBS and the LRR. Several of these alleles code for point mutations in motifs that are conserved among NBS-LRR resistance genes, including the third LRR, which suggests the importance of these motifs for resistance gene function.
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Affiliation(s)
- M J Axtell
- University of California, Department of Plant and Microbial Biology, Berkeley 94720, USA
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96
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Leach JE, Vera Cruz CM, Bai J, Leung H. Pathogen fitness penalty as a predictor of durability of disease resistance genes. ANNUAL REVIEW OF PHYTOPATHOLOGY 2001; 39:187-224. [PMID: 11701864 DOI: 10.1146/annurev.phyto.39.1.187] [Citation(s) in RCA: 181] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Host plant resistance has been used extensively for disease control in many crop species; however, the resistance conferred by many sources is not durable as a result of rapid changes in the pathogen. Although many resistance genes have been identified in plant germplasm, there is no easy way to predict the quality or durability of these resistance genes. In this review, we revisit the hypothesis that resistance genes imposing a high penalty to the pathogen for adaptation will likely be durable. By elucidating the molecular changes involved in pathogen adaptation and the associated fitness cost, a proactive approach may be developed to predict the durability of resistance genes available for deployment.
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Affiliation(s)
- J E Leach
- Department of Plant Pathology, 4024 Throckmorton Plant Sciences Center, Kansas State University, Manhattan, Kansas 66506-5502, USA.
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