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Hajjar H, Berry L, Wu Y, Touqui L, Vergunst AC, Blanc-Potard AB. Contribution of intramacrophage stages to Pseudomonas aeruginosa infection outcome in zebrafish embryos: insights from mgtC and oprF mutants. Sci Rep 2024; 14:6297. [PMID: 38491095 PMCID: PMC10943088 DOI: 10.1038/s41598-024-56725-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2023] [Accepted: 03/10/2024] [Indexed: 03/18/2024] Open
Abstract
Pseudomonas aeruginosa often colonizes immunocompromised patients, causing acute and chronic infections. This bacterium can reside transiently inside cultured macrophages, but the contribution of the intramacrophic stage during infection remains unclear. MgtC and OprF have been identified as important bacterial factors when P. aeruginosa resides inside cultured macrophages. In this study, we showed that P. aeruginosa mgtC and oprF mutants, particular the latter one, had attenuated virulence in both mouse and zebrafish animal models of acute infection. To further investigate P. aeruginosa pathogenesis in zebrafish at a stage different from acute infection, we monitored bacterial load and visualized fluorescent bacteria in live larvae up to 4 days after infection. Whereas the attenuated phenotype of the oprF mutant was associated with a rapid elimination of bacteria, the mgtC mutant was able to persist at low level, a feature also observed with the wild-type strain in surviving larvae. Interestingly, these persistent bacteria can be visualized in macrophages of zebrafish. In a short-time infection model using a macrophage cell line, electron microscopy revealed that internalized P. aeruginosa wild-type bacteria were either released after macrophage lysis or remained intracellularly, where they were localized in vacuoles or in the cytoplasm. The mgtC mutant could also be detected inside macrophages, but without causing cell damage, whereas the oprF mutant was almost completely eliminated after phagocytosis, or localized in phagolysosomes. Taken together, our results show that the main role of OprF for intramacrophage survival impacts both acute and persistent infection by this bacterium. On the other hand, MgtC plays a clear role in acute infection but is not essential for bacterial persistence, in relation with the finding that the mgtC mutant is not completely eliminated by macrophages.
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Affiliation(s)
- Hélène Hajjar
- Laboratory of Pathogens and Host Immunity (LPHI), Université de Montpellier, CNRS-UMR5294, INSERM, Montpellier, France
| | - Laurence Berry
- Laboratory of Pathogens and Host Immunity (LPHI), Université de Montpellier, CNRS-UMR5294, INSERM, Montpellier, France
| | - Yongzheng Wu
- Institut Pasteur, Université Paris Cité, CNRS UMR3691, Cellular Biology and Microbial Infection Unit, Paris, France
| | - Lhousseine Touqui
- Sorbonne Université, Inserm U938, Centre de Recherche Saint-Antoine (CRSA), Paris, France
- Institut Pasteur, Université de Paris Cité, Mucoviscidose et Bronchopathies Chroniques, Paris, France
| | - Annette C Vergunst
- Bacterial Virulence and Chronic Infections (VBIC), Université de Montpellier, INSERM, U1047, Nîmes, France.
| | - Anne-Béatrice Blanc-Potard
- Laboratory of Pathogens and Host Immunity (LPHI), Université de Montpellier, CNRS-UMR5294, INSERM, Montpellier, France.
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2
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Spiewak HL, Shastri S, Zhang L, Schwager S, Eberl L, Vergunst AC, Thomas MS. Burkholderia cenocepacia utilizes a type VI secretion system for bacterial competition. Microbiologyopen 2019; 8:e00774. [PMID: 30628184 PMCID: PMC6612558 DOI: 10.1002/mbo3.774] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2018] [Revised: 11/07/2018] [Accepted: 11/07/2018] [Indexed: 01/24/2023] Open
Abstract
Burkholderia cenocepacia is an opportunistic bacterial pathogen that poses a significant threat to individuals with cystic fibrosis by provoking a strong inflammatory response within the lung. It possesses a type VI secretion system (T6SS), a secretory apparatus that can perforate the cellular membrane of other bacterial species and/or eukaryotic targets, to deliver an arsenal of effector proteins. The B. cenocepacia T6SS (T6SS-1) has been shown to be implicated in virulence in rats and contributes toward actin rearrangements and inflammasome activation in B. cenocepacia-infected macrophages. Here, we present bioinformatics evidence to suggest that T6SS-1 is the archetype T6SS in the Burkholderia genus. We show that B. cenocepacia T6SS-1 is active under normal laboratory growth conditions and displays antibacterial activity against other Gram-negative bacterial species. Moreover, B. cenocepacia T6SS-1 is not required for virulence in three eukaryotic infection models. Bioinformatics analysis identified several candidate T6SS-dependent effectors that may play a role in the antibacterial activity of B. cenocepacia T6SS-1. We conclude that B. cenocepacia T6SS-1 plays an important role in bacterial competition for this organism, and probably in all Burkholderia species that possess this system, thereby broadening the range of species that utilize the T6SS for this purpose.
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Affiliation(s)
- Helena L. Spiewak
- Department of Infection, Immunity and Cardiovascular Disease, The Medical SchoolThe University of SheffieldSheffieldUK,Present address:
Northern Genetics Service, The Newcastle upon Tyne Hospitals NHS Foundation Trust, Institute of Genetic MedicineInternational Centre for LifeNewcastle upon TyneUK
| | - Sravanthi Shastri
- Department of Infection, Immunity and Cardiovascular Disease, The Medical SchoolThe University of SheffieldSheffieldUK
| | - Lili Zhang
- VBMI, INSERM, Université de MontpellierNîmesFrance,Present address:
Section of Molecular Biology, Division of Biological SciencesUniversity of California, San DiegoLa JollaCalifornia
| | - Stephan Schwager
- Department of Plant and Microbial BiologyUniversity of ZurichZurichSwitzerland,Present address:
Analytical ChemistrySynthes GmbHOberdorf BLSwitzerland
| | - Leo Eberl
- Department of Plant and Microbial BiologyUniversity of ZurichZurichSwitzerland
| | | | - Mark S. Thomas
- Department of Infection, Immunity and Cardiovascular Disease, The Medical SchoolThe University of SheffieldSheffieldUK
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3
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Gomes MC, Tasrini Y, Subramoni S, Agnoli K, Feliciano JR, Eberl L, Sokol P, O’Callaghan D, Vergunst AC. The afc antifungal activity cluster, which is under tight regulatory control of ShvR, is essential for transition from intracellular persistence of Burkholderia cenocepacia to acute pro-inflammatory infection. PLoS Pathog 2018; 14:e1007473. [PMID: 30513124 PMCID: PMC6301696 DOI: 10.1371/journal.ppat.1007473] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2018] [Revised: 12/20/2018] [Accepted: 11/19/2018] [Indexed: 01/22/2023] Open
Abstract
The opportunistic pathogen Burkholderia cenocepacia is particularly life-threatening for cystic fibrosis (CF) patients. Chronic lung infections with these bacteria can rapidly develop into fatal pulmonary necrosis and septicaemia. We have recently shown that macrophages are a critical site for replication of B. cenocepacia K56-2 and the induction of fatal pro-inflammatory responses using a zebrafish infection model. Here, we show that ShvR, a LysR-type transcriptional regulator that is important for biofilm formation, rough colony morphotype and inflammation in a rat lung infection model, is also required for the induction of fatal pro-inflammatory responses in zebrafish larvae. ShvR was not essential, however, for bacterial survival and replication in macrophages. Temporal, rhamnose-induced restoration of shvR expression in the shvR mutant during intramacrophage stages unequivocally demonstrated a key role for ShvR in transition from intracellular persistence to acute fatal pro-inflammatory disease. ShvR has been previously shown to tightly control the expression of the adjacent afc gene cluster, which specifies the synthesis of a lipopeptide with antifungal activity. Mutation of afcE, encoding an acyl-CoA dehydrogenase, has been shown to give similar phenotypes as the shvR mutant. We found that, like shvR, afcE is also critical for the switch from intracellular persistence to fatal infection in zebrafish. The closely related B. cenocepacia H111 has been shown to be less virulent than K56-2 in several infection models, including Galleria mellonella and rats. Interestingly, constitutive expression of shvR in H111 increased virulence in zebrafish larvae to almost K56-2 levels in a manner that absolutely required afc. These data confirm a critical role for afc in acute virulence caused by B. cenocepacia that depends on strain-specific regulatory control by ShvR. We propose that ShvR and AFC are important virulence factors of the more virulent Bcc species, either through pro-inflammatory effects of the lipopeptide AFC, or through AFC-dependent membrane properties.
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Affiliation(s)
| | - Yara Tasrini
- VBMI, INSERM, Université de Montpellier, Nîmes, France
| | - Sujatha Subramoni
- Department of Microbiology, Immunology, and Infectious Diseases, University of Calgary, Calgary, Canada
| | - Kirsty Agnoli
- Department of Plant and Microbial Biology, University of Zürich, Zürich, Switzerland
| | | | - Leo Eberl
- Department of Plant and Microbial Biology, University of Zürich, Zürich, Switzerland
| | - Pamela Sokol
- Department of Microbiology, Immunology, and Infectious Diseases, University of Calgary, Calgary, Canada
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4
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Mesureur J, Feliciano JR, Wagner N, Gomes MC, Zhang L, Blanco-Gonzalez M, van der Vaart M, O'Callaghan D, Meijer AH, Vergunst AC. Correction: Macrophages, but not neutrophils, are critical for proliferation of Burkholderia cenocepacia and ensuing host-damaging inflammation. PLoS Pathog 2017; 13:e1006795. [PMID: 29261811 PMCID: PMC5738098 DOI: 10.1371/journal.ppat.1006795] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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5
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Abstract
Opportunistic pathogens are a worldwide cause of mortality and morbidity, and infections with intrinsically antibiotic-resistant pathogens have a large clinical, social and economic impact. Bacteria belonging to the Burkholderia cepacia complex (Bcc), ubiquitous in natural and industrial environments, are notorious pathogens for individuals with cystic fibrosis (CF). In addition, Burkholderia cenocepacia is emerging as the culprit of non-CF related, sometimes fatal infections. Knowledge of the underlying infection mechanism of these pathogens is important for efficient treatment, however, to date not much is known about the lifestyle of Bcc bacteria during infection. In our recent study published in PLoS Pathogens, we provide experimental evidence that macrophages are critically important for proliferation of B. cenocepacia, and are major drivers of fatal pro-inflammatory infections in zebrafish larvae. This is in agreement with recent clinical information showing that B. cenocepacia is mainly localised in phagocytes in infected CF lungs. A predominant intramacrophage stage and a host-detrimental role for macrophages have major implications for treatment strategies of both CF and non-CF infections. Intracellular survival of bacteria traditionally classified as extracellular, including Staphylococcus aureus and Pseudomonas aeruginosa, is an emerging theme. Our finding that macrophages are essential for proliferation of B. cenocepacia in the host suggests a new paradigm for Bcc infections and urges the development of novel anti-infectious therapies to efficiently disarm these intrinsically antibiotic resistant facultative intracellular pathogens.
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Affiliation(s)
| | | | - Lili Zhang
- VBMI, INSERM, Univ. Montpellier, Nîmes, France.,Current address: Section of Molecular Biology, Division of Biological Sciences, University of California, San Diego, La Jolla, USA
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6
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Fernández-González E, Bakioui S, Gomes MC, O'Callaghan D, Vergunst AC, Sangari FJ, Llosa M. A Functional oriT in the Ptw Plasmid of Burkholderia cenocepacia Can Be Recognized by the R388 Relaxase TrwC. Front Mol Biosci 2016; 3:16. [PMID: 27200362 PMCID: PMC4853378 DOI: 10.3389/fmolb.2016.00016] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2016] [Accepted: 04/14/2016] [Indexed: 12/14/2022] Open
Abstract
Burkholderia cenocepacia is both a plant pathogen and the cause of serious opportunistic infections, particularly in cystic fibrosis patients. B. cenocepacia K56-2 harbors a native plasmid named Ptw for its involvement in the Plant Tissue Watersoaking phenotype. Ptw has also been reported to be important for survival in human cells. Interestingly, the presence of PtwC, a homolog of the conjugative relaxase TrwC of plasmid R388, suggests a possible function for Ptw in conjugative DNA transfer. The ptw region includes Type IV Secretion System genes related to those of the F plasmid. However, genes in the adjacent region shared stronger homology with the R388 genes involved in conjugative DNA metabolism. This region included the putative relaxase ptwC, a putative coupling protein and accessory nicking protein, and a DNA segment with high number of inverted repeats and elevated AT content, suggesting a possible oriT. Although we were unable to detect conjugative transfer of the Ptw resident plasmid, we detected conjugal mobilization of a co-resident plasmid containing the ptw region homologous to R388, demonstrating the cloned ptw region contains an oriT. A similar plasmid lacking ptwC could not be mobilized, suggesting that the putative relaxase PtwC must act in cis on its oriT. Remarkably, we also detected mobilization of a plasmid containing the Ptw oriT by the R388 relaxase TrwC, yet we could not detect PtwC-mediated mobilization of an R388 oriT-containing plasmid. Our data unambiguously show that the Ptw plasmid harbors DNA transfer functions, and suggests the Ptw plasmid may play a dual role in horizontal DNA transfer and eukaryotic infection.
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Affiliation(s)
- Esther Fernández-González
- Departamento de Biología Molecular, Instituto de Biomedicina y Biotecnología de Cantabria, Universidad de Cantabria, UC-SODERCAN-Consejo Superior de Investigaciones Científicas Santander, Spain
| | - Sawsane Bakioui
- Institut National de la Santé et de la Recherche Médicale, U1047Nimes, France; UFR de Médecine Site de Nimes, U1047, Université de MontpellierFrance
| | - Margarida C Gomes
- Institut National de la Santé et de la Recherche Médicale, U1047Nimes, France; UFR de Médecine Site de Nimes, U1047, Université de MontpellierFrance
| | - David O'Callaghan
- Institut National de la Santé et de la Recherche Médicale, U1047Nimes, France; UFR de Médecine Site de Nimes, U1047, Université de MontpellierFrance
| | - Annette C Vergunst
- Institut National de la Santé et de la Recherche Médicale, U1047Nimes, France; UFR de Médecine Site de Nimes, U1047, Université de MontpellierFrance
| | - Félix J Sangari
- Departamento de Biología Molecular, Instituto de Biomedicina y Biotecnología de Cantabria, Universidad de Cantabria, UC-SODERCAN-Consejo Superior de Investigaciones Científicas Santander, Spain
| | - Matxalen Llosa
- Departamento de Biología Molecular, Instituto de Biomedicina y Biotecnología de Cantabria, Universidad de Cantabria, UC-SODERCAN-Consejo Superior de Investigaciones Científicas Santander, Spain
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7
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Keriel A, Botella E, Estrach S, Bragagnolo G, Vergunst AC, Feral CC, O'Callaghan D. Brucella Intracellular Life Relies on the Transmembrane Protein CD98 Heavy Chain. J Infect Dis 2014; 211:1769-78. [PMID: 25505297 DOI: 10.1093/infdis/jiu673] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Accepted: 12/01/2014] [Indexed: 01/01/2023] Open
Abstract
Brucella are intracellular bacterial pathogens that use a type IV secretion system (T4SS) to escape host defenses and create a niche in which they can multiply. Although the importance of Brucella T4SS is clear, little is known about its interactions with host cell structures. In this study, we identified the eukaryotic protein CD98hc as a partner for Brucella T4SS subunit VirB2. This transmembrane glycoprotein is involved in amino acid transport, modulation of integrin signaling, and cell-to-cell fusion. Knockdown of CD98hc expression in HeLa cells demonstrated that it is essential for Brucella infection. Using knockout dermal fibroblasts, we confirmed its role for Brucella but found that it is not required for Salmonella infection. CD98hc transiently accumulates around the bacteria during the early phases of infection and is required for both optimal bacterial uptake and intracellular multiplication of Brucella. These results provide new insights into the complex interplay between Brucella and its host.
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Affiliation(s)
- Anne Keriel
- INSERM, U1047 Université Montpellier 1, UFR de Médecine, Nîmes
| | - Eric Botella
- INSERM, U1047 Université Montpellier 1, UFR de Médecine, Nîmes
| | - Soline Estrach
- INSERM, U1081, CNRS, UMR7284, Institute for Research on Cancer and Aging, University of Nice Sophia Antipolis, France
| | | | | | - Chloe C Feral
- INSERM, U1081, CNRS, UMR7284, Institute for Research on Cancer and Aging, University of Nice Sophia Antipolis, France
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8
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Abstract
In recent years the zebrafish has gained enormous attention in infection biology, and many protocols have been developed to study interaction of both human and fish pathogens, including viruses, fungi, and bacteria, with the host. Especially the extraordinary possibilities for live imaging of disease processes in the transparent embryos using fluorescent bacteria and cell-specific reporter fish combined with gene knockdown, transcriptome, and genetic studies have dramatically advanced our understanding of disease mechanisms. The zebrafish embryo is amenable to study virulence of both extracellular and facultative intracellular pathogens introduced through the technique of microinjection. Several protocols have been published that address the different sites of injection, antisense strategies, imaging, and production of transgenic fish in detail. Here we describe a protocol to study the virulence profiles, ranging from acute fatal to persistent, of bacteria belonging to the Burkholderia cepacia complex. This standard operating protocol combines simple survival assays, analysis of bacterial kinetics, analysis of the early innate immune response with qRT-PCR, and the use of transgenic reporter fish to study interactions with host phagocytes, and is also applicable to other pathogens.
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9
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den Dulk-Ras A, Vergunst AC, Hooykaas PJJ. Cre Reporter Assay for Translocation (CRAfT): a tool for the study of protein translocation into host cells. Methods Mol Biol 2014; 1197:103-121. [PMID: 25172277 DOI: 10.1007/978-1-4939-1261-2_6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Many pathogenic bacteria introduce virulence proteins, also called effector proteins, into host cells to accomplish infection. Such effector proteins are often translocated into host cells by bacterial type III (T3SS) or type IV secretion systems (T4SS). To better understand the molecular mechanisms underlying virulence, it is essential to identify the effector proteins and determine their functions. Several reporter assays have been established to identify translocated effector proteins and verify T3SS- or T4SS-dependent transport into host cells. Here we describe a protocol to monitor the translocation of candidate effector proteins using Cre recombinase as a reporter, and more specifically how this Cre Reporter Assay for Translocation (CRAfT) can be used to detect translocation of Vir proteins from Agrobacterium tumefaciens into yeast and plant cells. The assay can be adapted for the study of the T3SS or T4SS of human pathogens.
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Affiliation(s)
- Amke den Dulk-Ras
- Sylvius Laboratory, Institute of Biology Leiden, Leiden University, Sylviusweg 72, Leiden, The Netherlands
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10
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Kaplan-Türköz B, Koelblen T, Felix C, Candusso MP, O'Callaghan D, Vergunst AC, Terradot L. Structure of the Toll/interleukin 1 receptor (TIR) domain of the immunosuppressive Brucella effector BtpA/Btp1/TcpB. FEBS Lett 2013; 587:3412-6. [PMID: 24076024 DOI: 10.1016/j.febslet.2013.09.007] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2013] [Revised: 08/30/2013] [Accepted: 09/03/2013] [Indexed: 11/15/2022]
Abstract
BtpA/Btp1/TcpB is a virulence factor produced by Brucella species that possesses a Toll interleukin-1 receptor (TIR) domain. Once delivered into the host cell, BtpA interacts with MyD88 to interfere with TLR signalling and modulates microtubule dynamics. Here the crystal structure of the BtpA TIR domain at 3.15 Å is presented. The structure shows a dimeric arrangement of a canonical TIR domain, similar to the Paracoccus denitrificans Tir protein but secured by a unique long N-terminal α-tail that packs against the TIR:TIR dimer. Structure-based mutations and multi-angle light scattering experiments characterized the BtpA dimer conformation in solution. The structure of BtpA will help with studies to understand the mechanisms involved in its interactions with MyD88 and with microtubules.
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Affiliation(s)
- Burcu Kaplan-Türköz
- UMR 5086, BMSSI, CNRS - Université Lyon 1, Institut de Biologie et Chimie des Protéines, 7 passage du Vercors, F-69367, France
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11
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Lavigne JP, Vergunst AC, Goret L, Sotto A, Combescure C, Blanco J, O'Callaghan D, Nicolas-Chanoine MH. Virulence potential and genomic mapping of the worldwide clone Escherichia coli ST131. PLoS One 2012; 7:e34294. [PMID: 22457832 PMCID: PMC3311635 DOI: 10.1371/journal.pone.0034294] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2011] [Accepted: 02/27/2012] [Indexed: 11/19/2022] Open
Abstract
Recently, the worldwide propagation of clonal CTX-M-15-producing Escherichia coli isolates, namely ST131 and O25b:H4, has been reported. Like the majority of extra-intestinal pathogenic E. coli isolates, the pandemic clone ST131 belongs to phylogenetic group B2, and has recently been shown to be highly virulent in a mouse model, even though it lacks several genes encoding key virulence factors (Pap, Cnf1 and HlyA). Using two animal models, Caenorhabditis elegans and zebrafish embryos, we assessed the virulence of three E. coli ST131 strains (2 CTX-M-15- producing urine and 1 non-ESBL-producing faecal isolate), comparing them with five non-ST131 B2 and a group A uropathogenic E. coli (UPEC). In C. elegans, the three ST131 strains showed intermediate virulence between the non virulent group A isolate and the virulent non-ST131 B2 strains. In zebrafish, the CTX-M-15-producing ST131 UPEC isolates were also less virulent than the non-ST131 B2 strains, suggesting that the production of CTX-M-15 is not correlated with enhanced virulence. Amongst the non-ST131 B2 group isolates, variation in pathogenic potential in zebrafish embryos was observed ranging from intermediate to highly virulent. Interestingly, the ST131 strains were equally persistent in surviving embryos as the non-ST131-group B2 strains, suggesting similar mechanisms may account for development of persistent infection. Optical maps of the genome of the ST131 strains were compared with those of 24 reference E. coli strains. Although small differences were seen within the ST131 strains, the tree built on the optical maps showed that these strains belonged to a specific cluster (86% similarity) with only 45% similarity with the other group B2 strains and 25% with strains of group A and D. Thus, the ST131 clone has a genetic composition that differs from other group B2 strains, and appears to be less virulent than previously suspected.
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Affiliation(s)
- Jean-Philippe Lavigne
- Institut National de la Santé et de la Recherche Médicale, U1047, UFR Médecine, Université Montpellier 1, Nîmes, France.
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12
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Vergunst AC, Meijer AH, Renshaw SA, O'Callaghan D. Burkholderia cenocepacia creates an intramacrophage replication niche in zebrafish embryos, followed by bacterial dissemination and establishment of systemic infection. Infect Immun 2010; 78:1495-508. [PMID: 20086083 PMCID: PMC2849400 DOI: 10.1128/iai.00743-09] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2009] [Revised: 08/05/2009] [Accepted: 01/09/2010] [Indexed: 11/20/2022] Open
Abstract
Bacteria belonging to the "Burkholderia cepacia complex" (Bcc) often cause fatal pulmonary infections in cystic fibrosis patients, yet little is know about the underlying molecular mechanisms. These Gram-negative bacteria can adopt an intracellular lifestyle, although their ability to replicate intracellularly has been difficult to demonstrate. Here we show that Bcc bacteria survive and multiply in macrophages of zebrafish embryos. Local dissemination by nonlytic release from infected cells was followed by bacteremia and extracellular replication. Burkholderia cenocepacia isolates belonging to the epidemic electrophoretic type 12 (ET12) lineage were highly virulent for the embryos; intravenous injection of <10 bacteria of strain K56-2 killed embryos within 3 days. However, small but significant differences between the clonal ET12 isolates K56-2, J2315, and BC7 were evident. In addition, the innate immune response in young embryos was sufficiently developed to control infection with other less virulent Bcc strains, such as Burkholderia vietnamiensis FC441 and Burkholderia stabilis LMG14294. A K56-2 cepR quorum-sensing regulator mutant was highly attenuated, and its ability to replicate and spread to neighboring cells was greatly reduced. Our data indicate that the zebrafish embryo is an excellent vertebrate model to dissect the molecular basis of intracellular replication and the early innate immune responses in this intricate host-pathogen interaction.
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Affiliation(s)
- Annette C Vergunst
- INSERM, ESPRI 26, UFR Médecine, CS83021, Avenue Kennedy, 30908 Nimes, France.
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13
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Louwerse JD, van Lier MCM, van der Steen DM, de Vlaam CMT, Hooykaas PJJ, Vergunst AC. Stable recombinase-mediated cassette exchange in Arabidopsis using Agrobacterium tumefaciens. Plant Physiol 2007; 145:1282-93. [PMID: 17921337 PMCID: PMC2151714 DOI: 10.1104/pp.107.108092] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2007] [Accepted: 09/27/2007] [Indexed: 05/02/2023]
Abstract
Site-specific integration is an attractive method for the improvement of current transformation technologies aimed at the production of stable transgenic plants. Here, we present a Cre-based targeting strategy in Arabidopsis (Arabidopsis thaliana) using recombinase-mediated cassette exchange (RMCE) of transferred DNA (T-DNA) delivered by Agrobacterium tumefaciens. The rationale for effective RMCE is the precise exchange of a genomic and a replacement cassette both flanked by two heterospecific lox sites that are incompatible with each other to prevent unwanted cassette deletion. We designed a strategy in which the coding region of a loxP/lox5171-flanked bialaphos resistance (bar) gene is exchanged for a loxP/lox5171-flanked T-DNA replacement cassette containing the neomycin phosphotransferase (nptII) coding region via loxP/loxP and lox5171/lox5171 directed recombination. The bar gene is driven by the strong 35S promoter, which is located outside the target cassette. This placement ensures preferential selection of RMCE events and not random integration events by expression of nptII from this same promoter. Using root transformation, during which Cre was provided on a cotransformed T-DNA, 50 kanamycin-resistant calli were selected. Forty-four percent contained a correctly exchanged cassette based on PCR analysis, indicating the stringency of the selection system. This was confirmed for the offspring of five analyzed events by Southern-blot analysis. In four of the five analyzed RMCE events, there were no additional T-DNA insertions or they easily segregated, resulting in high-efficiency single-copy RMCE events. Our approach enables simple and efficient selection of targeting events using the advantages of Agrobacterium-mediated transformation.
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Affiliation(s)
- Jeanine D Louwerse
- Institute of Biology, Clusius Laboratory, Leiden University, 2333 AL Leiden, The Netherlands
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Hodges LD, Vergunst AC, Neal-McKinney J, den Dulk-Ras A, Moyer DM, Hooykaas PJJ, Ream W. Agrobacterium rhizogenes GALLS protein contains domains for ATP binding, nuclear localization, and type IV secretion. J Bacteriol 2006; 188:8222-30. [PMID: 17012398 PMCID: PMC1698208 DOI: 10.1128/jb.00747-06] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Agrobacterium tumefaciens and Agrobacterium rhizogenes are closely related plant pathogens that cause different diseases, crown gall and hairy root. Both diseases result from transfer, integration, and expression of plasmid-encoded bacterial genes located on the transferred DNA (T-DNA) in the plant genome. Bacterial virulence (Vir) proteins necessary for infection are also translocated into plant cells. Transfer of single-stranded DNA (ssDNA) and Vir proteins requires a type IV secretion system, a protein complex spanning the bacterial envelope. A. tumefaciens translocates the ssDNA-binding protein VirE2 into plant cells, where it binds single-stranded T-DNA and helps target it to the nucleus. Although some strains of A. rhizogenes lack VirE2, they are pathogenic and transfer T-DNA efficiently. Instead, these bacteria express the GALLS protein, which is essential for their virulence. The GALLS protein can complement an A. tumefaciens virE2 mutant for tumor formation, indicating that GALLS can substitute for VirE2. Unlike VirE2, GALLS contains ATP-binding and helicase motifs similar to those in TraA, a strand transferase involved in conjugation. Both GALLS and VirE2 contain nuclear localization sequences and a C-terminal type IV secretion signal. Here we show that mutations in any of these domains abolished the ability of GALLS to substitute for VirE2.
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Affiliation(s)
- Larry D Hodges
- Department of Microbiology, Oregon State University, Corvallis, OR 97331, USA
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15
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Abstract
An 18,228-bp region containing open reading frames predicted to be derived from the IncP plasmid or phage ancestors is present in the genomes of Brucella suis biovars 1 to 4, B. canis, B. neotomae, and strains isolated from marine mammals, but not in B. melitensis, B. abortus, B. ovis, and B. suis biovar 5. The presence of circular excision intermediates and the results of an analysis of sequenced bacterial genomes suggest that the region downstream of the guaA gene is a hotspot for site-specific integration of foreign DNA mediated by a CP4-like integrase.
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Affiliation(s)
- Jean-Philippe Lavigne
- Institut National de la Santé et de la Recherche Médicale, Unité 431, UFR de Médecine, CS 83021, Avenue J. F. Kennedy, 30908 Nimes Cedex 02, France
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16
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Vergunst AC, van Lier MCM, den Dulk-Ras A, Stüve TAG, Ouwehand A, Hooykaas PJJ. Positive charge is an important feature of the C-terminal transport signal of the VirB/D4-translocated proteins of Agrobacterium. Proc Natl Acad Sci U S A 2005; 102:832-7. [PMID: 15644442 PMCID: PMC545537 DOI: 10.1073/pnas.0406241102] [Citation(s) in RCA: 210] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Several human pathogens and the plant pathogen Agrobacterium tumefaciens use a type IV secretion system for translocation of effector proteins into host cells. How effector proteins are selected for transport is unknown, but a C-terminal transport signal is present in the proteins translocated by the A. tumefaciens VirB/D4 type IV secretion system. We characterized this signal in the virulence protein VirF by alanine scanning and further site-directed mutagenesis. The Cre recombinase was used as a reporter to measure the translocation efficiency of Cre-Vir fusions from A. tumefaciens to Arabidopsis. The data unambiguously showed that positive charge is an essential characteristic of the C-terminal transport signal. We increased the sensitivity of this translocation assay by modifying the Cre-induced readout in host cells from kanamycin resistance to GFP expression. This improvement allowed us to detect translocation of the VirD2 relaxase protein in the absence of transferred DNA, showing that attachment to the transferred DNA is not essential for transport by the VirB/D4 system. We also found another translocated effector protein, namely the VirD5 protein encoded by the tumor-inducing plasmid. According to secondary structure predictions, the C termini of all VirB/D4-translocated proteins identified so far are unstructured; however, they contain a characteristic hydropathic profile. Based on sequence alignments and mutational analysis of VirF, we conclude that the C-terminal transport signal for recruitment and translocation of effector proteins by the A. tumefaciens VirB/D4 system is hydrophilic and has a net positive charge with a consensus motif of R-X(7)-R-X-R-X-R-X-X(n)>.
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Affiliation(s)
- Annette C Vergunst
- Clusius Laboratory, Institute of Biology, Leiden University, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands
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Schulein R, Guye P, Rhomberg TA, Schmid MC, Schröder G, Vergunst AC, Carena I, Dehio C. A bipartite signal mediates the transfer of type IV secretion substrates of Bartonella henselae into human cells. Proc Natl Acad Sci U S A 2005; 102:856-61. [PMID: 15642951 PMCID: PMC545523 DOI: 10.1073/pnas.0406796102] [Citation(s) in RCA: 180] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Bacterial type IV secretion (T4S) systems mediate the transfer of macromolecular substrates into various target cells, e.g., the conjugative transfer of DNA into bacteria or the transfer of virulence proteins into eukaryotic host cells. The T4S apparatus VirB of the vascular tumor-inducing pathogen Bartonella henselae causes subversion of human endothelial cell (HEC) function. Here we report the identification of multiple protein substrates of VirB, which, upon translocation into HEC, mediate all known VirB-dependent cellular changes. These Bartonella-translocated effector proteins (Beps) A-G are encoded together with the VirB system and the T4S coupling protein VirD4 on a Bartonella-specific pathogenicity island. The Beps display a modular architecture, suggesting an evolution by extensive domain duplication and reshuffling. The C terminus of each Bep harbors at least one copy of the Bep-intracellular delivery domain and a short positively charged tail sequence. This biparte C terminus constitutes a transfer signal that is sufficient to mediate VirB/VirD4-dependent intracellular delivery of reporter protein fusions. The Bep-intracellular delivery domain is also present in conjugative relaxases of bacterial conjugation systems. We exemplarily show that the C terminus of such a conjugative relaxase mediates protein transfer through the Bartonella henselae VirB/VirD4 system into HEC. Conjugative relaxases may thus represent the evolutionary origin of the here defined T4S signal for protein transfer into human cells.
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Affiliation(s)
- Ralf Schulein
- Division of Molecular Microbiology, Biozentrum, University of Basel, Klingelbergstrasse 70, 4056 Basel, Switzerland
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Hubber A, Vergunst AC, Sullivan JT, Hooykaas PJJ, Ronson CW. Symbiotic phenotypes and translocated effector proteins of the Mesorhizobium loti strain R7A VirB/D4 type IV secretion system. Mol Microbiol 2004; 54:561-74. [PMID: 15469524 DOI: 10.1111/j.1365-2958.2004.04292.x] [Citation(s) in RCA: 122] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The symbiosis island of Mesorhizobium loti strain R7A contains genes with strong similarity to the structural vir genes (virB1-11; virD4) of Agrobacterium tumefaciens that encode the type IV secretion system (T4SS) required for T-DNA transfer to plants. In contrast, M. loti strain MAFF303099 lacks these genes but contains genes not present in strain R7A that encode a type III secretion system (T3SS). Here we show by hybridization analysis that most M. loti strains contain the VirB/D4 T4SS and not the T3SS. Strikingly, strain R7A vir gene mutants formed large nodules containing bacteroids on Leucaena leucocephala in contrast to the wild-type strain that formed only uninfected tumour-like structures. A rhcJ T3SS mutant of strain MAFF303099 also nodulated L. leucocephala, unlike the wild type. On Lotus corniculatus, the vir mutants were delayed in nodulation and were less competitive compared with the wild type. Two strain R7A genes, msi059 and msi061, were identified through their mutant phenotypes as possibly encoding translocated effector proteins. Both Msi059 and Msi061 were translocated through the A. tumefaciens VirB/D4 system into Saccharomyces cerevisiae and Arabidopsis thaliana, as shown using the Cre recombinase Reporter Assay for Translocation (CRAfT). Taken together, these results suggest that the VirB/D4 T4SS of M. loti R7A plays an analogous symbiotic role to that of T3SS found in other rhizobia. The heterologous translocation of rhizobial proteins by the Agrobacterium VirB/D4 T4SS is the first demonstration that rhizobial effector proteins are translocated into plant cells and confirms functional conservation between the M. loti and A. tumefaciens T4SS.
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Affiliation(s)
- Andree Hubber
- Department of Microbiology and Immunology, University of Otago, PO Box 56, Dunedin, New Zealand
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Vergunst AC, van Lier MCM, den Dulk-Ras A, Hooykaas PJJ. Recognition of the Agrobacterium tumefaciens VirE2 translocation signal by the VirB/D4 transport system does not require VirE1. Plant Physiol 2003; 133:978-88. [PMID: 14551327 PMCID: PMC281595 DOI: 10.1104/pp.103.029223] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/26/2003] [Revised: 07/18/2003] [Accepted: 08/14/2003] [Indexed: 05/22/2023]
Abstract
Agrobacterium tumefaciens uses a type IV secretion system to deliver a nucleoprotein complex and effector proteins directly into plant cells. The single-stranded DNA-binding protein VirE2, the F-box protein VirF and VirE3 are delivered into host cells via this VirB/D4 encoded translocation system. VirE1 functions as a chaperone of VirE2 by regulating its efficient translation and preventing VirE2-VirE2 aggregation in the bacterial cell. We analyzed whether the VirE1 chaperone is also essential for transport recognition of VirE2 by the VirB/D4 encoded type IV secretion system. In addition, we assayed whether translocation of VirF and VirE3, which also forms part of the virE operon, is affected by the absence of VirE1. We employed the earlier developed CRAFT (Cre recombinase Reporter Assay For Translocation) assay to detect transfer of Cre::Vir fusion proteins from A. tumefaciens into plants, monitored by stable reconstitution of a kanamycin resistance marker, and into yeast, screened by loss of the URA3 gene. We show that the C-terminal 50 amino acids of VirE2 and VirE3 are sufficient to mediate Cre translocation into host cells, confirming earlier indications of a C-terminal transport signal. This transfer was independent of the presence or absence of VirE1. Besides, the translocation efficiency of VirF is not altered in a virE1 mutant. The results unambiguously show that the VirE1 chaperone is not essential for the recognition of the VirE2 transport signal by the transport system and the subsequent translocation across the bacterial envelope into host cells.
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Affiliation(s)
- Annette C Vergunst
- Institute of Biology, Leiden University, Clusius Laboratory, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands.
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20
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Schrammeijer B, den Dulk-Ras A, Vergunst AC, Jurado Jácome E, Hooykaas PJJ. Analysis of Vir protein translocation from Agrobacterium tumefaciens using Saccharomyces cerevisiae as a model: evidence for transport of a novel effector protein VirE3. Nucleic Acids Res 2003; 31:860-8. [PMID: 12560481 PMCID: PMC149200 DOI: 10.1093/nar/gkg179] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Agrobacterium tumefaciens causes crown gall disease on a variety of plants. During the infection process Agrobacterium transfers a nucleoprotein complex, the VirD2 T-complex, and at least two Vir proteins, VirE2 and VirF, into the plant cell via the VirB/VirD4 type IV secretion system. Recently, we found that T-DNA could also be transferred from Agrobacterium to Saccharomyces cerevisiae. Here, we describe a novel method to also detect trans-kingdom Vir protein transfer from Agrobacterium to yeast, using the Cre/lox system. Protein fusions between Cre and VirE2 or VirF were expressed in AGROBACTERIUM: Transfer of the Cre-Vir fusion proteins from Agrobacterium to yeast was monitored by a selectable excision event resulting from site-specific recombination mediated by Cre on a lox-flanked transgene in yeast. The VirE2 and VirF proteins were transported to yeast via the virB-encoded transfer system in the presence of coupling factor VirD4, analogous to translocation into plant cells. The yeast system therefore provides a suitable and fast model system to study basic aspects of trans-kingdom protein transport from Agrobacterium into host cells. Using this method we showed that VirE2 and VirF protein transfer was inhibited by the presence of the Osa protein. Besides, we found evidence for a novel third effector protein, VirE3, which has a similar C-terminal signature to VirE2 and VirF.
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Affiliation(s)
- Barbara Schrammeijer
- Institute of Molecular Plant Sciences, Clusius Laboratory, Leiden University, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands
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21
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Vergunst AC, Schrammeijer B, den Dulk-Ras A, de Vlaam CM, Regensburg-Tuïnk TJ, Hooykaas PJ. VirB/D4-dependent protein translocation from Agrobacterium into plant cells. Science 2000; 290:979-82. [PMID: 11062129 DOI: 10.1126/science.290.5493.979] [Citation(s) in RCA: 287] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The Agrobacterium VirB/D4 transport system mediates the transfer of a nucleoprotein T complex into plant cells, leading to crown gall disease. In addition, several Virulence proteins must somehow be transported to fulfill a function in planta. Here, we used fusions between Cre recombinase and VirE2 or VirF to directly demonstrate protein translocation into plant cells. Transport of the proteins was monitored by a Cre-mediated in planta recombination event resulting in a selectable phenotype and depended on the VirB/D4 transport system but did not require transferred DNA.
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Affiliation(s)
- A C Vergunst
- Institute of Molecular Plant Sciences, Leiden University, Clusius Laboratory, Wassenaarseweg 64, 2333 AL, Leiden, Netherlands
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22
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Vergunst AC, Jansen LE, Fransz PF, de Jong JH, Hooykaas PJ. Cre/lox-mediated recombination in Arabidopsis: evidence for transmission of a translocation and a deletion event. Chromosoma 2000; 109:287-97. [PMID: 10968257 DOI: 10.1007/s004120000079] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Cre recombinase was used to mediate recombination between a chromosomally introduced loxP sequence in Arabidopsis thaliana (35S-lox-cre) and transferred DNA (T-DNA) originating from Agrobacterium tumefaciens (plox-npt), carrying a single loxP sequence. Constructs were designed for specific Cre-mediated recombination between the two lox sites, resulting in restoration of neomycin phosphotransferase (nptII) expression at the target locus. Kanamycin resistant (Km(r)) recombinants were obtained with an efficiency of about 1% compared with random integration. Molecular analyses confirmed that these were indeed due to recombination between the lox sites of the target and introduced T-DNA. However, polymerase chain reaction analysis revealed that these reflected site-specific integration events only in a minority (4%). The other events were classified as translocations/inversions (71%) or deletions (25%), and were probably caused by site-specific recombination between a randomly integrated T-DNA and the original target locus. We studied some of these events in detail, including a Cre-mediated balanced translocation event, which was characterized by a combination of molecular, genetic and cytogenetic experiments (fluorescence in situ hybridization to spread pollen mother cells at meiotic prophase I). Our data clearly demonstrate that Agrobacterium-mediated transfer of a targeting T-DNA with a single lox site allows the isolation of multiple chromosomal rearrangements, including translocation and deletion events. Given that the complete sequence of the Arabidopsis genome will have been determined shortly this method has significant potential for applications in functional genomics.
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Affiliation(s)
- A C Vergunst
- Institute of Molecular Plant Sciences, Leiden University, The Netherlands.
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Vergunst AC, Hooykaas PJ. Cre/lox-mediated site-specific integration of Agrobacterium T-DNA in Arabidopsis thaliana by transient expression of cre. Plant Mol Biol 1998; 38:393-406. [PMID: 9747847 DOI: 10.1023/a:1006024500008] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The Cre/lox system was used to obtain targeted integration of an Agrobacterium T-DNA at a lox site in the genome of Arabidopsis thaliana. Site-specific recombinants, and not random events, were preferentially selected by activation of a silent lox-neomycin phosphotransferase (nptII) target gene. To analyse the effectiveness of Agrobacterium-mediated transfer we used T-DNA vectors harbouring a single lox sequence (this vector had to circularize at the T-DNA left- and right-border sequences prior to site-specific integration) or two lox sequences (this vector allowed circularization at the lox sequences within the T-DNA either prior to or after random integration, followed by targeting of the circularized vector), respectively. Furthermore, to control the reversibility of the integration reaction, Cre recombinase was provided transiently by using a cotransformation approach. One precise stable integrant was found amongst the recombinant calli obtained after transformation with a double-lox T-DNA vector. The results indicate that Agrobacterium-mediated transformation can be used as a tool to obtain site-specific integration.
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Affiliation(s)
- A C Vergunst
- Institute of Molecular Plant Sciences, Leiden, The Netherlands
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24
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Affiliation(s)
- A C Vergunst
- Clusius Laboratory, Institute of Molecular Plant Sciences, Faculty of Mathematics and Natural Sciences, Leiden, The Netherlands
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Vergunst AC, Jansen LE, Hooykaas PJ. Site-specific integration of Agrobacterium T-DNA in Arabidopsis thaliana mediated by Cre recombinase. Nucleic Acids Res 1998; 26:2729-34. [PMID: 9592161 PMCID: PMC147585 DOI: 10.1093/nar/26.11.2729] [Citation(s) in RCA: 91] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In this study Agrobacterium tumefaciens transferred DNA (T-DNA) was targeted to a chromosomally introduced lox site in Arabidopsis thaliana by employing the Cre recombinase system. To this end, Arabidopsis target lines were constructed which harboured an active chimeric promoter-lox-cre gene stably integrated in the plant genome. A T-DNA vector with a promoterless lox -neomycin phosphotransferase (nptII) fusion was targeted to this genomic lox site with an efficiency of 1.2-2.3% of the number of random events. Cre-catalyzed site-specific recombination resulted in restoration of nptII expression by translational fusion of the lox-nptII sequence in the integration vector with the transcription and translation initiation sequences present at the target site, allowing selective enrichment on medium containing kanamycin. Simultaneously, the coding sequence of the Cre recombinase was disconnected from these same transcription and translation initiation signals by displacement, aimed at preventing the efficient reversible excision reaction. Of the site-specific recombinants, 89% were the result of precise integration. Furthermore, approximately 50% of these integrants were single copy transformants, based on PCR analysis. Agrobacterium T-DNA, which is transferred to plant cells as a single-stranded linear DNA structure, is in principle incompatible with Cre-mediated integration. Nevertheless, the results presented here clearly demonstrate the feasibility of the Agrobacterium -mediated transformation system, which is generally used for transformation of plants, to obtain site-specific integration.
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Affiliation(s)
- A C Vergunst
- Institute of Molecular Plant Sciences, Leiden University, Clusius Laboratory, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands.
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Wolters AA, Vergunst AC, van der Werff F, Koornneef M. Analysis of nuclear and organellar DNA of somatic hybrid calli and plants between Lycopersicon spp. and Nicotiana spp. Mol Gen Genet 1993; 241:707-18. [PMID: 7903413 DOI: 10.1007/bf00279915] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Protoplast fusion experiments between Lycopersicon esculentum or L. peruvianum and Nicotiana tabacum or N. plumbaginifolia were performed to investigate the possibility of producing symmetric and asymmetric somatic hybrids between these genera. These fusions, which involved 1.7 x 10(8) protoplasts, yielded 35 viable hybrid calli. Plant regeneration was successful with two calli. One of these regenerants flowered, but developed no fruits. Analysis of the nuclear DNA by means of dot blot hybridization with species-specific repetitive DNA probes combined with flow cytometry, revealed that the nuclei of most hybrid calli contained the same absolute amount of Nicotiana DNA as the Nicotiana parent or (much) less, whereas the amount of Lycopersicon DNA per nucleus was 2-5 times that of the parental genotype. Eighteen of the 34 hybrids analyzed possessed Lycopersicon chloroplast DNA (cpDNA), whereas the other 16 had DNA from Nicotiana chloroplasts. The cpDNA type was correlated with the nuclear DNA composition; hybrids with more than 2C Nicotiana nuclear DNA possessed Nicotiana chloroplasts, whereas hybrids with 2C or less Nicotiana nuclear DNA contained Lycopersicon chloroplasts. Mitochondrial DNA (mtDNA) composition was correlated with both nuclear DNA constitution and chloroplast type. Hybrids possessed only or mainly species-specific mtDNA fragments from the parent predominating in the nucleus and often providing the chloroplasts. The data are discussed in relation to somatic incompatibility which could explain the low frequency at which hybrids between Lycopersicon and Nicotiana species are obtained and the limited morphogenetic potential of such hybrids.
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Affiliation(s)
- A A Wolters
- Department of Genetics, Wageningen Agricultural University, The Netherlands
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