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Jaboulay C, Godeux AS, Doublet P, Vianney A. Regulatory Networks of the T4SS Control: From Host Cell Sensing to the Biogenesis and the Activity during the Infection. J Mol Biol 2021; 433:166892. [PMID: 33636165 DOI: 10.1016/j.jmb.2021.166892] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2020] [Revised: 02/17/2021] [Accepted: 02/17/2021] [Indexed: 02/03/2023]
Abstract
Delivery of effectors, DNA or proteins, that hijack host cell processes to the benefit of bacteria is a mechanism widely used by bacterial pathogens. It is achieved by complex effector injection devices, the secretion systems, among which Type 4 Secretion Systems (T4SSs) play a key role in bacterial virulence of numerous animal and plant pathogens. Considerable progress has recently been made in the structure-function analyses of T4SSs. Nevertheless, the signals and processes that trigger machine assembly and activity during infection, as well as those involved in substrate recognition and transfer, are complex and still poorly understood. In this review, we aim at summarizing the last updates of the knowledge on signaling pathways that regulate the biogenesis and the activity of T4SSs in important bacterial pathogens.
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Affiliation(s)
- C Jaboulay
- CIRI, Centre International de Recherche en Infectiologie, (Team: Legionella pathogenesis), Univ Lyon, Inserm, U1111, Université Claude Bernard Lyon 1, CNRS, UMR5308, ENS de Lyon, F-69007 Lyon, France.
| | - A S Godeux
- CIRI, Centre International de Recherche en Infectiologie, (Team: Horigene), Univ Lyon, Inserm, U1111, Université Claude Bernard Lyon 1, CNRS, UMR5308, ENS de Lyon, F-69007 Lyon, France
| | - P Doublet
- CIRI, Centre International de Recherche en Infectiologie, (Team: Legionella pathogenesis), Univ Lyon, Inserm, U1111, Université Claude Bernard Lyon 1, CNRS, UMR5308, ENS de Lyon, F-69007 Lyon, France
| | - A Vianney
- CIRI, Centre International de Recherche en Infectiologie, (Team: Legionella pathogenesis), Univ Lyon, Inserm, U1111, Université Claude Bernard Lyon 1, CNRS, UMR5308, ENS de Lyon, F-69007 Lyon, France
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2
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Czarnecka-Verner E, Salem TA, Gurley WB. Adaptation of the Agrobacterium tumefaciens VirG response regulator to activate transcription in plants. PLANT MOLECULAR BIOLOGY 2016; 90:217-31. [PMID: 26646288 DOI: 10.1007/s11103-015-0407-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Accepted: 11/11/2015] [Indexed: 06/05/2023]
Abstract
The Agrobacterium tumefaciens VirG response regulator of the VirA/VirG two-component system was adapted to function in tobacco protoplasts. The subcellular localization of VirG and VirA proteins transiently expressed in onion cells was determined using GFP fusions. Preliminary studies using Gal4DBD-VP16 fusions with VirG and Escherichia coli UhpA, and NarL response regulators indicated compatibility of these bacterial proteins with the eukaryotic transcriptional apparatus. A strong transcriptional activator based on tandem activation domains from the Drosophila fushi tarazu and Herpes simplex VP16 was created. Selected configurations of the two-site Gal4-vir box GUS reporters were activated by chimeric effectors dependent on either the yeast Gal4 DNA-binding domain or that of VirG. Transcriptional induction of the GUS reporter was highest for the VirE19-element promoter with both constitutive and wild-type VirG-tandem activation domain effectors. Multiple VirE19 elements increased the reporter activity proportionately, indicating that the VirG DNA binding domain was functional in plants. The VirG constitutive-Q-VP16 effector was more active than the VirG wild-type. In both the constitutive and wild-type forms of VirG, Q-VP16 activated transcription of the GUS reporter best when located at the C-terminus, i.e. juxtaposed to the VirG DNA binding domain. These results demonstrate the possibility of using DNA binding domains from bacterial response regulators and their cognate binding elements in the engineering of plant gene expression.
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Affiliation(s)
- Eva Czarnecka-Verner
- Department of Microbiology and Cell Science, Program of Plant Molecular and Cellular Biology, University of Florida, Bldg. 981, 1355 Museum Drive, P.O. Box 110700, Gainesville, FL, 32611-0700, USA.
| | - Tarek A Salem
- Department of Microbiology and Cell Science, Program of Plant Molecular and Cellular Biology, University of Florida, Bldg. 981, 1355 Museum Drive, P.O. Box 110700, Gainesville, FL, 32611-0700, USA
- Molecular Biology Department, Genetic Engineering and Biotechnology Institute, University of Sadat City, Sadat City, Egypt
| | - William B Gurley
- Department of Microbiology and Cell Science, Program of Plant Molecular and Cellular Biology, University of Florida, Bldg. 981, 1355 Museum Drive, P.O. Box 110700, Gainesville, FL, 32611-0700, USA.
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Hubber AM, Sullivan JT, Ronson CW. Symbiosis-induced cascade regulation of the Mesorhizobium loti R7A VirB/D4 type IV secretion system. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2007; 20:255-61. [PMID: 17378428 DOI: 10.1094/mpmi-20-3-0255] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
The Mesorhizobium loti R7A symbiosis island contains genes encoding a VirB/D4 type IV secretion system (T4SS) similar to that of Agrobacterium tumefaciens. This system has host-dependent effects on symbiosis that probably are due to translocation of two effector proteins, Msi059 and Msi061, into host cells. Here we report that, as in A. tumefaciens, the M. loti vir genes are transcriptionally regulated by a VirA/VirG two-component regulatory system. A virGN54D mutant gene of M. loti caused constitutive expression of lacZ reporter gene fusions to virB1, virD4, msi059, and msi061. Expression of these gene fusions also was activated by a NodD gene product from Rhizobium leguminosarum in the presence of the inducer naringenin, as was a virA::lacZ fusion. This activation was dependent on a nod box present 851 bp upstream of virA, and a mutant with the nod box deleted formed effective nodules on Leucaena leucocephala, the same symbiotic phenotype as other M. loti vir mutants. In contrast, the wild-type strain formed small, empty nodules whereas a nodD1 mutant was completely Nod-. These results indicate that the M. loti vir genes are induced in a symbiosis-specific manner that involves a two-tiered regulatory cascade, and that the vir effectors act after Nod factor during infection thread formation.
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Affiliation(s)
- Andree M Hubber
- Department of Microbiology and Immunology, University of Otago, PO Box 56, Dunedin, New Zealand
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Krishnamohan A, Balaji V, Veluthambi K. Efficient vir gene induction in Agrobacterium tumefaciens requires virA, virG, and vir box from the same Ti plasmid. J Bacteriol 2001; 183:4079-89. [PMID: 11395473 PMCID: PMC95292 DOI: 10.1128/jb.183.13.4079-4089.2001] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2000] [Accepted: 04/17/2001] [Indexed: 11/20/2022] Open
Abstract
The vir genes of octopine, nopaline, and L,L-succinamopine Ti plasmids exhibit structural and functional similarities. However, we observed differences in the interactions between octopine and nopaline vir components. The induction of an octopine virE(A6)::lacZ fusion (pSM358cd) was 2.3-fold higher in an octopine strain (A348) than in a nopaline strain (C58). Supplementation of the octopine virG(A6) in a nopaline strain with pSM358 did not completely restore virE(A6) induction. However, addition of the octopine virA(A6) to the above strain increased virE(A6) induction to a level almost comparable to that in octopine strains. In a reciprocal analysis, the induction of a nopaline virE(C58)::cat fusion (pUCD1553) was two- to threefold higher in nopaline (C58 and T37) strains than in octopine (A348 and Ach5) and L,L-succinamopine (A281) strains. Supplementation of nopaline virA(C58) and virG(C58) in an octopine strain (A348) harboring pUCD1553 increased induction levels of virE(C58)::cat fusion to a level comparable to that in a nopaline strain (C58). Our results suggest that octopine and L,L-succinamopine VirG proteins induce the octopine virE(A6) more efficiently than they do the nopaline virE(C58). Conversely, the nopaline VirG protein induces the nopaline virE(C58) more efficiently than it does the octopine virE(A6). The ability of Bo542 virG to bring about supervirulence in tobacco is observed for an octopine vir helper (LBA4404) but not for a nopaline vir helper (PMP90). Our analyses reveal that quantitative differences exist in the interactions between VirG and vir boxes of different Ti plasmids. Efficient vir gene induction in octopine and nopaline strains requires virA, virG, and vir boxes from the respective Ti plasmids.
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Affiliation(s)
- A Krishnamohan
- Department of Plant Biotechnology, School of Biotechnology, Madurai Kamaraj University, Madurai 625 021, Tamil Nadu, India
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Sage AE, Proctor WD, Phibbs PV. A two-component response regulator, gltR, is required for glucose transport activity in Pseudomonas aeruginosa PAO1. J Bacteriol 1996; 178:6064-6. [PMID: 8830708 PMCID: PMC178468 DOI: 10.1128/jb.178.20.6064-6066.1996] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
A 729-bp open reading frame (gltR) was identified in Pseudomonas aeruginosa PAO1 that encodes a product homologous to the two-component response regulator family of proteins. Disruption of gltR caused loss of glucose transport activity. Restoration of gltR resulted in wild-type levels of glucose transport. These findings indicate that gltR is required for expression of the glucose transport system in P. aeruginosa.
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Affiliation(s)
- A E Sage
- Department of Microbiology and Immunology, East Carolina University School of Medicine, Greenville, North Carolina 27858-4354, USA
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Abstract
PhoB is a response-regulator protein from Escherichia coli that controls an adaptive response to limiting phosphate. It is activated by autophosphorylation of a conserved aspartate residue within its regulatory domain. Its primary phospho-donor is its cognate histidine kinase PhoR; however, it also becomes phosphorylated when incubated with acetylphosphate. To further characterize its activation, PhoB was considered to be an acetylphosphatase whose enzymatic mechanism involves a phospho-enzyme intermediate. The kinetic constants for autophosphorylation were determined using 32P-and fluorescence-based assays and indicated that PhoB has a K(m) for acetylphosphate of between 7 and 8 mM. These constants are not consistent with an in vivo role for acetylphosphate in the normal control of the Pho regulon. In addition, when PhoB was phosphorylated by acetylphosphate it eluted from a high-performance liquid chromatography (HPLC) size-exclusion column in two peaks. The larger form of PhoB eluted from the column in a similar manner to a chemically cross-linked dimer of PhoB. The smaller form of PhoB is a monomer. Phosphorylated PhoB bound pho-box DNA approximately 10 times tighter than PhoB. These observations show that PhoB forms a dimer when phosphorylated and suggest that the characteristics of activated PhoB result from its dimerization.
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Affiliation(s)
- W R McCleary
- Department of Microbiology and Immunology, West Virginia University, Health Sciences Center, Morgantown 26505-9177, USA.
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Roitsch T, Jin S, Nester EW. The binding site of the transcriptional activator VirG from Agrobacterium comprises both conserved and specific nonconserved sequences. FEBS Lett 1994; 338:127-32. [PMID: 8307169 DOI: 10.1016/0014-5793(94)80349-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Virulence genes of Agrobacterium tumefaciens are transcriptionally activated in response to phenolic compounds and certain sugars. The transcription activator VirG specifically binds to fragments containing the conserved vir box sequence present in the promoter region of all vir genes. This study shows that both the vir box as well as specific nonconserved sequences downstream of the vir box are required for VirG binding and transcriptional activation. Insertion of the identified VirG binding site into the lac promoter resulted in transcriptional activation of this heterologous promoter in response to the plant phenolic signal molecule acetosyringone.
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Affiliation(s)
- T Roitsch
- Department of Microbiology, University of Washington, Seattle 98195
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Binns AN, Howitz VR. The genetic and chemical basis of recognition in the Agrobacterium: plant interaction. Curr Top Microbiol Immunol 1994; 192:119-38. [PMID: 7859503 DOI: 10.1007/978-3-642-78624-2_6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- A N Binns
- Department of Biology, University of Pennsylvania, Philadelphia 19104-6018
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9
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Abstract
The discovery in 1977 that Agrobacterium species can transfer a discrete segment of oncogenic DNA (T-DNA) to the genome of host plant cells has stimulated an intense interest in the molecular biology underlying these plant-microbe associations. This attention in turn has resulted in a series of insights about the biology of these organisms that continue to accumulate at an ever-increasing rate. This excitement was due in part to the notion that this unprecedented interkingdom DNA transfer could be exploited to create transgenic plants containing foreign genes of scientific or commercial importance. In the course of these discoveries, Agrobacterium became one of the best available models for studying the molecular interactions between bacteria and higher organisms. One extensively studied aspect of this association concerns the exchange of chemical signals between Agrobacterium spp. and host plants. Agrobacterium spp. can recognize no fewer than five classes of low-molecular-weight compounds released from plants, and other classes probably await discovery. The most widely studied of these are phenolic compounds, which stimulate the transcription of the genes needed for infection. Other compounds include specific monosaccharides and acidic environments which potentiate vir gene induction, acidic polysaccharides which induce one or more chromosomal genes, and a family of compounds called opines which are released from tumorous plant cells to the bacteria as nutrient sources. Agrobacterium spp. in return release a variety of chemical compounds to plants. The best understood is the transferred DNA itself, which contains genes that in various ways upset the balance of phytohormones, ultimately causing neoplastic cell proliferation. In addition to transferring DNA, some Agrobacterium strains directly secrete phytohormones. Finally, at least some strains release a pectinase, which degrades a component of plant cell walls.
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Affiliation(s)
- S C Winans
- Section of Microbiology, Cornell University, Ithaca, New York 14853
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Perez-Casal J, Caparon MG, Scott JR. Mry, a trans-acting positive regulator of the M protein gene of Streptococcus pyogenes with similarity to the receptor proteins of two-component regulatory systems. J Bacteriol 1991; 173:2617-24. [PMID: 1849511 PMCID: PMC207828 DOI: 10.1128/jb.173.8.2617-2624.1991] [Citation(s) in RCA: 275] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
In the Streptococcus pyogenes M6 strain D471, an insertion of the conjugative transposon Tn916 into a region 2 kb upstream of the promoter of emm6 (the structural gene for the M protein) rendered the strain M negative (M. G. Caparon and J. R. Scott, Proc. Natl. Acad. Sci. USA 84:8677-8681, 1987). In the present work, we show that this insertion mutation, mry-1, is 244 bp upstream of an open reading frame encoding a protein we call Mry. This protein is visible on a gel after transcription and translation in vitro. We have developed a technique for complementation analysis in S. pyogenes and have used it to show that the wild-type mry gene is dominant to two mutant alleles. This dominance indicates that Mry acts in trans as a positive regulator of the emm6 gene. The translated DNA sequence of mry has two regions of similarity to the motif common to the receptor protein of two-component regulatory systems. In addition, the N terminus of Mry has two regions resembling a helix-turn-helix motif. Mry does not appear to be a global regulator of virulence determinants in the group A streptococcus because there is no effect of the mry-1 mutation on production of the hyaluronic acid capsule or streptokinase.
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Affiliation(s)
- J Perez-Casal
- Microbiology and Immunology Department, Emory University Health Sciences Center, Atlanta, Georgia 30322
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11
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Cooley MB, D'Souza MR, Kado CI. The virC and virD operons of the Agrobacterium Ti plasmid are regulated by the ros chromosomal gene: analysis of the cloned ros gene. J Bacteriol 1991; 173:2608-16. [PMID: 2013576 PMCID: PMC207827 DOI: 10.1128/jb.173.8.2608-2616.1991] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The ros chromosomal gene is present in octopine and nopaline strains of Agrobacterium tumefaciens as well as in Rhizobium meliloti. This gene encodes a 15.5-kDa protein that specifically represses the virC and virD operons in the virulence region of the Ti plasmid. The ros gene was cloned from a genomic bank by electroporation and complementation in Agrobacterium cells. Reporter fusion to the ros gene indicates that the level of transcription is controlled in part by autoregulation. A consensus inverted repeat sequence present in the ros promoter and in the virC and virD promoters of pTiC58, pTiA6, and pRiA4b suggests that a specific Ros binding site exists in these promoters. In the virC and virD promoter region, this binding site is within a cluster of vir box consensus sequences in which the VirG protein binds. This suggests possible binding competition between Ros and VirG at the virC and virD promoters. That the Ros protein binds DNA is suggested by the presence of a 'zinc finger' consensus sequence in the protein.
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Affiliation(s)
- M B Cooley
- Davis Crown Gall Group, University of California, Davis 95616
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12
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Powell BS, Kado CI. Specific binding of VirG to the vir box requires a C-terminal domain and exhibits a minimum concentration threshold. Mol Microbiol 1990; 4:2159-66. [PMID: 2089226 DOI: 10.1111/j.1365-2958.1990.tb00577.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The positive regulatory protein VirG from the virulence region of the Ti plasmid of Agrobacterium tumefaciens was first demonstrated to possess DNA-binding capabilities using chromatographically purified protein and in vitro assays (Powell et al., 1989). This paper is an extension of that research and presents evidence on the in vivo DNA-binding properties of VirG using a transcription interference assay. VirG protein bound specifically to a 'vir box' response element and repressed transcription of a lacZ reporter gene, but increased transcription in the absence of a vir box. A biphasic response in specific DNA-binding was observed upon increasing virG expression, suggesting that specific binding was co-operatively affected by protein concentration. Certain TrpE'-'VirG hybrid proteins also bound the vir box, but required sequences distal to amino acid Arg-118 of the VirG polypeptide. These data further localize a DNA-binding domain within VirG, and support a modified model for the regulation of virulence genes in which transphosphorylation by the coregulator VirA functions to stabilize specific DNA-binding by low concentrations of VirG, resulting in gene activation. Otherwise, at high concentrations, VirG promotes expression of the virulence regulon without assistance from VirA as was shown previously (Rogowsky et al., 1987).
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Affiliation(s)
- B S Powell
- Department of Plant Pathology, University of California, Davis 95616
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Roitsch T, Wang H, Jin SG, Nester EW. Mutational analysis of the VirG protein, a transcriptional activator of Agrobacterium tumefaciens virulence genes. J Bacteriol 1990; 172:6054-60. [PMID: 2211523 PMCID: PMC526929 DOI: 10.1128/jb.172.10.6054-6060.1990] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The VirG protein of Agrobacterium tumefaciens is required in conjunction with the VirA protein for transcriptional activation of the virulence (vir) genes in response to plant phenolic compounds. These proteins are members of a family of two component regulatory systems. vir genes are activated via a cascade of phosphorylation reactions involving a specific aspartic acid residue of the VirG protein. We have conducted a mutational analysis of the VirG protein. By mutating conserved and nonconserved aspartic acid residues in the N-terminal domain, we demonstrated that two of three conserved aspartic acid residues located in two different regions are important for the phosphorylation of VirG by VirA phosphate. A third conserved N-terminal region was also shown to be critical for the biological function of VirG as a transcriptional activator. The identification of phosphorylatable but biologically inactive mutated VirG proteins suggests that not only phosphorylation but also a conformational change is necessary for its activity. We further demonstrated that phosphorylation is not required for sequence-specific binding to a vir gene regulatory sequence (vir box) and that the C-terminal domain is sufficient for DNA binding. The data support the model of a two-domain structure for the VirG protein and demonstrate that the sequence homologies to other two-component regulatory systems reflect both functional and structural homologies.
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Affiliation(s)
- T Roitsch
- Department of Microbiology, University of Washington, Seattle 98195
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Shimoda N, Toyoda-Yamamoto A, Nagamine J, Usami S, Katayama M, Sakagami Y, Machida Y. Control of expression of Agrobacterium vir genes by synergistic actions of phenolic signal molecules and monosaccharides. Proc Natl Acad Sci U S A 1990; 87:6684-8. [PMID: 11607097 PMCID: PMC54601 DOI: 10.1073/pnas.87.17.6684] [Citation(s) in RCA: 142] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Most virulence (vir) genes of Agrobacterium tumefaciens that are required for the formation of crown gall tumors are expressed in response to such plant signal molecules as acetosyringone and lignin precursors. The phenolic signals are transduced through a receptor VirA protein in the inner membrane of the bacterial cell. The expression of these genes triggers the transfer of a specific DNA segment, called transferred DNA (T-DNA), from the Ti plasmid to plant cells, and its integration into their nuclear DNA. We show here that a group of aldoses (L-arabinose, D-xylose, D-lyxose, D-glucose, D-mannose, D-idose, D-galactose, and D-talose) can markedly enhance acetosyringone-dependent expression of vir genes when the concentration of acetosyringone is limited (10 microM) but does not enhance the expression of noninducible genes. Likewise, a 2-deoxy-D-glucose, a nonmetabolized sugar, is also effective. When a deletion was introduced into the virA gene in the region encoding the periplasmic portion of the VirA protein, enhancement by glucose disappeared, but vir expression was induced by acetosyringone in this mutant. These results suggest that these sugars directly enhance a signaling process initiated by phenolic inducers that results in an increase in expression of the vir genes.
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Affiliation(s)
- N Shimoda
- Department of Biology, Faculty of Science, Nagoya University, Nagoya, Japan
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15
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Rogowsky PM, Powell BS, Shirasu K, Lin TS, Morel P, Zyprian EM, Steck TR, Kado CI. Molecular characterization of the vir regulon of Agrobacterium tumefaciens: complete nucleotide sequence and gene organization of the 28.63-kbp regulon cloned as a single unit. Plasmid 1990; 23:85-106. [PMID: 2194232 DOI: 10.1016/0147-619x(90)90028-b] [Citation(s) in RCA: 65] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The entire vir regulon of Agrobacterium tumefaciens was subcloned and the complete 28.6-kbp nucleotide sequence was determined. The regulon was cloned as a single unit into two replicons, one of which replicates at a high copy number in this bacterium, and a second which has broad-host-range features to replicate in other Gram-negative bacteria. These vir region plasmids are able to confer in trans the processing and transfer activities on a second plasmid containing the T-DNA. In the high copy number vir region plasmid pUCD2614, a moderate increase in basal vir gene expression was observed as judged by virE::cat fusion expression assays relative to the wild-type control plasmid. Furthermore, higher efficiencies of tobacco leaf disk transformation were observed than with the widely used vir helper plasmid pAL4404. The nucleotide sequence studies showed that the vir region consists of 28,631 bp comprising 24 open reading frames which encode proteins involved in tumorigenicity. Two open reading frames not previously characterized, virH and ORF5, were uncovered within the virD/virE intervening spacer region. Together these studies more completely characterize the structure and function of the vir regulon.
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Affiliation(s)
- P M Rogowsky
- Department of Plant Pathology, University of California, Davis 95616
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16
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Pazour GJ, Das A. virG, an Agrobacterium tumefaciens transcriptional activator, initiates translation at a UUG codon and is a sequence-specific DNA-binding protein. J Bacteriol 1990; 172:1241-9. [PMID: 2307647 PMCID: PMC208589 DOI: 10.1128/jb.172.3.1241-1249.1990] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The Agrobacterium tumefaciens Ti plasmid virG locus, in conjunction with virA and acetosyringone, activates transcription of the virulence (vir) genes. Insertional and deoxyoligonucleotide-directed mutagenesis studies showed that both octopine and nopaline Ti plasmid virG genes initiate translation at a UUG codon. VirG protein initiated at this UUG codon was found to be 241 amino acid residues in length and had an apparent molecular mass of 27.1 kilodaltons. A Salmonella typhimurium trp-virG transcriptional fusion was constructed to overproduce VirG. Agrobacterium cells containing this gene fusion showed a large increase in virG activity in the presence of virA and acetosyringone. Since the trp promoter is not under virA-virG control, this result indicates that modification of VirG is necessary for its full activity. VirG overproduced in Escherichia coli was purified from inclusion bodies. It was found to be a DNA-binding protein that preferentially bound DNA fragments containing the 5' nontranscribed regions of the virA, -B, -C, -D, and -G operons. Significant specific binding to the 5' nontranscribed region sequences of virE was not detected. DNase I footprinting of the upstream regions of virC-virD and virG showed that VirG binds to sequences around the vir box region.
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Affiliation(s)
- G J Pazour
- Department of Biochemistry, University of Minnesota, St. Paul 55108
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17
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Huang Y, Morel P, Powell B, Kado CI. VirA, a coregulator of Ti-specified virulence genes, is phosphorylated in vitro. J Bacteriol 1990; 172:1142-4. [PMID: 2298696 PMCID: PMC208549 DOI: 10.1128/jb.172.2.1142-1144.1990] [Citation(s) in RCA: 80] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
High-level expression of a chimeric virA gene was obtained by replacing the first 524 codons of virA with the first half of trpE. The encoded fusion protein was isolated and found to exhibit autokinase activity. Therefore, a kinase domain is in the C-terminal portion of VirA, and protein phosphorylation may be an important feature of VirA function.
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Affiliation(s)
- Y Huang
- Department of Plant Pathology, University of California, Davis 95616
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18
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The regulatory VirG protein specifically binds to a cis-acting regulatory sequence involved in transcriptional activation of Agrobacterium tumefaciens virulence genes. J Bacteriol 1990; 172:531-7. [PMID: 2404941 PMCID: PMC208474 DOI: 10.1128/jb.172.2.531-537.1990] [Citation(s) in RCA: 114] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Virulence genes of Agrobacterium tumefaciens are induced in parallel in the presence of plant phenolic compounds such as acetosyringone and the two regulatory vir genes virA and virG. In this study we identified a cis-acting regulatory sequence in the 5'-noncoding region of the virE operon that is essential for this activation. To do this, we constructed a series of deletion mutants by using exonuclease Bal 31. Western blot (immunoblot) analysis showed that the 70 base pairs upstream of the transcriptional start site were sufficient for full virE gene induction. A conserved dodecadeoxynucleotide sequence (vir box), which was previously identified in the nontranscribed sequences of all vir genes, was located at 5' end of the minimum required promoter sequence. Deletion of this vir box only completely abolished induction of the virE gene. This demonstrates that the vir box functions as an upstream regulatory sequence. To study the role of the VirG protein in the activation process, we overproduced the native-sized VirG protein in Escherichia coli by fusing the lacZ' start codon ATG with the second virG codon AAA using site-directed mutagenesis. The VirG protein was purified and renatured from E. coli and was shown to bind to a specific sequence in two vir gene promoters. Footprinting analysis of the virE and virB promoters identified the 12-base-pair vir box as the VirG-binding core sequence.
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Abstract
Bacteria can respond to a variety of environmental stimuli by means of systems generally composed of two proteins. The first protein (sensor or transmitter) is usually a transmembrane protein with cytoplasmic and extracytoplasmic domains. The extracytoplasmic domain (sensor) senses the environment and transfers the signal through the transmembrane domain to the cytoplasmic domain (transmitter), which has kinase activity. The second protein is located in the cytoplasm and contains an amino-terminal domain (receiver), which can be phosphorylated by the transmitter, and a carboxy-terminal region (regulator), which regulates gene expression by binding to DNA. The transmitter and receiver modules (the kinase and its target) are conserved in all signal-transducing systems and are the 'core structure' of this two-component system. The sensors and the regulators vary according to the stimuli they respond to and the DNA structure they interact with. On the basis of their sequence homology, the proteins belonging to such two-component systems can be classified into different families, which are summarized in this review.
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Affiliation(s)
- R Gross
- Sclavo Research Centre, Siena, Italy
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Morel P, Powell BS, Rogowsky PM, Kado CI. Characterization of the virA virulence gene of the nopaline plasmid, pTiC58, of Agrobacterium tumefaciens. Mol Microbiol 1989; 3:1237-46. [PMID: 2796735 DOI: 10.1111/j.1365-2958.1989.tb00274.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
We have determined the complete nucleotide sequence of a 4.8 kilobase fragment encompassing the virA locus of the nopaline-type plasmid, pTiC58, of Agrobacterium tumefaciens. virA is composed of a single open reading frame of 2499 nucleotides, capable of encoding a protein of 91.3 kiloDaltons. A trpE::virA gene fusion was used to confirm the reading frame of virA. High nucleotide and amino acid sequence homologies were observed between pTiC58 virA and the virA sequences of three octopine-type plasmids. Strong homologies in amino acid sequence were observed between pTiC58 VirA and seven bacterial proteins which control various regulons. Two hydrophobic domains within VirA are also consistent with a model in which VirA acts as a membrane-bound sensor of plant signal molecules.
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Affiliation(s)
- P Morel
- Davis Crown Gall Group, Department of Plant Pathology, University of California, Davis 95616
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