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Lacroix B, Citovsky V. Genetic factors governing bacterial virulence and host plant susceptibility during Agrobacterium infection. ADVANCES IN GENETICS 2022; 110:1-29. [PMID: 37283660 PMCID: PMC10241481 DOI: 10.1016/bs.adgen.2022.08.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Several species of the Agrobacterium genus represent unique bacterial pathogens able to genetically transform plants, by transferring and integrating a segment of their own DNA (T-DNA, transferred DNA) in their host genome. Whereas in nature this process results in uncontrolled growth of the infected plant cells (tumors), this capability of Agrobacterium has been widely used as a crucial tool to generate transgenic plants, for research and biotechnology. The virulence of Agrobacterium relies on a series of virulence genes, mostly encoded on a large plasmid (Ti-plasmid, tumor inducing plasmid), involved in the different steps of the DNA transfer to the host cell genome: activation of bacterial virulence, synthesis and export of the T-DNA and its associated proteins, intracellular trafficking of the T-DNA and effector proteins in the host cell, and integration of the T-DNA in the host genomic DNA. Multiple interactions between these bacterial encoded proteins and host factors occur during the infection process, which determine the outcome of the infection. Here, we review our current knowledge of the mechanisms by which bacterial and plant factors control Agrobacterium virulence and host plant susceptibility.
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Nabi N, Ben Hafsa A, Gaillard V, Nesme X, Chaouachi M, Vial L. Evolutionary classification of tumor- and root-inducing plasmids based on T-DNAs and virulence regions. Mol Phylogenet Evol 2022; 169:107388. [PMID: 35017066 DOI: 10.1016/j.ympev.2022.107388] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2018] [Revised: 11/15/2020] [Accepted: 12/08/2021] [Indexed: 11/19/2022]
Abstract
Tumor-inducing (Ti) and root-inducing (Ri) plasmids of Agrobacterium that display a large diversity are involved in crown gall and hairy root plant diseases. Their phylogenetic relationships were inferred from an exhaustive set of Ti and Ri plasmids (including 36 new complete Ti plasmids) by focusing on T-DNA and virulence regions. The opine synthase gene content of T-DNAs revealed 13 opine types corresponding to former classifications based on opines detected in diseased plants, while the T-DNA gene content more finely separate opine types in 18 T-DNA organizations. This classification was supported by the phylogeny of T-DNA oncogenes of Ti plasmids. The five gene organizations found in Ti/Ri vir regions was supported by the phylogeny of common vir genes. The vir organization was found to be likely an ancestral plasmid trait separating "classic" Ti plasmids (with one or two T-DNAs) and "Ri and vine-Ti" plasmids. A scenario generally supported by the repABC phylogeny. T-DNAs likely evolved later with the acquisition of opine characteristics as last steps in the Ti/Ri plasmid evolution. This novel evolutionary classification of Ti/Ri plasmids was found to be relevant for accurate crown gall and hairy root epidemiology.
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Affiliation(s)
- Nesrine Nabi
- Unité de Recherche UR17ES30 Génomique, Biotechnologie et Stratégies Antivirales, Institut Supérieur de Biotechnologie, Université de Monastir, Monastir, Tunisie.
| | - Ahmed Ben Hafsa
- Unité de Recherche UR17ES30 Génomique, Biotechnologie et Stratégies Antivirales, Institut Supérieur de Biotechnologie, Université de Monastir, Monastir, Tunisie
| | - Vincent Gaillard
- Laboratoire d'Ecologie Microbienne (LEM), UCBL, CNRS, INRAE, VetAgro Sup, Univ Lyon, F-69622 Villeurbanne Cedex, France
| | - Xavier Nesme
- Laboratoire d'Ecologie Microbienne (LEM), UCBL, CNRS, INRAE, VetAgro Sup, Univ Lyon, F-69622 Villeurbanne Cedex, France
| | - Maher Chaouachi
- Unité de Recherche UR17ES30 Génomique, Biotechnologie et Stratégies Antivirales, Institut Supérieur de Biotechnologie, Université de Monastir, Monastir, Tunisie
| | - Ludovic Vial
- Laboratoire d'Ecologie Microbienne (LEM), UCBL, CNRS, INRAE, VetAgro Sup, Univ Lyon, F-69622 Villeurbanne Cedex, France.
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Lacroix B, Citovsky V. Pathways of DNA Transfer to Plants from Agrobacterium tumefaciens and Related Bacterial Species. ANNUAL REVIEW OF PHYTOPATHOLOGY 2019; 57:231-251. [PMID: 31226020 PMCID: PMC6717549 DOI: 10.1146/annurev-phyto-082718-100101] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Genetic transformation of host plants by Agrobacterium tumefaciens and related species represents a unique model for natural horizontal gene transfer. Almost five decades of studying the molecular interactions between Agrobacterium and its host cells have yielded countless fundamental insights into bacterial and plant biology, even though several steps of the DNA transfer process remain poorly understood. Agrobacterium spp. may utilize different pathways for transferring DNA, which likely reflects the very wide host range of Agrobacterium. Furthermore, closely related bacterial species, such as rhizobia, are able to transfer DNA to host plant cells when they are provided with Agrobacterium DNA transfer machinery and T-DNA. Homologs of Agrobacterium virulence genes are found in many bacterial genomes, but only one non-Agrobacterium bacterial strain, Rhizobium etli CFN42, harbors a complete set of virulence genes and can mediate plant genetic transformation when carrying a T-DNA-containing plasmid.
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Affiliation(s)
- Benoît Lacroix
- Department of Biochemistry and Cell Biology, State University of New York, Stony Brook, New York 11794-5215, USA;
| | - Vitaly Citovsky
- Department of Biochemistry and Cell Biology, State University of New York, Stony Brook, New York 11794-5215, USA;
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Wang L, Lacroix B, Guo J, Citovsky V. Transcriptional Activation of Virulence Genes of Rhizobium etli. J Bacteriol 2017; 199:e00841-16. [PMID: 28069822 PMCID: PMC5331667 DOI: 10.1128/jb.00841-16] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Accepted: 01/03/2017] [Indexed: 01/24/2023] Open
Abstract
Recently, Rhizobium etli, in addition to Agrobacterium spp., has emerged as a prokaryotic species whose genome encodes a functional machinery for DNA transfer to plant cells. To understand this R. etli-mediated genetic transformation, it would be useful to define how its vir genes respond to the host plants. Here, we explored the transcriptional activation of the vir genes contained on the R. etli p42a plasmid. Using a reporter construct harboring lacZ under the control of the R. etli virE promoter, we show that the signal phenolic molecule acetosyringone (AS) induces R. etli vir gene expression both in an R. etli background and in an Agrobacterium tumefaciens background. Furthermore, in both bacterial backgrounds, the p42a plasmid also promoted plant genetic transformation with a reporter transfer DNA (T-DNA). Importantly, the R. etli vir genes were transcriptionally activated by AS in a bacterial species-specific fashion in regard to the VirA/VirG signal sensor system, and this activation was induced by signals from the natural host species of this bacterium but not from nonhost plants. The early kinetics of transcriptional activation of the major vir genes of R. etli also revealed several features distinct from those known for A. tumefaciens: the expression of the virG gene reached saturation relatively quickly, and virB2, which in R. etli is located outside the virB operon, was expressed only at low levels and did not respond to AS. These differences in vir gene transcription may contribute to the lower efficiency of T-DNA transfer of R. etli p42a than of T-DNA transfer of pTiC58 of A. tumefaciensIMPORTANCE The region encoding homologs of Agrobacterium tumefaciens virulence genes in the Rhizobium etli CE3 p42a plasmid was the first endogenous virulence system encoded by the genome of a non-Agrobacterium species demonstrated to be functional in DNA transfer and stable integration into the plant cell genome. In this study, we explored the transcriptional regulation and induction of virulence genes in R. etli and show similarities to and differences from those of their A. tumefaciens counterparts, contributing to an understanding and a comparison of these two systems. Whereas most vir genes in R. etli follow an induction pattern similar to that of A. tumefaciens vir genes, a few significant differences may at least in part explain the variations in T-DNA transfer efficiency.
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Affiliation(s)
- Luyao Wang
- Department of Biochemistry and Cell Biology, State University of New York, Stony Brook, New York, USA
- Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, Key Laboratory of Monitoring and Management of Crop Diseases and Pest Insects, Ministry of Agriculture, Engineering Center of Bioresource Pesticide in Jiangsu Province, Nanjing, Jiangsu Province, China
| | - Benoît Lacroix
- Department of Biochemistry and Cell Biology, State University of New York, Stony Brook, New York, USA
| | - Jianhua Guo
- Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, Key Laboratory of Monitoring and Management of Crop Diseases and Pest Insects, Ministry of Agriculture, Engineering Center of Bioresource Pesticide in Jiangsu Province, Nanjing, Jiangsu Province, China
| | - Vitaly Citovsky
- Department of Biochemistry and Cell Biology, State University of New York, Stony Brook, New York, USA
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Dequivre M, Diel B, Villard C, Sismeiro O, Durot M, Coppée JY, Nesme X, Vial L, Hommais F. Small RNA Deep-Sequencing Analyses Reveal a New Regulator of Virulence in Agrobacterium fabrum C58. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2015; 28:580-589. [PMID: 26024442 DOI: 10.1094/mpmi-12-14-0380-fi] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Novel ways of regulating Ti plasmid functions were investigated by studying small RNAs (sRNAs) that are known to act as posttranscriptional regulators in plant pathogenic bacteria. sRNA-seq analyses of Agrobacterium fabrum C58 allowed us to identify 1,108 small transcripts expressed in several growth conditions that could be sRNAs. A quarter of them were confirmed by bioinformatics or by biological experiments. Antisense RNAs represent 24% of the candidates and they are over-represented on the pTi (with 62% of pTi sRNAs), suggesting differences in the regulatory mechanisms between the essential and accessory replicons. Moreover, a large number of these pTi antisense RNAs are transcribed opposite to those genes involved in virulence. Others are 5'- and 3'-untranslated region RNAs and trans-encoded RNAs. We have validated, by rapid amplification of cDNA ends polymerase chain reaction, the transcription of 14 trans-encoded RNAs, among which RNA1111 is expressed from the pTiC58. Its deletion decreased the aggressiveness of A. fabrum C58 on tomatoes, tobaccos, and kalanchoe, suggesting that this sRNA activates virulence. The identification of its putative target mRNAs (6b gene, virC2, virD3, and traA) suggests that this sRNA may coordinate two of the major pTi functions, the infection of plants and its dissemination among bacteria.
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Affiliation(s)
- M Dequivre
- 1Université de Lyon, F-69622, Lyon, France
- 2Université Lyon 1, F-69622 Villeurbanne, France
- 3CNRS, UMR 5240 Microbiologie Adaptation et Pathogénie, F-69622 Villeurbanne, France
| | - B Diel
- 1Université de Lyon, F-69622, Lyon, France
- 2Université Lyon 1, F-69622 Villeurbanne, France
- 3CNRS, UMR 5240 Microbiologie Adaptation et Pathogénie, F-69622 Villeurbanne, France
- 4CNRS, UMR 5557 Ecologie Microbienne, F-69622 Villeurbanne, France
- 5INRA, USC 1364 Ecologie Microbienne, F-69622 Villeurbanne, France
| | - C Villard
- 1Université de Lyon, F-69622, Lyon, France
- 2Université Lyon 1, F-69622 Villeurbanne, France
- 3CNRS, UMR 5240 Microbiologie Adaptation et Pathogénie, F-69622 Villeurbanne, France
| | - O Sismeiro
- 6Plate-forme Transcriptome et Epigénome, Département Génomes et Génétique, Institut Pasteur, 25 rue du Dr. Roux, F75015 Paris, France
| | - M Durot
- 7CEA/DSV/FAR/IG/Genoscope and CNRS UMR8030 Laboratoire d'Analyses Bioinformatiques en Métabolisme et Génomique, 2 rue Gaston Crémieux 91057 Evry cedex, France
- 8Total New Energies USA, 5858 Horton Street, Emeryville, CA 94608, U.S.A
| | - J Y Coppée
- 6Plate-forme Transcriptome et Epigénome, Département Génomes et Génétique, Institut Pasteur, 25 rue du Dr. Roux, F75015 Paris, France
| | - X Nesme
- 1Université de Lyon, F-69622, Lyon, France
- 2Université Lyon 1, F-69622 Villeurbanne, France
- 4CNRS, UMR 5557 Ecologie Microbienne, F-69622 Villeurbanne, France
- 5INRA, USC 1364 Ecologie Microbienne, F-69622 Villeurbanne, France
| | - L Vial
- 1Université de Lyon, F-69622, Lyon, France
- 2Université Lyon 1, F-69622 Villeurbanne, France
- 4CNRS, UMR 5557 Ecologie Microbienne, F-69622 Villeurbanne, France
- 5INRA, USC 1364 Ecologie Microbienne, F-69622 Villeurbanne, France
| | - F Hommais
- 1Université de Lyon, F-69622, Lyon, France
- 2Université Lyon 1, F-69622 Villeurbanne, France
- 3CNRS, UMR 5240 Microbiologie Adaptation et Pathogénie, F-69622 Villeurbanne, France
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6
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Kado CI. Historical account on gaining insights on the mechanism of crown gall tumorigenesis induced by Agrobacterium tumefaciens. Front Microbiol 2014; 5:340. [PMID: 25147542 PMCID: PMC4124706 DOI: 10.3389/fmicb.2014.00340] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Accepted: 06/19/2014] [Indexed: 11/13/2022] Open
Abstract
The plant tumor disease known as crown gall was not called by that name until more recent times. Galls on plants were described by Malpighi (1679) who believed that these extraordinary growth are spontaneously produced. Agrobacterium was first isolated from tumors in 1897 by Fridiano Cavara in Napoli, Italy. After this bacterium was recognized to be the cause of crown gall disease, questions were raised on the mechanism by which it caused tumors on a variety of plants. Numerous very detailed studies led to the identification of Agrobacterium tumefaciens as the causal bacterium that cleverly transferred a genetic principle to plant host cells and integrated it into their chromosomes. Such studies have led to a variety of sophisticated mechanisms used by this organism to aid in its survival against competing microorganisms. Knowledge gained from these fundamental discoveries has opened many avenues for researchers to examine their primary organisms of study for similar mechanisms of pathogenesis in both plants and animals. These discoveries also advanced the genetic engineering of domesticated plants for improved food and fiber.
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Affiliation(s)
- Clarence I Kado
- Davis Crown Gall Group, Department of Plant Pathology, University of California, Davis Davis, CA, USA
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7
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Someya T, Nonaka S, Nakamura K, Ezura H. Increased 1-aminocyclopropane-1-carboxylate deaminase activity enhances Agrobacterium tumefaciens-mediated gene delivery into plant cells. Microbiologyopen 2013; 2:873-80. [PMID: 24000136 PMCID: PMC3831647 DOI: 10.1002/mbo3.123] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2013] [Revised: 07/11/2013] [Accepted: 07/21/2013] [Indexed: 11/15/2022] Open
Abstract
Agrobacterium-mediated transformation is a useful tool for the genetic modification in plants, although its efficiency is low for several plant species. Agrobacterium-mediated transformation has three major steps in laboratory-controlled experiments: the delivery of T-DNA into plant cells, the selection of transformed plant cells, and the regeneration of whole plants from the selected cells. Each of these steps must be optimized to improve the efficiency of Agrobacterium-mediated plant transformation. It has been reported that increasing the number of cells transformed by T-DNA delivery can improve the frequency of stable transformation. Previously, we demonstrated that a reduction in ethylene production by plant cells during cocultivation with A. tumefaciens-expressing 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase resulted in increased T-DNA delivery into the plant cells. In this study, to further improve T-DNA delivery by A. tumefaciens, we modified the expression cassette of the ACC deaminase gene using vir gene promoter sequences. The ACC deaminase gene driven by the virD1 promoter was expressed at a higher level, resulting in a higher ACC deaminase activity in this A. tumefaciens strain than in the strain with the lac promoter used in a previous study. The newly developed A. tumefaciens strain improves the delivery of T-DNA into Solanum lycopersicum (tomato) and Erianthus ravennae plants and thus may be a powerful tool for the Agrobacterium-mediated genetic engineering of plants.
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Affiliation(s)
- Tatsuhiko Someya
- Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba-shi, Ibaraki, 305-8572, Japan
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8
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Natural genetic engineering of plant cells: the molecular biology of crown gall and hairy root disease. World J Microbiol Biotechnol 1996; 12:327-51. [DOI: 10.1007/bf00340209] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Revised: 02/07/1996] [Accepted: 02/10/1996] [Indexed: 11/26/2022]
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9
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Jin S, Song YN, Deng WY, Gordon MP, Nester EW. The regulatory VirA protein of Agrobacterium tumefaciens does not function at elevated temperatures. J Bacteriol 1993; 175:6830-5. [PMID: 8226624 PMCID: PMC206806 DOI: 10.1128/jb.175.21.6830-6835.1993] [Citation(s) in RCA: 60] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Previous studies have shown that Agrobacterium tumefaciens causes tumors on plants only at temperatures below 32 degrees C, and virulence gene expression is specifically inhibited at temperatures above 32 degrees C. We show here that this effect persists even when the virA and virG loci are expressed under the control of a lac promoter whose activity is temperature independent. This finding suggests that one or more steps in the signal transduction process mediated by the VirA and VirG proteins are temperature sensitive. Both the autophosphorylation of VirA and the subsequent transfer of phosphate to VirG are shown to be sensitive to high temperatures (> 32 degrees C), and this correlates with the reduced vir gene expression observed at these temperatures. At temperatures of 32 degrees C and higher, the VirA molecule undergoes a reversible inactivation while the VirG molecule is not affected. vir gene induction is temperature sensitive in an acetosyringone-independent virA mutant background but not in a virG constitutive mutant which is virA and acetosyringone independent. These observations all support the notion that the VirA protein is responsible for the thermosensitivity of vir gene expression. However, an Agrobacterium strain containing a constitutive virG locus still cannot cause tumors on Kalanchoe plants at 32 degrees C. This strain induces normal-size tumors at temperatures up to 30 degrees C, whereas the wild-type Agrobacterium strain produces almost no tumors at 30 degrees C. These results suggest that at temperatures above 32 degrees C, the plant becomes more resistant to infection by A. tumefaciens and/or functions of some other vir gene products are lost in spite of their normal levels of expression.
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Affiliation(s)
- S Jin
- Department of Microbiology, University of Washington, Seattle 98195
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10
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D'Souza-Ault MR, Cooley MB, Kado CI. Analysis of the Ros repressor of Agrobacterium virC and virD operons: molecular intercommunication between plasmid and chromosomal genes. J Bacteriol 1993; 175:3486-90. [PMID: 8501053 PMCID: PMC204748 DOI: 10.1128/jb.175.11.3486-3490.1993] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The virulence genes of the Agrobacterium tumefaciens Ti plasmid are regulated both positively and negatively. The products of the genes of the virC and virD operons play an important role in host specificity and T-DNA processing. These operons are transcribed in opposite directions and therefore bear diametrically oriented promoters. These promoters are positively regulated by the VirG protein, which is believed to be activated through phosphorylation by a histidine kinase encoded by the virA gene. The virC and virD operons are also regulated by a 15.5-kDa repressor protein encoded by the ros chromosomal gene. A mutation in ros causes the constitutive expression of virC and virD in the complete absence of the VirG protein. It appears, therefore, that the Ros repressor interacts with the regulatory region of these operons. The Ros repressor is shown here to bind to an upstream sequence (Ros box) comprising 40 bp bearing a 9-bp inverted repeat, TATATTTCA/TGTAATATA, in the promoter region of these operons. The affinity for this sequence is specific and tenacious, since the addition of at least a 20,000-fold excess of competitor DNA failed to remove the Ros protein coding sequence from the Ros box. DNase I footprint analysis showed that the Ros box overlaps the binding site of VirG (Vir box). This result suggests that virC and virD transcription is modulated by Ros and VirG proteins.
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Affiliation(s)
- M R D'Souza-Ault
- Department of Plant Pathology, University of California, Davis 95616
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11
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Rossi L, Hohn B, Tinland B. The VirD2 protein of Agrobacterium tumefaciens carries nuclear localization signals important for transfer of T-DNA to plant. MOLECULAR & GENERAL GENETICS : MGG 1993; 239:345-53. [PMID: 8391110 DOI: 10.1007/bf00276932] [Citation(s) in RCA: 81] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Agrobacterium tumefaciens is able to transfer a piece of DNA, the T-DNA, to the nucleus of the plant cell. The VirD2 protein is required for the production of the T-DNA, it is tightly linked to the T-DNA and it is thought to direct it to the plant genome. Two nuclear localization signals (NLS), one in the N-terminal part and one in the C-terminal part of the VirD2 protein, have been shown to be able to target marker proteins to the plant nucleus. Here we analyze nuclear entry of the T-DNA complex using a new and very sensitive assay for T-DNA transfer. We show that optimal T-DNA transfer requires the VirD2 NLS located in the C-terminal part of the protein, whereas mutations in the N-terminal NLS coding sequence seem to have no effect on T-DNA transfer.
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Affiliation(s)
- L Rossi
- Friedrich Miescher-Institut, Basel, Switzerland
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12
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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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13
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Castle LA, Smith KD, Morris RO. Cloning and sequencing of an Agrobacterium tumefaciens beta-glucosidase gene involved in modifying a vir-inducing plant signal molecule. J Bacteriol 1992; 174:1478-86. [PMID: 1537792 PMCID: PMC206542 DOI: 10.1128/jb.174.5.1478-1486.1992] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Induction of Agrobacterium tumefaciens virulence genes by plant phenolic compounds is essential for successful T-DNA transfer to a host plant. In Douglas fir needles, the major virulence region inducer is the glycoside coniferin (J. W. Morris and R. O. Morris, Proc. Natl. Acad. Sci. USA 87:3612-3618, 1990). Agrobacterium strains with high beta-glucosidase activity respond to coniferin and infect Douglas fir seedlings, whereas most strains with low beta-glucosidase activity fail to respond to coniferin and are avirulent on this host. We have cloned two beta-glucosidase genes from A. tumefaciens B3/73 and sequenced one of them, cbg1. It appears to be part of a polycistronic unit and shows a high bias for GC-rich codons. When expressed in Escherichia coli, Cbg1 beta-glucosidase hydrolyzes coniferin but not cellobiose. The 88-kDa predicted product of cbg1 is highly similar to one other bacterial beta-glucosidase and several fungal beta-glucosidases. There is little homology between Cbg1 and other bacterial beta-glucosidases, including an Agrobacterium cellobiase.
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Affiliation(s)
- L A Castle
- Biochemistry Department, University of Missouri-Columbia 65211
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14
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Pazour GJ, Das A. Characterization of the VirG binding site of Agrobacterium tumefaciens. Nucleic Acids Res 1990; 18:6909-13. [PMID: 2263453 PMCID: PMC332749 DOI: 10.1093/nar/18.23.6909] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Expression of Agrobacterium tumefaciens virulence (vir) genes is dependent on the presence of a conserved 'vir box' sequence in their 5' nontranscribed regions. The location and number of these sequences vary considerably in different vir genes. Site-directed mutagenesis was used to identify the functional vir box(es) of virB, virC and virD. For virB expression both vir box B1 and B2 are required but only the vir box B1 is absolutely essential. Of the five vir boxes of virC and virD two are required for virC expression while only one vir box is required for virD expression. To investigate the minimum sequences necessary for vir gene induction a deletion derivative of virE that lacks the vir box region was used. This mutant is not induced by acetosyringone. The inducibility of this promoter was restored when a synthetic deoxyoligonucleotide dGTTTCAATTGAAAC was introduced at a location analogous to that of the wild type vir box sequence. Mutational analysis indicate that the functional vir box sequence is 14 residues in length, contains a dyad symmetry and has the consensus sequence d ryTncAaTTGnAaY [corrected] (r = purine, y = pyrimidine).
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Affiliation(s)
- G J Pazour
- Department of Biochemistry, University of Minnesota, St Paul 55108
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15
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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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Shirasu K, Morel P, Kado CI. Characterization of the virB operon of an Agrobacterium tumefaciens Ti plasmid: nucleotide sequence and protein analysis. Mol Microbiol 1990; 4:1153-63. [PMID: 2233252 DOI: 10.1111/j.1365-2958.1990.tb00690.x] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The virulence regulon of the Agrobacterium tumefaciens TiC58 plasmid is composed of six operons, virA, virB, virG, virC, virD and virE, which direct the transfer of T-DNA into plant cells. The 9.5 kbp virB operon is the largest of these operons and its entire nucleotide sequence was determined and found to contain eleven open reading frames (ORFs). Gene fusions of each VirB ORF to T7 phi 10 were made and overexpressed in Escherichia coli to confirm that they encode proteins of predicted size. Hydrophobic analysis of these peptide sequences revealed nine proteins that contain hydrophobic spanning regions including signal-peptide-like sequences. These data suggest that the majority of VirB proteins may associate with bacterial cell membranes, while the two additional proteins possess a potential ATP-binding site. Strong homologies in amino acid sequences were observed between nopaline- and octopine-type plasmids. Specific differences in amino acid sequence encoded by VirB ORFs of nopaline and octopine Ti plasmid and a functional role of the gene products are discussed.
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Affiliation(s)
- K Shirasu
- Department of Plant Pathology, University of California, Davis 95616
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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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Aoyama T, Takanami M, Oka A. Signal structure for transcriptional activation in the upstream regions of virulence genes on the hairy-root-inducing plasmid A4. Nucleic Acids Res 1989; 17:8711-25. [PMID: 2479910 PMCID: PMC335038 DOI: 10.1093/nar/17.21.8711] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The inducibility of the vir genes (virA, -B, -C, -D, -E, and -G) on pRiA4 was examined at the transcriptional level, and the RNA-starting sites were determined by S1-nuclease mapping and primer-extension experiments. All of these genes were inducible, while virA, -E, and -G were transcribed even under noninducing conditions. Each transcription of virB, -C, -D, and -E was initiated at one particular site, but that of virA and -G occurred at two and three sites, respectively, depending on the conditions used. In the DNA region upstream from each inducible transcript, one or more blocks of six base-pairs, 5'TGATAACT3' (vir box), were found to be placed characteristically. These blocks were phasing with an interval of 11 base-pairs, and the most upstream one in each upstream region was preceded by an additional block in the inverted orientation. Although the distance between the block(s) and the promoter varied with the vir gene, every block was placed in a phase nearly opposite to the -35 and -10 regions of the promoter.
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Affiliation(s)
- T Aoyama
- Laboratory of Molecular Biology, Kyoto University, Japan
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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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