Agrobacterium-Mediated Horizontal Gene Transfer

Kado, Clarence I.

doi:10.1007/978-1-4899-1739-3_1

Cited by 22 publications

(12 citation statements)

References 167 publications

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“…tumefaciens causes crown gall tumors in a wide variety of dicotyledonous plants by transferring the oncogenic DNA fragments (T-DNA) from the tumor-inducing (Ti) plasmid to individual plant cells (252,555). Genes located on T-DNA are expressed inside the infected plant cells, and some of them direct the overproduction of plant growth hormones (37, 91).…”

Section: Host Detection During Agrobacterium-plant Interactionsmentioning

confidence: 99%

Detection of and Response to Signals Involved in Host-Microbe Interactions by Plant-Associated Bacteria

Brencic

Winans

2005

Microbiol Mol Biol Rev

337

208

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Diverse interactions between hosts and microbes are initiated by the detection of host-released chemical signals. Detection of these signals leads to altered patterns of gene expression that culminate in specific and adaptive changes in bacterial physiology that are required for these associations. This concept was first demonstrated for the members of the family Rhizobiaceae and was later found to apply to many other plant-associated bacteria as well as to microbes that colonize human and animal hosts. The family Rhizobiaceae includes various genera of rhizobia as well as species of Agrobacterium. Rhizobia are symbionts of legumes, which fix nitrogen within root nodules, while Agrobacterium tumefaciens is a pathogen that causes crown gall tumors on a wide variety of plants. The plant-released signals that are recognized by these bacteria are low-molecular-weight, diffusible molecules and are detected by the bacteria through specific receptor proteins. Similar phenomena are observed with other plant pathogens, including Pseudomonas syringae, Ralstonia solanacearum, and Erwinia spp., although here the signals and signal receptors are not as well defined. In some cases, nutritional conditions such as iron limitation or the lack of nitrogen sources seem to provide a significant cue. While much has been learned about the process of host detection over the past 20 years, our knowledge is far from being complete. The complex nature of the plant-microbe interactions makes it extremely challenging to gain a comprehensive picture of host detection in natural environments, and thus many signals and signal recognition systems remain to be described

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Section: Host Detection During Agrobacterium-plant Interactionsmentioning

confidence: 99%

Detection of and Response to Signals Involved in Host-Microbe Interactions by Plant-Associated Bacteria

Brencic

Winans

2005

Microbiol Mol Biol Rev

337

208

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“…The DNA transfer system employed by this rhizoplane inhabitant is encoded by vir genes located on a resident Ti plasmid. The DNA transfer system is highly promiscuous, as evidenced by its transfer activity of the T-DNA into plants, fungi (8,9,14), and actinomycetes (23).…”

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confidence: 99%

Genetic and Environmental Factors Affecting T-Pilin Export and T-Pilus Biogenesis in Relation to Flagellation of Agrobacterium tumefaciens

et al. 2000

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The T pilus, primarily composed of cyclic T-pilin subunits, is essential for the transmission of the Ti-plasmid T-DNA from Agrobacterium tumefaciens to plant cells. Although the virB2 gene of the 11-gene virB operon was previously demonstrated to encode the full-length propilin, and other genes of this operon have been implicated as members of a conserved transmembrane transport apparatus, the role of each virB gene in T-pilin synthesis and transport and T-pilus biogenesis remained undefined. In the present study, each virB gene was examined and was found to be unessential for T-pilin biosynthesis, except virB2, but was determined to be essential for the export of the T-pilin subunits and for T-pilus formation. We also find that the genes of the virD operon are neither involved in T-pilin export nor T-pilus formation. Critical analysis of three different virD4 mutants also showed that they are not involved in T-pilus biogenesis irrespective of the A. tumefaciens strains used. With respect to the environmental effects on T-pilus biogenesis, we find that T pili are produced both on agar and in liquid culture and are produced at one end of the A. tumefaciens rod-shaped cell in a polar manner. We also report a novel phenomenon whereby flagellum production is shut down under conditions which turn on T-pilus formation. These conditions are the usual induction with acetosyringone at pH 5.5 of Ti-plasmid vir genes. A search of the vir genes involved in controlling this biphasic reaction in induced A. tumefaciens cells revealed that virA on the Ti plasmid is involved and that neither virB nor virD genes are needed for this reaction. The biphasic reaction therefore appears to be mediated through a two-component signal transducing system likely involving an unidentified vir gene in A. tumefaciens.Agrobacterium tumefaciens is uniquely adapted for the horizontal transmission of DNA. The DNA transfer system employed by this rhizoplane inhabitant is encoded by vir genes located on a resident Ti plasmid. The DNA transfer system is highly promiscuous, as evidenced by its transfer activity of the T-DNA into plants, fungi (8, 9, 14), and actinomycetes (23).The products of the vir genes have been extensively studied in order to gain insights into the DNA transfer mechanism. Comparative studies of the nucleotide sequences of the vir genes with those of broad-host-range plasmids have revealed significant homologies between genes involved in DNA processing as well as plasmid transfer via bacterial conjugation, suggesting that the mechanism for T-DNA transfer could be a conjugation process (24,29,30,35,41,43,48). Using the F plasmid as a classic example, bacterial conjugation requires a conjugative pilus, whose propilin subunit is encoded by traA (17). The TraA propilin is processed from a 12.7-kDa propilin into a 7.2-kDa pilin with an acetylated N terminus (17). VirB2, encoded by the virB operon of the Ti plasmid, is a homolog of TraA and is processed like TraA by generating a 7.2-kDa protein from a 12.3-kDa full-length holoprotein (2...

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“…Recently, the ipt gene on the T-DNA of the Ti plasmid was also found to be negatively regulated despite the fact that the gene is regulated by eukaryotic transcriptional machinery in the host plant [1]. The negatively-regulated virulence genes are contained in the virC and virD operons, whose products process the T-DNA at its left and right borders for transfer from the bacterial cell to the plant host cell (reviewed recently in [2,3]). For nopaline-type Ti plasmids such as pTiC58, the T-DNA is a speci¢c 25-kb sector of the Ti plasmid and contains the plant oncogenes ipt, iaaM and iaaH, whose promoters are regulated by the plant transcription system recognizing their TATA boxes [4,5] to synthesize isopentenyl transferase, tryptophan monooxygenase and indoleacetamide amidohydrolase, respectively.…”

Section: Introductionmentioning

confidence: 99%

A single amino acid substitution beyond the C2H2-zinc finger in Ros derepresses virulence and T-DNA genes in Agrobacterium tumefaciens

Archdeacon

2000

FEMS Microbiology Letters

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Ros is a chromosomally-encoded repressor containing a novel C2H2 zinc finger in Agrobacterium tumefaciens. Ros regulates the expression of six virulence genes and an oncogene on the Ti plasmid. Constitutive expression of these genes occurs in the spontaneous mutant 4011R derived from the octopine strain Ach-5, resulting in T-DNA processing in the absence of induction, and in the biosynthesis of cytokinin. Interestingly, the mutation in 4011R is an Arg to Cys conversion at amino acid residue 125 near the C-terminus well outside the zinc finger of Ros. Yet, Ros bearing this mutation is unable to bind to the Ros-box and is unable to complement other ros mutants. ß

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Agrobacterium-Mediated Horizontal Gene Transfer

Cited by 22 publications

References 167 publications

Detection of and Response to Signals Involved in Host-Microbe Interactions by Plant-Associated Bacteria

Detection of and Response to Signals Involved in Host-Microbe Interactions by Plant-Associated Bacteria

Genetic and Environmental Factors Affecting T-Pilin Export and T-Pilus Biogenesis in Relation to Flagellation of Agrobacterium tumefaciens

A single amino acid substitution beyond the C2H2-zinc finger in Ros derepresses virulence and T-DNA genes in Agrobacterium tumefaciens

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