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Molecular characterization of the virulence gene virA of the Agrobacterium tumefaciens octopine Ti plasmid |
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| Authors: | Leo S. Melchers Dave V. Thompson Ken B. Idler Saskia T. C. Neuteboom Ruud A. de Maagd Rob A. Schilperoort Paul J. J. Hooykaas |
| Affiliation: | (1) Biochemistry Laboratory, Department of Plant Molecular Biology, Leiden University, Wassenaarseweg 64, 2333 AL Leiden, Netherlands;(2) Advanced Research Division, Agrigenetics Corporation, 5649 East Buckeye Road, 53716 Madison, WI, USA;(3) Abbott Laboratories, Abbott Park, 60064, IL, USA;(4) Botanical Laboratory, Department of Plant Molecular Biology, Leiden University, Nonnensteeg 3, 2311 VJ Leiden, Netherlands |
| Abstract: | The virulence loci play an essential role in tumor formation by Agrobacterium tumefaciens. Induction of vir gene expression by plant signal molecules is solely dependent on the virulence loci virA and virG. This study focused on the virA locus of the octopine type Ti plasmid pTi15955. The nucleic acid sequence of a 5.7-kilobase fragment encompassing virA was determined. Genetic analysis of this region revealed that virA contains one open reading frame coding for a protein of 91 639 daltons. Immunodetection with antibodies raised against a 35-kDa VirA fusion protein produced in E. coli identified by the VirA product in wild-type Agrobacterium cells. Moreover, it is shown that the VirA protein is located in the cytoplasmic membrane fraction of Agrobacterium. These data confirm the proposed regulatory function of VirA whereby VirA acts as a membrane sensor protein to identify plant signal molecules in the environment. The proposed sensory function of VirA strikingly resembles the function of the chemotaxis receptor proteins of E. coli. |
| Keywords: | Agrobacterium virA sequence gene regulation membrane protein fusion proteins |
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