Ti plasmid containing Rhizobium meliloti are non-tumorigenic on plants,despite proper virulence gene induction and T-strand formation |
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Authors: | R J M van Veen H den Dulk-Ras R A Schilperoort P J J Hooykaas |
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Institution: | (1) Department of Plant Molecular Biology, Biochemical Laboratory, Leiden University, Wassenaarseweg 64, NL-2333 AL Leiden, The Netherlands |
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Abstract: | We examined the expression of the vir genes of the Agrobacterium tumefaciens Ti plasmid in Rhizobium meliloti, which remains non-tumorigenic on plants after introduction of a Ti- or Ri-plasmid. Both the levels of virulence (vir) gene expression, induced by the plant phenolic compound acetosyringone, and of subsequent T-strand formation were comparable to what is observed in Agrobacterium. In contrast to the situation in Agrobacterium, though, vir induction in R. meliloti did not require a low pH (5.3) of the induction medium and the optimum temperature for induction in R. meliloti was significantly lower than in Agrobacterium. At 37°C no induction of the vir genes was found both in Agrobacterium and R. meliloti. We postulate that the lack of tumorigenicity of Ti carrying R. meliloti strains is due either to a lack of proper attachment of the bacteria to plant cells, or to an improper assembly of a virB-determined essential structure in the cell wall of R. meliloti. |
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Keywords: | Agrobacterium tumefaciens Rhizobium meliloti Vir gene expression T-strands Chromosomal virulence genes |
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