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By jpeza - Posted on 26 Mayo 2009
We have investigated the factors which contribute to the host specificity of a tumor inducing plasmid of Agrobacterium, pTiAg162, which confers a narrow host range. Determinants both within the T-DNA and virulence regions contribute to host specificity. Within the T-DNA a defective cytokinin biosynthetic gene limits host range. Nucleotide sequence analysis revealed a large deletion in the 5' coding region of this gene when compared with the homologous gene from the wide host range tumor inducing plasmid, pTiA6. Introduction of the wide host range cytokinin biosynthetic gene into the T-DNA of the limited host range strain expanded the host range and suppressed the rooty morphology of tumors incited by the limited host range strain. Two genes from the virulence region of the wide host range plasmid, designated virA and virC, must also be introduced into the limited host range strain in order to restore a wide host range phenotype. The wide host range strain is avirulent on some cnltivars of Vitis plants on which the limited host range strain induces tumors. This avirulence is apparently due to a hypersensitive response in which infected plant cells are killed at the site of inoculation. Mutations within the virC locus of the wide host range plasmid prevented the hypersensitive response and allowed the formation of tumors by the wide host range strain.
Department of Microbiology and Immunology, University of Washington, Seattle, WA 98195
Brenda Lowe 2, Alice Montoya 1,, Robert Rubin 1, William Krul 2, Milton Gordon a, 3, and Eugene Nester
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