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Discrete Regions of the Sensor Protein VirA Determine the Strain-Specific Ability of Agrobacterium to Agroinfect Maize

March 1997 , Volume 10 , Number  2
Pages  221 - 227

J. D. Heath , 1 M. I. Boulton , 2 D. M. Raineri , 1 S. L. Doty , 1 A. R. Mushegian , 1 T. C. Charles , 1 J. W. Davies , 2 and E. W. Nester 1

1University of Washington, Department of Microbiology, Box 357242, Seattle 98195-7242 U.S.A.; 2John Innes Centre, Colney Lane, Norwich NR4 7UH, U.K.

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Accepted 6 December 1996.

The ability of Agrobacterium strains to infect transformation-recalcitrant maize plants has been shown to be determined mainly by the virA locus, implicating vir gene induction as the major factor influencing maize infection. In this report, we further explore the roles of vir induction-associated bacterial factors in maize infection using the technique of agroinfection. The Ti plasmid and virA source are shown to be important in determining the ability of a strain to infect maize, and the monosaccharide binding protein ChvE is absolutely required for maize agroinfection. The linker domain of VirAC58 from an agroinfection-competent strain, C58, is sufficient to convert VirAA6 of a nonagroinfecting strain, A348, to agroinfection competence. The periplasmic domain of VirAC58 is also able to confer a moderate level of agroinfection competence to VirAA6. In addition, the VirAA6 protein from A348 is agroinfection competent when removed from its cognate Ti plasmid background and placed in a pTiC58 background. The presence of a pTiA6-encoded, VirAA6-specific inhibitor is hypothesized and examined.

Additional keywords: host range, plant transformation, two-component system.

© 1997 The American Phytopathological Society