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

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 VirA_C58 from an agroinfection-competent strain, C58, is sufficient to convert VirA_A6 of a nonagroinfecting strain, A348, to agroinfection competence. The periplasmic domain of VirA_C58 is also able to confer a moderate level of agroinfection competence to VirA_A6. In addition, the VirA_A6 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, VirA_A6^-specific inhibitor is hypothesized and examined.