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-recalcit rant maize plants has been shown to be determined mainly by the virA l ocus, implicating vir gene induction as the major factor influencing m aize infection, In this report, we further explore the roles of vir in duction-associated bacterial factors in maize infection using the tech nique 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 ma ize agroinfection, The linker domain of VirA(C58) from an agroinfectio n-competent strain, C58, is sufficient to convert VirA(A6) of a nonagr oinfecting strain, A348, to agroinfection competence, The periplasmic domain of VirA(C58) is also able to confer a moderate level of agroinf ection competence to VirA(A6). In addition, the VirA(A6), protein from A348 is agroinfection competent when removed from its cognate Ti plas mid background and placed in a pTiC58 background. The presence of a pT iA6-encoded, VirA(A6)-specific inhibitor is hypothesized and examined.