Fig. 1.

Model for signal perception in Agrobacterium. Three factors, low pH, sugar and phenolic compound (Acetosyringone:AS) are sensed by ChvG/ChvI, ChvE and VirA/VirG regulatory systems, respectively. Under neutral pH, ExoR remain bounded to ChvG and make them inactive which get activated under low pH by proteolytic cleavage and dissociation of ExoR. This allow the ChvG for autophosphorylation and transfer phosphate group to ChvI response regulator which then activate VirG. Sugar and low pH induces the ChvE for binding and activation of VirA. Simultaneously, AS perceived by cytoplasmic domain of VirA which allow the autophosphorylation of VirA. VirA phosphorylates VirG and induce it for activation of Vir operon for activation of other virulence proteins