Component of a regulatory phosphorelay system that controls B.abortus cell growth, division, and intracellular survival inside mammalian host cells. This signaling pathway is composed of CckA, ChpT, CtrA and CpdR. CpdR is a response regulator substrate of ChpT. Unphosphorylated CpdR controls steady-state levels of CtrA in the B.abortus cell, likely via CtrA destabilization and activation of its proteolysis. Is phosphorylated by ChpT-P on Asp-52. Deletion of cpdR does not result in a gross defect in cell morphology and has no effect on intracellular B.abortus replication and/or survival in human macrophages.