Functions as two-component phosphorelay mediators between cytokinin sensor histidine kinases and response regulators (B-type ARRs). Plays an important role in propagating cytokinin signal transduction. Dwarf, narrow leaf, sterility and small grain phenotypes. Lacks the conserved active histidine at position 79 that mediates the phosphotransfer. Shows a conserved HPt domain that may have some alternative degenerated phosphorelay role in cell signaling.