Cytokinin receptor related to bacterial two-component regulators. Functions as a histidine kinase and transmits the stress signal to a downstream MAPK cascade. ATP + protein L-histidine = ADP + protein N-phospho-L-histidine. Histidine-containing phosphotransfer domain (HPt) contains an active histidine that mediates the phosphotransfer. Activation probably requires a transfer of a phosphate group between a His in the transmitter domain and an Asp of the receiver domain.