Isolated polynucleotides that encode cytokinin-sensing histidine kinase polypeptides, and the encoded polypeptides, are described. Expression cassettes comprising the polynucleotides of the invention and plants and plant cells that are transformed with the polynucleotides are described. Methods of using the cytokinin-sensing histidine kinase polypeptides and polynucleotides to modulate histidine kinase activity and/or histidine kinase levels in plants and plant cells are further described.