CKI1, a histidine kinase homolog implicated in cytokinin signal transduction

Although cytokinin plays a central role in plant development, little is known about cytokinin signal transduction. Five Arabidopsis thaliana mutants that exhibit typical cytokinin responses, including rapid cell division and shoot formation in tissue culture in the absence of exogenous cytokinin, were isolated by activation transferred DNA tagging. A gene, CKI1, which was tagged in four of the five mutants and induced typical cytokinin responses after introduction and overexpression in plants, was cloned. CKI1 encodes a protein similar to the two-component regulators. These results suggest that CKI1 is involved in cytokinin signal transduction, possibly as a cytokinin receptor.