Genes involved in cytokinin signal transduction

Although cytokinin plays a central role in plant develop ment, our knowledge about the signal transduction pathway initiated by this plant hormone is fragmentary, By randomly introducing enhancer elements into the Arabidopsis genome through Agrobacterium-mediated transformation, 5 cytokinin independent mutant calli (cki1-1, -2, -3, -4 and cki2) were obtained. These mutants exhibit typical cytokinin responses, including rapid proliferation, chloroplast differentiation, shoot induction and inhibition of root formation, in the absence of cytokinin, The CKI1 gene encodes a product similar to the sensor histidine kinases of two-component systems, and its overexpression in plants induces typical cytokinin responses (Kakimoto 1996), Here I report that overexpression of this gene did not alter the auxin requirement of Arabidopsis, Another mutant, many shoots, which was also identified on the same screening, produced many adventitious shoots on cotyledons, petioles and true leaves.