Abstract
Arabidopsis has three cytokinin receptors, CRE1/WOL/AHK4, AHK2 and AHK3, which function as histidine kinases. We have previously reported that CRE1 mutants are less responsive to cytokinins than the wild-type. To understand redundant and specific functions of cytokinin receptors, we have examined cytokinin responsiveness of mutants that lack one, two, or three of the receptor-genes. The affected degree of cytokinin-responsiveness depended on both which gene was disrupted and what assay system was used. On the other hand, double mutants are less responsive to cytokinins than corresponding single mutants in most assay systems. These results indicate that three cytokinin-receptors have partially overlapping functions. Surprisingly, the triple mutant was recovered, which was infertile and very small yet carrying basic organs-roots, leaves and inflorescences. These results indicate that cytokinins are not essential for the formation of basic plant body elements, although they are required for normal growth and fertility.
