CYTOKININ SIGNAL TRANSDUCTION AND TWO-COMPONENT REGULATORY SYSTEM

摘要

This review has presented a framework for the Arabidopsis two-component regulatory systems that are involved in the intracellular transduction of signals from cytokinin, ethylene, and light. With regard to cytokinin signal transduction, cytokinin recognition by CRE1, AHK2, and AHK3 is followed by a phosphorelay signal transfer that involves AHPs and B-type ARRs (Fig. 3). The organization of this system, the structural characteristics of the component proteins, and their molecular activities resemblethose of bacterial systems, suggesting that the His-Asp phosphorelay signal transduction system is a powerful device in plat cells for a variety of environmental stress responses. Meanwhile, characteristics that are not seen in prokaryotes have been elucidated for plants. Three sensor kinases, five AHPs, and multiple B-type ARRs (probably almost all of the B-type ARRs) are involved in cytokinin signal transduction and transactivate multiple A-type ARR genes. In prokaryotes, a histidine kinase generallypartners with a cognate response regulator in a specific one-to-one manner, and phosphorelay swapping among multiple molecular species is rare. Furthermore, there is no equivalent of ETR1 in prokaryotes, for which a partner response regulator is absent.Although the elements of the two-component regulatory systems of plants do not differ markedly from those of bacteria, the plant systems collectively employ complex cross-talk networks to govern different adaptive responses.