Compilation and characterization of Arabidopsis thaliana response regulators implicated in His-Asp phosphorelay signal transduction

His-Asp phosphorelays are evolutionary-conserved powerful biological tactic s for intracellular signal transduction. Such a phosphorelay is generally m ade up of "sensor histidine (His)-kinases", "response regulators", and "his tidine-containing (HPt) phosphotransmitters''. In the higher plant, Arabido psis thaliana, results from recent intensive studies suggested that His-Asp phosphorelays may be widely used for propagating environmental stimuli, su ch as phytohormones (e.g., ethylene and cytokinin). In this study, we first inspected extensively the occurrence of Arabidopsis response regulators in order to compile and characterize them. The results showed that this highe r plant has, at least, 14 members of the family of response regulators that can be classified into two distinct subtypes (type-A and type-B), as judge d from their structural designs, biochemical properties, and expression pro files. Comparative studies were conducted for each representative (ARR3 and ARR4 for type-A, and ARR10 for type-B). It was suggested that expression o f the type-A response regulator is cytokinin-inducible, while that of the t ype-B response regulator appears to be not. Results from yeast two-hybrid a nalyses suggested that the type-B response regulator may have an ability to stably interact with a set of HPt phosphotransmitters (AHPs). These and ot her results will be discussed with special reference to the His-Asp phospho relay signaling network in Arabidopsis thaliana.