Abstract
A phytohormone, abscisic acid (ABA) induces stomatal closure to reduce transpirational water loss via elaborate signal transduction in guard cells. Histidine kinases are known to function in the histidine-to-aspartate phosphorelay signal system. In plants, perception of phytohormones, ethylene and cytokinin, is composed of the signal system. In this study, we reported that gene disruption of an Arabidopsis histidine kinase, AHK5 causes ABA hypersensitivity of guard cells. In the ahk5-1 mutant, ABA-induced stomatal closure was enhanced. Furthermore, inhibitory effect of ABA on inward rectifying potassium channel currents of guard cell plasma membrane was stronger in the ahk5-1 mutant than in wild type. These results suggest that AHK5 functions as a negative regulator of ABA signaling in Arabidopsis guard cells.
