H2O2-Perzeption und Signaltransduktion: Funktionelle und strukturelle Charakterisierung der Arabidopsis Histidinkinase 5 (AHK5)

Abstract

Hydrogen peroxide (H2O2) is not only a toxic substance which leads to oxidative damage, but also serves as signal molecule in several developmental processes. The Arabidopsis Histidine Kinase 5 (AHK5) functions in H2O2-dependent stomatal closure (Desikan et al. 2008) and plays a role in ethlyene and absicic acid (ABA) dependent root growth (Iwama et al. 2007). Since ethylene and ABA are also leading to cellular H2O2 production, AHK5 is expected to be involved H2O2 dependent processes somehow. To elucidate the involvement of AHK5 in H2O2-dependent processes we performed physiological, biochemical and cell biological experiments. Since senescence is an H2O2 dependent process, we studied ahk5-plants during leaf senescence and could show that AHK5 positively regulates leaf senescence in Arabidopsis thaliana. Interestingly, by determination of in planta H2O2 contents during senescence and several applied stresses, we further could demonstrate that ahk5 is not a H2O2 production mutant but could be a H2O2 sensing mutant. Additionally, to analyze the molecular function and structure of AHK5 we performed in vitro experiments using recombinant produced proteins. Furthermore, by doing in vivo experiments we proved whether AHK5 acts as a H2O2 / redox dependent sensor histidine kinase. Due to this results we could show, that AHK5 signaling occurs via multi-step phosphorelay (MSP) and H2O2 increases AHK5 activity. Finally we present our working model how H2O2 perception and signal transduction through AHK5 occurs.