Identifizierung und Charakterisierung von Phytochrom A-abhängigen HIR-Reaktionsmodulen

• Antragsteller: Professor Dr. Andreas Hiltbrunner; Professor Dr. Eberhard Schäfer
• Fachliche Zuordnung: Pflanzenphysiologie
• Förderung: Förderung von 2013 bis 2017
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 233625604

Phytochromes are red/far-red light receptors important for plant growth and development. In Arabidopsis there are five phytochromes with phyA and phyB playing a dominant role. phyA is essential for seedling establishment in canopy shade, where the spectral composition of the light environment is dominated by far-red light. Even though the photophysical properties of phyA and phyB are virtually identical, responses mediated by phyA have an action peak in far-red light, whereas phyB dependent responses are triggered by red light. One essential step in phytochrome signalling is the light induced nuclear transport of phytochromes. phyA depends on the two functional homologs FHY1 and FHL for nuclear accumulation. FHY1/FHL bind to the light-activated form of phyA in the cytosol and transport it into the nucleus. We recently proposed a kinetic model to explain phyA dependent far-red light perception at the molecular level and we defined a minimal module essential for shifting the phyA action peak from red to far-red light. The degradation of phyA and its interaction with the nuclear transport facilitators FHY1 and FHL are key elements of this shifting module. In the proposed project we want to investigate this shifting module in more detail and analyse the contribution of FHY1/FHL-phyA complex association/dissociation and phyA degradation to the far-red light shift of the phyA action peak. To this end, we want to identify the FHY1/FHL binding site in phyA and generate phyA mutants with decreased or increased binding to FHY1/FHL. In addition, we want to generate transgenic lines expressing phyA versions with increased stability to test the effect of altered degradation on the phyA action spectrum. Importantly, mathematical analyses and experimental data predict the existence of additional shifting modules that contribute to the red to far-red light shift of the phyA action peak. In the project subject to this proposal we want to identify and characterise these shifting modules. We will search for the missing shifting modules by analysing key properties of phyA, including the formation of sequestered areas of phytochrome (SAPs), the kinetics of nuclear transport, as well as dark reversion and degradation of Pfr and Pr in the nucleus and the cytosol. These analyses will enable us to determine the kinetic parameters that are essential for phyA to work as a sensor for far-red light. In addition, we also want to test the function of reaction parameters by action spectroscopy and measure detailed action spectra for different mutants and transgenic lines.

• DFG-Verfahren: Sachbeihilfen