Role of PCH1 and PCHL in regulation of phytochrome action and photobody formation

• Applicant: Professor Dr. Andreas Hiltbrunner
• Subject Area: Plant Physiology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 562237420

Plants as sessile, photo-autotrophic organisms rely on the ability to sense light in order to optimise their photosynthetic performance and adapt to changes in the environment. To utilise light as source of information, they are equipped with various photoreceptors, including the red/far-red light sensing phytochromes. Seed plants contain several types of phytochromes, including phyA and phyB. PhyB is primarily active in light conditions with a high red light content, such as sunlight, while phyA is most active in light conditions enriched in far-red light, as for instance in deep canopy shade. Light-activated phytochromes translocate into the nucleus where they assemble into membrane-less structures called photobodies. Photobodies form by liquid-liquid phase separation and have been associated with phytochrome action. Phytochrome mutants with altered photobody formation typically show altered physiological activity. In a previous project, we identified PCH1 and PCHL as phytochrome-binding proteins that colocalise with phyB in photobodies and promote phyB photobody formation and physiological activity. PCH1 and PCHL contain intrinsically disordered domains, which are known to drive liquid-liquid phase separation, and preliminary data show that PCH1 forms condensates in vitro. In the proposed project, we want to investigate if and how PCH1 and PCHL control the photobody formation of phyB. Preliminary data show that PCH1 and in particular PCHL also affect the physiological activity of phyA, but the role of PCH1 and PCHL in phyA-dependent light signalling has not been investigated so far. Thus, understanding how PCH1 and PCHL control phyA activity and photobody formation is another aim of the proposed project.

• DFG Programme: Research Grants