Regulation of the COP1/SPA ubiquitin ligase in Arabidopsis light signaling

• Applicant: Professorin Dr. Ute Höcker
• Subject Area: Plant Physiology ; Plant Cell and Developmental Biology
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 578768309

Plants constantly monitor the ambient light environment in order to adapt growth, development and metabolism to the changing light conditions and seasons - with the aim of optimizing photosynthesis, reproduction and ultimately survival and fitness. Downstream of the light-sensing photoreceptors (phytochromes and cryptochromes), the CONSTITUTIVELY PHOTOMORPHOGENIC1/SUPPRESSOR OF PHYTOCHROME A-105 (COP1/SPA) E3 ubiquitin ligase acts to suppress light signaling in darkness. It polyubiquitinates positive regulators of light signaling, mainly transcription factors, and thereby targets those for degradation in the 26S proteasome. In the light, the phytochrome and cryptochrome photoreceptors bind to the COP1/SPA complex and inhibit its activity via multiple mechanisms. COP1 also exists in humans where it acts as an important, but light-independent, E3 ligase. SPA proteins, in contrast, are specific to the green lineage. Hence, SPA proteins may have evolved to place the activity of COP1 under the control of light, an essential environmental factor primarily for plants. We previously identified the transcription factor TCP3 as a non-canonical target of COP1/SPA that lacks a classical COP1-interacting motif, the VP motif. We therefore aim to identify the COP1/SPA-interacting motif in TCP3 followed by co-crystallization with COP1-WD. We will also investigate whether VP-carrying photoreceptors are capable of displacing TCP3 from binding to COP1/SPA in the light. We perform proximity labeling to identify novel interactors/the composition of the higher-order COP1/SPA complex in different tissues. To obtain structure-function information on the higher-order COP1/SPA complex we will conduct a combination of structural, protein-protein interaction and activity assays.

• DFG Programme: Research Grants