Activity and specificity of the COP1/SPA ubiquitin ligase in Arabidopsis light signaling and photomorphogenesis

• Applicant: Professorin Dr. Ute Höcker
• Subject Area: Plant Physiology ; Plant Cell and Developmental Biology
• Term: since 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 277860145

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. Here, we will mechanistically define the regulation of the COP1/SPA activity by photoreceptors, in particular by cryptochromes and blue light. Moreover, we will investigate the molecular mechanisms defining functional specificity among the different SPA proteins, including the identification of COP1/SPA interaction partners using proximity labeling.

• DFG Programme: Research Grants