Light signaling in the basal land plants Physcomitrella patens and Marchantia polymorpha

• Applicant: Professorin Dr. Ute Höcker
• Subject Area: Plant Cell and Developmental Biology
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 310298882

In the seed plant Arabidopsis, the E3 ubiquitin ligase COP1/SPA is a key negative regulator required to suppress light signaling in darkness. It controls growth and development throughout the plant life cycle, including seedling etiolation, shade avoidance and photoperiodic flowering. The COP1/SPA complex consists of COP1 and SPA proteins which cooperate to ubiquitinate positive regulators of light signaling - mainly transcription factors - in darkness. Light exposure inactivates the COP1/SPA complex, thereby allowing these transcription factors to accumulate and light signaling to proceed. While COP1/SPA function is well characterized in Arabidopsis, nothing is known about the evolution of these essential intermediates of light signaling. COP1 also exists in animals, suggesting an ancient origin. SPA genes, in contrast, are specific to the green lineage, indicating that COP1/SPA cooperative function has evolved in the green lineage, possibly to place the activity of COP1 under the control of light. Orthologs of COP1 and SPA genes are present in the bryophytes Physcomitrella patens and Marchantia polymorpha, both model systems for early land plants. Our genetic analyzes demonstrate that SPA gene functions in Physcomitrella are distinct from those of their well-characterized Arabidopsis counterparts. Also, light signaling in Physcomitrella appears to be less interconnected with endogenous developmental programs (e.g. meristem activity) than in seed plants. Thus, a comparative analysis of light signaling in two bryophytes (Physcomitrella and Marchantia) and seed plants will greatly advance our knowledge on the evolution of adaptive responses to the light environment in land plants. We will analyze the functions of Physcomitrella and Marchantia COP1- and SPA-like genes through a combination of genetic and biochemical approaches. We will focus on the following main questions: 1) To what extent do COP1- and SPA-like proteins from these bryophytes cooperate, i.e. require each other for activity? 2) To what extent are COP1- and SPA-like proteins interconnected with signaling in darkness and in the light? 3) What are the functions of transcription factors interacting with bryophyte COP1 and/or SPA, i.e. to what extent are output responses conserved between bryophytes and seed plants.

• DFG Programme: Research Grants