Photosynthesis is the most fundamental process for life on Earth. Sunlight is highly variable and fluctuates both in intensity and duration, which induces short and longterm responses in photosynthetic organisms. Photosynthetic organisms have evolved several processes to cope with environmental stresses, including light fluctuations. Many thylakoid properties and functions are regulated by diverse protein phosphorylations, ranging from thylakoid ultrastructural changes and the optimization of excitation energy between the two photosystems via Lightharvesting complexes (LHCs) to signaling mechanisms for long-term regulation, maintaining proteostasis, and thereby ultimately regulating photosynthesis via photoprotection mechanisms.

My PhD research is divided into three major projects. The first one gives evolutionary insights into the two main thylakoid kinases, STN7 and STN8 in Physcomitrium patens (previously Physcomitrella patens), and their target proteins. Physcomitrium patens differs from angiosperms in their photoprotection strategy via LHCII phosphorylations (LHCB6 and LHCBM) and in formation of a Photosystem (PS)I-supercomplex, PSI-large, depending on LHCBM phosphorylation.

The second project focuses on angiosperm model species Arabidopsis thaliana and deals with protein phosphorylation-related changes in thylakoid architecture. The study reveals that the phosphorylation dynamics of LHCII and CURT1B respond co-operatively to fluctuating light intensities. The findings also suggest that CURT1B phosphorylation contributes to the fine-tuning of thylakoid membrane structure and function in response to light conditions.

The third project delves into the potential association between calcium signaling and induction of photoprotective mechanisms, by providing a novel screening tool to identify calcium-dependent chloroplast proteins. Calcium-transient dependent phosphorylation of essential proteins involved in the repair of PSII, including THF1, HCF136, and FTSH protease were disclosed. Additionally, the study proposes a potential link of calcium in PSI-Fd-FNR interaction. Moreover, this study not only identifies the new phosphorylation targets but also presents opportunities for exploring the intricate interplay between calcium signaling and protein phosphorylation processes. Taken together, my PhD research helps in understanding the regulation of photosynthesis, provides new tools for photosynthesis research and will thereby contribute to engineering photosynthetically resilient organisms to cope with changing environmental conditions for improving the production of food, feed and renewable energy.