The pH-Sensing in Photo synthetic Protection: The Role of Light-Harvesting Complexes and PsbS
Plants must acclimate to dynamic light environments to mainta in photosynthetic efficiency. Under high-light conditions, the rapid induction of NPQ is essential for the dissipation of excess excitatio n energy. Understanding the molecular mechanism of NPQ is a prerequis ite for engineering crops with optimised photoprotective responses. A lthough the PsbS protein has been identified as a key pH-sensor for N PQ, its precise mechanism of action remains debated despite more than two decades of research. This thesis investigates the molecular inte ractions of NPQ components to clarify some of the unresolved aspects of the NPQ mechanism. In Chapter 2, we examine the differences in NPQ mechanisms between Chlamydomonas and Arabidopsis. We show that LHCII trimers do not switch into a quenched state after protonation, eithe r in detergent or in a more native lipid environment within liposomes . Furthermore, we demonstrate that protonation of the possible pH-sen sing amino acids in Lhcb1 is not required to restore NPQ in vivo, sug gesting that LHCII is not able to sense low pH by itself. In Chapter 3, we extend our analysis beyond LHCII trimers to include monomeric L hcb proteins. We investigate pH-induced quenching changes in these co mplexes and evaluate how the surrounding lipid environment influences their quenching behaviour. In Chapter 4, we explore potential intera ction partners of PsbS. Using a chemical crosslinker, we compare thyl akoid protein interactions under dark and NPQ conditions to identify possible interaction changes associated with NPQ activation. In Chapt er 5, we assess whether a covalently linked PsbS dimer is still capab le of contributing to NPQ. We demonstrate that PsbS dimers are capabl e of inducing NPQ, however, with reduced efficiency compared to WT. T his stoichiometric reduction suggests that only one monomeric unit wi thin the dimer is actively engaging in quenching interactions.
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DESCRIPTION: Plants must acclimate to dynamic light environments to ma intain photosynthetic efficiency. Under high-light conditions, the ra pid induction of NPQ is essential for the dissipation of excess excit ation energy. Understanding the molecular mechanism of NPQ is a prere quisite for engineering crops with optimised photoprotective response s. Although the PsbS protein has been identified as a key pH-sensor f or NPQ, its precise mechanism of action remains debated despite more than two decades of research. This thesis investigates the molecular interactions of NPQ components to clarify some of the unresolved aspe cts of the NPQ mechanism. In Chapter 2, we examine the differences in NPQ mechanisms between Chlamydomonas and Arabidopsis. We show that L HCII trimers do not switch into a quenched state after protonation, e ither in detergent or in a more native lipid environment within lipos omes. Furthermore, we demonstrate that protonation of the possible pH -sensing amino acids in Lhcb1 is not required to restore NPQ in vivo, suggesting that LHCII is not able to sense low pH by itself. In Chap ter 3, we extend our analysis beyond LHCII trimers to include monomer ic Lhcb proteins. We investigate pH-induced quenching changes in thes e complexes and evaluate how the surrounding lipid environment influe nces their quenching behaviour. In Chapter 4, we explore potential in teraction partners of PsbS. Using a chemical crosslinker, we compare thylakoid protein interactions under dark and NPQ conditions to ident ify possible interaction changes associated with NPQ activation. In C hapter 5, we assess whether a covalently linked PsbS dimer is still c apable of contributing to NPQ. We demonstrate that PsbS dimers are ca pable of inducing NPQ, however, with reduced efficiency compared to W T. This stoichiometric reduction suggests that only one monomeric uni t within the dimer is actively engaging in quenching interactions. Mo re information on the thesis The pH-Sensing in Photosynthetic Protection: The Role of Light-Harvesting Complexes and PsbS END:VEVENT END:VCALENDAR