title: LHCSR1 induces a fast and reversible pH-dependent fluorescence quenching in LHCII in Chlamydomonas reinhardtii cells.
abstract: To avoid photodamage, photosynthetic organisms are able to thermally dissipate the energy absorbed in excess in a process known as nonphotochemical quenching (NPQ). Although NPQ has been studied extensively, the major players and the mechanism of quenching remain debated. This is a result of the difficulty in extracting molecular information from in vivo experiments and the absence of a validation system for in vitro experiments. Here, we have created a minimal cell of the green alga Chlamydomonas reinhardtii that is able to undergo NPQ. We show that LHCII, the main light harvesting complex of algae, cannot switch to a quenched conformation in response to pH changes by itself. Instead, a small amount of the protein LHCSR1 (light-harvesting complex stress related 1) is able to induce a large, fast, and reversible pH-dependent quenching in an LHCII-containing membrane. These results strongly suggest that LHCSR1 acts as pH sensor and that it modulates the excited state lifetimes of a large array of LHCII, also explaining the NPQ observed in the LHCSR3-less mutant. The possible quenching mechanisms are discussed.
authors.affiliation: Biophysics of Photosynthesis, Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam and LaserLab Amsterdam, 1081 HV, Amsterdam, The Netherlands;
authors.forename: Emine
authors.initials: E
authors.lastname: Dinc
authors.affiliation: Biophysics of Photosynthesis, Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam and LaserLab Amsterdam, 1081 HV, Amsterdam, The Netherlands;
authors.forename: Lijin
authors.initials: L
authors.lastname: Tian
authors.affiliation: Biophysics of Photosynthesis, Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam and LaserLab Amsterdam, 1081 HV, Amsterdam, The Netherlands;
authors.forename: Laura M
authors.initials: LM
authors.lastname: Roy
authors.affiliation: Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63130;
authors.forename: Robyn
authors.initials: R
authors.lastname: Roth
authors.affiliation: Department of Biology, Washington University, St. Louis, MO 63130.
authors.forename: Ursula
authors.initials: U
authors.lastname: Goodenough
authors.affiliation: Biophysics of Photosynthesis, Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam and LaserLab Amsterdam, 1081 HV, Amsterdam, The Netherlands; R.Croce@vu.nl.
authors.forename: Roberta
authors.initials: R
authors.lastname: Croce
mesh_terms: D016825:Chlamydomonas reinhardtii / Q000528:radiation effects*; D005453:Fluorescence; D006863:Hydrogen-Ion Concentration; D045342:Light-Harvesting Protein Complexes / Q000528:radiation effects*
chemical_list: D045342:Light-Harvesting Protein Complexes
keywords: green algae; light-harvesting; nonphotochemical quenching; photosynthesis; thylakoid membranes