- Photosystem I (PSI) is a large pigment–protein complex mediating light-driven charge separation and generating a highly negative redox potential, which is eventually utilized to produce organic matter. In plants and algae, PSI possesses outer antennae, termed light-harvesting complex I (LHCI), which increase the energy flux to the reaction center. The number of outer antennae for PSI in the green alga Chlamydomonas reinhardtii is known to be larger than that of land plants. However, their exact number and location remain to be elucidated.
- In green algae, light-harvesting complex stress-related 3 (LHCSR3) is responsible for the pH-dependent dissipation of absorbed light energy, a function vital for survival under high-light conditions. LHCSR3 binds the photosystem II and light-harvesting complex II (PSII–LHCII) supercomplex and transforms it into an energy-dissipative form under acidic conditions, but the molecular mechanism remains unclear. Here we show that in the green alga Chlamydomonas reinhardtii, LHCSR3 modulates the excitation energy flow and dissipates the excitation energy within the light-harvesting complexes of the PSII supercomplex.