TY - JOUR TI - The photosystem I supercomplex from a primordial green alga Ostreococcus tauri harbors three light-harvesting complex trimers AU - Ishii, Asako AU - Shan, Jianyu AU - Sheng, Xin AU - Kim, Eunchul AU - Watanabe, Akimasa AU - Yokono, Makio AU - Noda, Chiyo AU - Song, Chihong AU - Murata, Kazuyoshi AU - Liu, Zhenfeng AU - Minagawa, Jun A2 - Kramer, David M A2 - Kleine-Vehn, Jürgen A2 - Green, Beverley VL - 12 PY - 2023 DA - 2023/03/23 SP - e84488 C1 - eLife 2023;12:e84488 DO - 10.7554/eLife.84488 UR - https://doi.org/10.7554/eLife.84488 AB - As a ubiquitous picophytoplankton in the ocean and an early-branching green alga, Ostreococcus tauri is a model prasinophyte species for studying the functional evolution of the light-harvesting systems in photosynthesis. Here, we report the structure and function of the O. tauri photosystem I (PSI) supercomplex in low light conditions, where it expands its photon-absorbing capacity by assembling with the light-harvesting complexes I (LHCI) and a prasinophyte-specific light-harvesting complex (Lhcp). The architecture of the supercomplex exhibits hybrid features of the plant-type and the green algal-type PSI supercomplexes, consisting of a PSI core, an Lhca1-Lhca4-Lhca2-Lhca3 belt attached on one side and an Lhca5-Lhca6 heterodimer associated on the other side between PsaG and PsaH. Interestingly, nine Lhcp subunits, including one Lhcp1 monomer with a phosphorylated amino-terminal threonine and eight Lhcp2 monomers, oligomerize into three trimers and associate with PSI on the third side between Lhca6 and PsaK. The Lhcp1 phosphorylation and the light-harvesting capacity of PSI were subjected to reversible photoacclimation, suggesting that the formation of OtPSI-LHCI-Lhcp supercomplex is likely due to a phosphorylation-dependent mechanism induced by changes in light intensity. Notably, this supercomplex did not exhibit far-red peaks in the 77 K fluorescence spectra, which is possibly due to the weak coupling of the chlorophyll a603-a609 pair in OtLhca1-4. KW - photosystem I KW - Ostreococcus tauri KW - prasinophyte KW - state transitions KW - light-harvesting complex KW - phosphorylation JF - eLife SN - 2050-084X PB - eLife Sciences Publications, Ltd ER -