The photosystem I supercomplex from a primordial green alga Ostreococcus tauri harbors three light-harvesting complex trimers

• Published in: eLife Vol. 12
• Main Authors: Ishii, Asako, Shan, Jianyu, Sheng, Xin, Kim, Eunchul, Watanabe, Akimasa, Yokono, Makio, Noda, Chiyo, Song, Chihong, Murata, Kazuyoshi, Liu, Zhenfeng, Minagawa, Jun
• Format: Journal Article
• Language: English
• Published: England eLife Sciences Publications, Ltd 23-03-2023; eLife Sciences Publications Ltd
• Subjects: Chlorophyll; Chlorophyta - metabolism; Computational and Systems Biology; light-harvesting complex; Light-Harvesting Protein Complexes - chemistry; Light-Harvesting Protein Complexes - metabolism; Ostreococcus tauri; phosphorylation; Photosynthesis; photosystem I; Photosystem I Protein Complex - chemistry; Plant Biology; prasinophyte; state transitions; computational biology; light-harvesting complex; systems biology; prasinophyte; Ostreococcus tauri; photosystem I; plant biology; phosphorylation; state transitions
• ISSN: 2050-084X; 2050-084X
• DOI: 10.7554/elife.84488

As a ubiquitous picophytoplankton in the ocean and an early-branching green alga,
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
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
PSI-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
603-
609 pair in
Lhca1-4.