Visual overview of this lab’s work

Plants and algae have versatile abilities to acclimate themselves to changing environments. We are interested in these acclimation processes, and how they efficiently yet safely harness sunlight for photosynthesis under fluctuating light conditions. Using a model green alga, we are studying the molecular mechanisms underlying photoacclimation of photosynthetic machinery. We are also applying knowledge obtained in the studies of this model green alga to various photosynthetic organisms, including phytoplankton and vascular plants, to explore how environmentally important photosynthetic organisms thrive in their ecological niche.

I. Plant and Algal PSII–LHCII Supercomplexes: Structure, Evolution and Energy Transfer.

Photosynthesis is the process conducted by plants and algae to capture photons and store their energy in chemical forms. The light-harvesting, excitation transfer, charge separation and electron transfer in photosystem II (PSII) are the critical initial reactions of photosynthesis and thereby largely determine its overall efficiency. Knowledge about the architectures and assemblies of plant and green algal PSII–light harvesting complex II (LHCII) supercomplexes are rapidly accumulating (Figure 1). We made pair-wise comparative analyses between the supercomplexes from plants and green algae to gain insights about the evolution of the PSII–LHCII supercomplexes involving the peripheral small PSII subunits that might have been acquired during the evolution (Figure 2) nd about the energy transfer pathways that define their light-harvesting and photoprotective properties (Figure 3) (Sheng et al., Plant Cell Physiol., 62:1108-1120).
 

Figure 1. The overall architecture of PSII–LHCII supercomplexes from C. reinhardtii and vascular plants (C₂S₂ from Spinacia oleracea, C₂S₂M₂ from pea). Sheng et al. (2021) Plant Cell Physiol., 62:1108-1120.
 

Figure 2. Superposition of green algal and plant PSII–LHCII supercomplexes and evolutionary insights from pea C₂S₂M₂ and C. reinhardtii C₂S₂M₂L₂ supercomplexes. Sheng et al. (2021) Plant Cell Physiol., 62:1108-1120.
 

Figure 3. Förster resonance energy transfer (FRET) networks of green algal and plant PSII-LHCII supercomplexes and major energy transfer pathways. Sheng et al. (2021) Plant Cell Physiol., 62:1108-1120.

II. Structural basis of LhcbM5-mediated state transitions in green algae.

In green algae and plants, state transitions serve as a short-term light-acclimation process in the regulation of the light-harvesting capacity of photosystems I and II (PSI and PSII, respectively). During the process, a portion of light-harvesting complex II (LHCII) is phosphorylated, dissociated from PSII and binds with PSI to form the supercomplex PSI–LHCI–LHCII. We reported high-resolution structures of PSI–LHCI–LHCII from Chlamydomonas reinhardtii, revealing the mechanism of assembly between the PSI–LHCI complex and two phosphorylated LHCII trimers containing all four types of LhcbM protein (Figure 4). Two specific LhcbM isoforms, namely LhcbM1 and LhcbM5, directly interact with the PSI core through their phosphorylated amino terminal regions. Furthermore, biochemical and functional studies on mutant strains lacking either LhcbM1 or LhcbM5 indicate that only LhcbM5 is indispensable in supercomplex formation. The results unravel the specific interactions and potential excitation energy transfer routes between green algal PSI and two phosphorylated LHCIIs (Pan et al., Nat. Plants, 7:1119-1131).
 

Figure 4. Surface representation of the CrPSI–LHCI–LHCII supercomplex from the pph1;pbcp mutant strain, with pThr residues from LhcbM1 and LhcbM5 highlighted in red. b, Detailed interaction between the N-terminal region of LhcbM1 and PSI core subunits PsaH and PsaL. c, Sequence alignment of the interaction-related regions of LhcbM1, PsaL and PsaH from C. reinhardtii (Cr) with Lhcb2, PsaL and PsaH from Zm, respectively. Conserved and variant residues involved in intersubunit interactions are indicated by blue and red asterisks, respectively. d, Structural comparison of N-terminal five residues (shown as sticks) of CrLhcbM1 (carbon atoms coloured green) and ZmLhcb2 (carbon atoms coloured white). The PSI core is shown in electrostatic surface mode with red and blue representing acidic and basic regions, respectively. e, Detailed interactions between the N-terminal region of LhcbM5 and the PSI core subunit PsaH. Hydrogen bond interactions are shown as black dashed lines. Pan et al. (2021) Nat. Plants, 7:1119-1131.

This division is currently recruiting graduate students. 

• Annual Report 2021（PDF）

Pan, X., Tokutsu, R., Li, A., Takizawa, K., Song, C., Murata, K., Yamasaki, T., Liu, Z., Minagawa, J., Li, M. (2022). Structural basis of LhcbM5-mediated state transitions in green algae. Nat Plants 7, 1119-1131.

Kim, E., Watanabe, A., Duffy, C. D. P., Ruban, A. V., Minagawa, J. (2020). Multimeric and monomeric photosystem II supercomplexes represent structural adaptations to low- and high-light conditions. J Biol Chem 295, 14537-14545.
 
Sheng, X., Watanabe, A., Li, A., Kim, E., Song, C., Murata, K., Song, D., Minagawa, J., and Liu, Z. (2019). Structural insight into light harvesting for photosystem II in green algae. Nat Plants 5, 1320-1330.
 
Tokutsu, R., Fujimura-Kamada, K., Matsuo, T., Yamasaki, T., and Minagawa, J. (2019). The CONSTANS flowering complex controls the protective response of photosynthesis in the green alga Chlamydomonas. Nat Commun 10, 4099.
 
Aihara, Y., Fujimura-Kamada, K., Yamasaki, T., and Minagawa, J. (2019). Algal photoprotection is regulated by the E3 ligase CUL4-DDB1^DET1. Nat Plants 5, 34-40.

Aihara, Y., Maruyama, S., Baird, A.H., Iguchi, A., Takahashi, S., and Minagawa, J. (2019). Green fluorescence from cnidarian hosts attracts symbiotic algae. Proc Natl Acad Sci U S A 116, 2118-2123.
 
Kosuge, K., Tokutsu, R., Kim, E., Akimoto, S., Yokono, M., Ueno, Y., and Minagawa, J. (2018). LHCSR1-dependent fluorescence quenching is mediated by excitation energy transfer from LHCII to photosystem I in Chlamydomonas reinhardtii. Proc Natl Acad Sci U S A 115, 3722-3727.
 
Petroutsos, D., Tokutsu, R., Maruyama, S., Flori, S., Greiner, A., Magneschi, L., Cusant, L., Kottke, T., Mittag, M., Hegemann, P., Finazzi, G., Minagawa, J. (2016). A blue light photoreceptor mediates the feedback regulation of photosynthesis. Nature 537, 563-566.
 
Nagy, G., Ünnep, R., Zsiros, O., Tokutsu, R., Takizawa, K., Porcar, L., Moyet, L., Petroutsos, D., Garab, G., Finazzi, G., and Minagawa, J. (2014). Chloroplast remodeling during state transitions in Chlamydomonas reinhardtii as revealed by noninvasive techniques in vivo. Proc Natl Acad Sci U S A 111, 5042-5047.
 
Tokutsu, R. and Minagawa, J. (2013). Energy-dissipative supercomplex of photosystem II associated with LHCSR3 in Chlamydomonas reinhardtii.  Proc Natl Acad Sci U S A 110, 10016-10021.
 
Iwai, M., Takizawa, K., Tokutsu, R., Okamuro, A., Takahashi, Y., Minagawa, J. (2010). Isolation of the elusive supercomplex driving cyclic electron transfer in photosynthesis. Nature 464, 1210-1213.

Professor MINAGAWA, Jun TEL: +81 564 55 7515 E-mail: minagawa@nibb.ac.jp