Research by ZHANG Xing hailed as one of China’s Top 10 Scientific Discoveries of 2019

The Basic Research Management Center of the Ministry of Science and Technology announced China’s Top 10 Scientific Discoveries of 2019 recently. With the collaborative efforts of research teams led by SHEN Jianren and KUANG Yanyun from the CAS Institute of Botany, SUI Senfang from Tsinghua University, and ZHANG Xing from the Zhejiang University School of Medicine, the supermolecular organization and function of a huge number of protein subunits and pigments of the PSII-LHCII supercomplex were successfully deciphered. This scientific achievement was named one of China’s Top 10 Scientific Discoveries of 2019.

Photosynthesis is the most important chemical reaction on the earth. It converts solar energy into chemical energy and provides food and oxygen for most life on the planet. It is not only the engine of environmental changes and the origin and evolution of advanced life but also the cornerstone of the genesis and development of human civilizations. Photosystem II (PSII) in the thylakoid membranes of plants, algae, and cyanobacteria catalyzes light-induced oxidation of water by which light energy is converted into chemical energy and molecular oxygen is produced. In higher plants and most eukaryotic algae, the PSII core is surrounded by light-harvesting antenna complex II (LHCII), forming a PSII–LHCII supercomplex. In order to harvest energy efficiently in low–light-intensity underwater conditions, a complete PSII–LHCII supercomplex (C2S2M2N2) of the green alga Chlamydomonas reinhardtii (Cr) contains more antenna subunits and pigments than the dominant PSII–LHCII supercomplex (C2S2M2) of plants. The detailed structure and energy transfer pathway of the Cr-PSII–LHCII remain elusive.

Researchers reported the high-resolution crystal structure of Phaeodactylum tricornutum FCP, the structure of the PSII-FCPII supercomplex of Bacillariophyceae, the structure of the PSI-LHCI supercomplx of the green alga Bryopsis corticulans Setchell and the structure of the PSII-LHCII supercomplex (C2S2M2N2) of the green alga Chlamydomonas reinhardtii. These research findings open a door for simulating artificial photosynthesis, breeding new crops, and building smart plant factories.  

The research team led by ZHANG Xing was primarily responsible forthe cryoelectron microscopy structure of a complete, C2S2M2N2-type PSII–LHCII supercomplex from C. reinhardtii at 3.37-Å resolution. Their research revealed that the Cr-C2S2M2N2 supercomplex is organized as a dimer, with 3 LHCII trimers, 1 CP26, and 1 CP29 peripheral antenna subunits surrounding each PSII core. The N-LHCII trimer partially occupies the position of CP24, which is present in the higher-plant PSII–LHCII but absent in the green alga. The M trimer is rotated relative to the corresponding M trimer in plant PSII–LHCII. In addition, some unique features were identified in the green algal PSII core. The arrangement of a huge number of pigments rendered it possible to deduce possible energy transfer pathways from the peripheral antennae to the PSII core.