Study Gives Insights into Plants' Light Harvesting Process Under Low Light

The primary light reaction of photosynthesis in plants happens at photosystem II (PSII), a membrane-embedded supramolecular machine that catalyzes the water-splitting reaction. Surrounding the PSII is a number of peripheral antenna complexes that dynamically associate with it to form the PSII-LHCII supercomplexes of variable sizes in response to different light conditions.

Isolated from Arabidopsis and peas, the C2S2M2-type supercomplex is the largest stable form of PSII-LHCII supercomplex, and crucial for plants to achieve optimal light-harvesting efficiency when they are under low-light conditions. Structural analysis of the C2S2M2 supercomplex is an important step to understanding the molecular mechanisms that plants use in light harvesting, light energy transfer, and PSII functional regulation.

A team of researchers from the Institute of Biophysics (IBP) at the Chinese Academy of Sciences (CAS) used cryo-electron microscopy (cryo-EM) to resolve structures of C2S2M2-type PSII-LHCII supercomplex from peas at 2.7 and 3.2Å resolution, respectively. The study revealed the overall structural features and the arrangement of each individual subunit, as well as the sophisticated pigment network and the complete energy transfer pathways within the supercomplex. The comparison of two C2S2M2 structures suggests the potential mechanism of functional regulation on the light-harvesting process and the oxygen-evolving activity of plant PSII.

More details are available in the paper "Structure and assembly mechanism of plant C2S2M2-type PSII-LHCII supercomplex" published in Science.