In situ structures of plant photosystem supercomplexes

Area of Science:

• Plant biology
• Molecular and structural biology
• Biophysics

Background:

• Photosynthesis converts light energy into chemical energy via photosystems I (PSI) and II (PSII) in thylakoid membranes.
• Previous studies lacked insight into the native organization of photosystems within chloroplasts.

Purpose of the Study:

• To determine the native structure and organization of photosystem supercomplexes in rice chloroplasts.
• To provide a molecular framework for understanding the high efficiency of plant photosynthesis.

Main Methods:

• In situ cryo-electron microscopy (cryo-EM) of Oryza sativa (rice) chloroplasts.
• Structural determination of photosystem supercomplexes in their native membrane environment.
• Excitation energy transfer calculations.

Main Results:

• Resolved the C₂S₂M₂L₄-type PSII-light harvesting complex II (LHCII) supercomplex, including previously unobserved LHCII trimers.
• Identified diverse PSII-LHCII dimer architectures and higher-order assemblies.
• Determined high-resolution structures of PSI-LHCI-LHCII and PSI-LHCI supercomplexes.
• Revealed extensive networks of lipids, pigments, and cofactors within supercomplexes.

Conclusions:

• The native architecture of PSII may form a structural 'skeleton' influencing thylakoid morphology and grana stacking.
• The resolved supercomplex structures provide the first molecular basis for the efficiency of plant photosynthesis.
• In situ cryo-EM is a powerful tool for studying native protein organization in membranes.