Structural study of monomeric and dimeric photosystem I-LHCI supercomplexes from a bryophyte

Area of Science:

• Photosynthesis research
• Plant molecular biology
• Structural biology

Background:

• Photosystem I (PSI) and light-harvesting complexes (LHCs) are crucial for solar energy capture in plants.
• Liverworts like Marchantia polymorpha represent early land plants that adapted to harsh terrestrial conditions.

Purpose of the Study:

• To determine the high-resolution cryo-electron microscopic structures of PSI-LHCI monomer and homodimer from Marchantia polymorpha.
• To compare the PSI-LHCI structure with other bryophytes and identify key structural differences.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to obtain structures.
• High-resolution structural analysis to identify cofactors and protein interactions.

Main Results:

• Determined the structures of PSI-LHCI monomer (1.94 Å) and homodimer (2.52 Å) from M. polymorpha.
• Identified specific interactions (PsaG, PsaH, PsaM, PsaB) stabilizing the monomer-monomer interface and mediating dimerization.
• Revealed structural differences compared to moss PSI-LHCI.

Conclusions:

• The study provides atomic-level structural insights into PSI-LHCI in an early land plant.
• Structural features identified likely contribute to M. polymorpha's adaptation to terrestrial light environments.
• PsaM plays a critical role in PSI-LHCI dimerization.