Unique structural attributes of the PSI-NDH supercomplex in Physcomitrium patens.

Area of Science:

• Plant molecular biology
• Photosynthesis research
• Evolutionary botany

Background:

• Cyclic electron transport around Photosystem I (PSI) protects plants under varying light.
• Proton Gradient Regulation 5 protein/Proton Gradient Regulation 5-like photosynthetic phenotype 1 protein (PGR5/PGRL1) and NADH dehydrogenase-like complex (NDH) mediate this process.
• Angiosperm NDH complexes interact with two PSI units via LHCA5 and LHCA6 antennae for stability.

Purpose of the Study:

• To investigate the evolutionary origins of the PSI-NDH supercomplex.
• To provide structural evidence for PSI-NDH supercomplex formation in the moss Physcomitrium patens (Pp).
• To understand the structural flexibility and adaptive mechanisms at the PSI-NDH interface.

Main Methods:

• Single particle electron microscopy was used to determine the structure of the Pp PSI-NDH supercomplex.
• Comparative analysis of structural configurations in Pp versus angiosperms.

Main Results:

• Physcomitrium patens forms a PSI-NDH supercomplex with a unique ability to bind a single PSI in two distinct configurations.
• One configuration resembles the angiosperm model, while the other shows a novel, rotated PSI orientation.
• This flexibility is attributed to variable LHCA5 incorporation, indicating early evolutionary adaptation.

Conclusions:

• The structural flexibility in Pp's PSI-NDH supercomplex highlights an early evolutionary adaptation for photosynthetic diversity.
• This variability appears to have decreased with increasing structural complexity in vascular plants.
• The study clarifies the evolutionary trajectory of PSI-NDH supercomplexes and emphasizes the dynamic nature of photosynthetic adaptation.