eLife assessment
This important study reports a high-resolution cryoEM structure of the supercomplex between photosystem I (PSI) and fucoxanthin chlorophyll a/c-binding proteins (FCPs) from the model diatom Thalassiosira pseudonana CCMP1335, with subunits, protein:protein interactions and pigments not previously seen in other diatoms or red/green photosynthetic lineages. Combining structural, sequence, and phylogenetic analyses, the authors provide convincing evidence of conserved motifs crucial for the binding of FCPs, leading to interesting speculation about the mechanisms governing the assembly of PSI-FCP supercomplexes in diatoms and their implications for related PSI-LHC supercomplexes in plants. The findings set the basis for functional experiments that will further advance the fields of photosynthesis, bioenergy, ocean biogeochemistry, and understanding of evolutionary relationships between photosynthetic organisms.