Structure of giant kelp Photosystem I-FCP uncovers drivers of antenna evolution across the red lineage.

Weissman, Jenevieve D; Maturana, Pablo; Oung, Hui M O; Riddle, Reece; Wyatt, Gabrielle; Dubinin, Viktoria G T; Zerbe, Philipp; Maldonado, María · Nat Commun · 2026

basic_science · Level V

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Abstract

Brown algae and other red-algae-derived organisms are major contributors to global CO<sub>2</sub> fixation via photosynthesis. To understand the photosynthetic function of brown algae, we obtained the structure of giant kelp Macrocystis pyrifera photosystem I (PSI) with a fucoxanthin-chlorophyll-protein (FCP) antenna and compared it to known structures from the red-algal lineage. We identified differences in M. pyrifera's antenna composition, architecture, and chlorophyll networks, as well as a pronounced variation in transmembrane hydrophobic thickness across the PSI-FCP supercomplex, with implications for photochemical function. Our work lays the foundation to understand kelp's high photosynthetic productivity and reveals drivers of antenna conservation and diversification for the red lineage.