Light harvesting is essential for photosynthesis, and the diversity of light-harvesting systems enables photosynthetic organisms to acquire unique niches and thrive. Prasinophytes are marine green algae that diverge early in the evolution of photosynthetic eukaryotes and use a distinct light-harvesting complex known as Lhcp as their primary antenna. Lhcp consists of proteins and pigments unique to prasinophytes but shares some structural and functional features with the plant-type light-harvesting complex LHCII. Here, we use cryo-electron microscopy to determine the structure of Lhcp from the prasinophyte Ostreococcus tauri at 1.94 Å resolution, revealing all pigments responsible for light harvesting. The results show that the trimeric structure of Lhcp is stabilized by pigments, including a distinctive carotenoid identified as the cis-isomer of esterified antheraxanthin B. Comparison of Lhcp and plant-type LHCII reveals that while their core architecture is conserved, structural differences underlie their functional divergence. This work provides insight into the evolution of light-harvesting systems and highlights how structural diversity contributes to ecological adaptation.
© 2025. The Author(s).