A research group led by Graduate Student Yuma Yamamoto and Associate Professor Ryo Nagao from the Faculty of Agriculture at Shizuoka University, in collaboration with Unit Leader Naoshi Dohmae and his colleagues from RIKEN, isolated and analyzed photosynthetic pigment-protein complexes from the green alga Tetraselmis striata NIES-1019. They discovered unique carotenoids common to all complexes, revealing the potential existence of a distinctive light-harvesting strategy. This was determined through pigment analysis, fluorescence and absorption spectral measurements, and molecular phylogenetic analysis. The complexes were also shown to represent a unique evolutionary lineage. The results were published in Photosynthesis Research on May 26.
Provided by Shizuoka University
Photosynthetic organisms use sunlight to synthesize organic matter and oxygen from water and carbon dioxide in order to support life activity through the process of oxygenic photosynthesis. This is carried out by membrane protein complexes such as PSI and PSII found in photosynthetic organisms, including cyanobacteria, algae, and land plants. Light-harvesting complexes (LHCs) are bound to these systems, supporting the efficient capture and transfer of light energy.
LHCs contain pigments such as chlorophyll and carotenoids. Green algae, in particular, are primary endosymbiotic algae that possess LHCs for both PSI and PSII and are considered key to understanding the evolution and structural diversity of LHCs.
The genus Tetraselmis belongs to Chlorodendrophyceae, considered one of the earliest-diverging lineages within the green plant kingdom. These unicellular green algae have strong environmental tolerance and are expected to be utilized in health foods and other applications. However, the LHC composition and pigment-binding characteristics of algae belonging to this group were not well understood.
In this study, photosynthetic pigment-protein complexes (LHC, PSI-LHCI, PSII-LHCII) were purified from T. striata NIES-1019 and analyzed. As a result, carotenoids such as loroxanthin decenoate, which are loroxanthin derivatives not reported in other algae, were detected in all complexes. This suggests a possible evolutionary acquisition specific to the genus Tetraselmis.
The genus Tetraselmis has attracted attention in the fields of aquaculture, biofuel, and health foods due to its production of nutritionally valuable lipids and pigments. Molecular phylogenetic analysis revealed that its composition as PSII peripheral antenna is conserved. It also suggested that the structure of PSI peripheral antenna may differ from other green algae.
These results demonstrate that the composition of photosynthetic pigment-proteins and light-harvesting mechanisms have changed in a diverse way during the evolutionary process of green algae, providing important insights for understanding the evolutionary diversity of photosynthesis in green algae.
Nagao commented: "Early-diverging lineages of green algae like the genus Tetraselmis are valuable models for understanding the diversity of photosynthetic pigments and the evolution of light-harvesting complexes. In this research, we were able to clarify how these algae acquired their unique pigment-protein complexes and obtain clues for understanding the evolutionary adaptation of photosynthesis."
Journal Information
Publication: Photosynthesis Research
Title: Biochemical and phylogenetic analyses of light-harvesting complexes from Tetraselmis striata
DOI: 10.1007/s11120-025-01152-7
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