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MINI REVIEW article

Front. Photobiol.

Sec. Light Reactions of Photosynthesis

Volume 3 - 2025 | doi: 10.3389/fphbi.2025.1571863

This article is part of the Research Topic Heterogeneity in Photobiology of Phototrophs – Emerging Questions and Microscopic Methods View all 3 articles

Multiphase CO2-dependent photosynthesis in marine diatoms

Provisionally accepted
  • 1 Kobe University, Kobe, Hyōgo, Japan
  • 2 Kwansei Gakuin University, Nishinomiya, Hyōgo, Japan

The final, formatted version of the article will be published soon.

    Diatoms, one of the most ubiquitous phytoplankton in the oceans, have evolved a pyrenoid-based CO2-concentrating mechanism (CCM) to utilize limited CO2 in seawater for photosynthesis. Recent proteomics analyses and molecular biological tools have deepened our understanding of the molecular mechanisms involved in diatom chloroplast architecture and the CCM. Here, we provide an update to our knowledge of the processes involved in high affinity photosynthesis for dissolved inorganic carbon (DIC) in diatoms. Based on the phenotype of genome-edited mutants, we propose a model of the diatom CCM composed of four phases of CO2-dependent photosynthesis at (I) less than 0.1 mM, (II) 0.1−2 mM, (III) 2−10 mM, and (IV) more than 10 mM of DIC concentrations, in which the rate-determining steps are the capture of unfixed CO2 in the chloroplast stroma at Phases I and II, the evolution of CO2 in the pyrenoid-penetrating thylakoid lumen at Phase III, and DIC transport to the stroma at Phase IV. Under natural seawater containing 2 mM DIC mainly in the form of HCO3−, the photosynthesis of marine diatoms is likely primarily in Phase III, shifting to Phase II when available CO2 is limited.

    Keywords: Photosynthesis, Pyrenoid, Pyrenoid-penetrating thylakoid membranes, marine diatoms, CO2-concentrating mechanism

    Received: 06 Feb 2025; Accepted: 18 Mar 2025.

    Copyright: © 2025 Shimakawa and Matsuda. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

    * Correspondence:
    Ginga Shimakawa, Kobe University, Kobe, 657-8501, Hyōgo, Japan
    Yusuke Matsuda, Kwansei Gakuin University, Nishinomiya, 662-8501, Hyōgo, Japan

    Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

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