Understanding of green algal pyrenoid as a phase-separating and CO<sub>2</sub>-concentrating organelle

Yamano Takashi

doi:10.5685/plmorphol.35.3

<p>Pyrenoids are suborganelles in chloroplasts of algae and hornworts and can be observed under a light microscope. Pyrenoids are formed by aggregating the CO₂-fixing enzyme RubisCO and play a central role in the efficient CO₂ fixation reaction, especially in aquatic conditions. The molecular mechanism of pyrenoid formation and its relationship to the CO₂- concentration mechanism have been dramatically improved using the model green alga Chlamydomonas reinhardtii. Pyrenoid in Chlamydomonas is formed by the liquid-liquid phase separation of RubisCO and multivalent RubisCO-binding protein with disordered regions. This concept has been argued to apply to pyrenoid formation in other algal species. In this review, I introduce recent studies on the Chlamydomonas pyrenoid structure of pyrenoid and the CO₂-concentrating mechanism. I provide a perspective that the functional components of the pyrenoid, (1) pyrenoid matrix, (2) starch sheaths and peripheral proteins, and (3) pyrenoid tubules structure, are universal structures acquired by algae through convergent evolution across lineages to achieve the purpose of CO₂ concentration around RubisCO. Understanding the principles behind the regulation, structure, and formation of pyrenoids will provide not only a basic understanding of a nonmembrane organelle of cell biology but also a molecular basis for the future introduction of pyrenoids into land plants to enhance photosynthetic performance and yield.</p>

Understanding of green algal pyrenoid as a phase-separating and CO<sub>2</sub>-concentrating organelle

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