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  • The role of BST4 in the pyrenoid ofChlamydomonas reinhardtii. bioRxiv : the preprint server for biology Adler, L., Lau, C. S., Shaikh, K. M., van Maldegem, K. A., Payne-Dwyer, A. L., Lefoulon, C., Girr, P., Atkinson, N., Barrett, J., Emrich-Mills, T. Z., Dukic, E., Blatt, M. R., Leake, M. C., Peltier, G., Spetea, C., Burlacot, A., McCormick, A. J., Mackinder, L. C., Walker, C. E. 2023


    In many eukaryotic algae, CO2 fixation by Rubisco is enhanced by a CO2-concentrating mechanism, which utilizes a Rubisco-rich organelle called the pyrenoid. The pyrenoid is traversed by a network of thylakoid-membranes called pyrenoid tubules, proposed to deliver CO2. In the model alga Chlamydomonas reinhardtii (Chlamydomonas), the pyrenoid tubules have been proposed to be tethered to the Rubisco matrix by a bestrophin-like transmembrane protein, BST4. Here, we show that BST4 forms a complex that localizes to the pyrenoid tubules. A Chlamydomonas mutant impaired in the accumulation of BST4 (bst4) formed normal pyrenoid tubules and heterologous expression of BST4 in Arabidopsis thaliana did not lead to the incorporation of thylakoids into a reconstituted Rubisco condensate. Chlamydomonas bst4 mutant did not show impaired growth at air level CO2. By quantifying the non-photochemical quenching (NPQ) of chlorophyll fluorescence, we show that bst4 displays a transiently lower thylakoid lumenal pH during dark to light transition compared to control strains. When acclimated to high light, bst4 had sustained higher NPQ and elevated levels of light-induced H2O2 production. We conclude that BST4 is not a tethering protein, but rather is an ion channel involved in lumenal pH regulation possibly by mediating bicarbonate transport across the pyrenoid tubules.

    View details for DOI 10.1101/2023.06.15.545204

    View details for PubMedID 38014171