Adler Liat, Lau Chun Sing, Shaikh Kashif M, van Maldegem Kim A, Payne-Dwyer Alex L, Lefoulon Cecile, Girr Philipp, Atkinson Nicky, Barrett James, Emrich-Mills Tom Z, Dukic Emilija, Blatt Michael R, Leake Mark C, Peltier Gilles, Spetea Cornelia, Burlacot Adrien, McCormick Alistair J, Mackinder Luke C M, Walker Charlotte E
Institute of Molecular Plant Sciences, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3BF, UK.
Centre for Engineering Biology, University of Edinburgh, Edinburgh EH9 3BF, UK.
Plant Physiol. 2024 Dec 2;196(4):2374-2394. doi: 10.1093/plphys/kiae450.
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, which are proposed to deliver CO2. In the model alga Chlamydomonas (Chlamydomonas reinhardtii), 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 (Arabidopsis thaliana) did not lead to the incorporation of thylakoids into a reconstituted Rubisco condensate. Chlamydomonas bst4 mutants did not show impaired growth under continuous light at air level CO2 but were impaired in their growth under fluctuating light. By quantifying the non-photochemical quenching (NPQ) of chlorophyll fluorescence, we propose that bst4 has a transiently lower thylakoid lumenal pH during dark-to-light transition compared to control strains. We conclude that BST4 is not a tethering protein but is most likely a pyrenoid tubule ion channel involved in the ion homeostasis of the lumen with particular importance during light fluctuations.
在许多真核藻类中，核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）的二氧化碳固定作用通过一种二氧化碳浓缩机制得以增强，该机制利用一种富含Rubisco的细胞器——淀粉核。淀粉核被称为淀粉核小管的类囊体膜网络贯穿，人们认为这些小管用于输送二氧化碳。在模式藻类莱茵衣藻（Chlamydomonas reinhardtii）中，有人提出淀粉核小管通过一种类贝斯特罗芬跨膜蛋白BST4与Rubisco基质相连。在此，我们表明BST4形成一个定位于淀粉核小管的复合体。一个在BST4积累方面存在缺陷的莱茵衣藻突变体（bst4）形成了正常的淀粉核小管，并且BST4在拟南芥（Arabidopsis thaliana）中的异源表达并未导致类囊体整合到重组的Rubisco凝聚物中。莱茵衣藻bst4突变体在空气水平二氧化碳浓度下持续光照条件下生长未受影响，但在波动光照下生长受到损害。通过量化叶绿素荧光的非光化学猝灭（NPQ），我们提出与对照菌株相比，bst4在从暗到光的转变过程中类囊体腔pH值短暂降低。我们得出结论，BST4不是一种连接蛋白，而很可能是一种淀粉核小管离子通道，参与腔的离子稳态，在光照波动期间尤为重要。
