Heise Carolin M, Heß Daniel A, Walke Peter, Voß Maren, Schubert Hendrik, Hess Wolfgang R, Hagemann Martin
Plant Physiology Department, Faculty of Mathematics and Natural Sciences, University of Rostock, Einsteinstr. 3, 18059, Rostock, Germany.
Aquatic Ecology Department, Faculty of Mathematics and Natural Sciences, University of Rostock, Einsteinstr. 3, 18059, Rostock, Germany.
New Phytol. 2025 Aug;247(3):1218-1233. doi: 10.1111/nph.70283. Epub 2025 Jun 13.
Oxygenic photosynthesis in streptophytic algae, such as Charophyceae, is often impeded by low CO levels in aquatic habitats. Consequently, many algal groups evolved a CO-concentrating mechanism (CCM). However, its presence in Charophyceae remains controversial. To explore this, we analyzed the acclimation of photosynthesis, carbon isotope composition, and gene expression in Chara braunii under varying inorganic carbon (Ci) conditions. The photosynthetic activity changed complementarily under low- or high-Ci levels. Notably, the Ci compensation point of photosynthesis was significantly lower in thalli grown at ambient Ci than in elevated Ci. Correspondingly, the delta C levels were lower in thalli from high than low Ci. These results indicate that C. braunii performs a CCM under low Ci, which is suppressed under high Ci. Transcriptomic analyses of algae from different Ci cultivations provided insight into Ci-regulated genes and pointed to the possible association between carbonic anhydrases and aquaporins with the CCM. Collectively, our results indicate that C. braunii expresses a CCM allowing efficient use of CO and bicarbonate under limiting Ci conditions. A tentative scenario is provided summarizing the role of potential players in the CCM.
轮藻门藻类（如轮藻纲）中的氧光合作用常常受到水生栖息地中低二氧化碳水平的阻碍。因此，许多藻类群体进化出了一种二氧化碳浓缩机制（CCM）。然而，其在轮藻纲中的存在仍存在争议。为了探究这一点，我们分析了不同无机碳（Ci）条件下布氏轮藻的光合作用适应、碳同位素组成和基因表达。在低Ci或高Ci水平下，光合活性呈互补变化。值得注意的是，在环境Ci浓度下生长的藻体中，光合作用的Ci补偿点显著低于高Ci浓度下生长的藻体。相应地，高Ci条件下藻体的δC水平低于低Ci条件下的藻体。这些结果表明，布氏轮藻在低Ci条件下具有CCM，而在高Ci条件下受到抑制。对不同Ci培养条件下的藻类进行转录组分析，有助于了解Ci调控基因，并指出碳酸酐酶和水通道蛋白与CCM之间可能存在的关联。总的来说，我们的结果表明，布氏轮藻表达一种CCM，使其能够在有限的Ci条件下有效利用二氧化碳和碳酸氢盐。我们提供了一个初步的设想，总结了CCM中潜在参与者的作用。
