Reef-building corals regularly experience changes in intra- and extracellular H+ concentrations ([H+]) due to physiological and environmental processes. Stringent control of [H+] is required to maintain the homeostatic acid-base balance in coral cells and is achieved through the regulation of intracellular pH (pHi). This task is especially challenging for reef-building corals that share an endosymbiotic relationship with photosynthetic dinoflagellates (family Symbiodinaceae), which significantly affect the pHi of coral cells. Despite their importance, the pH regulatory proteins involved in the homeostatic acid-base balance have been scarcely investigated in corals. Here, we report in the coral Stylophora pistillata a full characterization of the genomic structure, domain topology and phylogeny of three major H+ transporter families that are known to play a role in the intracellular pH regulation of animal cells; we investigated their tissue-specific expression patterns and assessed the effect of seawater acidification on their expression levels. We identified members of the Na+/H+ exchanger (SLC9), vacuolar-type electrogenic H+-ATP hydrolase (V-ATPase) and voltage-gated proton channel (HvCN) families in the genome and transcriptome of S. pistillata. In addition, we identified a novel member of the HvCN gene family in the cnidarian subclass Hexacorallia that has not been previously described in any species. We also identified key residues that contribute to H+ transporter substrate specificity, protein function and regulation. Last, we demonstrated that some of these proteins have different tissue expression patterns, and most are unaffected by exposure to seawater acidification. In this study, we provide the first characterization of H+ transporters that might contribute to the homeostatic acid-base balance in coral cells. This work will enrich the knowledge of the basic aspects of coral biology and has important implications for our understanding of how corals regulate their intracellular environment.

中文翻译：

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细胞内 pH 调节：Stylophora pistillata 中 H+转运蛋白的表征和功能研究

由于生理和环境过程，造礁珊瑚经常经历细胞内和细胞外 H+ 浓度 ([H+]) 的变化。需要严格控制 [H+] 以维持珊瑚细胞中的稳态酸碱平衡，这是通过调节细胞内 pH (pHi) 来实现的。对于与光合鞭毛藻（共生科）具有内共生关系的造礁珊瑚来说，这项任务尤其具有挑战性，这会显着影响珊瑚细胞的 pHi。尽管它们很重要，但在珊瑚中几乎没有研究涉及稳态酸碱平衡的 pH 调节蛋白。在这里，我们在珊瑚 Stylophora pistillata 中报告了基因组结构的完整特征，已知在动物细胞的细胞内 pH 调节中起作用的三个主要 H+ 转运蛋白家族的结构域拓扑和系统发育；我们研究了它们的组织特异性表达模式，并评估了海水酸化对其表达水平的影响。我们在雌蕊的基因组和转录组中鉴定了 Na+/H+ 交换器 (SLC9)、液泡型生电 H+-ATP 水解酶 (V-ATPase) 和电压门控质子通道 (HvCN) 家族的成员。此外，我们在刺胞动物亚纲 Hexacorallia 中鉴定了 HvCN 基因家族的一个新成员，该成员以前在任何物种中都没有描述过。我们还确定了有助于 H+ 转运蛋白底物特异性、蛋白质功能和调节的关键残基。最后的，我们证明了这些蛋白质中的一些具有不同的组织表达模式，并且大多数不受海水酸化的影响。在这项研究中，我们首次描述了可能有助于珊瑚细胞内稳态酸碱平衡的 H+ 转运蛋白。这项工作将丰富珊瑚生物学基本方面的知识，并对我们理解珊瑚如何调节其细胞内环境具有重要意义。