High-CO2 induced ocean acidification (OA) reduces the calcium carbonate (CaCO3) saturation level (Ω) and the pH of oceans. Consequently, OA is causing a serious threat to several ecologically and economically important biomineralising molluscs. Biomineralisation is a highly controlled biochemical process by which molluscs deposit their calcareous structures. In this process, shell matrix proteins aid the nucleation, growth and assemblage of the CaCO3 crystals in the shell. These molluscan shell proteins (MSPs) are, ultimately, responsible for determination of the diverse shell microstructures and mechanical strength. Recent studies have attempted to integrate gene and protein expression data of MSPs with shell structure and mechanical properties. These advances made in understanding the molecular mechanism of biomineralisation suggest that molluscs either succumb or adapt to OA stress. In this review, we discuss the fate of biomineralisation process in future high-CO2 oceans and its ultimate impact on the mineralised shell's structure and mechanical properties from the perspectives of limited substrate availability theory, proton flux limitation model and the omega myth theory. Furthermore, studying the interplay of energy availability and differential gene expression is an essential first step towards understanding adaptation of molluscan biomineralisation to OA, because if there is a need to change gene expression under stressors, any living system would require more energy than usual. To conclude, we have listed, four important future research directions for molecular adaptation of molluscan biomineralisation in high-CO2 oceans: 1) Including an energy budgeting factor while understanding differential gene expression of MSPs and ion transporters under OA. 2) Unraveling the genetic or epigenetic changes related to biomineralisation under stressors to help solving a bigger picture about future evolution of molluscs, and 3) Understanding Post Translational Modifications of MSPs with and without stressors. 4) Understanding carbon uptake mechanisms across taxa with and without OA to clarify the OA theories on Ω.

中文翻译：

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软体动物生物矿化对高CO2海洋的分子适应性-已知和未知。

高CO2诱导的海洋酸化（OA）降低了碳酸钙（CaCO3）的饱和度（Ω）和海洋的pH。因此，OA对几种在生态和经济上很重要的生物矿化软体动物造成了严重威胁。生物矿化是高度受控的生化过程，通过该过程软体动物沉积其钙质结构。在此过程中，壳基质蛋白有助于壳中CaCO3晶体的成核，生长和组装。这些软体动物壳蛋白（MSP）最终负责确定各种壳的微观结构和机械强度。最近的研究试图整合具有壳结构和机械性能的MSP的基因和蛋白质表达数据。在理解生物矿化的分子机制方面取得的这些进展表明，软体动物要么屈服，要么适应OA胁迫。在这篇综述中，我们从有限的基质可利用性理论，质子通量限制模型和欧米茄神话理论的角度讨论了未来高CO2海洋中生物矿化过程的命运及其对矿化壳结构和力学性能的最终影响。此外，研究能量供应和差异基因表达之间的相互作用是理解软体动物生物矿化适应OA的必不可少的第一步，因为如果需要在应激源下改变基因表达，那么任何生物系统都将需要比平时更多的能量。最后，我们列出了 在高CO2海洋中进行软体动物生物矿化的分子适应的四个重要的未来研究方向：1）包括能源预算因素，同时了解OA下MSP和离子转运蛋白的差异基因表达。2）揭示在应激源下与生物矿化相关的遗传或表观遗传学变化，以帮助解决关于软体动物未来进化的大图，以及3）了解带有或不带有应激源的MSP的翻译后修饰。4）了解有和没有OA的整个类群的碳吸收机制，以阐明有关Ω的OA理论。2）揭示在应激源下与生物矿化相关的遗传或表观遗传学变化，以帮助解决关于软体动物未来进化的大图，以及3）了解带有或不带有应激源的MSP的翻译后修饰。4）了解有和没有OA的整个类群的碳吸收机制，以阐明有关Ω的OA理论。2）揭示在应激源下与生物矿化相关的遗传或表观遗传学变化，以帮助解决关于软体动物未来进化的大图，以及3）了解带有或不带有应激源的MSP的翻译后修饰。4）了解有和没有OA的整个类群的碳吸收机制，以阐明有关Ω的OA理论。