Molecular biomineralization of octocoral skeletons: calcite versus aragonite (MINORCA)

生物矿化是指生物体产生矿物质的过程。这一过程塑造了地球历史上大部分时期贝壳和骨骼的壮观多样性，并形成了珊瑚礁的三维框架，珊瑚礁是地球上最多样化的生态系统之一。珊瑚虫珊瑚是当今建造珊瑚礁的主要生物，它们产生不同形态的碳酸钙(CaCO3)。文石和八珊瑚方解石是文石和八珊瑚方解石的矿藏，文石类太阳穴是一个显著的例外。然而，珊瑚产生不同的CaCO3多晶型的原因和方式尚不清楚。在地球历史的某些时期，海水镁钙摩尔比的变化被认为是在分支起源时优先选择特定CaCO3多晶型的驱动因素。虽然在分子水平上对珊瑚的生物矿化过程进行了较好的研究，但八珊瑚的知识仍然缺乏，但对于完全了解珊瑚控制和对抗环境变化的影响的能力是必要的。在这里，我们将结合转录组和蛋白质组的方法来鉴定和表征八珊瑚生物矿化工具包中涉及的基因谱系。我们将使用三个具有刚性骨架的物种作为模型，我们在我们的研究水族馆中养殖这些物种，并最近为它们生成参考转录：文石型八珊瑚Heliopora Blue ulea和钙化的Tubipora musica，为了进行比较分析，还将使用文石型单孢子虫。将采用三种不同的策略来实现该项目的目标：第一，将挖掘现有的目标物种的转录本，并将其与珊瑚和其他分类群(例如，钙质海绵、软体动物、腕足类、棘皮动物)的公开数据进行比较，以识别与生物矿化相关的蛋白质。第二，对于我们的每个目标物种，骨骼蛋白质组(即，包裹在骨骼中的有机基质蛋白)将被描述为进一步表征可能参与生物矿化的蛋白质。第三，我们将把我们的三个目标物种暴露在人工方解石海一样的海水中(MMG：CA=1)，因为显然在那些条件下，文石珊瑚开始产生方解石但导致这种CaCO3多态转变的分子过程尚不清楚。我们将在短期和长期的实验中监测生物矿化相关基因的差异表达，旨在填补这一知识空白。通过关注产生不同CaCO3多态的珊瑚并采用不同的实验方法，我们将提供关于珊瑚生物矿化，特别是八珊瑚生物矿化的新数据，这可能有助于我们进一步了解在变化的海洋中控制生物矿化的生物过程。

Biomineralization refers to the process by which organisms produce minerals. This process that has shaped the spectacular diversity of shells and skeletons throughout large periods of the Earth's history, and forms the three dimensional framework of coral reefs, one of the most diverse ecosystem on the planet. Anthozoan corals, main reef builders today, produce different polymorphs of calcium carbonate (CaCO3). Scleractinians deposit aragonite and octocorals calcite, with a notable exception, the aragonitic Heliopora. It is however unknown why and how corals produce different CaCO3 polymorphs. Changes in the molar ratio of seawater Mg:Ca during certain periods of Earth history have been proposed as drivers of preferential selection of specific CaCO3 polymorphs at clade origin. While the process of biomineralization is comparatively well studied at the molecular level in Scleractinia, knowledge is still deficient in Octocorallia but necessary for a complete understanding of the ability of corals to control and counter the effects of environmental changes.Here we will combine transcriptomic and proteomic approaches to identify and characterize the gene repertoire involved in the octocoral biomineralization toolkit. We will use three species with a rigid skeleton, which we culture in our research aquaria and for which we recently generated reference transcriptomes, as models: the aragonitic octocoral Heliopora coerulea and the calcitic Tubipora musica, and, to allow comparative analyses, the aragonitic scleractinian Montipora digitata. Three different strategies will be employed to achieve the project's objectives:First, the existing target species transcriptomes will be data mined and compared with published data on corals and other taxa (e.g., calcareous sponges, molluscs, brachiopods, echinoderms) to identify biomineralization-related proteins.Second, for each of our target species, the skeletal proteomes (i.e. organic matrix proteins occluded in the skeleton) will be characterized to further characterize proteins putatively involved in biomineralization.Third, we will expose our three target species to artificial Calcite Sea-like seawater (with a mMg:Ca = 1), because apparently aragonitic corals start to produce calcite under those conditions, but the molecular processes responsible for such CaCO3 polymorph shift are unknown yet. We will monitor the differential expression of biomineralization-related genes in short- and longer-term experiments aiming to fill that knowledge gap.By focusing on corals that produce different CaCO3 polymorphs and employing different experimental approaches, we will provide novel data on coral biomineralization in general, and octocoral biomineralization in particular, which might help to further our understanding of the biological processes that control biomineralization in changing oceans.