Environmentally regulated genes as basis for coral reef resilience

热带珊瑚礁是海洋生物多样性最重要的中心之一，提供了宝贵的生态系统服务，因为数百万人在经济上依赖珊瑚礁及其生物。全球变暖和海洋酸化等多种自然和人为压力因素可能导致本世纪内珊瑚礁的急剧减少。由于二氧化碳的人为增加，特别是海水温度的升高和ph的降低，海洋生物的压力预计会增加。珊瑚礁的未来在很大程度上取决于硬核珊瑚适应这些环境条件变化的能力。它们的适应潜力取决于它们进化新特征或调节现有基因表达的能力。然而，当前的气候变化发生在前所未有的短时间内，阻止了珊瑚礁珊瑚通过进化新特征来适应。因此，它们生存的主要策略可能在于已经编码在它们基因组中的表型可塑性。例如，某些基因响应环境条件变化的上调，可以在个体基因水平上或在群体水平上通过基因型的正选择来实现，基因型的表达水平增加。由于预适应过程和/或在极端环境条件下某些生态位的积极选择，在种群中可能存在偏离表达水平的个体。因此，对造礁珊瑚未来的预测在很大程度上取决于对环境调节基因功能的了解，而这方面的研究在很大程度上尚未得到研究。因此，我们开始在两性珊瑚中探索环境控制基因的基因组基础。本研究确定了珊瑚Acropora millepora及其编码红色荧光蛋白amFP597 （RFP）的基因为研究环境调控基因调控可塑性的理想模型系统。RFP被认为具有光保护功能，优化浅水生长。我们发现rfp编码基因在光照下被强烈上调。不同颜色的千缕草对光照气候变化的响应是相同的。然而，我们确定了两种变体之间在转录本绝对数量上的强烈差异：例如，与绿色变体相比，红色变体中暴露在光下和阴影组织中的RFP转录本浓度都高出五倍以上。这些结果表明，保护珊瑚蛋白的组织浓度不仅取决于编码基因的环境控制，还取决于基因对刺激的形态特异性最大反应。颜色变体之间转录水平的可变性似乎是遗传固定的，因为物种内的颜色差异在相同的环境条件下保留。因此，这一引人注目的调控可塑性案例为研究环境调控基因的基因组基础提供了理想的条件。我们将评估两种最有可能解释观察到的RFP转录水平差异的遗传情景：A)颜色变体具有不同的RFP编码基因变体，其序列发生改变，例如，在基因调控区域（启动子）。B) rfp编码基因在不同的颜色变体中以不同的拷贝数存在。为了解决在A. millepora中实现哪种情况的问题，我们将对绿色，棕色和红色变体中的rfp编码基因进行深入分析。所需的珊瑚已在国家海洋科学院珊瑚实验室的实验水族系统内饲养和繁殖。我们将运用一套先进的分子生物学技术，对珊瑚礁珊瑚的基因调控策略获得前所未有的见解。

Tropical coral reefs are among the most important centres of marine biodiversity, providing invaluable ecosystem services as millions of people are economically dependent on the reef and its creatures. A multiplicity of natural and anthropogenic stressors such as global warming and ocean acidification might result in a dramatic loss of coral reefs within this century. Increasing stress for marine organisms is expected in response to the anthropogenic increase in CO2, especially to rising seawater temperatures and decreasing pH. The future of coral reefs is strongly dependent on the capability of scleractinian corals to adapt to these changes in environmental conditions. Their adaptation potential is defined by their capacity to evolve new traits or to regulate the expression of existing genes. However, current climate change happens over an unprecedented short period of time, preventing an adaptation of reef corals by evolution of new traits. Consequently, their main strategy for survival may lie in the phenotypic plasticity that is already encoded in their genome. Up-regulation of certain genes in response to changing environmental conditions, for instance, can be realized on the level of the individual gene or on the population level by the positive selection of genotypes which show increased expression levels. Individuals with deviating expression levels can be present in a population as result of preadaptation processes and / or by positive selection in certain ecological niches with extreme environmental conditions. Hence, predictability of the future of reef-building corals depends strongly on knowledge of the functioning of environmentally regulated genes, an aspect as yet largely unstudied. Therefore, we set out to explore the genomic basis of environmentally controlled genes in hermatypic corals. We identified the coral Acropora millepora and its gene encoding the red fluorescent protein amFP597 (RFP) as ideal model system to study the regulatory plasticity of environmentally controlled genes. The RFP is considered to fulfill a photoprotective function, optimizing growth in shallow waters. We found that the RFP-encoding gene is strongly up-regulated by light. It shows the same response to changes in the light climate in different colour morphs of A. millepora. However, we determined strong differences between the morphs regarding the absolute amount of transcripts: The RFP transcript concentration was, for instance, more than five-fold higher both in the light exposed and shaded tissue in the red morph compared to the green morph. These results imply that the tissue concentration of a protective coral protein depends not only on the environmental control of the encoding gene but also on the morphotype-specific maximal response of the gene to a stimulus. The variability in transcript levels among the colour morphs appears to be genetically fixed as colour differences within species are retained under identical environmental conditions. Therefore, this striking case of regulatory plasticity offers ideal conditions to study the genomic basis of environmentally regulated genes. We will evaluate two genetic scenarios most likely to explain the observed differences in the RFP transcript levels: A) The colour morphs possess different variants of the RFP-encoding gene with altered sequences, for instance, in the gene regulatory region (promoter). B) The RFP-encoding gene is present in different copy numbers among the colour morphs. To address the question which scenario is realised in A. millepora, we will perform an in-depth analysis of the RFP-encoding gene in the green, brown and red colour morphs. The required corals are already kept and propagated in the experimental aquarium system of the Coral Laboratory at NOCS. We will apply a suite of advanced molecular biological techniques to gain unprecedented insights in gene regulation strategies in reef corals.