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可能导致珊瑚礁在本世纪内急剧丧失。增加压力的海洋生物，预计在响应人为增加二氧化碳，特别是海水温度上升和pH值下降。珊瑚礁的未来在很大程度上取决于石珊瑚的能力，以适应这些变化的环境条件。它们的适应潜力由它们进化新特征或调节现有基因表达的能力来定义。然而，目前的气候变化发生在前所未有的短时间内，阻止了珊瑚礁通过进化新特征的适应。因此，它们的主要生存策略可能在于它们基因组中已经编码的表型可塑性。例如，某些基因响应于变化的环境条件的上调可以在个体基因水平上或群体水平上通过阳性选择表现出增加的表达水平的基因型来实现。具有偏离表达水平的个体可以作为适应前过程和/或在极端环境条件下的某些生态位中的正选择的结果而存在于群体中。因此，造礁珊瑚未来的可预测性在很大程度上取决于对环境调节基因功能的了解，这一点在很大程度上尚未得到研究。因此，我们着手探索造礁石珊瑚中环境控制基因的基因组基础。我们确定了珊瑚Acropora millepora及其编码红色荧光蛋白amFP 597（RFP）的基因作为理想的模型系统来研究环境控制基因的调控可塑性。RFP被认为是实现光保护功能，优化生长在浅水沃茨。我们发现，RFP编码基因是强烈上调光。不同颜色的A.千孔珊瑚然而，我们确定了变体之间关于转录物绝对量的强烈差异：例如，与绿色变体相比，红色变体中的RFP转录物浓度在光暴露和阴影组织中均高出五倍以上。这些结果意味着，保护性珊瑚蛋白的组织浓度不仅取决于环境控制的编码基因，但也对形态特异性的最大响应的基因刺激。颜色变体之间的转录水平的变异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。我们将评估最有可能解释观察到的RFP转录水平差异的两种遗传情况：A）颜色变体具有RFP编码基因的不同变体，其序列发生改变，例如，在基因调控区（启动子）中。B）RFP编码基因在颜色变体中以不同的拷贝数存在。为了解决在A. millepora，我们将进行深入分析的RFP编码基因的绿色，棕色和红色的颜色变体。所需的珊瑚已经在国家海洋科学委员会珊瑚实验室的实验性水族箱系统中饲养和繁殖。我们将应用一套先进的分子生物学技术，在珊瑚礁的基因调控策略中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.