RUI: Biochemical adaptation to temperature in the coral-dinoflagellate symbiosis

RUI：珊瑚-甲藻共生中对温度的生化适应

• 批准号: 1654249
• 负责人: Peter Fields
• 金额: $ 25.18万
• 依托单位: Franklin and Marshall College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-03-01 至 2023-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1654249&HistoricalAwards=false
• 关键词: RUI; Biochemical; adaptation; temperature; coral

Reef-building corals throughout the tropical oceans depend on a relationship with single-celled algae (Symbiodinium) that live within coral tissue and that provide the coral most of its energy. However, coral bleaching, a process in which corals expel these algal symbionts in response to environmental stress, has been occurring at increasing rates over the past few decades. Bleaching is especially widespread during times of high water temperature, and often leads to the death of the coral and damage to the reef. Indeed, there is concern that much of the coral reef habitat will be lost in the next fifty years due to the impacts of ocean warming and coral bleaching. This project aims to increase biologists' understanding of why bleaching occurs, by comparing the temperature sensitivity of important enzymes in corals to those of different types of Symbiodinium. The researchers hypothesize that one reason bleaching occurs is because corals are adapted to live at higher temperatures than the algae (which live not only within coral tissue but also free in the water), and furthermore that different types of algae may be more or less adapted to withstand high temperature. The research will provide opportunities for teaching and training undergraduates interested in careers in science, as well as in-depth summer opportunities for socioeconomically disadvantaged high school students. The results of the study will help researchers better predict the likely extent of future bleaching events, and the possibility that corals and algae may be able to adapt to withstand increasing water temperatures.This project will test two specific hypotheses: First, that there is a mismatch in adaptation temperature between the partners, leading to a loss of metabolic function in Symbiodinium at higher temperatures. The hypothesis is based on the observation that Symbiodinium occur in the coral host, but also are free-living in environments across a broad, and often cooler, temperature range. At the biochemical level, adaptation to a eurythermal environment requires enzymes to maintain catalytic rate and substrate affinity over a wide temperature range, but might concomitantly reduce structural stability. To test this hypothesis, metabolic enzymes occurring both in corals and Symbiodinium will be expressed recombinantly, and temperature sensitivity of kinetic parameters of enzyme function will be assessed. Thermal stability of each enzyme also will be measured through residual activity and circular dichroism spectrometry. A second hypothesis is that Symbiodinium types differing in thermal tolerance are biochemically adapted to different temperatures. It has been shown that different clades of Symbiodinium have varying thermal sensitivities, providing the holobiont different levels of resistance to heat-induced bleaching. The hypothesis will be tested by examining representative enzymes from different Symbiodinium types using the approaches described above. In addition, because Symbiodinium orthologs are structurally similar, 3D models of target enzymes will be examined to determine the extent, location, and types of amino acid substitutions that lead to changes in thermal sensitivity; the temperature-adaptive importance of these substitutions will be confirmed through site-directed mutagenesis followed by expression, enzyme kinetics and stability analyses.

整个热带海洋的造礁珊瑚依赖于与单细胞藻类（共生藻类）的关系，这些藻类生活在珊瑚组织中，并为珊瑚提供大部分能量。然而，在过去的几十年里，珊瑚白化（珊瑚为应对环境压力而排出这些藻类共生体的过程）的发生速度越来越快。在水温高的时候，白化现象尤其普遍，经常导致珊瑚死亡和珊瑚礁受损。事实上，人们担心，由于海洋变暖和珊瑚白化的影响，大部分珊瑚礁栖息地将在未来50年内消失。该项目旨在通过比较珊瑚中重要酶对不同类型共生菌的温度敏感性，提高生物学家对白化发生的原因的理解。研究人员推测，白化现象发生的一个原因是珊瑚比藻类适应了更高的温度（藻类不仅生活在珊瑚组织内，还在水中自由生活），此外，不同类型的藻类可能或多或少地适应了高温。这项研究将为对科学事业感兴趣的本科生提供教学和培训机会，并为社会经济条件较差的高中生提供深入的暑期机会。这项研究的结果将帮助研究人员更好地预测未来白化事件的可能程度，以及珊瑚和藻类适应不断升高的水温的可能性。本项目将测试两个具体假设：第一，伴侣之间的适应温度不匹配，导致共生菌在较高温度下代谢功能丧失。这一假设是基于对共生菌的观察，共生菌出现在珊瑚宿主体内，但也在一个广泛的、通常较冷的温度范围内自由生活。在生化水平上，对低温环境的适应需要酶在很宽的温度范围内保持催化速率和底物亲和力，但可能会降低结构稳定性。为了验证这一假设，我们将在珊瑚和共生菌中重组表达代谢酶，并评估酶功能动力学参数的温度敏感性。每种酶的热稳定性也将通过残余活性和圆二色光谱测定。第二种假设是，不同类型的共生菌在耐热性上是不同的，它们在生物化学上适应了不同的温度。已有研究表明，共生菌的不同分支具有不同的热敏性，从而为全息生物提供了不同程度的耐热性。该假设将通过使用上述方法检查来自不同共生菌类型的代表性酶来验证。此外，由于共生菌同源物在结构上是相似的，因此将检查目标酶的3D模型，以确定导致热敏性变化的氨基酸取代的程度、位置和类型；这些取代的温度适应性重要性将通过位点定向诱变，随后的表达，酶动力学和稳定性分析来证实。