Development of novel genetic tools for studying dinoflagellates and coral bleaching

珊瑚白化是全球变暖造成的最具灾难性的环境后果之一。即使受影响的珊瑚恢复，恢复也非常缓慢，结果是生物多样性大量丧失。珊瑚是动物和藻类之间的一种非凡的共生关系，通常属于被称为甲藻的群体，以及一个被称为共生藻的亚群体。腰鞭毛虫生活在珊瑚细胞内，通过光合作用为珊瑚细胞提供营养。作为回报，他们得到了人身保护。在珊瑚漂白过程中，共生关系破裂，珊瑚排出甲藻共生体。这似乎是水温升高的结果，但为什么这会导致共生关系破裂还不清楚。科学家们普遍认为这是由于甲藻的光合区室（叶绿体）的光合作用受到了干扰。由于某种原因，随着温度的升高，光合作用的反应变得不平衡。这可能导致甲藻产生称为活性氧的有毒化学物质。珊瑚认识到这种危险并驱逐了腰鞭毛虫。我们对为什么温度升高会引起叶绿体的干扰知之甚少，我们知之甚少的原因之一是因为缺乏修改叶绿体的遗传工具。叶绿体有一些自己的DNA，它包含了制造蛋白质的信息，这些蛋白质在光合作用中很重要。如果我们能改变甲藻的叶绿体，我们就能把蛋白质的基因放进去，这将有助于告诉我们哪里出了问题，以及我们如何使它变得更好。问题是甲藻很难进行基因改造。最近，我们成功地修改了另一种甲藻的叶绿体，称为Amphidinium。这种菌株不会形成珊瑚共生体，但重要的是，我们的工作表明，甲藻叶绿体的遗传修饰是可能的。由于技术原因，该方法不适用于珊瑚共生体Symbiodinium，但我们认为我们已经找到了解决这些问题的方法，基于对共生体叶绿体的研究。我们已经培育出了不能通过光合作用生长的共生藻菌株，因为它们失去了一个叶绿体基因。将基因放回去可以让菌株再次生长良好。我们的项目将测试我们是否可以成功地将丢失的光合作用基因放回已经丢失的甲藻叶绿体中。这将使我们的非光合作用菌株能够再次进行光合作用。这项技术将为将来对甲藻进行受控改变开辟道路。由于我们可以将共生藻重新构建到它们的珊瑚宿主中，我们对甲藻叶绿体进行遗传修饰的能力将为研究珊瑚漂白中出现的生物化学问题以及我们如何避免它的发生开辟一套全新的工具。

Coral bleaching is one of the most catastrophic environmental consequences of global warming. Even if the corals affected recover, the recovery is very slow and there is a massive loss of biodiversity as a result. Corals are a remarkable symbiosis between an animal and an alga, usually belonging to the group known as dinoflagellate algae, and a sub-group called Symbiodinium. The dinoflagellates live inside the coral cells and provide them with nutrients that they make by photosynthesis. In return they get physical protection. In coral bleaching the symbiosis breaks down and the corals expel the dinoflagellate symbionts. This seems to happen as a result of increased water temperature, but exactly why this should cause the symbiosis to break down is not clear. Scientists generally think it is due to some disturbance of photosynthesis in the photosynthetic compartment of dinoflagellates, the chloroplast. For some reason the reactions of photosynthesis become out of balance as temperature rises. Probably this results in the production of toxic chemicals called reactive oxygen species by the dinoflagellates. The coral recognises this danger and expels the dinoflagellates.We know very little about why raised temperature causes the disturbance in the chloroplasts, and one of the reasons we know so little is because of a lack of genetic tools to modify the chloroplast. The chloroplast has some of its own DNA and this contains the information to make proteins that are important in photosynthesis. If we could modify the dinoflagellate chloroplast, we could put in genes for proteins that would help to tell us what is going wrong and how we might make it better. The problem is that dinoflagellates are very difficult to modify genetically. Recently we managed to modify the chloroplast of another dinoflagellate, called Amphidinium. This strain does not form coral symbioses, but importantly our work shows that genetic modification of dinoflagellate chloroplasts is possible. For technical reasons the method does not work with the coral symbiont Symbiodinium, but we think we have found a way round these problems, based on research into Symbiodinium chloroplasts. We have made strains of Symbiodinium that are not able to grow well by photosynthesis because they have lost one of their chloroplast genes. Putting the gene back will allow the strains to grow well again.Our project will test if we can successfully get the missing photosynthesis gene back into dinoflagellate chloroplasts that have lost it. This will make our non-photosynthetic strains able to carry out photosynthesis once again. This technique will open the way to making controlled changes to the dinoflagellates in the future. As we can reconstitute Symbiodinium into their coral hosts, our ability to modify dinoflagellate chloroplasts genetically will open up a whole new set of tools for studying biochemically what goes wrong in coral bleaching and how we might be able to avoid it happening.