Diatom Sensory Mechanisms: Drivers of Global Marine Productivity

海洋支撑着全球很大一部分生物多样性。维持海洋食物链底层生命的是光合微生物，统称为浮游植物。这些生物对调节气候、吸收大气中的二氧化碳至关重要。我们呼吸的氧气几乎有一半是由它们产生的。浮游植物最为人所知的可能是它们在海洋中形成大规模的“藻华”，这是由于物理和生物因素共同引发的种群快速增长。由于释放有害毒素，一些浮游植物大量繁殖会对海洋生态系统、渔业和人类健康产生负面影响。气候变化和营养污染的影响导致了更严重和频繁的水华。然而，许多水华不是由有害物种引起的，对维持包括鱼类种群在内的海洋生态系统至关重要。为了更好地理解控制藻华动态和毒性的因素，我们需要更多地了解触发它们突然增殖和随后死亡的分子过程。在海洋的许多地方，氮和磷等营养物质供应不足。这可能会限制浮游植物的生长，并导致微生物之间为生存而竞争。在海洋环境中，多种物理因素的结合可导致营养物的零星增加。这是能够刺激浮游植物细胞快速增殖并导致藻华形成的因素之一。硅藻是现代海洋中最成功的浮游植物群之一。硅藻特别善于发现有利的条件，并且通常是第一个在水华形成的早期阶段占据主导地位的。此外，它们在脉冲营养供应区域的成功表明，它们具有感知和响应营养波动的复杂机制。然而，介导硅藻细胞对关键环境刺激的细胞反应的感觉机制仍然知之甚少。这代表了一个重大的知识缺口，特别是因为协调适应环境的信号机制可能是硅藻生态成功和全球影响的基础。我制作了一个尖端的工具包来研究硅藻是如何利用信号分子钙来感知环境变化的，钙在细胞内起着信使的作用。这导致了一个引人注目的发现，即硅藻利用钙来检测营养物质磷的脉冲。这种新的营养信号机制不同于植物和动物，并指出了这些生物之间营养感知的根本差异，这需要阐明。我将剖析这一信号通路的具体组成部分，以确定它如何帮助硅藻快速响应不断变化的营养条件，并促进华花的形成。使用我的创新工具，我还将研究硅藻感觉系统的其他未知方面。除了物理因素外，硅藻与其他微生物（如竞争对手、寄生虫和捕食者）的生物相互作用可以关键地调节它们的生长和开花发育。在我提案的第二部分，我将研究硅藻如何能够感知并改变它们的行为以与它们的微生物邻居相互作用。由于营养供应和细菌都可以控制有害硅藻的毒素产生，一个关键的目标将是扩大我的分子工具包到形成有毒水华的硅藻伪尼齐亚多系列。这项研究将确定控制全球重要浮游植物群动态的机制，这些浮游植物群支持我们的一些主要海洋资源。此外，这项工作将提供调控过程和“主调控”的见解，协调细胞对影响硅藻生长和有害硅藻物种毒性的关键环境驱动因素的反应，使我们能够更好地预测藻华的形成和毒性。

The oceans support a large proportion of global biodiversity. Sustaining life at the base of marine food chains are photosynthetic microbes, known collectively as phytoplankton. These organisms are vital in regulating our climate, absorbing carbon dioxide from the atmosphere. They also generate almost half the oxygen we breathe. Phytoplankton are probably best known for their formation of massive 'algal blooms' in the ocean, due to rapid population growth triggered by a combination of physical and biological factors. Due to the release of harmful toxins, some phytoplankton blooms can have a negative impact on marine ecosystems, fisheries and human health. Effects of climate change and nutrient pollution have led to more severe and frequent blooms. However, many blooms are not caused by harmful species, and are vital for sustaining marine ecosystems including fish populations. To better understand factors that control bloom dynamics and toxicity, we need to learn more about the molecular processes that trigger their sudden proliferation, and subsequent demise.In many parts of the ocean, nutrients such as nitrogen and phosphorus are in scarce supply. This can limit phytoplankton growth, and cause competition between microbes for survival. In the marine environment a combination of physical factors can lead to sporadic increases in nutrients. This is one of the factors that can stimulate rapid proliferation of phytoplankton cells and lead to algal bloom formation. One of the most successful phytoplankton groups in modern oceans is the diatoms. Diatoms are particularly good at detecting favourable conditions and are often the first to dominate the early stages of bloom formation. Moreover, their success in regions of pulsed nutrient supply suggests that they possess sophisticated mechanisms for sensing and responding to fluctuations in nutrients. However, the sensory mechanisms that mediate the cellular responses of diatom cells to key environmental stimuli remain poorly understood. This represents a major knowledge gap, especially since it is the signalling mechanisms that coordinate acclimation to the environment that likely underpin the ecological success and global impact of the diatoms.I have generated a cutting-edge toolkit to study how diatoms are able to sense changes in their environment using the signalling molecule calcium, which functions as a messenger within the cell. This has led to the remarkable discovery that diatoms use calcium for detecting pulses of the nutrient phosphorus. This novel nutrient signalling mechanism is distinct from plants and animals and points to fundamental differences in nutrient perception between these organisms, which need to be elucidated. I will dissect specific components of this signalling pathway to identify how it helps diatoms respond rapidly to changing nutrient conditions and contribute towards bloom formation. Using my innovative tools, I will also examine other unknown aspects of the diatom sensory system. Alongside physical factors, biological interactions of diatoms with other microbes such as competitors, parasites and predators can critically regulate their growth and bloom development. In the second part of my proposal I will examine how diatoms are able to sense, and alter their behaviour to interact with, their microbial neighbours. Since both nutrient supply and bacteria can govern toxin production by harmful diatoms, a key objective will be to expand my molecular tool kit to the toxic bloom-forming diatom Pseudo-nitzschia multiseries.This research will identify mechanisms that govern dynamics of a globally important phytoplankton group that supports some of our major marine resources. The work will moreover provide insight of regulatory processes and 'master-regulators' that coordinate cellular responses to key environmental drivers that impact diatom growth and toxicity of harmful diatom species, allowing us to better predict bloom formation and toxicity.