Diatom Sensory Mechanisms: Drivers of Global Marine Productivity

海洋支撑着全球生物多样性的很大比例。在海洋食物链的底部维持生命的是光合作用的微生物，统称为浮游植物。这些生物在调节我们的气候、吸收大气中的二氧化碳方面至关重要。它们也产生了我们呼吸的几乎一半的氧气。浮游植物最为人所知的可能是它们在海洋中形成了大规模的“藻华”，这是由于物理和生物因素共同引发的种群快速增长。由于有害毒素的释放，一些浮游植物水华可能对海洋生态系统、渔业和人类健康产生负面影响。气候变化和养分污染的影响导致了更严重和更频繁的水华。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。为了更好地了解控制水华动态和毒性的因素，我们需要更多地了解触发它们突然繁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，多种物理因素会导致营养物质的零星增加。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。现代海洋中最成功的浮游植物群之一是硅藻。硅藻特别善于发现有利的条件，往往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地区的成功表明，它们拥有复杂的机制来感知和响应营养的波动。然而，调节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。这代表着一个重大的知识鸿沟，特别是因为它是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。我已经生成了一个尖端工具包，研究硅藻如何能够使用信号分子钙来感知环境的变化，钙在细胞内起着信使的作用。这导致了硅藻使用钙来检测营养磷的脉冲的惊人发现。这种新的营养信号机制不同于植物和动物，并指出这些生物之间在营养感知上的根本差异，这些差异需要阐明。我将剖析这一信号通路的特定组成部分，以确定它如何帮助硅藻对不断变化的营养条件做出快速反应，并对水华的形成做出贡献。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水华发育。在我的提案的第二部分，我将研究硅藻如何能够感知并改变它们的行为，以便与它们的微生物邻居相互作用。由于营养物质的供应和细菌都可以控制有害硅藻产生的毒素，一个关键的目标将是将我的分子工具箱扩展到有毒的形成水华的硅藻伪菱形藻多系列。这项研究将确定控制一个全球重要浮游植物群动态的机制，该浮游植物群支持我们的一些主要海洋资源。此外，这项工作还将提供对调控过程的洞察和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水华的形成和毒性。

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.