Dissecting the integration of phosphorus and nitrogen nutrition signals in diatoms

磷(P)和氮(N)是制约植物和藻类生长的主要营养物质。这些营养素的环境水平可能是高度动态的。因此，了解光合作用的真核生物如何在这些营养物质的供应波动的条件下优化生长和P和N的获取是至关重要的。除了在长时间的营养匮乏中存活下来外，这还需要能够感知并迅速适应营养补充。我们将利用一组重要的水生微藻--硅藻--作为研究营养感应、饥饿和串扰机制的模型系统。硅藻对P和N有效性的变化表现出极高的敏感性，通常在营养供应差异很大的沿海和河口生态系统中占据主导地位。我们最近发现，硅藻利用通用的第二信使钙离子来快速感知和协调细胞对磷补充的早期反应。然而，P-Ca~(2+)信号转导的分子成员(基因和蛋白质)以及它们如何协调下游适应尚不清楚。此外，我们目前还不知道硅藻的磷感应机制如何与已知的磷饥饿信号机制相协调，以优化硅藻对磷供应波动的反应。最后，P和N信号之间的双向串扰对于调节这些重要营养物质的平衡获取的重要性仍有待确定。这项建议的目的是解决上述问题，以便更好地了解光合作用真核生物如何感知和响应P和N供应的变化，并在动态的营养环境中优化生长。我们将利用最先进的基因编辑方法(CRISPR-CAS9)方面的成熟专业知识来表征P-钙信号通路的候选基因。对突变体的研究将使我们能够准确地评估硅藻如何产生和协调P-Ca~(2+)信号来调节硅藻对磷饥饿的恢复反应。我们还将研究P-Ca~(2+)信号是否以及P-Ca~(2+)信号的哪些成分由硅藻P饥饿反应的主调控子PSR1控制。最后，我们将研究N的有效性如何影响P信号和获取，以确保这些重要营养物质的平衡获取。这项研究将极大地促进对光合作用真核生物的营养感知和串扰机制的理解。由于硅藻在进化上不同于陆地植物和绿藻，这些发现将使我们能够比较和对比不同光合作用类群之间的营养信号机制。因此，这一提议为深入了解光合作用真核生物的营养感知和串扰机制的进化提供了一个前所未有的机会。通过这样做，我们的工作将为旨在提高其他光合作用真核生物对N和P的利用的研究工作提供信息，例如重要的作物物种。利用硅藻等微藻去除废水中的磷和氮也引起了极大的兴趣，以减轻营养流失的有害影响。因此，这项研究可以为优化菌株/条件，以最大限度地提高磷和氮的回收率提供信息。更广泛地说，这项研究还可以帮助更好地管理营养物质流失和藻类水华，将人类对宝贵的水生生态系统的破坏降至最低。

Phosphorus (P) and nitrogen (N) are the major nutrients constraining growth of plants and algae. Environmental levels of these nutrients can be highly dynamic. It is therefore critical to understand how photosynthetic eukaryotes optimise growth and P and N acquisition, in conditions with fluctuating supply of these nutrients. Alongside surviving prolonged periods of nutrient deprivation, this requires being able to perceive and rapidly adapt to nutrient replenishment. We will employ an important group of aquatic microalgae, the diatoms, as a model system for investigating nutrient sensing, starvation and crosstalk mechanisms. Diatoms exhibit exquisite sensitivity to changes in P and N availability, and often dominate in coastal and estuarine ecosystems where nutrient supply can vary dramatically. We have recently discovered that diatoms employ the universal second messenger, Ca2+, for rapidly sensing and coordinating early cellular responses to P replenishment. However, the molecular players (genes and proteins) underlying P-Ca2+ signalling, and how they coordinate downstream adaptations are unknown. Furthermore, we do not currently know how diatom P sensing mechanisms are coordinated with known P starvation signalling mechanisms to optimise diatom responses to fluctuating P supply. Finally, the importance of bidirectional cross-talk between P and N signalling for mediating balanced acquisition of these vital nutrients remains to be determined. The aim of this proposal is to address the above questions in order to better understand how photosynthetic eukaryotes perceive and respond to changes in the supply of P and N, and optimise growth in dynamic nutrient environments. We will employ established expertise in state-of-the-art gene editing approaches (CRISPR-Cas9) to characterise candidate genes of the P-Ca2+ signalling pathway. Examination of mutants will enable us to assess precisely how diatoms generate and coordinate P-Ca2+ signals to regulate diatom recovery responses from P starvation. We will also characterise whether, and what components of P-Ca2+ signaling are controlled by the master regulator of diatom P starvation responses, PSR1. Finally, we will investigate how N availability influences P-signalling and acquisition, to ensure the balanced acquisition of these vital nutrients. This research will significantly advance understanding of nutrient sensing and crosstalk mechanisms in photosynthetic eukaryotes. As diatoms are evolutionarily distinct from land plants and green algae, the findings will allow us to compare and contrast nutrient signalling mechanisms between diverse photosynthetic taxa. As such, this proposal offers an unprecedented opportunity to gain insight of the evolution of nutrient perception and crosstalk mechanisms in photosynthetic eukaryotes. In doing so, our work will inform research efforts aiming to enhance N and P usage by other photosynthetic eukaryotes, such as important crop species. There is also great interest in using microalgae such as diatoms for removal of P and N from wastewater, to mitigate the harmful impacts of nutrient run-off. This research could therefore inform the optimisation of strains/conditions to maximise P and N recovery. More broadly, the research could also help better manage nutrient run-off and algal blooms, minimising human damage to valuable aquatic ecosystems.