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元素。这些营养素的环境水平可以是高度动态的。因此，了解光合真核生物如何在这些营养物质供应波动的条件下优化生长和P和N的获取至关重要。除了在长时间的营养缺乏中生存外，这还需要能够感知并快速适应营养补充。我们将采用一组重要的水生微藻，硅藻，作为一个模型系统，调查营养感应，饥饿和串扰机制。硅藻对磷和氮的有效性变化表现出极高的敏感性，通常在营养供应变化剧烈的沿海和河口生态系统中占主导地位。我们最近发现，硅藻采用通用的第二信使，Ca 2+，快速感应和协调早期细胞反应磷补充。然而，P-Ca 2+信号传导的分子参与者（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磷传感机制与已知的磷饥饿信号机制协调，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介导这些重要营养素的平衡获取的重要性仍有待确定。该提案的目的是解决上述问题，以更好地了解光合真核生物如何感知和响应P和N供应的变化，并优化动态营养环境中的生长。我们将利用最先进的基因编辑方法（CRISPR-Cas9）的成熟专业知识来筛选P-Ca 2+信号通路的候选基因。突变体的检查将使我们能够准确地评估硅藻如何产生和协调P-Ca 2+信号来调节硅藻从P饥饿中恢复的反应。我们还将探讨是否，以及什么成分的P-Ca 2+信号控制的主调节硅藻磷饥饿反应，PSR 1。最后，我们将研究氮的可用性如何影响P-信号和收购，以确保这些重要的营养素的平衡收购。这项研究将大大推进光合真核生物的营养传感和串扰机制的理解。由于硅藻在进化上与陆地植物和绿色藻类不同，这些发现将使我们能够比较和对比不同光合类群之间的营养信号机制。因此，这一建议提供了一个前所未有的机会，以了解光合真核生物的营养感知和串扰机制的演变。在这样做的过程中，我们的工作将为旨在提高其他光合真核生物（如重要的作物物种）对N和P的利用率的研究工作提供信息。利用硅藻等微藻去除废水中的磷和氮，减轻营养流失的有害影响，也引起了极大的兴趣。因此，这项研究可以为菌株/条件的优化提供信息，以最大限度地提高P和N的回收率。更广泛地说，这项研究还可以帮助更好地管理营养流失和藻类水华，最大限度地减少人类对宝贵的水生生态系统的破坏。

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.