SPECIAL - SPECIfying the mechanisms of activation of cALcium signalling in root legume endosymbiosis

氮(N)和磷(P)是影响植物生产力的主要常量营养元素。它们对植物生长的各个方面都是必不可少的，是作物成熟和种子生产所需的大量物质。然而，土壤中磷和氮的有效性很低，导致为维持作物产量而使用昂贵的化肥。这种广泛而昂贵的农用化学做法通过土壤、水和空气污染给我们的环境和人类健康带来了严重的代价，并在很大程度上加剧了全球变暖。减少化肥投入量对于保护我们的健康和环境至关重要。但是，我们如何才能在不降低作物产量的情况下减少化肥的使用？植物已经进化出与根相关的内生共生体相互作用的能力，从大气中获取氮，并克服生长的磷限制。丛枝菌根(AM)共生，提供磷酸盐、氮素和其他养分，存在于80%的陆地植物中，包括豆类、面包小麦和玉米。豆科植物的根还可以与固氮菌(根瘤菌)联系在一起，根瘤菌在根瘤内将氮气还原为植物可利用的NH3形式。因此，将根内共生菌用作肥料的自然来源可以作为解决方案的一部分，从而在不降低产量的情况下减少化肥使用量。虽然已经开发了以根内共生菌为基础的生物肥料产品，但由于植物建立内共生菌的能力受到土壤质量、流行气候和基因的影响，其效率仍然很低。近年来，增强内共生菌的新的遗传解决方案对以内共生菌为基础的生物肥料至关重要。值得注意的是，核钙信号的激活对内共生体的发育至关重要。虽然激活的机制尚不清楚，但这种信号会受到环境因素(非生物和生物胁迫)的影响。因此，了解核钙信号是如何被激活的，可以为更好地抵抗抑制根内共生体激活的环境胁迫的工程作物开辟道路。在这个项目中，我们的目标是确定核钙信号激活的机制。在大量前期工作的基础上，我们已经确定了一种新的核膜成分，它是激活核钙信号的直接必需的。这种核成分具有核“受体”的所有特征：1)能够感知由内共生菌诱导的大分子因子；2)能够通过磷酸化调节离子通道的活性。我们将进一步描述这种核“受体”的特征，并确定激活它的大分子成分(S)，以产生启动内共生的核钙信号。了解这种新的分子成分对于了解环境因素如何抑制内共生至关重要。因此，从长远来看，该项目将为加强作物内共生和减少化肥使用的方法提供基础。

Nitrogen (N) and Phosphorus (P) are major macronutrients impacting plant productivity. They are essential for all aspects of plant growth and are required in large quantities for crop maturation and seed production. However, P and N are poorly available in soils, leading to costly chemical fertiliser applications to sustain crop yields. This extensive, and expensive agrochemical practice comes at a severe cost to our environment and human health via soil, water and air pollution, and contributes substantially to global warming. Lowering chemical fertiliser inputs is essential to protect our health and environment. But how can we reduce the use of chemical fertilizer without decreasing crop yields? Plants have evolved the ability to interact with root-associated endosymbionts to access N from atmospheric N2 and to overcome P limitation of growth. The Arbuscular Mycorrhizal (AM) symbiosis, which delivers phosphate, nitrogen, and other nutrient, is present in 80 % of land plants, including legumes, bread wheat and maize. Legume roots can also associate with nitrogen-fixing bacteria (rhizobia), which reduce N2 to the plant-usable form NH3, within root nodules. Thus, the use of root endosymbionts as a natural source of fertilizer can be part of the solution to reduce fertilizer use without decreasing yield. Although biofertilizer products based on root endosymbionts have been developed, their efficiency remains poor because the capacity of plants to establish endosymbioses is affected by soil quality, prevailing climate and genotype. In recent years it has become clear that new genetic solutions to enhance endosymbioses are essential for endosymbiont based biofertilizers. Notably activation of nuclear calcium signals is essential for the development of endosymbioses. Although the mechanism of activation is unknown, this signalling is impaired by environmental factors (abiotic and biotic stresses). Thus, understanding how nuclear calcium signals are activated can open the way for engineering crops that are more resistant to the environmental stresses that inhibit the activation of root endosymbioses. In this project we aim to identify the mechanism of nuclear calcium signalling activation. Based on extensive preliminary work, we have identified a novel nuclear membrane component which is directly required for the activation of nuclear calcium signalling. This nuclear component has all the characteristics of a nuclear "receptor"; 1) capable of perceiving macromolecular factors induced by endosymbionts, and 2) capable of modulating the activity of ion channels via phosphorylation. We will characterise this nuclear "receptor" further and identify the macromolecular component(s) that activate it, to generate nuclear calcium signals, that initiate endosymbioses. Understanding this new molecular component is essential to understand how environmental factors inhibit endosymbioses. Thus, in the longer term, this project will provide the basis for methods that enhance endosymbioses in crops and reduce the use of chemical fertilizers.