Perception and integration of nutritional signals in plant root systems: Solving the mystery of K-Fe-P interactions.

矿物质元素是人体营养所必需的。例如，钾(K)是人体的主要电解质，是肾脏、肌肉、神经和心脏功能所必需的。铁(Fe)是使细胞能量代谢的氧化还原酶的一种成分，也是将氧气输送到大脑和外周组织的血红蛋白的组成部分。矿物质是通过植物进入食物链的。它们的根系积极地在土壤中寻找有益的矿物质营养，并在特殊运输蛋白的帮助下提取它们。对于人类来说，矿物质营养对植物健康是必不可少的。根系对粮食作物产量和营养价值的重要性已被认识到，根系研究已成为粮食安全的中心阶段。植物可以感知土壤中矿质养分有效性的信号，并将其转化为适应根系形状和运输活动的发育和生理过程，从而最大限度地提高觅食和吸收能力。如果我们想要提高作物的养分利用效率，我们需要了解在土壤条件和根系适应之间起调节作用的信号通路。潜在的机制是复杂的。根系既是感知养分有效性的受体，又是进行养分吸收的效应者。为了达到最佳效果，它们需要对单个根部分的生长和在不同细胞中的运输进行不同的调控。在没有中央大脑的情况下，这涉及到局部和系统的信号和反应。根还需要整合关于不同营养的信息并确定其响应的优先顺序，这需要各个营养信号通路之间的串扰。我们最近的几个发现应该能够更好地理解植物如何处理多种营养信号和调节根系结构。我们鉴定了模式植物拟南芥的两种不同生态型，它们对低钾供应的反应不同。哥伦比亚(Col-0)的加入保持了主根的生长，但停止了侧根的伸长，从而显示出一个又长又窄的根系。相比之下，卡塔尼亚(Ct-1)停止了主根的生长，但延伸了侧根，从而显示出一个短而大的根系。当钾素供应充足时，这两个材料看起来非常相似。令人惊讶的是，我们可以通过低铁低钾处理将Ct-1根型转化为Col-0根型--这两个材料现在都形成了又长又窄的根构型。铁在Col-0对低磷胁迫下的根系反应中起着重要作用，但两个材料对低磷胁迫的反应相似(仅抑制主根)。显然，Col-0/Ct-1为我们提供了一个很好的实验模型，以发现支持植物在营养胁迫下的发育决定的分子过程，并揭示营养-营养相互作用。在这个项目中，我们将结合电生理方法和共聚焦显微镜与分子遗传学和自动根表型来解决以下问题：根细胞如何感知低K，以及与铁氧化还原代谢的联系是什么？哪些细胞过程是主根抑制的基础？哪些信号将主根的发育反应与侧根的发育反应联系起来？不同的根构型如何影响养分的吸收和叶片中的最终养分含量？哪些基因决定了根构型对营养信号的反应？这项研究的结果有望导致详细了解将土壤来源的营养信号与根系发育和养分吸收联系起来的基本生物学过程和遗传成分。特别是，我们将提供关于K、P和Fe这三种基本营养素之间功能关系的新信息，这将对未来改善作物表现和营养质量的努力具有非常重要的价值。

Mineral elements are essential to human nutrition. For example, potassium (K) is the major electrolyte in the human body and is required for kidney, muscle, nerve and heart functions. Iron (Fe) is a component of redox enzymes enabling cellular energy metabolism and of hemoglobin carrying oxygen to the brain and to the peripheral tissues. Minerals are introduced into the food chain through plants. Their root systems actively forage the soil for beneficial mineral nutrients and extract them with the help of specialized transport proteins. As for humans, mineral nutrition is essential for plant health. The importance of the root system for yield and nutritional value of food crops has been recognized, and root research has taken a center stage in food security.Plants can perceive signals about mineral nutrient availability in the soil and translate them into developmental and physiological processes that adapt root shape and transport activity, thereby maximizing foraging and uptake capacity. If we want to enhance nutrient usage efficiency of crops we need to understand the signaling pathways that mediate between soil conditions and root adaptations. The underlying mechanisms are complicated. Root systems act simultaneously as receptors perceiving nutrient availability and as effectors carrying out nutrient uptake. To achieve the best result they need to differentially regulate growth of individual root parts and transport in different cells. Without a centralized brain this involves both local and systemic signals and responses. Roots also need to integrate information on different nutrients and prioritize their responses, which requires crosstalk between individual nutrient signaling pathways.We have recently made several discoveries that should enable a better understanding of how plants process multiple nutrient signals and regulate root system architecture. We identified two different ecotypes of the model species Arabidopsis thaliana that respond differently to low K supply. The Columbia (Col-0) accession maintains growth of the primary root but halts lateral root extension, thus displaying a long, narrow root system. By contrast, Catania (Ct-1) halts main root growth but extends lateral roots thus displaying a short, bulky root system. Both accessions look very similar when K supply is sufficient. Surprisingly, we could transform the Ct-1 root phenotype into the Col-0 root phenotype by subjecting the plants to low Fe together with low K - both accessions now developed long, narrow root architectures. Fe is known to play a role in root responses of Col-0 to low P, nevertheless, both accessions showed a similar response to low P (inhibition of main root only). Clearly, the Col-0/Ct-1 pair provides us with an excellent experimental model to discover the molecular processes that underpin developmental decisions of plants under nutrient stress, and to unravel nutrient-nutrient interactions.In this project, we will combine electrophysiological methods and confocal microscopy with molecular genetics and automated root phenotyping to address the following questions: How is low-K perceived by root cells and what is the link to Fe redox metabolism? Which cellular processes underlie main root inhibition? Which signals link developmental responses of the main root with those of the lateral roots? How do different root architectures impact on nutrient uptake and on final nutrient contents in the leaves? Which genes determine root architectural responses to nutrient signals? The results from this study can be expected to lead to a detailed understanding of the fundamental biological processes and genetic components that link soil-derived nutrient signals with root development and nutrient uptake. In particular we will provide new information on the functional relationship between three essential nutrients, K, P and Fe, which will be invaluable for future efforts to improve crop performance and nutritional quality.