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）是人体中的主要电解质，是肾脏、肌肉、神经和心脏功能所必需的。铁（Fe）是能够使细胞能量代谢的氧化还原酶和将氧运送到大脑和外周组织的血红蛋白的组分。矿物质通过植物进入食物链。它们的根系积极地在土壤中寻找有益的矿物质营养，并在专门的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至关重要。根系对粮食作物产量和营养价值的重要性已得到公认，根系研究已成为粮食安全研究的中心。植物可以感知土壤中矿质营养有效性的信号，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。如果我们想提高作物的养分利用效率，我们需要了解土壤条件和根系适应之间的信号通路。其内在机制是复杂的。根系同时作为感受养分有效性的受体和进行养分吸收的效应器。为了达到最佳效果，他们需要差异化地调节各个根部分的生长和在不同细胞中的运输。如果没有一个集中的大脑，这涉及到局部和系统的信号和反应。根还需要整合不同营养素的信息并优先考虑它们的反应，这需要单个营养信号通路之间的串扰。我们最近的几项发现应该能够更好地理解植物如何处理多种营养信号并调节根系结构。我们确定了两种不同的生态型的模式物种拟南芥，不同的低钾供应。哥伦比亚（Col-0）加入保持主根的生长，但停止侧根的延伸，从而显示出一个长，窄的根系。相比之下，卡塔尼亚（Ct-1）停止主根生长，但延长侧根，从而显示出短，庞大的根系。当钾供应充足时，两种材料看起来非常相似。令人惊讶的是，我们可以通过使植物经受低Fe和低K来将Ct-1根表型转化为Col-0根表型-这两个品种现在都形成了长而窄的根结构。铁是已知的Col-0的根响应低P发挥作用，然而，这两个加入表现出类似的反应低P（抑制主根只）。显然，Col-0/Ct-1对为我们提供了一个很好的实验模型，以发现营养胁迫下植物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，我们将联合收割机电生理方法和共聚焦显微镜与分子遗传学和自动化根表型分析相结合，以解决以下问题：根细胞如何感知低钾，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？哪些信号将主根和侧根的发育反应联系起来？不同的根构型如何影响养分吸收和叶片中的最终养分含量？哪些基因决定根构型对养分信号的反应？这项研究的结果可以预期导致详细了解基本的生物过程和遗传成分，将土壤来源的养分信号与根系发育和养分吸收联系起来。特别是，我们将提供新的信息，三个必需营养素，钾，磷和铁，这将是非常宝贵的，为今后的努力，以提高作物的性能和营养品质之间的功能关系。

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.