Signal Transduction in Root Gravitropism

根向地性中的信号转导

• 批准号: 9874445
• 负责人: Simon Gilroy
• 金额: $ 23.57万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-09-01 至 2003-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9874445&HistoricalAwards=false
• 关键词: Signal; Transduction; Root; Gravitropism

Gravity is a fundamental signal that regulates plant growth and form. Despite its importance to plant success, the cellular and molecular events whereby higher plants sense and respond to the gravity signal are essentially unknown. Roots offer an almost unique advantage for studying these events in that sensing and response occur in well defined, spatially distinct regions. It is thought that in the root gravity is perceived in the columella cells of the root cap. These cells then generate a signal that is translocated to the growth zone. This signal then elicits asymmetrical growth through a mechanism that may involve redistributions of auxin, H+ and Ca2+. The events in the columella cells that lead to gravity perception remain poorly understood. In a widely accepted model for the initial process of gravity sensing (the starch statolith hypothesis), the settling of amyloplasts in the columella cells initiates the signaling systems that lead to gravity perception. However, the molecular components of the gravity perception machinery in the cap cells remain essentially unknown. This signaling system must translate sedimentation of statoliths to a cellular signal encoding the direction of gravity. Changes in cytoplasmic pH and columella cell wall Ca2+ and pH have been shown to occur rapidly after gravistimulation of the root of Arabidopsis thaliana. This rapid induction of ion fluxes suggests activation of ion transporters that are closely associated with the initial gravity sensing events. Inhibition of these changes in Ca2+ or pH also inhibits the graviresponse of the root, suggesting they are required for the gravitropic signaling processes of the root cap to proceed. The goal of this research is therefore to define how these ion fluxes are activated in the gravity sensing cells of the root cap using Arabidopsis thaliana as a model system. Understanding how gravity leads to the activation of the ion transporters responsible for these fluxes should provide insight into some of the initial molecular changes that encode the gravity signal in the columella cells of the root cap.Several approaches to this problem will be investigated:(1) H+, Ca2+ and K+ fluxes will be monitored in the cytoplasm, cell walls and medium around columella cells in the intact gravistimulated root cap. These ionic changes will be monitored in living, graviresponding roots using a range of novel, fluorescent, ion imaging probes.(2) The activities of cytoplasmic regulators of signaling or ion transport activities, such as second messengers and the actin and tubulin cytoskeleton, will be altered by application of inhibitors and activators to the columella cells. The effect of these factors on inhibiting or mimicking the gravitational regulation of H+ and Ca2+ fluxes will then be assessed.(3) As there is extensive evidence for a role of calmodulin in ion transporter regulation as well as in the graviresponse, calmodulin activity will be manipulated and its effect on the gravistimulated ion fluxes monitored. In addition, a novel green fluorescent protein-based indicator of calmodulin activity will be used to image potential gravity-induced calmodulin activation domains within the columella cell cytoplasm.(4) In order to test the starch statolith model of gravity perception, laser tweezers will be used to displace amyloplasts in the columella cells in non-gravity stimulated roots. Gravity-like effects on the regulation of H+ and Ca2+ fluxes will then be assessed. Induction of a gravity-like activation of columella cell ion transport by amyloplast displacement would strongly support the starch statolith model for gravity perception in the Arabidopsis root cap.Results from this research will extend the understanding of the gravity sensing machinery used by plants. In particular, these investigations will help identify molecular candidates for the initial elements of the plant gravity sensing system of the root.

重力是调节植物生长和形式的基本信号。尽管对植物成功的重要性，但细胞和分子事件具有较高的植物感知并响应重力信号的事件本质上是未知的。根源为研究这些事件提供了几乎独特的优势，因为感应和响应发生在定义良好的空间不同区域中。人们认为在根帽的哥伦氏菌细胞中感知了根部的重力。然后，这些细胞产生一个转移到生长区的信号。然后，该信号通过一种可能涉及生长素，H+和Ca2+的重新分布的机制引起不对称的生长。导致重力感知的小肠细胞中的事件仍然很少理解。在广泛接受的重力传感过程（淀粉statolith假说）的广泛接受模型中，小肠细胞中淀粉样品的沉降启动了导致重力感知的信号系统。但是，盖细胞中重力感知机制的分子成分基本上未知。该信号系统必须将statoliths沉积转化为编码重力方向的细胞信号。在拟南芥根的重量刺激后，已证明细胞质pH和小甲虫细胞壁Ca2+和pH的变化迅速发生。离子通量的快速诱导表明激活与初始重力传感事件密切相关的离子转运蛋白。抑制Ca2+或pH中这些变化的抑制也抑制了根部的重力，这表明它们是根帽的重力信号传导过程所必需的。因此，这项研究的目的是定义如何使用拟南芥作为模型系统在根盖的重力传感细胞中激活这些离子通量。了解重力如何导致负责这些通量的离子转运蛋白的激活，应洞悉一些最初的分子变化，这些最初的分子变化编码了根帽的毛ca虫细胞中的重力信号。将研究该问题的几个问题方法：（1）H+，Ca2+和k+ flux在细胞植物中围绕圆形和中等元素中的collum grols collum collum collum collum collum collum collum collum and collum collum collum of Medim copters collum collum collum collum collum collum and collum colt collum and Medim of Medim copters群。这些离子的变化将在生存中，使用一系列新型，荧光，离子成像探针的根源监测。（2）信号传导或离子传输活性的细胞质调节剂的活性，例如第二元使者以及肌动蛋白和小管蛋白细胞骨骼，将通过抑制剂和活性细胞的施加来改变。这些因素对抑制或模仿H+和Ca2+通量的重力调节的影响将评估。（3）由于有广泛的证据表明钙调蛋白在离子转运蛋白调节中的作用以及在Graviresponse中的作用，因此将操纵钙调蛋白的活性及其对压力降压的降压剂的影响。此外，新型的基于钙调蛋白活性的基于绿色荧光蛋白的指标将用于成像潜在的重力诱导的钙调蛋白细胞胞质中的钙调蛋白活化域。（4）为了测试重力感知的淀粉统计模型，激光镊子将用于稳定性蛋白菌细胞中的激光晶粒剂抑制蛋白菌细胞中的蛋白酶刺激性细胞。然后将评估对H+和Ca2+通量调节的重力样影响。促淀粉样品的诱导柱细胞离子转运的重力样激活将在拟南芥根帽中强烈支持淀粉statolith模型，以实现重力感知。这项研究的结果将扩展对植物使用的重力感应机械的理解。特别是，这些研究将有助于确定根部植物重力传感系统初始元素的分子候选物。