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态的基本信号。尽管重力信号对植物的成功很重要，但高等植物感知和响应重力信号的细胞和分子事件基本上是未知的。根为研究这些事件提供了几乎独特的优势，因为感知和响应发生在明确的、空间上不同的区域。据认为，在根中重力是在根冠的小柱细胞中感知的。然后这些细胞产生信号并转移到生长区。然后，该信号通过可能涉及生长素、H+ 和 Ca2+ 重新分配的机制引发不对称生长。导致重力感知的小柱细胞中的事件仍然知之甚少。在重力感应初始过程的广泛接受的模型中（淀粉平衡石假说），淀粉体在小柱细胞中的沉降启动了导致重力感知的信号系统。然而，帽细胞中重力感知机制的分子成分仍然基本上未知。该信号系统必须将平衡石的沉降转化为编码重力方向的细胞信号。拟南芥根受重力刺激后，细胞质 p​​H 值和小柱细胞壁 Ca2+ 和 pH 值会迅速发生变化。这种离子通量的快速诱导表明离子转运蛋白的激活与初始重力感应事件密切相关。抑制 Ca2+ 或 pH 的这些变化也会抑制根的重力反应，表明它们是根冠的重力信号过程进行所必需的。因此，本研究的目标是使用拟南芥作为模型系统来定义如何在根盖的重力感应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，应有助于深入了解编码根冠小柱细胞中重力信号的一些初始分子变化。将研究解决此问题的几种方法：（1）将监测完整重力刺激根盖中小柱细胞周围细胞质、细胞壁和介质中的 H+、Ca2+ 和 K+ 通量。这些离子变化将使用一系列新颖的荧光离子成像探针在活的重力响应根中进行监测。（2）信号传导或离子转运活性的细胞质调节剂的活性，例如第二信使以及肌动蛋白和微管蛋白细胞骨架，将通过对小柱细胞应用抑制剂和激活剂来改变。然后将评估这些因素对抑制或模拟 H+ 和 Ca2+ 通量的重力调节的影响。(3) 由于有大量证据表明钙调蛋白在离子转运蛋白调节以及重力响应中的作用，因此将操纵钙调蛋白活性并监测其对重力刺激离子通量的影响。此外，一种新型的基于绿色荧光蛋白的钙调蛋白活性指示剂将用于对小柱细胞胞质内潜在的重力诱导的钙调蛋白激活域进行成像。(4)为了测试重力感知的淀粉平衡石模型，将使用激光镊子置换非重力刺激的根中的小柱细胞中的淀粉体。然后将评估 H+ 和 Ca2+ 通量调节的类重力效应。通过淀粉质体置换诱导小柱细胞离子运输的类重力激活将有力地支持拟南芥根冠重力感知的淀粉平衡石模型。这项研究的结果将扩展对植物使用的重力感应机制的理解。特别是，这些研究将有助于确定植物根部重力感应系统初始元素的候选分子。