Signal Transduction in Root Gravitropism

MCB0212099 PI：Gilroy，SimonPROJECT摘要重力是调节植物生长和形态的基本信号。尽管它对植物的成功很重要，但高等植物感知和响应这种最普遍和持续的环境信号的细胞和分子事件基本上是未知的。在根中，重力在根冠的柱状细胞中被感知，这一信号通过一种可能涉及不对称生长素重新分配的机制在伸长区转化为定向生长。本研究的目标是以拟南芥的根为模型系统，确定小柱细胞中产生的与重力相关的初始信号事件的细胞和分子性质。以前的研究已经发现，细胞质和细胞壁pH的变化是根冠柱状细胞重力信号的重要初始事件。此外，最近的证据表明，钙离子的高度局部性变化，可能靠近膜表面，也伴随着这些细胞中一些最早的重力感知事件。因此，研究将集中于表征这些与重力有关的H+和Ca~(2+)通量是如何产生的，以及它们是如何被重力信号转导系统的假定组件(如肌动蛋白细胞骨架)调制的。此外，还将构建基于Cameleon绿色荧光蛋白钙传感器的转基因钙传感器，并针对液泡、内质网和质膜。这些新型传感器将用于评估膜相关的钙微域是否确实与重力信号有关。该研究计划的最终目标是为柱状细胞开发单细胞信使核糖核酸图谱，以便对根冠不同区域的基因表达模式进行分类。初步分析的目标将是描绘肌动蛋白和肌球蛋白基因家族，因为这些基因家族代表着编码产生重力感知生化信号事件的部分力传递网络的有力候选者。植物的生长和形态与重力的发育影响密不可分。然而，尽管植物在调节发育方面发挥了基本作用，但植物感知和响应重力的确切机制仍不清楚。因此，这项研究计划的结果将寻求定义根部的分子机制，使其能够感觉到引力。该项目将专注于开发基于显微镜的成像方法，以可视化离子水平的动态变化，这些离子被认为向根的敏感细胞发出重力刺激的信号。对这些信号事件的理解不仅有助于更全面地了解植物如何感知和响应环境，而且还有可能通过操纵植物重力传感系统中特定组件的响应性来发现调控植物发育的策略。

MCB0212099 PI: Gilroy, SimonPROJECT ABSTRACTGravity 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 this most pervasive and constant of environmental signals are essentially unknown. In the root, gravity is perceived in the columella cells of the root cap and this signal is converted to oriented growth in the elongation zone through a mechanism likely involving asymmetrical auxin redistribution. The goal of this research project is to define the cell and molecular nature of the initial gravity-related signaling events generated in the columella cells, using the roots of Arabidopsis thaliana as a model system. Previous research has identified changes in cytoplasmic and cell wall pH as important initial events in gravity signaling in the root cap columella cells. In addition, recent evidence suggests highly localized changes in Ca2+, likely close to membrane surfaces, also accompany some of the earliest events of gravity perception in these cells. Research will therefore concentrate on characterizing how these gravity-related H+ and Ca2+ fluxes are generated and how they are modulated by putative components of the gravity signal transduction system such as the actomyosin cytoskeleton. In addition, transgenic Ca2+ sensors based on the Cameleon green fluorescent protein Ca2+ sensor will be constructed and targeted to the vacuolar, endoplasmic reticulum and plasma membranes. These novel sensors will be used to assess whether membrane-associated Ca2+ microdomains are indeed associated with gravity signaling. The final goal of the research program is to develop single cell mRNA profiling for the columella cells in order to catalog gene expression patterns within the different regions of the root cap. Initial analysis will be targeted at profiling the actin and myosin gene families as these represent strong candidates for encoding parts of the force transmissive network that generates the biochemical signaling events of gravity perception. Plant growth and form are inextricably linked to the developmental impacts of gravity. Yet, despite its fundamental role in regulating development, the precise mechanism whereby plants sense and respond to gravity remains unknown. Results from this research program will therefore seek to define the molecular machinery of the root that allows it to sense gravitational forces. The project will focus on developing microscope-based imaging approaches to visualize the dynamic changes in the levels of ions that are thought to signal the gravity stimulus to the sensitive cells of the root. An understanding of these signaling events should not only help provide a more complete understanding of how plants sense and respond to their environment, but also holds the potential to uncover strategies to regulate plant development through manipulating the responsiveness of defined components of this plant gravity sensing system.