Signal Transduction in Arabidopsis Root Gravitropism

重力是调节植物生长和形态的基本信号。尽管重力对植物的成功至关重要，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。据认为，在根茎中，帽细胞可以感知重力，并通过一种涉及生长素和Ca2+分布不对称的机制将该信号转化为不对称生长。许多争论可以追溯到我们对相互作用的信号系统的相对无知，这些信号系统破坏、协调和整合了这些热带反应。因此，本研究的目标是利用拟南芥的根作为模型系统，在细胞水平上定义这些关键的向重力信号系统以及它们如何相互作用。提出了用激光烧蚀法确定根盖重力感知细胞的单细胞分辨率实验。然后，单个细胞壁的荧光标记将用于绘制根伸长区域单个细胞生长反应的时间和空间组成部分。共聚焦和比例荧光成像将应用于完整的根可视化Ca2+和ph依赖的信号反应，因为根响应重力。这些第二信使的信号相关变化将通过微注射Ca2+和ph相关信号分子及其拮抗剂来模拟或阻断定义的感知和反应细胞。最后，实验将进行，以产生确定的梯度生长素，Ca2+和pH在完整植物的根组织中使用这些假定的调节剂笼形式的局部释放。这些实验将直接验证这些调节因子的不对称性参与了沿完整根协调热带生长的假设。研究结果将扩展我们对根系重力响应的理解，并有助于定义植物器官对环境信号的生长响应的相互作用。

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. It is thought that in the root gravity is perceived in cap cells and that this signal is converted to asymmetrical growth through a mechanism involving asymmetrical auxin and Ca2+ distribution. Much of the debate can be traced to our relative ignorance of the interacting signaling systems that tranduce, coordinate and integrate these tropic responses. The goal of this research is therefore to define these critical gravetropic signaling systems and how they interact, to the cellular level, using the roots of Arabidopsis thaliana as a model system. Experiments are proposed using laser ablation to define the graviperceptive cells of the root cap with single cell resolution. Fluorescence tagging of single cell walls will then be used to map the temporal and spatial components of individual cellular growth response in the elongating region of the root. Confocal and ratio fluorescent imaging will be applied to the intact root to visualize Ca2+- and pH-dependent signaling responses as the root responds to gravity. Signal related changes in these second messengers will then be mimicked or blocked by microinjecting the defined perceptive and responsive cells with Ca2+ and pH-related signaling molecules and their antagonists. Finally, experiments will be performed to generate defined gradients of auxin, Ca2+ and pH in root tissue in intact plants using localized release of caged forms of these putative regulators. These experiments will directly test the hypothesis that asymmetries in these regulators are involved in coordinating the tropic growth along the intact root. Results from the research will extend our understanding of gravity responses in roots specifically, and help define the interactions that integrate the growth responses of plant organs to environmental signals in general.