微丝及其结合蛋白、顶端钙离子梯度、活性氧、小G蛋白等等都在根毛细胞的顶端生长中发挥着十分重要的功能，但是细胞骨架和信号系统在根毛细胞生长调控中是如何协同起作用的仍有待解析。申请人之前的研究证明了拟南芥MAP18蛋白可以依赖钙离子调控微丝从而控制花粉管顶端生长的方向，初步的观察结果又表明MAP18可能参与了根毛细胞的生长调控。本项目拟通过分析小G蛋白ROP2和Ca2+是如何调节MAP18的亚细胞定位从而影响MAP18与微丝骨架的作用来影响细胞顶端生长的，MAP18对ROS的产生和分布所形成的正反馈信号，以及囊泡运输对MAP18定位的负反馈信号的相关调节机制等内容进行研究，从而建立起一个信号转导系统通过MAP18蛋白的介导调控细胞骨架动态进而影响根毛细胞极性生长的途径。研究结果对深入了解植物细胞极性生长过程中信号转导系统和细胞骨架间的调控机制有重要的科学理论意义。

Actin filaments, actin-binding proteins, the tip-focused calcium gradient, ROS, and small G proteins are key factors involved in polar growth of root hais and pollen tubes. However, it is largely unknown about the coordination between these signal components and the cytokeleton. We previously reported that a Arabidopsis microtubule-associated protein, MAP18, functions in controlling the direction of pollen tube growth by its Ca2+-dependent F-actin-severing activity. Our preliminary observations indicated that MAP18 may also function in root hair growth. In this project, studies about how the subcellular localization of MAP18 is regulated by a small G protein ROP2 and Ca2+ to further affect the actin cytoskeleton in root hair cells; how MAP18 affects the production and contribution of ROS, forming as a positive feedback; and how the vesicle trafficking takes place as a negative feedback on MAP18 positioning will be carried out. Thess studies will establish a pathway of signal transduction system mediated by MAP18 protein to regulate the cytoskeleton involved in root hair polar growth.