真核细胞生长和极性建立等过程都离不开分泌囊泡的胞内运输和胞吐作用，但对于分泌囊泡的定向运输及其与质膜之间互作的分子网络仍有待深入研究。我们在前期研究中发现Formin家族成员AtFH5定位于花粉细胞内分泌囊泡上，既促进微丝聚合延伸，又特异地与萌发位点处的质膜识别和融合，为研究分泌囊泡的运输和胞吐作用提供了有力的研究材料。本项目拟以拟南芥花粉为模型，综合利用多种技术手段开展以下三个方面的工作：1）验证微丝骨架的聚合推动AtFH5所标记囊泡运动的假说，深入研究分泌囊泡定向运输的动力学基础；2）研究微丝骨架相关蛋白与Exocyst复合体互作在囊泡栓系质膜过程中的作用，解析分泌囊泡特异识别花粉萌发位点的分子机理；3）研究微丝骨架相关蛋白与SNARE蛋白互作在囊泡与质膜融合过程中作用的分子机制。该研究不仅能解析微丝骨架系统的新功能，同时有助于深入理解细胞内囊泡运输、胞吐作用和极性生长的分子调控网络。

In Eukaryotes the intracellular vesicle trafficking and the exocytosis are critical for a bulk of essential physiological processes including cell growth and polarity establishment. However, the molecular mechanism underlying the directional transportation of secretory vesicles as well as their interactions with the plasma membrane remains further investigations. In previous studies, we observed that a formin protein, AtFH5, localized at secretory vesicles in pollen grains and promoted the polymerization and elongation of actin filaments. Moreover, AtFH5-localized vesicles specifically translocated to the prospective germination site, where they fused with the plasma membrane. These behaviors make AtFH5-localized vesicles an excellent marker for studying the transportation and exocytosis of the secretory vesicles in plant cells. In this proposal, we plan to use Arabidopsis pollen cells as a model and perform following experiments to pursue the molecular mechanism controlling the behaviors of AtFH5-localized vesicles. First of all, we will test our hypothesis that the polymerization and elongation of actin filaments promote the mobility of AtFH5-labeled vesicles. We aim to investigate the molecular mechanism contributing to the driving force of the secretory vesicle transportation in plant cells. Secondly, we will investigate the functions of the Exocyst complex in tethering AtFH5-labeled vesicles to the plasma membrane, through which we intend to analyze the molecular mechanism of how AtFH5 recognizes the prospective germination site. Thirdly, we will focus on deciphering how secretory vesicles fuse with the plasma membrane. For this purpose, we will investigate the functions of SNARE proteins in the fusion process of AtFH5-labeled vesicles with the plasma membrane. Our proposal will not only analyze the new functions of actin cytoskeleton in plant cells. In addition, it will shed light on the molecular mechanism of vesicle trafficking, exocytosis and polar growth in eukaryotic cells.