众所周知，微丝细胞骨架的动态组装控制花粉管的极性生长。然而到目前为止，人们对花粉管如何精密调控微丝的动态组装还知之甚少。
中科院植物研究所黄善金研究组对花粉中高度表达的微丝相关蛋白VILLIN5进行了功能解析，发现拟南芥缺失VILLIN5之后花粉管中微丝的稳定性迅速下降，进而影响花粉管生长，说明拟南芥VILLIN5很可能通过稳定微丝调控极性生长。
利用体外生化分析和全内反射荧光显微技术，研究人员发现，VILLIN5具有微丝成束和依赖于钙离子的微丝切割功能，同时还发现生理水平的钙离子浓度足以激活VILLIN5的切割活性。
该研究为植物VILLIN在细胞内的生理学功能提供了直接证据，丰富了人们对该蛋白家族作用的理解，暗示VILLIN5很可能通过协同钙离子信号调控花粉管生长。该研究成果为阐明微丝细胞骨架与植物细胞极性生长的关系，进而建立植物细胞极性生长的调控网络提供了重要的实验证据。（生物谷Bioon.com）
生物谷推荐英文摘要：
The Plant Cell doi：10.1105/tpc.110.076257
Arabidopsis VILLIN5, an Actin Filament Bundling and Severing Protein, Is Necessary for Normal Pollen Tube Growth[W]
Hua Zhanga,b,1, Xiaolu Qua,b,1, Chanchan Baoa,b, Parul Khuranac, Qiannan Wanga,b, Yurong Xiea, Yiyan Zhenga,b, Naizhi Chena, Laurent Blanchoind, Christopher J. Staigerc and Shanjin Huanga,2
a Center for Signal Transduction and Metabolomics, Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
b Graduate School of Chinese Academy of Sciences, Beijing, 100049, China
c Department of Biological Sciences and Bindley Bioscience Center, Purdue University, West Lafayette, Indiana 47907-2064
d Institut de Recherches en Technologie et Sciences pour le Vivant, Laboratoire de Physiologie Cellulaire Végétale, Commissariat à l’Energie Atomique/Centre National de la Recherche Scientifique/Université Joseph Fourier, F38054 Grenoble, France
A dynamic actin cytoskeleton is essential for pollen germination and tube growth. However, the molecular mechanisms underlying the organization and turnover of the actin cytoskeleton in pollen remain poorly understood. Villin plays a key role in the formation of higher-order structures from actin filaments and in the regulation of actin dynamics in eukaryotic cells. It belongs to the villin/gelsolin/fragmin superfamily of actin binding proteins and is composed of six gelsolin-homology domains at its core and a villin headpiece domain at its C terminus. Recently, several villin family members from plants have been shown to sever, cap, and bundle actin filaments in vitro. Here, we characterized a villin isovariant, Arabidopsis thaliana VILLIN5 (VLN5), that is highly and preferentially expressed in pollen. VLN5 loss-of-function retarded pollen tube growth and sensitized actin filaments in pollen grains and tubes to latrunculin B. In vitro biochemical analyses revealed that VLN5 is a typical member of the villin family and retains a full suite of activities, including barbed-end capping, filament bundling, and calcium-dependent severing. The severing activity was confirmed with time-lapse evanescent wave microscopy of individual actin filaments in vitro. We propose that VLN5 is a major regulator of actin filament stability and turnover that functions in concert with oscillatory calcium gradients in pollen and therefore plays an integral role in pollen germination and tube growth.
