Cell Edges Accumulate Gamma Tubulin Complex Components and Nucleate Microtubules following Cytokinesis in Arabidopsis thaliana

Microtubules emanate from distinct organizing centers in fungal and animal cells. In plant cells, by contrast, microtubules initiate from dispersed sites in the cell cortex, where they then self-organize into parallel arrays. Previous ultrastructural evidence suggested that cell edges participate in microtubule nucleation but so far there has been no direct evidence for this. Here we use live imaging to show that components of the gamma tubulin nucleation complex (GCP2 and GCP3) localize at distinct sites along the outer periclinal edge of newly formed crosswalls, and that microtubules grow predominantly away from these edges. These data confirm a role for cell edges in microtubule nucleation, and suggest that an asymmetric distribution of microtubule nucleation factors contributes to cortical microtubule organization in plants, in a manner more similar to other kingdoms than previously thought.微管在真菌与动物细胞中均源自特定的组织中心。与之形成鲜明对比的是，植物细胞内的微管起始于细胞皮层中的分散位点，并在此处自组装为平行阵列。既往超微结构研究证据提示，细胞边缘参与微管成核过程，但迄今尚未有直接实验证据证实这一假说。本研究通过活细胞成像技术证实，γ微管蛋白成核复合物（gamma tubulin nucleation complex）的组分GCP2与GCP3定位于新形成横隔壁的外侧周质边缘的特定位点，且微管主要从这些边缘向外延伸生长。上述数据证实了细胞边缘在微管成核中的功能，并提示微管成核因子的不对称分布参与植物皮层微管的组织过程，其机制较此前所认为的更接近于其他生物界。