ER-TO-GOLGI TRANSPORT IN HIGHER PLANT CELLS: NEW STRUCT & A NEW MECHANISM

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 植物高尔基体的堆叠沿着肌动蛋白丝束以“走走停停”的运动模式行进。 这种停止和前进模式的特征是快速直线位移（前进阶段）和在设定位置随机摆动（停止阶段）之间的交替。 摆动的高尔基体堆栈与ER出口位点（tER）标记的Sec 13蛋白，COPII囊泡运输机制的一个组成部分瞬时。 这表明，ER-高尔基体运输在植物细胞中发生在这两个隔间之间的短暂相互作用。 我们已经调查了高尔基堆栈和ER在拟南芥和苜蓿根分生组织和柱细胞，使用电子断层扫描和免疫电镜。 通过AtSar 1 p抗血清标记的出芽COPII囊泡的存在来鉴定tER位点。 一小部分的高尔基体堆栈位于ER出口网站附近，这些高尔基体似乎是通过核糖体排除矩阵连接到的tER网站。 内质网出口网站往往是组织周围的顺式侧关闭高尔基体堆栈。 所有的COPII囊泡周围的核糖体排除矩阵，无论是在萌芽和转移到高尔基体。 COPII囊泡被认为是停靠高尔基体堆栈的高尔基体基质内，这些总是显示一个小的，不规则形状的顺式最池。 高尔基栈不连接到ER出口网站包含几个COPII囊泡在其矩阵和缺乏特征性的顺式脑池组装中间体。 在根柱细胞中，ER定位于细胞质的皮层区域。 细胞皮质中的高尔基体堆叠也通过基质与ER输出位点偶联，并显示组装的顺式池;靠近细胞中心的那些缺乏这些结构。 总之，这些研究结果表明，COPII囊泡介导的运输过程中发生的“停止”阶段的高尔基体运动，并停止的过程涉及的核糖体之间的形成COPII囊泡和高尔基体基质的顺式侧的排除矩阵的瞬时连接的形成。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Plant Golgi stacks travel along actin filament bundles in a "Stop and Go" pattern of movement. This Stop and Go pattern is characterized by alternations between rapid straight displacements (go phase), and random wiggling at set locations (stop phase). Wiggling Golgi stacks are associated transiently with ER export sites (tER) marked by the Sec13 protein, a component of the COPII vesicular transport machinery. This suggests that the ER-to-Golgi transport in plant cells takes place during transient interactions between these two compartments. We have investigated Golgi stacks and the ER in Arabidopsis thaliana and in alfalfa root meristem and columella cells, using electron tomography and immunoelectron microscopy. tER sites were identified by the presence of budding COPII vesicles labeled by antisera against AtSar1p. A fraction of the Golgi stacks were located close to ER export sites, and these Golgi appeared to be connected to the tER sites through a ribosome-excluding matrix. ER export sites tend to be organized around the cis-side of close Golgi stacks. All of the COPII vesicles were surrounded by a ribosome-excluding matrix, both while budding and during their transfer to the Golgi. COPII vesicles were seen within the Golgi matrix of docked Golgi stacks and these always displayed a small, irregularly shaped cis-most cisterna. Golgi stacks not connected to ER export sites contained few COPII vesicles in their matrices and lacked characteristic cis-cisternal assembly intermediates. In root columella cells, the ER is confined to cortical region of the cytoplasm. Golgi stacks in the cell cortex were also coupled to ER export sites via a matrix and displayed assembling cis-cisternae; those near the cell's center lacked these structures. Together, these findings demonstrate that COPII vesicle-mediated transport occurs during the "stop" phase of Golgi movement, and that the process of stopping involves the formation of transient links between the ribosome-excluding matrix of forming COPII vesicles and the cis-side of the Golgi matrix.