Data for: Plasmodesmal endoplasmic reticulum proteins regulate intercellular trafficking of Cucumber mosaic virus in Arabidopsis

Plasmodesmata (PD) are plasma membrane (PM)-lined cytoplasmic nanochannels that mediate in cell-to-cell communication across the cell wall. A range of proteins are embedded in the PD PM and endoplasmic reticulum (ER) and function in regulating PD-mediated symplasmic trafficking. However, knowledge of the nature and function of the ER-embedded proteins, in the intercellular movement of non-cell-autonomous proteins, is limited. Here, we report the functional characterization of two ER luminal proteins, AtBiP1/2, and two ER integral membrane proteins, AtERdj2A/B, which are located within the PD. These PD proteins were identified as interacting proteins with Cucumber mosaic virus (CMV) movement protein (MP) in coimmunoprecipitation studies, using an Arabidopsis-derived plasmodesmal-enriched cell wall protein preparation (PECP). The AtBiP1/2 PD location was confirmed by transmission electron microscopy-based immunolocalization, and their AtBiP1/2 signal peptides (SPs) function in PD targeting. In vitro/in vivo pull-down assays revealed the association between AtBiP1/2 and CMV MP, mediated by AtERdj2A, through the formation of an AtBiP1/2-AtERdj2-CMV MP complex within PD. The role of this complex in CMV infection was established, as systemic infection was retarded in bip1/bip2w and erdj2b mutants. Our findings provide a model for a mechanism by which the CMV MP mediates in cell-to-cell trafficking of its viral ribonucleoprotein complex.

胞间连丝（Plasmodesmata，PD）是被质膜（plasma membrane，PM）包被的细胞质纳米通道，可介导跨细胞壁的细胞间通讯。多种蛋白嵌入PD相关质膜与内质网（endoplasmic reticulum，ER），在调控PD介导的共质体运输（symplasmic trafficking）中发挥功能。然而，目前对于嵌入内质网的蛋白在非细胞自主蛋白（non-cell-autonomous proteins）的细胞间移动过程中的本质与功能，相关认知仍较为有限。
本研究对两种定位于PD的内质网腔蛋白AtBiP1/2，以及两种内质网整合膜蛋白AtERdj2A/B进行了功能表征。这些PD蛋白是通过采用拟南芥（Arabidopsis）来源的胞间连丝富集型细胞壁蛋白制剂（plasmodesmal-enriched cell wall protein preparation，PECP）开展免疫共沉淀（coimmunoprecipitation）实验时，与黄瓜花叶病毒（Cucumber mosaic virus，CMV）运动蛋白（movement protein，MP）互作筛选得到的互作蛋白。
通过基于透射电子显微镜（transmission electron microscopy）的免疫定位（immunolocalization）实验，证实了AtBiP1/2定位于PD，且其信号肽（signal peptides，SPs）可介导PD靶向定位。体外/体内下拉实验（pull-down assays）揭示，AtERdj2A可介导AtBiP1/2与CMV运动蛋白的结合，三者在PD内形成AtBiP1/2-AtERdj2-CMV MP复合物。
该复合物在CMV侵染中的作用得到验证：bip1/bip2w与erdj2b突变体的系统侵染进程均受到阻滞。本研究的发现为CMV运动蛋白介导病毒核糖核蛋白复合物（viral ribonucleoprotein complex）的细胞间运输机制提供了理论模型。