Dual targeting of a virus movement protein to ER and plasma membrane subdomains is essential for plasmodesmata localization.
Dual targeting of a virus movement protein to ER and plasma membrane subdomains is essential for plasmodesmata localization.
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DOI：
10.1371/journal.ppat.1006463
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发表时间：
2017-06
期刊：
影响因子：
6.7
通讯作者：
Namba S
中科院分区：
文献类型：
--
作者：
Ishikawa K;Hashimoto M;Yusa A;Koinuma H;Kitazawa Y;Netsu O;Yamaji Y;Namba S
植物病毒运动蛋白定位于胞间连丝上，促进病毒在细胞间的运动。许多研究表明，MP使用通过ER或通过质膜（PM）的途径。此外，最近的研究报道，ER-PM接触位点和PM微结构域，这是在ER和PM中发现的亚结构域，参与病毒细胞间的运动。然而，先前尚未描述MP业务中的这些子域与PD的功能关系。在这里，我们证明了无花果花叶病毒MP（MPFMV）的细胞内贩运使用活细胞成像，专注于其ER导向信号肽（SPFMV）。瞬时表达的MPFMV主要分布在PD和PM的斑片状微区。ER转运效率的调查显示，SPFMV具有相当低的效率相比，SP的良好特征的植物蛋白，钙网蛋白和CLAVATA 3。缺乏SPFMV的MPFMV突变体专门定位于PM微结构域，而SP嵌合体，其中MPFMV的SP被钙网蛋白或CLAVATA 3的SP取代，专门定位于ER的节点，其标记有拟南芥突触结合蛋白1，ER-PM接触位点的主要成分。从这些结果中，我们推测，SPFMV的低易位效率有助于ER易位和微区定位群体的产生，这两者都是PD定位所必需的。与这一假设相一致，SP缺陷型MPFMV与SP嵌合体共表达时定位于PD。在这里，我们提出了一个新的模型为细胞内贩运的病毒MP。未能易位的MPFMV的相当大一部分被转移到微区，而成功易位到ER中的MPFMV的其余部分随后定位到ER-PM接触位点，并在微区定位的MPFMV进入PD中起重要作用。通过胞间连丝（PD）的细胞间分子运输是植物发育不可或缺的。植物病毒也利用细胞间运输系统建立系统感染。病毒运动蛋白（MPs）具有定位于PD并自主移动到邻近细胞的能力，在促进病毒细胞间运动中起重要作用。因此，了解MP如何达到PD对于病毒学和植物细胞生物学具有重要意义。本研究以无花果花叶病毒运动蛋白（MPFMV）的N端信号肽（SP）为主要研究对象，分析了MPFMV的胞内运输。SP是一种将蛋白质引导至内质网的短肽，经常在多种蛋白质中发现，但很少在植物病毒蛋白中发现。本研究以MPFMV的SP为研究对象，探讨ER易位与PD定位的关系。我们发现MPFMV的SP具有相当低的易位效率，并有助于产生两个不同的群体。每个人口本地化的ER和PM的专门的子域，是必不可少的PD本地化，表明这些子域和PD功能相关。因此，我们的发现为植物细胞间的运动提供了新的见解。
Plant virus movement proteins (MPs) localize to plasmodesmata (PD) to facilitate virus cell-to-cell movement. Numerous studies have suggested that MPs use a pathway either through the ER or through the plasma membrane (PM). Furthermore, recent studies reported that ER-PM contact sites and PM microdomains, which are subdomains found in the ER and PM, are involved in virus cell-to-cell movement. However, functional relationship of these subdomains in MP traffic to PD has not been described previously. We demonstrate here the intracellular trafficking of fig mosaic virus MP (MPFMV) using live cell imaging, focusing on its ER-directing signal peptide (SPFMV). Transiently expressed MPFMV was distributed predominantly in PD and patchy microdomains of the PM. Investigation of ER translocation efficiency revealed that SPFMV has quite low efficiency compared with SPs of well-characterized plant proteins, calreticulin and CLAVATA3. An MPFMV mutant lacking SPFMV localized exclusively to the PM microdomains, whereas SP chimeras, in which the SP of MPFMV was replaced by an SP of calreticulin or CLAVATA3, localized exclusively to the nodes of the ER, which was labeled with Arabidopsis synaptotagmin 1, a major component of ER-PM contact sites. From these results, we speculated that the low translocation efficiency of SPFMV contributes to the generation of ER-translocated and the microdomain-localized populations, both of which are necessary for PD localization. Consistent with this hypothesis, SP-deficient MPFMV became localized to PD when co-expressed with an SP chimera. Here we propose a new model for the intracellular trafficking of a viral MP. A substantial portion of MPFMV that fails to be translocated is transferred to the microdomains, whereas the remainder of MPFMV that is successfully translocated into the ER subsequently localizes to ER-PM contact sites and plays an important role in the entry of the microdomain-localized MPFMV into PD. Intercellular trafficking of molecules through plasmodesmata (PD) is indispensable for plant development. Plant viruses also use the intercellular trafficking system to establish systemic infection. Virus movement proteins (MPs), which have abilities to localize to PD and to move to the adjacent cells autonomously, play important roles in facilitating virus cell-to-cell movement. Hence, understanding how MPs reach PD has great significance for virology and plant cell biology. In this study, we analyzed the intracellular trafficking of fig mosaic virus movement protein (MPFMV) mainly based on its N-terminal signal peptide (SP). SPs, short peptides directing proteins to the ER, are frequently found in a diverse array of proteins, but rarely found in plant virus proteins. We focused on the SP of MPFMV and investigated the relationship between ER translocation and PD localization. We showed that the SP of MPFMV had quite low translocation efficiency and contributes to generating two distinct populations. Each population localized to specialized subdomains of the ER and PM, and was essential for PD localization, indicating that these subdomains and PD are functionally related. Thus, our findings offer new insights into cell-to-cell movement in plants.