Uncovering Molecular Mechanisms Underlying Cell-to-Cell Movement and Long-Distance Trafficking of Viruses in Plants

植物病毒感染所有主要农作物，每年在全球范围内造成数十亿美元的经济损失。作为专性的细胞内寄生虫，植物病毒只能在寄主植物中繁殖。为了建立系统感染，当后代病毒在主要感染的细胞中成功繁殖时，新生的病毒基因组必须在本地传播到邻近细胞，称为细胞间移动，并进一步系统地移动到植物的其他部分，称为远程移动。病毒的细胞间移动是通过胞间连丝(PD)进行的，胞间连丝是植物界特有的一种特殊的细胞间细胞器。PD是一种结构复杂的微通道，它穿过细胞壁，在相邻细胞之间建立细胞质和内膜的连续性。PD允许小分子在细胞间扩散，调节大分子或大分子复合体(如病毒颗粒和核蛋白复合体)的细胞间运输。病毒通过PD的细胞间运动是由病毒编码蛋白(S)介导的一个活跃过程。长距离移动是病毒从叶肉细胞通过束鞘细胞、韧皮部薄壁组织和伴生细胞进入韧皮部筛分元件(SE)的过程，在那里它们被转移，然后在遥远的地点卸货，从那里将发生进一步的感染。由于帕金森病的复杂性和参与病毒传播的各种细胞类型，病毒细胞间运动的分子机制尚不清楚。我们最近的研究表明，植物马铃薯Y病毒是已知的最大和最重要的一组病毒，通过两种病毒蛋白如CI和P3N-PIPO的协调作用，在PD形成特殊的结构，促进病毒的细胞间运动。我们最新的基因研究还表明，(1)外壳蛋白(CP)是马铃薯Y病毒系统性传播所必需的；以及(2)除了病毒基因组复制和细胞间移动外，马铃薯Y病毒CI蛋白在病毒的长距离移动中也发挥着独特的、必不可少的作用。在这项建议中，我们建议进一步研究PD形成锥形结构的途径，以及CI和CP如何参与病毒的全身运动。我们还将确定马铃薯Y病毒细胞间和长距离运动所需的宿主基因产物，并进一步鉴定它们的功能。因此，这一建议将促进我们对病毒局部和系统传播的了解，并直接有助于开发新的抗病毒策略。此外，拟议工作取得的成果还将有助于更好地了解基本的细胞过程，如细胞到细胞和植物中大分子复合体的长途运输，从而通过促进基础细胞和分子生物学的知识为生命科学做出贡献。

Plant viruses infect all major crops and cause economic losses of multibillion dollars worldwide each year. As obligate intracellular parasites, plant viruses can only multiply in their host plants. In order to establish a systemic infection, upon successful reproduction of progeny viruses in primarily infected cells, the nascent viral genome must spread locally to neighboring cells, termed cell-to-cell movement, and further move systemically to other parts of the plant, named long-distance movement. Cell-to-cell movement of viruses occurs through plasmodesmata (PD), a specialized intercellular organelle, unique to the plant kingdom. PD are structurally complex microchannels that cross the cell wall and establish cytoplasmic and endomembrane continuity between neighbouring cells. PD allow small molecules to diffuse between cells and regulate the intercellular trafficking of macromolecules or macromolecular complexes such as viral particles and ribonucleic protein complexes. Viral cell-to-cell movement through PD is an active process mediated by virus-encoded protein(s). Long-distance movement is the process by which the virus moves from the mesophyll via bundle sheath cells, phloem parenchyma, and companion cells into phloem sieve elements (SE) where they are translocated, and then unloaded at a remote site from which further infection will occur. Due to the complexity of PD and various types of cells involved in viral spread, the molecular mechanism of viral intercellular movement is poorly understood. Our recent studies have shown that plant potyviruses, the largest and most agricultural important group of known viruses, form a special structure at PD via the coordinated action of two viral proteins, e.g., CI and P3N-PIPO, to facilitate viral cell-to-cell movement. Our most recent genetic work has also demonstrated that (1) the coat protein (CP) is required for systemic spread of potyviruses; and (2) in addition to viral genome replication and cell-to-cell movement, the potyviral CI protein also plays a distinct, essential role in viral long-distance movement. In this proposal, we propose to further investigate the pathways recruited for the formation of conical structures at PD and how CI and CP are involved in viral systemic movement. We will also identify host gene products required in potyviral cell-to-cell and long-distance movement, and further characterize their functional roles. Therefore, this proposal will advance our knowledge of viral local and systemic spread and directly contribute to the development of novel antiviral strategies. Moreover, the results obtained from the proposed work will also help better understanding of essential cellular processes such as cell-to-cell and long-distance trafficking of macromolecular complexes in plants, and thus contribute to life science by advancing knowledge in fundamental cell and molecular biology.