Mechanisms of phloem-mediated RNA traffic

在多细胞生物体中，细胞相互发送信号以协调决定生长和发育的基因表达模式。在植物中，被称为胞间连丝的细胞质通道形成了细胞间信号传递的一条途径。此外，维管组织韧皮部形成通道网络，以允许远距离细胞或器官之间的信号传递。越来越多的证据表明，选定的RNA和蛋白质运输从细胞到细胞通过胞间连丝和从器官到器官通过韧皮部。RNA运输似乎在植物发育、生理和防御中具有重要作用。该项目解决了如何在植物中调节RNA交通的问题，使用类病毒交通作为一个高度易处理的模型系统。类病毒是感染植物的小的致病性RNA。它们不编码蛋白质，可以在受感染的植物中系统地复制和移动。很可能类病毒RNA已经进化出利用预先存在的细胞机制通过胞间连丝和韧皮部运输的能力。这项工作有三个目标：1）测试RNA在系统运输期间使用不同机制进入和离开韧皮部的假设，2）鉴定控制RNA的韧皮部离开的细胞边界，以及3）鉴定介导韧皮部离开的RNA基序。该项目的结果有望产生关于RNA结构和细胞因子的新见解，这些结构和细胞因子对细胞间交通至关重要。这些见解可能会影响内源性植物RNA交通如何调节细胞过程的基础生长和发育，以及病毒RNA如何系统地传播感染的研究。

In a multicellular organism, cells signal each other to coordinate gene expression patterns that dictate growth and development. In plants, cytoplasmic channels called plasmodesmata form one pathway for cell-cell signaling. Furthermore, the vascular tissue phloem forms a network of channels to allow signaling between distant cells or organs. Increasing evidence indicates that selected RNAs and proteins traffic from cell to cell through plasmodesmata and from organ to organ through the phloem. RNA traffic appears to have important roles in plant development, physiology, and defense. This project addresses the question of how RNA traffic is regulated in a plant, using viroid traffic as a highly tractable model system. Viroids are small pathogenic RNAs that infect plants. They do not encode proteins and can replicate and move systemically within an infected plant. It is likely that viroid RNAs have evolved the capacity to utilize pre-existing cellular mechanisms to traffic through plasmodesmata and the phloem. This work has three objectives: 1) testing the hypothesis that an RNA uses different mechanisms to enter and exit the phloem during systemic traffic, 2) identifying the cellular boundary that controls phloem exit of an RNA, and 3) identifying the RNA motif(s) that mediates phloem exit. Results from this project are expected to yield novel insights about the RNA structures and cellular factors that are important for intercellular traffic. Such insights may impact studies on how endogenous plant RNAs traffic to regulate cellular processes underlying growth and development and how viral RNAs traffic systemically to spread infection.