Mechanisms of phloem-mediated RNA traffic

在多细胞生物中，细胞之间相互传递信号，协调决定生长发育的基因表达模式。在植物中，称为胞间连丝的细胞质通道形成细胞间信号传导的一条途径。此外，维管组织韧皮部形成一个通道网络，允许远处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和蛋白质通过胞间连丝从一个细胞传递到另一个细胞，通过韧皮部从一个器官传递到另一个器官。RNA转运似乎在植物发育、生理和防御中起着重要作用。该项目解决了RNA在植物中是如何被调节的问题，使用类病毒传输作为一个高度可处理的模型系统。类病毒是感染植物的小致病性rna。它们不编码蛋白质，可以在受感染的植物内复制和系统移动。类病毒rna很可能已经进化出了利用已有的细胞机制通过胞间连丝和韧皮部进行运输的能力。这项工作有三个目标：1)测试假设，即RNA在系统运输过程中使用不同的机制进入和退出韧皮部；2)识别控制韧皮部退出的RNA的细胞边界；3)识别介导韧皮部退出的RNA基序。该项目的结果有望产生对细胞间交通重要的RNA结构和细胞因子的新见解。这些见解可能会影响研究内源性植物rna如何调节细胞生长发育过程，以及病毒rna如何系统地传输以传播感染。

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.