Faculty of Bioengineering and Bioinformatics, Moscow State University, Moscow 119991, Russia.
Department of Virology, Biological Faculty, Moscow State University, Moscow 119234, Russia.
Plant Sci. 2019 Jul;284:99-107. doi: 10.1016/j.plantsci.2019.04.005. Epub 2019 Apr 9.
Phloem-mobile mRNAs are assumed to contain sequence elements directing RNA to the phloem translocation pathway. One of such elements is represented by tRNA sequences embedded in untranslated regions of many mRNAs, including those proved to be mobile. Genomic RNAs of a number of plant viruses possess a 3'-terminal tRNA-like structures (TLSs) only distantly related to genuine tRNAs, but nevertheless aminoacylated and capable of interaction with some tRNA-binding proteins. Here, we elaborated an experimental system for analysis of RNA phloem transport based on an engineered RNA of Potato virus X capable of replication, but not encapsidation and movement in plants. The TLSs of Brome mosaic virus, Tobacco mosaic virus and Turnip yellow mosaic virus were demonstrated to enable the phloem transport of foreign RNA. A miRNA precursor, pre-miR390b, was also found to render RNA competent for the phloem transport. In line with this, sequences of miRNA precursors were identified in a Cucurbita maxima phloem transcriptome, supporting the hypothesis that, at least in some cases, miRNA phloem signaling can involve miRNA precursors. Collectively, the data presented here suggest that RNA molecules can be directed into the phloem translocation pathway by structured RNA elements such as those of viral TLSs and miRNA precursors.
韧皮部移动 mRNA 被认为含有指导 RNA 进入韧皮部转运途径的序列元件。这样的元件之一是嵌入许多 mRNA 的非翻译区的 tRNA 序列，包括那些被证明是移动的 mRNA。一些植物病毒的基因组 RNA 具有 3'末端 tRNA 样结构 (TLSs)，这些结构与真正的 tRNA 只有远缘关系，但仍然可以被氨酰化，并能够与一些 tRNA 结合蛋白相互作用。在这里，我们构建了一个基于 Potato virus X 工程 RNA 的实验系统，该 RNA 能够复制，但不能在植物中包装和运动。Brome mosaic virus、Tobacco mosaic virus 和 Turnip yellow mosaic virus 的 TLSs 被证明能够使外源 RNA 进行韧皮部运输。miRNA 前体 pre-miR390b 也被发现使 RNA 能够进行韧皮部运输。与此一致的是，在 Cucurbita maxima 韧皮部转录组中鉴定到了 miRNA 前体的序列，支持了这样的假设，即至少在某些情况下，miRNA 韧皮部信号可以涉及 miRNA 前体。总之，这里提出的数据表明，RNA 分子可以通过结构 RNA 元件（如病毒 TLSs 和 miRNA 前体）被定向进入韧皮部转运途径。
