Viroids: Small Probes for Exploring the Vast Universe of RNA Trafficking in Plants

Abstract

Cell-to-cell and long-distance trafficking of RNA is a rapidly evolving frontier of integrative plant biology that broadly impacts studies on plant growth and development, spread of infectious agents and plant defense responses. The fundamental questions being pursued at the forefronts revolve around function, mechanism and evolution. In the present review, we will first use specific examples to illustrate the biological importance of cell-to-cell and long-distance trafficking of RNA. We then focus our discussion on research findings obtained using viroids that have advanced our understanding of the underlying mechanisms involved in RNA trafficking. We further use viroid examples to illustrate the great diversity of trafficking machinery evolved by plants, as well as the promise for new insights in the years ahead. Finally, we discuss the prospect of integrating findings from different experimental systems to achieve a systems-based understanding of RNA trafficking function, mechanism and evolution.Wang Y, Ding B (2010) Viroids: Small probes for exploring the vast universe of RNA trafficking in plants.

A Three-Dimensional RNA Motif inPotato spindle tuber viroidMediates Trafficking from Palisade Mesophyll to Spongy Mesophyll inNicotiana benthamiana

“…Lacking proteincoding capacity and helper viruses, viroid RNAs most likely interact directly with preexisting cellular machineries to move from cell to cell and from organ to organ to establish systemic infections. Therefore, viroids provide simple models to investigate the RNA structural elements critical for cell-to-cell trafficking (Ding and Wang, 2009;Wang and Ding, 2010). The 359-nucleotide genome of PSTVd folds into a rod-like secondary structure that has been supported by biophysical, structural and mutational studies (Flores et al, 2005;Owens, 2007;Ding, 2009).…”

Viroid-specific small RNA in plant disease

“…Distinct loops in native viroid structures have been proposed to be involved in either type of movement (cell-to-cell and long-distance). 40,41 In this model, these RNA motifs are thought to interact with certain host proteins that enable viroid trafficking. A series of proteins that appear to be specific viroid binding partners have been identified in the past decade; these include in cucumber phloem protein 2 that interacts with HSVd, [42][43][44] and in tale cress the ribosomal protein L5 and transcription factor IIIA that interact in vitro with PSTVd.…”

Pumilio-Based RNA In Vivo Imaging

“…Plasmodesmata serve as intercellular conduits for different species of RNA between plant cells, including siRNAs mediating systemic posttranscriptional silencing (1), miRNAs involved in developmental control (2), the infectious genomes of RNA viruses and viroids (3,4), and cellular mRNAs (5,6). Therefore, techniques which permit the sequence-specific, dynamic localisation of RNAs in live cells are a valuable tool to study plasmodesmata function.…”