Viroids and RNA Trafficking in Plants

Abstract

Cell-to-cell trafficking of RNA is a newly discovered mechanism of gene regulation at the whole plant level. The RNAs that traffic within a plant range from mRNAs to non coding RNAs including microRNAs and small interfering RNAs. The mechanisms underlying such trafficking remain largely unknown. Recent studies on Potato spindle tuber viroid (PSTVd), a non coding, circular, and infectious RNA, have demonstrated that distinct three-dimensional (3D) structural motifs in an RNA mediate trafficking across specific cellular boundaries. This 3D motif-mediated cell-specific trafficking mechanism may well apply to the trafficking regulation of cellular RNAs. In this review, we summarize examples of RNA trafficking that functions in plant gene regulation and development and then discuss the utility of PSTVd to identify RNA motifs mediating trafficking. We finally highlight outstanding issues for future investigations.