Long distance RNA movement

Abstract

Contents Summary29I.Introduction29II.Phloem as a conduit for macromolecules30III.Classes of phloem transported RNAs and their function32IV.Mode of RNA transport35V.Conclusions37Acknowledgements37References37 Summary In higher plants, small noncoding RNAs and large messenger RNA (mRNA) molecules are transported between cells and over long distances via the phloem. These large macromolecules are thought to get access to the sugar‐conducting phloem vessels via specialized plasmodesmata (PD). Analyses of the phloem exudate suggest that all classes of RNA molecules, including silencing‐induced RNAs (siRNAs), micro RNAs (miRNAs), transfer RNAs (tRNAs), ribosomal RNA (rRNAs) and mRNAs, are transported via the vasculature to distant tissues. Although the functions of mobile siRNAs and miRNAs as signalling molecules are well established, we lack a profound understanding of mobile mRNA function(s) in recipient cells and tissues, and how they are selected for transport. A surprisingly high number of up to thousands of mRNAs were described in diverse plant species such as cucumber, pumpkin, Arabidopsis and grapevine to move long distances over graft junctions to distinct body parts. In this review, we present an overview of the classes of mobile RNAs, the potential mechanisms facilitating RNA long‐distance transport, and the roles of mobile RNAs in regulating transcription and translation. Furthermore, we address potential function(s) of mobile protein‐encoding mRNAs with respect to their characteristics and evolutionary constraints.

Intercellular delivery of small RNAs in plant gametes

“…Although both Dicer and AGO are involved in easiRNA biogenesis, the mechanism by which the transfer of easiRNAs proceeds from the companion cell to gametes remains elusive. It is well known that long-distance movement of small RNAs in the sporophytes is via phloem (Kehr & Kragler, 2018), while the cellto-cell short-range movement of small RNAs is thought to occur via plasmodesma (Liu & Chen, 2018;Reagan et al, 2018), a membrane-lined cytoplasmic communication channel for plant cells (Nicolas et al, 2017). However, no plasmodemata exists between the vegetative cell and sperm.…”

Potential mechanisms of microRNA mobility

“…In plants, intercellular miRNA signaling in vivo is mediated by plasmodesmata, small channels in the cell wall that resemble GJs in animals . This cell to cell transfer of genetic information has been described to coordinate growth and regulate systemic responses to environmental stimuli . Upon nutrient deprivation, miR‐359 and miR‐399 are translocated from leaf to root and induce a reduction of their mRNA targets in Arabidopsis thaliana .…”

Comprehensive transcriptome profiling and phenotyping of rootstock and scion in a tomato/potato heterografting system

“…Plant vascular systems transport various compounds including essential substances that regulate development or long-distance signaling molecules that mediate root-to-shoot communication (Notaguchi and Okamoto 2015). RNA molecules are transported between cells via the vasculature to distant tissues following the convection flow of the phloem stream (Kehr and Kragler 2018). Grafting, which induces phenotypic variation in morphology, stress tolerance, yield and quality, has been extensively investigated (Warschefsky et al 2016).…”