Long distance RNA movement

2 April 2018, by Julia Kehr

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
arethoughttogetaccesstothesugar-conductingphloemvesselsviaspecializedplasmodesmata
(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.

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