tRNA-Related Sequences Trigger Systemic mRNA Transport in Plants

Abstract

In plants, protein-coding mRNAs can move via the phloem vasculature to distant tissues, where they may act as non-cellautonomous signals. Emerging work has identified many phloem-mobile mRNAs, but little is known regarding RNA motifs triggering mobility, the extent of mRNA transport, and the potential of transported mRNAs to be translated into functional proteins after transport. To address these aspects, we produced reporter transcripts harboring tRNA-like structures (TLSs) that were found to be enriched in the phloem stream and in mRNAs moving over chimeric graft junctions. Phenotypic and enzymatic assays on grafted plants indicated that mRNAs harboring a distinctive TLS can move from transgenic roots into wild-type leaves and from transgenic leaves into wild-type flowers or roots; these mRNAs can also be translated into proteins after transport. In addition, we provide evidence that dicistronic mRNA:tRNA transcripts are frequently produced in Arabidopsis thaliana and are enriched in the population of graft-mobile mRNAs. Our results suggest that tRNA-derived sequences with predicted stem-bulge-stem-loop structures are sufficient to mediate mRNA transport and seem to be necessary for the mobility of a large number of endogenous transcripts that can move through graft junctions.

Selective Targeting of Mobile mRNAs to Plasmodesmata for Cell-to-Cell Movement

“…3 and 4 important intercellular cytoplasmic connecting channels for exchange of various macro-314 and micro-molecules (Turnbull and Lopez-Cobollo, 2013). The selective targeting of 315 mobile mRNA to PD (Figure 3 and 4) further supports that the trafficking of mobile 316 mRNA is triggered by specific RNA sequences rather than transcript abundance (Huang 317 and Yu, 2009;Zhang et al, 2016). The differential targeting of mobile and non-mobile 318 mRNAs may be a determining step for RNA movement.…”

“…In addition, 73 recent evidence indicates that the transfer RNA (tRNA)-like structure on a subset of 74 mobile mRNAs is a signal triggering mRNA movement (Zhang et al, 2016). Thus, how 75 mobile mRNA is translocated cell-to-cell remains to be elucidated.…”

“…4A-D), which suggests that 355 plant endogenous RBPs may target mobile mRNAs to PD. These RBPs may recognize a 356 specific structure on mobile mRNAs (e.g., the tRNA-like structures) to direct the 357 movement of mobile mRNAs (Zhang et al, 2016). The different structure motifs on 358 mobile mRNAs may recruit specific RBPs at particular stages, or reciprocally, the 359 enrolled RBPs may induce a conformational change in mRNA structure for further 360 transport (Edelmann et al, 2017).…”

A stable tRNA-like molecule is generated from the long noncoding RNA GUT15 in Arabidopsis

“…Accordingly, we conclude that the presence of a tRNA coding sequence in the host protein-coding genes does not interfere with gene splicing. Interestingly, Zhang and coworkers [38] revealed an additional role of tRNA sequences in systemic mRNA transport in plants. These authors found that mobile mRNAs in Arabidopsis are enriched in tRNA-like motifs or are transcribed from genes located in close proximity to annotated tRNA loci, which form di-cistronic mRNA-tRNA transcripts at a high frequency (according to paired-end RNA-seq data).…”

Ticket to Ride: tRNA-Related Sequences and Systemic Movement of mRNAs

“…To test the role of TLSs in the mobility of plant transcripts, Zhang et al (2016) used DISRUPTION OF MEIOTIC CONTROL1 (DMC1); silencing of DMC1, or the presence of a truncated, dominant-negative DMC1 ( DN DMC1) causes pollen defects and male sterility. Thus, male sterility provides a readout for translocation of DN DMC1 mRNA fusions moving from the rootstock into a grafted, wild-type scion.…”