RNA Motifs and Modification Involve in RNA Long-Distance Transport in Plants

Abstract

A large number of RNA molecules have been found in the phloem of higher plants, and they can be transported to distant organelles through the phloem. RNA signals are important cues to be evolving in fortification strategies by long-distance transportation when suffering from various physiological challenges. So far, the mechanism of RNA selectively transportation through phloem cells is still in progress. Up to now, evidence have shown that several RNA motifs including Polypyrimidine (poly-CU) sequence, transfer RNA (tRNA)-related sequence, Single Nucleotide Mutation bound with specific RNA binding proteins to form Ribonucleotide protein (RNP) complexes could facilitate RNA mobility in plants. Furthermore, some RNA secondary structure such as tRNA-like structure (TLS), untranslation region (UTR) of mRNA, stem-loop structure of pre-miRNA also contributed to the mobility of RNAs. Latest researchs found that RNA methylation such as methylated 5′ cytosine (m5C) played an important role in RNA transport and function. These studies lay a theoretical foundation to uncover the mechanism of RNA transport. We aim to provide ideas and clues to inspire future research on the function of RNA motifs in RNA long-distance transport, furthermore to explore the underlying mechanism of RNA systematic signaling.

The m6A RNA Demethylase ALKBH9B Plays a Critical Role for Vascular Movement of Alfalfa Mosaic Virus in Arabidopsis

“…An intriguing observation was that the percentage of infected non-inoculated rosette leaves was higher than that observed for floral stems in alkbh9b plants. This result could be explained by the existence of an alternative way to invade the plant from source to sink leaves that avoids the phloem and that has been demonstrated for a strain of potato virus A ( Vuorinen et al, 2011 ; Wang et al, 2021 ). This proves that, even though it is a quite slow and inefficient alternative route for systemic infection, viruses may invade stems and upper non-inoculated leaves by a cell-to-cell movement through epidermal and mesophyll cells of infected young leaves.…”

“…Therefore, as proposed above for cell-to-cell movement, putative interactions between PD resident proteins of phloem-cellular components and AMV RNAs and/or virions may be affected by the m 6 A status of the vRNAs. Among other functions, methylation has been proposed to affect the systematic transport of plant RNAs modulating their stability ( Wang et al, 2021 ) or the recognition of TLS by tRNA-specific proteins involved in viral transport ( Lezzhov et al, 2019 ). Here, we have found that the lack of ALKBH9B does not affect the viral particle stability, but m 6 A might, for instance, affect the AMV TLS and, consequently, the host-virus interactions required for the transport among specific phloem cells.…”

“…According to our results and contrary to m 5 C, increased levels of m 6 A would decline AMV loading into the phloem and consequently long-distance transport. It is worth noting that Wang et al (2021) recently discussed that the reasons why m 5 C favors the systemic movement of RNAs are unknown so far, and they could be diverse. This would justify the discrepancies between the processing of RNAs harboring one or another modification.…”

Mobile Flowering Locus T RNA – Biological Relevance and Biotechnological Potential

“…For example, no Ile-tRNA or very few Arg-tRNA but a few Asp-tRNA molecules were detected; however, Cys, Leu, Phe, Try, Trp, and Ser tRNAs were predominantly present in the phloem sap ( Zhang et al, 2009 ). These tRNAs have been predicted to serve as long-distance signals ( Zhang et al, 2009 , 2016 ; Lezzhov et al, 2019 ; Wang et al, 2021 ), suggesting that tRNA or tRNA-like structure could be an important factor, if not the determinant for systemic RNA movement. Indeed, in the ViGE systems, like the FT mRNA/102 nt- FT RNA element, Met, Gly, and Ile tRNAs were also found to improve transgenerational gene editing when they were fused to sgRNA ( Ellison et al, 2020 ).…”

Long‐distance communication through systemic macromolecular signaling mediates stress defense responses in plants

“…The study also found that the total mRNA abundance in leaves is not a good indicator of transcriptome migration from the leaves to roots and that increasing the expression level of nonmobile mRNAs in companion cells does not promote mobility. In addition, RNA secondary structures such as TLs, the untranslated regions (UTRs) of mRNA and the stem‐loop structure of pre‐miRNA also have an impact on RNA transport (Wang et al, 2021). Studies have shown that the conserved SRBP1 family promotes the intercellular migration of noncellular autogeneic si/miRNAs in plants.…”