Should I Stay or Should I Go? Abundance as a New Null Hypothesis for Determination of mRNA Mobility

mRNA can be transported long distances within a plant via the phloem sap. Specific mobile transcripts are reported to influence flowering as well as leaf, tuber, and root development, and mobile mRNAs have been suggested to serve as long-distance signaling molecules within the plant (reviewed in Spiegelman et al., 2013). Among the several questions surrounding long-distance transport of mRNAs is what mechanism determines which transcripts are mobile. A recent report indicates that a much higher proportion of transcripts are mobile than previously thought. Thieme et al. (2015) grafted two different ecotypes of Arabidopsis thaliana and identified more than 2000 genes corresponding to mobile mRNAs. Such widespread trafficking poses further questions about what role these mobile transcripts might play in the plant, as well as the degree to which their mobility is sequence specific