Mobile mRNA is one of the most important long-distance signals in plant vascular system. They play important roles in responding to environmental cues, such as photoperiod. There are numerous studies on mobile mRNAs in plants and thousand of mRNAs have been detected in phloem sap. One of the BEL1-like genes, designated StBEL5, has transcripts that move long distance from leaf to stolon tips and enhance tuberization. However, not many mobile mRNAs have been characterized. The mechanism of the long-distance movement of mRNAs is not clear. In this dissertation, we conducted research on different levels to characterize known mobile mRNA and to explore unknown mobile mRNAs. We verified movement of StBEL5 RNA to roots correlated with increased growth, changes in morphology, and accumulation of GA2-oxidase1, YUCCA1, and isopentenyl transferase transcripts. Making use of the potato genome and current experimental data, a comprehensive profile of the StBEL family is presented in this study as well. Combining Laser Capture Microdissection and RNA-seq, we provide a dynamic approach to the study of phloem tissue and a comprehensive picture of the mechanisms associated with long-distance signaling. We identified 17- and 18k transcripts in the phloem-associated tissue of petiole and stem in potato, respectively. These data provide valuable insights into potentially novel phloem-mobile RNAs and phloem-associated RNA-binding proteins.