AUTHOR=Hannapel David J., Sharma Pooja , Lin Tian 

TITLE=Phloem-mobile messenger RNAs and root development

JOURNAL=Frontiers in Plant Science

VOLUME=4

YEAR=2013

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2013.00257

DOI=10.3389/fpls.2013.00257

ISSN=1664-462X

ABSTRACT=<p>Numerous signal molecules move through the phloem to regulate development, including proteins, secondary metabolites, small RNAs and full-length transcripts. Several full-length mRNAs have been identified that move long distances in a shootward or rootward direction through the plant vasculature to modulate both floral and vegetative processes of growth. Here we discuss two recently discovered examples of long-distance transport of full-length mRNAs into roots and the potential target genes and pathways for these mobile signals. In both cases, the mobile RNAs regulate root growth. Previously, RNA movement assays demonstrated that transcripts of <italic>StBEL5</italic>, a transcription factor from the three-amino-loop-extension superclass, move through the phloem to stolon tips to enhance tuber formation in potato (<italic>Solanum tuberosum</italic> L.). <italic>StBEL5</italic> mRNA originates in the leaf and its movement to stolons is induced by a short-day photoperiod. Movement of <italic>StBEL5</italic> RNA to roots correlated with increased growth and the accumulation of several transcripts associated with hormone metabolism, including <italic>GA2-oxidase1, YUCCA1a</italic> and <italic>-c</italic>, several <italic>Aux/IAA</italic> types, and <italic>PIN1, -2</italic>, and <italic>-4</italic> was observed. In another example, heterografting techniques were used to identify phloem-mobile <italic>Aux/IAA</italic> transcripts in <italic>Arabidopsis</italic>. Movement assays confirmed that these <italic>Aux/IAA</italic> transcripts are transported into the root system where they suppress lateral root formation. Phloem transport of both <italic>StBEL5</italic> and <italic>Aux/IAA</italic> RNAs are linked to hormone metabolism and both target auxin synthesis genes or auxin signaling processes. The mechanisms of transport for these mobile RNAs, the impact they have on controlling root growth, and a potential transcriptional connection between the BEL1/KNOX complex and <italic>Aux/IAA</italic> genes are discussed.</p>