RNA as a signalling molecule - Intercellular Communication in Plants - page 77

overanearly constant number of cells could participate in non-cell autonomous
regulation of gene expression through miRNA trafficking. For instance, movement
of miRNAs over a set number of cells could generate gradients of gene expression
in meristems and primordia. As explained before, we are currently screening for
Arabidopsis mutants with altered patterns of short-distance spread of SULPHUR
and GFP silencing. If cell-to-cell movement of RNA silencing has developmental
functions, we predict that some of these mutants will exhibit aberrant or modified
morphology.
Note added in proof: A recent report describes the isolation of siRNAs and several
miRNAs in cucurbit phloem sap, suggesting that at least some of those molecules
may have the potential to move over long distances. This work describes a protein
that specifically trafficks single-stranded small RNAs between cells (Yoo et al .,
2004).
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