Mixing and matching: the essence of plant systemic silencing?

In plants and some animals, posttranscriptional RNA silencing can be manifested beyond its sites of initiation, because of the movement of signaling molecules that must have RNA components to account for the nucleotide sequence specificity of their effects. In a recent study carried out in Arabidopsis thaliana, interesting clues were provided that suggest mechanisms by which systemic RNA silencing signals might be produced and perceived between distant plant organs.