Cell-to-cell and long-distance siRNA movement in plants: mechanisms and biological implications

► RNA silencing moves in plants from cell-to-cell and over long distances. ► Short interfering (si)RNAs, not longer precursors, are the nucleic acid involved. ► siRNAs direct long-distance post-transcriptional and chromatin-based silencing. ► All classes of endogenous siRNAs have the potential to move in Arabidopsis. ► Epiallelism and trans-generational memory may arise from siRNA mobility.