Possible involvement of the phloem lectin in long-distance viroid movement

Incubation with cucumber phloem exudate in vitro results in a dramatic decr ease in the electrophoretic mobility of Hop stunt viroid. UV cross-linking and a combination of size exclusion and ion exchange chromatography indicat e that this phenomenon reflects a previously unsuspected ability of phloem protein 2, a dimeric lectin and the most abundant component of phloem exuda te, to interact with RNA. In light of its demonstrated ability to move from cell to cell via plasmodesmata as well as long distances in the phloem, ou r results suggest that phloem protein 2 may facilitate the systemic movemen t of viroids and, possibly, other RNAs in vivo.