Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 13, 1999
Publication Date: N/A
Interpretive Summary: Viroids are the smallest known agents of infectious disease - small, highly structured RNA molecules lacking the protein coat characterisitic of conventional viruses. A wide variety of crop species are susceptible to viroid infection, and several of the resulting diseases are of considerable economic importance. A lack of conventional genetic resistance has frustrated breeders' efforts to produce plants that are resistant/immune to viroid diseases, and we are trying to identify novel strategies to create such resistance de novo. This study describes the ability of cucumber phloem lectin, a well-characterized protein from the vascular system of this plant, to bind a variety of RNA molecules (especially Hop stunt viroid). Viroids are thought to move throughout infected plants as protein-RNA complexes, and thus interfering with the interaction between viroids and phloem lectin may render the plant resistant to infection. Our results will be of greatest interest to other researchers interested in how viruses and other RNA moelcules move in plants. Additional research in necessary before we can begin efforts to develop disease-resistant plants.
Incubation with cucumber phloem exudate in vitro results in a dramatic decrease in the electrophoretic mobility of Hop stunt viroid. UV crosslinking and a combination of size exclusion and ion exchange chromatography indicate that this phenomenon reflects a previously unsuspected ability of phloem protein 2, a dimeric lectin and most abundant component of phloem exudate, 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, our results suggest that phloem protein 2 may facilitate the systemic movement of viroids and possibly other RNAs in vivo.