Identification of an in vitro ribonucleoprotein complex between a viroid RNA and a phloem protein from cucumber plants.

We used the interaction of Hop stunt viroid (HSVd) and cucumber plants to investigate the involvement of phloem proteins in the systemic transport of RNA molecules. A ribonucleoprotein complex, stable even at high salt and temperature conditions, was detected in vitro between HSVd-RNA and the phloem exudate obtained from sectioned internodes from cucumber plants. The phloem protein 2 was recovered from this ribonucleoprotein complex and its RNA-binding properties as demonstrated by gel retardation analysis. The involvement of this protein in the movement of RNAs in cucumber is discussed.