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Possible Involvement of the Phloem Lectin in Long-Distance Viroid Movement

July 2001 , Volume 14 , Number  7
Pages  905 - 909

R. A. Owens , 1 M. Blackburn , 2 and B. Ding 3

1Molecular Plant Pathology Laboratory, USDA-ARS, Beltsville, MD 20705, U.S.A.; 2Insect Biocontrol Laboratory, USDA-ARS, Beltsville, MD 20705, U.S.A.; 3Department of Plant Biology and Plant Biotechnology Center, Ohio State University, Columbus 43210, U.S.A.

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Accepted 19 March 2001.

Incubation with cucumber phloem exudate in vitro results in a dramatic decrease in the electrophoretic mobility of Hop stunt viroid. UV cross-linking 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 the 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.

Additional keyword: RNA-binding protein.

The American Phytopathological Society, 2001