Batuman, O., S. Tolkowsky Laboratory, Virology Department, Volcani Center, Bet Dagan 50250, Israel
Mawassi, M., S. Tolkowsky Laboratory, Virology Department, Volcani Center, Bet Dagan 50250, Israel
Bar-Joseph, M., S. Tolkowsky Laboratory, Virology Department, Volcani Center, Bet Dagan 50250, Israel

In an attempt to utilize post-transcriptional gene silencing (PTGS) as a means to impart resistance against Citrus tristeza virus (CTV) into citrus plants, the p23 + 3′UTR sequence (p23U) of the VT strain of CTV was engineered to fold into a double-stranded (ds) RNA structure. The resulting construct (p23UI) was introduced into Nicotiana benthamiana and Alemow (Citrus macrophylla) plants by Agrobacterium-mediated transformation. Transgenic p23UI- N. benthamiana were resistant to infection with a viral vector made of Grapevine virus A (GVA) + p23U (GVA-p23U), as indicated by the absence of the chimeric virus from inoculated plants. Inoculation of transgenic p23UI Alemow plants with CTV resulted in delayed appearance of symptoms in 9 out of the 70 transgenic plants. However, none of the plants showed durable resistance, as indicated by the obtaining of similar Northern hybridization signals from both transgenic and non-transgenic citrus plants. The possible causes for the failure of transgenic citrus plants to confer durable resistance to CTV are discussed. © Springer Science+Business Media, LLC 2006.