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A High Level of Transgenic Viral Small RNA Is Associated with Broad Potyvirus Resistance in Cucurbits

October 2011 , Volume 24 , Number  10
Pages  1,220 - 1,238

Diana Leibman,1 Dalia Wolf,2 Vinod Saharan,3 Aaron Zelcer,2 Tzahi Arazi,4 Shiboleth Yoel,1 Victor Gaba,1 and Amit Gal-On1

1Department of Plant Pathology and Weed Science and 2Department of Vegetable Research, ARO The Volcani Center, Bet Dagan 50250, Israel; 3Department of Molecular Biology and Biotechnology, Maharana Pratap University of Agriculture and Technology, Udaipur-313001, Rajasthan, India; 4Department of Ornamental Horticulture, ARO The Volcani Center, Israel

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Accepted 15 June 2011.

Gene-silencing has been used to develop resistance against many plant viruses but little is known about the transgenic small-interfering RNA (t-siRNA) that confers this resistance. Transgenic cucumber and melon lines harboring a hairpin construct of the Zucchini yellow mosaic potyvirus (ZYMV) HC-Pro gene accumulated different levels of t-siRNA (6 to 44% of total siRNA) and exhibited resistance to systemic ZYMV infection. Resistance to Watermelon mosaic potyvirus and Papaya ring spot potyvirus-W was also observed in a cucumber line that accumulated high levels of t-siRNA (44% of total siRNA) and displayed significantly increased levels of RNA-dependent RNA (RDR)1 and Argonaute 1, as compared with the other transgenic and nontransformed plants. The majority of the t-siRNA sequences were 21 to 22 nucleotides in length and sense strand biased. The t-siRNA were not uniformly distributed throughout the transgene but concentrated in “hot spots” in a pattern resembling that of the viral siRNA peaks observed in ZYMV-infected cucumber and melon. Mutations in ZYMV at the loci associated with the siRNA peaks did not break this resistance, indicating that hot spot t-siRNA may not be essential for resistance. This study shows that resistance based on gene-silencing can be effective against related viruses and is probably correlated with t-siRNA accumulation and increased expression of RDR1.

© 2011 The American Phytopathological Society