Molecular Plant-Microbe Interactions (Oct 2011)

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

  • Diana Leibman,
  • Dalia Wolf,
  • Vinod Saharan,
  • Aaron Zelcer,
  • Tzahi Arazi,
  • Shiboleth Yoel,
  • Victor Gaba,
  • Amit Gal-On

DOI
https://doi.org/10.1094/MPMI-05-11-0128
Journal volume & issue
Vol. 24, no. 10
pp. 1220 – 1238

Abstract

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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.