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Differential Virulence by Strains of Cucumber mosaic virus is Mediated by the 2b Gene

September 2002 , Volume 15 , Number  9
Pages  947 - 955

Bu-Jun Shi , 1 , 2 Peter Palukaitis , 3 and Robert H. Symons 1

1Department of Plant Science, Waite Institute, Adelaide University, Glen Osmond, SA, 5064, Australia; 2Department of Molecular Bioscience, Adelaide University, North Terrace, Adelaide, 5005, Australia; 3Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, United Kingdom

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Accepted 13 May 2002.

The approximately 12-kDa 2b protein, encoded by all cucumoviruses, had been shown to play an important role in viral long-distance movement, hypervirulence, and suppression of post-transcriptional gene silencing. The role of the 2b gene in the hypervirulence of Cucumber mosaic virus (CMV) and whether hypervirulence was linked to movement were analyzed using a hybrid virus (CMV-qw), generated by replacing the 2b gene in a subgroup II strain, Q-CMV, with the 2b gene from a subgroup IA strain, WAII-CMV. CMV-qw was more virulent than Q-CMV or WAII-CMV on most of the host plant species tested. Northern blot and nucleotide sequence analyses demonstrated that CMV-qw was stably maintained during the course of infection and upon passage. Kinetic studies revealed that the hypervirulence induced by the hybrid virus was associated with neither increased viral RNA accumulation nor more rapid viral movement per se, suggesting that other functions of the 2b protein are important in determining the hypervirulence.

© 2002 The American Phytopathological Society