Departamento de Biología de Plantas, Centro de Investigaciones Biológicas, CSIC, Campus de la Ciudad Universitaria, Av. Ramiro de Maeztu 9, 28040 Madrid, Spain
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Accepted 20 March 2006.
Recombination is a frequent phenomenon in RNA viruses whose net result is largely influenced by selective pressures. RNA silencing in plants acts as a defense mechanism against viruses and can be used to engineer virus resistance. Here, we have investigated the influence of RNA silencing as a selective pressure to favor recombinants of PVX-HCT, a chimeric Potato virus X (PVX) vector carrying the helper-component proteinase (HC-Pro) gene from Plum pox virus (PPV). All the plants from two lines expressing a silenced HC-Pro transgene were completely resistant to PPV. However a significant proportion became infected with PVX-HCT. Analysis of viral RNAs accumulating in silenced plants revealed that PVX-HCT escaped silencing-based resistance by removal of the HC-Pro sequences that represented preferential targets for transgene-promoted silencing. The virus vector also tended to lose the HC-Pro insert when infecting transgenic plants containing a nonsilenced HC-Pro transgene or wild-type (wt) Nicotiana benthamiana plants. Nevertheless, loss of HC-Pro sequences was faster in nonsilenced transgenic plants than in wt plants, suggesting the transgene plays a role in promoting a higher selective pressure in favor of recombinant virus versions. These results indicate that the outcome of recombination processes depends on the strength of selection pressures applied to the virus.
HC-Pro transgenic plants
© 2006 The American Phytopathological Society