Centro Nacional de Biotecnología (C.S.I.C.), Campus de la Universidad Autónoma de Madrid, 28049 Madrid, Spain
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Accepted 26 October 1998.
Plum pox potyvirus (PPV) infection of transgenic Nicotiana benthamiana plants that expressed the PPV NIb RNA replicase carrying a Gly to Val mutation at the GDD motif (NIbV lines) induced a phenotype of virus resistance and transgene silencing, which was not transmissible to the progeny after self-fertilization (H. S. Guo and J. A. García, Mol. Plant-Microbe Interact. 10:160-170, 1997). Here, we demonstrate that the induced resistance of NIbV plants is mitotically stable after plant propagation by grafting and by in vitro regeneration. Virus replication or residual virus RNA seem not to be required to maintain transgene silencing and virus resistance. Analysis by PCR (polymerase chain reaction) amplification after treatment with methylation-sensitive restriction nucleases indicates that DNA methylation is associated with establishment and maintenance of transgene silencing and virus resistance. Restoration of transgene activity and susceptibility to PPV in sexual progeny correlated with resetting of transgene DNA methylation. On the basis of these and other published results, we present a general model for post-transcriptional gene silencing in which RNA signals, generated either by a silenced nuclear gene or by virus replication, both activate a specific cytoplasmic RNA degradation pathway and induce changes (in particular, DNA methylation) in homologous nuclear genes that switch them from an active to a silenced status.
virus-induced gene silencing.
© 1999 The American Phytopathological Society