The present invention concerns a method of genetic modification of a TGB-3
wild type viral sequence for reducing or suppressing the possible
deleterious effects of the agronomic properties of a transformed plant or
plant cell by said TGB-3 viral sequence, comprising the following
successive steps: submitting said sequence to point mutation(s) which
allow the substitution of at least one amino-acid into a different
amino-acid; selecting genetically modified TGB-3 wild type viral
sequences having said point mutation(s) and which are not able to promote
cell-to-cell movement of a mutant virus having a dysfunctional TGB-3 wild
type viral sequence, when expressed in trans from a replicon; further
selecting among said genetically modified TGB-3 viral sequences, the
specifically genetically modified sequence which inhibits infection with
a co-inoculated wild type virus when the mutant form was expressed from a
replicon, and recovering said specifically genetically modified TGB-3
viral sequence. The invention further relates to genetically modified
TGB-3 viral sequences suitable to induce gene silencing. In particular
hairpin constructs based on such sequences proved highly efficient to
induce a PTGS mechanism and degradation of the whole of RNA2 thereby.
When plants are transformed accordingly the spread of the virus in the
plant is significantly reduced or blocked.