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.