Inducible antiviral activity and rapid production of the Ribosome-Inactivating Protein I from Phytolacca heterotepala in tobacco

We studied the in vitro and in planta antiviral activity of the PhRIP I, a type 1 Ribosome-Inactivating Protein originally purified from leaves of the Phytolacca heterotepala. This protein inhibited protein translation in a cell-free assay and limited the local lesion formation from PVX infection on tobacco leaves. We used a transient expression system based on leaf infiltration with recombinant Agrobacteria to show that tobacco can produce a correctly processed PhRIP I enzyme that retains its antiviral activity. Hence, it is possible to rapidly yield in plants a type 1 RIP by means of this transient expression system. To analyse the possible increase of virus resistance in plants, Nicotiana tabacum lines that were transformed with the PhRIP I coding sequence under the control of the wound-inducible PGIP promoter were challenged by PVX. A significantly lower number of viral lesions compared to untransformed plants was observed only after the induction of the transgene, indicating that the controlled gene expression of an antiviral protein can increase virus resistance.