Overexpression of a RNA silencing suppressor, B2 protein encoded by Flock House virus , in tobacco plants results in tolerance to salt stress

RNA silencing is an evolutionarily conserved defense response against virus invasion and suppression of silencing is a counter-defense mechanism acquired by viruses. The B2 protein encoded by insect Flock House virus (FHVB2) is a well-known RNA silencing suppressor (RSS). It is capable of reversing the suppression of GFP reporter gene in planta . In this study the effect of point mutation and deletions of FHVB2 on the in planta RSS activity was quantified and validated. The results showed drastic reduction in RSS activity of point mutant and deletion constructs. It is known that viruses like Cucumber mosaic virus can enhance the ability of plants to tolerate abiotic stress although the underlying mechanism is not known. Since the non-plant virus encoded FHVB2 is functionally similar to Cucumber mosaic virus encoded 2b and can act as a RSS in plants, it was used to understand if there is any role of host RNA silencing activity in imparting stress tolerance. FHVB2 was overexpressed in tobacco and transgenics analyzed for response to different abiotic stress conditions. The transgenic plants could tolerate high concentrations of salt and showed enhanced accumulation of proline. Transient assays using point mutant and deletion constructs indicate that functional RSS activity is not required for salt tolerance.