Study of virus resistance mediated by inverted repeats derived from 5′ and 3′ ends of coat protein gene of Potato virus Y

Two inverted repeats cDNA fragments derived from 5′ and 3′ ends of PVYN CP gene were cloned respectively,and the corresponding expression vectors pROKII-5′ IR and pROKII-3′ IR were constructed.Recombinant binary vectors were then introduced into tobacco(NC89) plants via Agrobacterium tumefaciens-mediated transformation.166 and 126 transgenic plants transformed with pROKII-5′ IR and pROKII-3′ IR were obtained,respectively.Resistance tests indicated that plants transformed with pROKII-3′ IR were highly resis-tant to PVY infection,and the proportion of disease resistant transgenic plants was 69%,while plants transformed with pROKII-5′ IR were susceptible to PVYN infection.Southern blot results indicated that there were no obvious correlation between the copy numbers of transgene and resistance.Northern blot results revealed an inverse correlation between transgenic transcript accumulation and virus resistance,it demonstrating that the resistance was RNA mediated.The results demonstrated that the hpRNA(hairpin RNA) with 50 bp-stem derived from the 3′ end of the CP gene is sufficient to induce RNA-mediated gene silencing.This information is useful in production of transgenic plants which are resistant to multi-virus infections.