how is nematode- resistance introduced into tobacco plants using genetic engineering?

Nematode resistance in tobacco plants is brought about by RNA interference (RNAi). In this technique, a complementary RNA binds to mRNA to form a ds RNA, which cannot translate and hence, its expression is blocked. A nematode specific gene is introduced in the host plant, when this plant is infested by the nematode, the nematode specific gene is triggered and it produces a single stranded RNA which is complementary to the RNA produced by the nematode in order to infect the host plant. This complementary RNA binds to the mRNA of the nematode to form a double stranded RNA that cannot be translated. Hence, the nematode is not able to infect the trangenic plant.