25.

(a) Tobacco plants are damaged severely when infested with Meloidegyne incognitia. Name and explain the strategy that is adopted to stop this infestation.

(b) Name the vector used for introducing the nematode specific gene in tobacco plant.

(a) RNA interference or RNAi is a method adopted to prevent infestation of roots of tobacco plants by a nematode Meloidogyne incognita.  The method involves silencing of a specific mRNA by a complementary RNA and the formation of ds RNA. The ds RNA, cannot be translated and its expression is blocked. These RNAi genes can be incorporated into the tobacco plant through vectors. The source of this complementary RNA could be from an infection by viruses having RNA genomes or mobile genetic elements (transposons) that replicate via an RNA intermediate. Since the dsRNA cannot be transcribed thus the parasite cannot survive and the plant is protected from it.

(b) Agrobacterium vectors are used for introducing nematode specific genes into the tobacco plant. The DNA is introduced in such a way that it produces both sense and anti-sense RNA in the host cells. The two RNA’s being complementary to each other form double stranded (dsRNA) that initiates RNAi and thus, silences the specific mRNA, of the nematode. The consequence was that the parasite could not survive in a transgenic host expressing specific interfering RNA. The transgenic plant therefore got itself protected from the parasite.