How are transgenic tobacco plants produced to solve this problem?

Explanation

Pest resistant transgenic tobacco plants are produced using phenomenon of RNA silencing. The plants resistant to nematode pests and viral infection are engineered by silencing gene expression through complementary double stranded RNA (dsRNA) called RNA interference (RNAI) or RNA silencing or RNA mediated interference. The introductions of double-stranded RNA into the cells of plants, invertebrates or mammals leads to a sequence-specific degradation of homologous gene transcripts or mRNA, RNAi is a natural phenomenon of cellular defence in all eukaryotic cells. The source of this complementary dsRNA could be from infection by riboviruses having RNA genomes or the mobile genetic elements (transposons) that replicate via RNA. Intermediate synthetic oligonucleotides are also used to modulate gene expression in mammalian cells.
RNAi mechanism is used as a defence against viruses and nematodes. For example, the nematode parasite and Meloidegyne incognitia in the roots of tobacco plant cause great decline in tobacco yield. For providing resistance against infection of this nematode, the nematode-specific genes are introduced into the host plant using vector Agrobacterium. These transgenes in the host cells produce both sense and antisense RNA. Being complementary, the two RNA strands for a double-stranded RNA (URNA). The long dsRNAs are cleaved by RNase enzyme into small interfering RNAs (siRNAs).
The siRNA molecules bind to protein complex forming RNA-induced silencing complex. This complex has a helicase activity. It unwinds the two strands of dsRNA. Its antisense RNA strand pairs with the functional RNA molecule of nematode and cuts it at the site where antisense strand is bound. This is called silencing of target mRNA. As a consequence, nematode parasite cannot survive in the transgenic host plant.