Question

(a) Tobacco plants are damaged severely when infested with Meloidogyne incognita. Name and explain the strategy that is adopted to stop this infestation.
(b) Name the vector used for introducing nematode specific genes in the tobacco plant.

Answer 1

Hint: Meloidogyne incognita infects the roots of tobacco plants. It causes a great reduction in yield. This infestation can be stopped by using a cellular mechanism that uses a gene’s own DNA sequence of the gene to turn it off, a process that researchers call silencing. This mechanism involves the blocking of gene function by inserting a short sequence of ribonucleic acid that matches the part of the target gene’s sequence, thus no proteins are produced.

Complete step by step answer:
(a) RNA interference is the method used to develop nematode resistance in tobacco plants. It is a biological mechanism that leads to post- transcriptional gene silencing. The steps involved in this process are; At first, the disease- causing genes are identified and isolated from the nematode Meloidogyne incognita. Then this gene would be incorporated into the genome of tobacco plants with the help of a vector. It is then introduced into the tobacco plant in such a way that both sense and antisense mRNA is produced. These RNAs being complementary to each other get paired to form double-stranded RNA. This double-stranded RNA induces RNAi in the tobacco plants which neutralize the mRNA of the nematode. Thus, the nematode is unable to live in such a transgenic host. Therefore, the tobacco plant became resistant to pests.
(b) The vector used for introducing nematode specific genes in tobacco plants is Agrobacterium tumefaciens. It is used for the transfer of a small segment of DNA into the plant genome by the process called transformation. They are extensively used for the genetic engineering of plants.

Additional information:
- RNAi is an RNA-dependent gene silencing process that is controlled by the RNA-induced silencing complex (RISC).
- it is initiated by short double- stranded RNA molecules in a cell’s cytoplasm. When the dsRNA is exogenous the RNA is imported directly into the cytoplasm.
- The initiating dsRNA can also be endogenous as in pre- microRNAs expressed from RNA coding genes.

Note:
- Agrobacterium is the causative agent of crown gall disease. It is a rod- shaped gram- negative bacterium.
- It is a phytopathogenic bacterium capable of transferring a segment of its genome to plant cells.
- The segment termed ‘T-DNA’ resides in the bacterium on a large plasmid. It can be induced to integrate into the plant nuclear genome randomly by a set of virulence genes.