(a) Write the scientific name of the nematode that infests the tobacco plants and the part that it infests. (b) How is Agrobacterium used to protect tobacco plant from this attack ?

The correct answer is:
(a)
• Meloidogyne incognitain (referred to as Meloidegyne incognitia in the option)
• Roots
(b) By using an Agrobacterium vector, nematode-specific genes are introduced into the host plant. The introduction of this DNA produces both sense and anti-sense RNA in the host cells. These two RNAs, being complementary to each other, form a double-stranded RNA (dsRNA) that initiates RNA interference (RNAi) and thus silences the specific mRNA of the nematode. Consequently, the parasite cannot survive in the transgenic host.

Step-by-step Explanation:

Part (a): Nematode and Plant Part Infested
The nematode that infests tobacco plants is scientifically named Meloidogyne incognita. It specifically attacks the roots of tobacco plants, leading to a significant reduction in the crop yield.

Part (b): Mechanism of Protection using Agrobacterium tumefaciens (RNA interference)
The protection strategy is based on the biological process of RNA interference (RNAi), which is a method of cellular defense in all eukaryotic organisms. Here is how it is executed step-by-step:

1. Vector-Mediated Gene Transfer:
Using Agrobacterium vectors, nematode-specific genes are introduced into the tobacco host plant. Agrobacterium acts as a natural genetic engineer, capable of transferring a specific DNA fragment (T-DNA) into the host genome.

2. Production of Sense and Anti-sense RNA:
The introduced foreign DNA is designed in such a way that, upon transcription inside the host plant cells, it produces both sense RNA and anti-sense RNA.

3. Formation of Double-Stranded RNA (dsRNA):
Because the sense and anti-sense RNA molecules are fully complementary to each other, they hybridize (bind together) to form a stable double-stranded RNA (dsRNA).

4. Activation of RNA Interference (RNAi):
The presence of double-stranded RNA inside the plant cells triggers the RNAi cellular machinery. The dsRNA is cleaved into small interfering RNAs (siRNAs).

5. Silencing of Nematode mRNA:
When the nematode feeds on the roots of this transgenic tobacco plant, these silencing molecules enter the nematode's body. They bind complementarily to the specific target mRNA of the nematode and initiate its degradation. Without this target mRNA, essential proteins required by the parasite cannot be translated.

6. Survival Prevention:
Due to the silencing of its vital genes, the nematode parasite is unable to survive in the host plant expressing these specific dsRNA molecules. Thus, the transgenic plant becomes resistant to the nematode infection.