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Biotechnology and its Applications - Applications in Agriculture (Bt Cotton, RNA interference)

Grade 12CBSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Bt Cotton is a genetically modified crop containing the toxin genes from the soil bacterium BacillusBacillus thuringiensisthuringiensis.

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The Bt toxin protein exists as inactive protoxins in the bacterium but is converted into an active form due to the alkaline pHpH of the insect's midgut, which solubilizes the crystals.

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The activated toxin binds to the surface of midgut epithelial cells, creating pores that cause cell swelling and lysis, eventually leading to the death of the insect.

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Specific Bt toxin genes are used for different pests: cryIAccryIAc and cryIIAbcryIIAb control cotton bollworms, while cryIAbcryIAb controls corn borer.

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RNA interference (RNAiRNAi) is a method of cellular defense in all eukaryotic organisms that involves the silencing of a specific mRNAmRNA due to a complementary double-stranded RNA (dsRNAdsRNA) molecule.

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In RNAiRNAi, the dsRNAdsRNA binds to and prevents translation of the mRNAmRNA (silencing), effectively protecting the plant from parasites like the nematode MeloidogyneMeloidogyne incognitaincognita.

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Agrobacterium vectors are used to introduce nematode-specific genes into the host plant, producing both sense and anti-sense RNARNA to form the dsRNAdsRNA required for interference.

📐Formulae

Inactive Protoxin→Alkaline pH (Insect Midgut)Active Toxin\text{Inactive Protoxin} \xrightarrow{\text{Alkaline } pH \text{ (Insect Midgut)}} \text{Active Toxin}

Sense RNA+Antisense RNA→dsRNA (Double-stranded RNA)\text{Sense RNA} + \text{Antisense RNA} \rightarrow \text{dsRNA (Double-stranded RNA)}

dsRNA+mRNA→mRNA Silencing (No Translation)\text{dsRNA} + \text{mRNA} \rightarrow \text{mRNA Silencing (No Translation)}

💡Examples

Problem 1:

Why does the Bt toxin not kill the BacillusBacillus thuringiensisthuringiensis bacterium itself, but kills insects like the cotton bollworm?

Solution:

The Bt toxin exists as an inactive protoxin in the bacterium. It requires an alkaline pHpH to become solubilized and active. The bacterium does not provide this environment, but the midgut of the insect has an alkaline pHpH (pH>7.0pH > 7.0), which triggers the activation of the toxin.

Explanation:

This is a case of biochemical activation triggered by environmental pHpH changes. In the insect gut, the reaction is: Protoxin→pH>7Active Toxin\text{Protoxin} \xrightarrow{pH > 7} \text{Active Toxin}.

Problem 2:

Name the specific genes responsible for controlling cotton bollworms and corn borers in biotechnology.

Solution:

Cotton bollworms are controlled by the genes cryIAccryIAc and cryIIAbcryIIAb. The corn borer is controlled by the gene cryIAbcryIAb.

Explanation:

These are specific CryCry genes isolated from BacillusBacillus thuringiensisthuringiensis and incorporated into the crop genome to provide resistance against specific orders of insects.

Problem 3:

How is the nematode MeloidogyneMeloidogyne incognitaincognita prevented from infecting tobacco plants using RNAiRNAi?

Solution:

Using AgrobacteriumAgrobacterium vectors, nematode-specific genes are introduced into the tobacco plant. These genes produce both sense and anti-sense RNARNA in the host cells. These two RNAsRNAs are complementary and form a dsRNAdsRNA. When the nematode feeds on the plant, the dsRNAdsRNA initiates RNAiRNAi and silences the specific mRNAmRNA of the nematode, preventing protein synthesis and survival.

Explanation:

The mechanism relies on the principle of complementary base pairing where dsRNAdsRNA prevents the translation of essential parasitic proteins.

Applications in Agriculture (Bt Cotton, RNA interference) Revision - Class 12 Biology CBSE