Question

Non-GM herbicide tolerant rice varieties viz. PB 1979 and PB 1985 have been developed by mutating gene encoding for which one of the following enzymes?

• A. Acetolactate synthase
• B. Glutamine synthetase
• C. 5-Enolpyruvylshikimate-3-phosphate (EPSP) synthase
• D. Acetoacetate synthase

Hint:

Imidazolinone-tolerant (Clearfield) crops and sulfonylurea-tolerant crops are developed by selecting mutations in the ALS (Acetolactate Synthase) gene.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Herbicide tolerance in crop plants can be introduced through non-genetically modified (non-GM) approaches, such as mutation breeding, to alter the binding site of target enzymes so that the herbicide can no longer inhibit them.

Step 2: Detailed Explanation:
The Indian Agricultural Research Institute (IARI) developed the non-GM herbicide-tolerant rice varieties Pusa Basmati 1979 (PB 1979) and Pusa Basmati 1985 (PB 1985).
These varieties are resistant to Imidazolinone herbicides, which typically act by inhibiting the enzyme Acetolactate Synthase (ALS, also known as acetohydroxyacid synthase).
ALS is the key enzyme that catalyzes the first step in the biosynthesis of essential branched-chain amino acids (valine, leucine, and isoleucine).
Through induced mutation breeding, the gene encoding for Acetolactate synthase was mutated to create a structural change that prevents the binding of the herbicide while maintaining normal enzymatic activity.

Step 3: Final Answer:
Therefore, the mutated gene encodes the Acetolactate synthase enzyme, corresponding to option (A).