Question

A drought tolerant rice genotype was found to be associated with a missense mutation in the gene A. Which one or more of the following experiments is/are appropriate to validate whether the mutation in A is the causal factor for drought tolerance?

• A. Introduce the same mutation in a drought sensitive rice genotype and test if it becomes drought tolerant.
• B. Delete the wild-type A in drought sensitive plant and test if it becomes drought tolerant.
• C. Determine the stability of the protein encoded by the wild-type and the mutant forms of A.
• D. Repair the mutation in the drought tolerant rice genotype and test if it becomes drought sensitive.

Hint:

To establish causality of a mutation: (i) introduce it in sensitive background and check phenotype, (ii) revert it in tolerant background and see if phenotype is lost.

Answer 1

The Correct Option is A, D

Step 1: Understanding the hypothesis. The rice genotype’s drought tolerance is linked with a missense mutation in gene A. To prove causality, we must show that introducing this mutation confers tolerance, and correcting it removes tolerance. This is the classical “gain-of-function” and “reversion” test. Step 2: Evaluate options. (A) If we introduce the same mutation into a sensitive genotype and the plant gains tolerance, this strongly supports causality. ✔️ (B) Simply deleting wild-type A may not mimic the missense mutation; it could produce loss-of-function phenotypes unrelated to tolerance. Not conclusive. ❌ (C) Measuring protein stability may reveal biochemical consequences but does not directly test phenotypic causality in plants. ❌ (D) Repairing the mutation in a tolerant genotype to wild type and observing loss of tolerance is a definitive reverse genetics test. ✔️ Thus, correct validation experiments are (A) and (D).