The feedback control of the branched amino acid biosynthesis pathway in Arabidopsis is given below. The activity of Acetohydroxyacid Synthase (AHAS) enzyme is feedback inhibited by Leucine and Valine synergistically, whereas Isopropyl malate synthase (IPMS) enzyme activity is inhibited by Leucine only. Feedback resistant mutant lines of AHAS and IPMS genes are ahas2-1p and ipms1-1p, respectively.

The phenotype of these feedback resistant mutants was analyzed by growing them in the following Murashige and Skoog (MS) medium combinations.

1. MS medium only
2. MS medium supplemented with Leu only
3. MS medium supplemented with Val + Leu
4. MS medium supplemented with Val only

Correct option is C

Key points based on the provided feedback regulation:

• AHAS enzyme is synergistically inhibited by Leucine and Valine. So, the ahas2-1p mutant, which is feedback resistant, will likely grow in conditions where Leu or Val + Leu are present but may be limited in other conditions.

• IPMS enzyme is only inhibited by Leucine. Therefore, the ipms1-1p mutant, which is feedback resistant, will grow in conditions that contain Leu, but it might not grow in conditions where Leu is absent or insufficient.

Evaluating the options:

1. Option 1: ahas2-1p will grow in (C) only, and ipms1-1p will grow in (B) only.

   • This is incorrect because ahas2-1p will also grow in (A) and ipms1-1p will grow in both (A) and (B).

2. Option 2: ahas2-1p will grow only in (D) and ipms1-1p will grow in both (A) and (B).

   • This is incorrect because ahas2-1p will grow in more conditions than just (D), and ipms1-1p will grow in more than just (A) and (B).

3. Option 3: ahas2-1p will grow in both (A) and (C) and ipms1-1p will grow in both (A) and (B).

   • This is correct. ahas2-1p (the mutant for AHAS) will grow in MS medium only (A) and MS medium supplemented with Val + Leu (C) because it is resistant to Leu and Val feedback inhibition. ipms1-1p (the mutant for IPMS) will grow in MS medium only (A) and MS medium supplemented with Leu only (B), as it is resistant to Leu inhibition.

4. Option 4: Both ahas2-1p and ipms1-1p mutants will grow in (A) only.

   • This is incorrect because both mutants will grow in additional combinations as explained above.