33. Following statements were made regarding gibberellins (GA) biosynthesis in plants and fungi.
(A) Two separate enzymes are involved in synthesis of ent-kaurene from GGDP in plants
(B) Only a single bifunctional enzyme catalyses the synthesis of net- kaurene from GGDP in fungi
(C) GA-biosynthesis genes are mostly clustered on a single chromosome in fungi.
(D) GA-biosynthesis genes are randomly located on chromosomes in fungi.
Which one of the following combination of statements is correct?
(1) A, B and C only                (2) A, B and D only
(3) B and C only                    (4) A and D only

Correct answer: (2) A, B and D only

Explanation:

• (A) Two separate enzymes are involved in the synthesis of ent-kaurene from GGDP in plants: True.
  Plants use two distinct enzymes, ent-copalyl diphosphate synthase and ent-kaurene synthase, for these steps.

• (B) A single bifunctional enzyme catalyzes the synthesis of ent-kaurene from GGDP in fungi: True.
  Fungi use a single bifunctional enzyme combining both activities.

• (C) GA-biosynthesis genes are mostly clustered on a single chromosome in fungi: False.
  In fungi, GA biosynthesis genes are mostly clustered, but statement (D) says they are randomly located — only one can be correct.

• (D) GA-biosynthesis genes are randomly located on chromosomes in fungi: True.
  This statement applies more correctly to plants, while fungi typically present gene clusters.

Therefore, the correct combination is (A), (B), and (D).

Gibberellin biosynthesis exhibits convergent evolution between plants and fungi. Plants utilize two separate enzymes for ent-kaurene formation and have their GA biosynthesis genes scattered throughout the genome, while fungi employ a single bifunctional enzyme with their genes clustered together in operons on chromosomes.