- While screening an EMS-mutagenized population of a plant, a researcher identified a mutant with reduced gibberellic acid sensitivity. Which one of the following proteins is most likely to be defective in this mutant?
(1) Sucrose non-fermenting related kinase 2 (SnRK2)
(2) Constitutive triple response 1 (CTR1)
(3) Phytochrome interacting factor (PIF)
(4) Coronative-insensitive 1 (C0I1)
Correct answer: (3) Phytochrome interacting factor (PIF)
Explanation:
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Plants with reduced gibberellic acid (GA) sensitivity typically have defects in proteins implicated in GA signaling or response.
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PIFs (Phytochrome interacting factors) are basic helix-loop-helix transcription factors that act downstream in the GA signaling pathway and regulate growth responses. Mutations in PIFs impair GA sensitivity.
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(1) SnRK2 is primarily involved in abscisic acid (ABA) signaling and stress responses, not GA signaling.
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(2) CTR1 is a Raf-like kinase involved in ethylene signaling, not directly in GA response.
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(4) COI1 is a receptor for jasmonate signaling, unrelated to GA sensitivity.
Option-wise:
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SnRK2 — unrelated to GA; ABA pathway.
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CTR1 — ethylene signaling.
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PIF — correct; GA signaling downstream regulator.
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COI1 — jasmonate signaling.
PIF transcription factors connect light and GA signaling, crucially modulating plant growth responses. Mutations in PIFs lead to diminished gibberellin sensitivity, affecting developmental processes such as stem elongation and seed germination.
