Q62. Identify the CORRECT statements
In Arabidopsis, vernalization is associated with
P. Chromatin modification at the FLC (FLOWERING LOCUS C) locus
Q. Degradation of the FLC protein
R. Inactivating the FLC protein by post-translational modification
S. Down-regulation of FLC transcript
Correct Answer: (B) P, S
Vernalization in Arabidopsis thaliana accelerates flowering after prolonged cold exposure by repressing the floral inhibitor FLC (FLOWERING LOCUS C). This involves specific epigenetic and transcriptional changes at the FLC locus.
Option Analysis
P. Chromatin modification at the FLC locus
True. Vernalization induces repressive histone modifications like H3K27me3 and reduces active marks like H3K4me3 at the FLC locus, leading to stable epigenetic silencing.
Q. Degradation of the FLC protein
False. While FLC protein levels decrease post-vernalization, this results from reduced transcription, not targeted protein degradation.
R. Inactivating the FLC protein by post-translational modification
False. No evidence supports post-translational inactivation of FLC; repression occurs primarily through chromatin changes and lowered transcript levels.
S. Down-regulation of FLC transcript
True. Prolonged cold directly reduces FLC mRNA levels, which persists epigenetically to promote flowering.
Introduction: Unlocking Flowering with Vernalization in Arabidopsis
Vernalization in Arabidopsis enables winter-annual plants to flower after cold exposure by targeting the FLC (FLOWERING LOCUS C) gene, a major flowering repressor. This process hinges on chromatin modification at the FLC locus and down-regulation of FLC transcript, critical for GATE Life Sciences exam prep.
Vernalization Mechanism
Vernalization senses prolonged cold (4–12 weeks) to epigenetically silence FLC.
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Cold initiates VIN3 expression, recruiting Polycomb proteins for H3K27me3 deposition at FLC chromatin.
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Active H3K4me3 marks deplete, stabilizing repression mitotically through cell divisions.
FLC normally blocks FT and SOC1, flowering promoters; its silencing allows the transition.
FLC Repression Details
| Aspect | Description | Evidence [Citation] |
|---|---|---|
| Chromatin Changes (P) | H3K27me3 enrichment; H3K4me3 reduction | Correct |
| Transcript (S) | FLC mRNA sharply declines post-cold | Correct |
| Protein Degradation (Q) | Levels drop indirectly, not via ubiquitin | Incorrect |
| Post-Trans Mod (R) | No phosphorylation/glycosylation inactivation | Incorrect |
This table clarifies why options P and S are accurate for vernalization in Arabidopsis.
GATE Exam Insights
For competitive exams like GATE Life Sciences, focus on epigenetic control: vernalization memory persists via Polycomb-mediated chromatin states, not protein-level changes. Variants in FLC silencing explain ecotype differences.
