Phytochrome photoreceptors exist as P_R and P_FR. Following are certain statements regarding the function of P_FR:

A. P_FR form induces phosphorylation and ubiquitin linked degradation of PIFs transcription factor.
B. P_FR -mediated degradation of PIFs inhibits photomorphogenesis.
C. P_FR inhibits the activity of COPI.
D. P_FR increases the stability of transcription factors HFR 1, HY5, and LAF1.

Which one of the following combinations is correct?

Correct option is B

Explanation-

​A. PFR form induces phosphorylation and ubiquitin linked degradation of PIFs transcription factor.
Correct – This is a well-known mechanism where active phytochrome PFR leads to PIF degradation via phosphorylation and the ubiquitin-proteasome pathway.

B.  PFR -mediated degradation of PIFs inhibits photomorphogenesis.
 Incorrect – Degradation of PIFs actually promotes photomorphogenesis, because PIFs are repressors of photomorphogenesis.

C. PFR inhibits the activity of COPI.
Correct – PFR inhibits COP1 (a negative regulator of photomorphogenesis), leading to accumulation of positive transcription factors.

D. PFR increases the stability of transcription factors HFR1, HY5, and LAF1. 
Correct – These transcription factors promote photomorphogenesis, and PFR helps stabilize them.

Correct Combination: A, C and D only
Option a - A, C and D only .


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