The following statements are made regarding the functioning of phytochromes A and B in plants during light signalling.
A. Phytochrome B (PhyB) lacks nuclear localization signal (NLS) and after perceiving light, it takes hours for nuclear import.
B. Phytochrome A (PhyA) contains NLS and its nuclear import occurs rapidly.
C. Pfr form of PhyA depends on FAR-RED ELONGATED HYPOCOTYL 1 (FHY1) and its homolog FHL for nuclear import.
D. Pfr form of PhyB depends on FHY1 and its homolog FHL for nuclear import.
Which one of the following options represents all correct statement(s)?

Correct option is B

Correct Answer:
(b) C only
Explanation:
Phytochrome A (PhyA) does not contain an intrinsic NLS and therefore depends on the shuttle proteins FHY1 and FHL for the nuclear import of its active Pfr form.
Phytochrome B (PhyB), in contrast, contains its own NLS and undergoes rapid nuclear import after red-light exposure, independent of FHY1/FHL. Hence, only statement C is correct.
Information Booster :
· PhyA primarily mediates far-red light responses, while PhyB mainly responds to red light.
· Nuclear localization is essential for phytochrome-regulated gene expression.
· FHY1/FHL act as nuclear transport facilitators specifically for PhyA.
· Differential nuclear import mechanisms help diversify light signalling pathways.
Additional Information (Incorrect Options):
Statement A: Incorrect because PhyB has an NLS and enters the nucleus rapidly.
Statement B: Incorrect since PhyA lacks an intrinsic NLS despite rapid nuclear import.
Statement D: Incorrect because PhyB nuclear import does not require FHY1/FHL.