Plant phytochrome B is an asymmetric dimer with unique signalling potential

Area of Science:

• Plant biology
• Molecular photoreception
• Structural biology

Background:

• Plant photoperception relies on phytochromes (Phy), bilin-containing photoreceptors.
• Understanding Phy signaling is limited by the lack of 3D structural data.

Purpose of the Study:

• To determine the 3D structure of Arabidopsis PhyB in its inactive (Pr) state.
• To elucidate the structural basis of PhyB's dimeric organization and its implications for signaling.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine the structure of Arabidopsis PhyB.
• Biochemical analysis was employed to understand domain interactions and their effects on photoreceptor function.

Main Results:

• A novel dimeric structure of PhyB was revealed, differing significantly from prokaryotic phytochromes.
• The structure shows head-to-head association of C-terminal domains and head-to-tail association of N-terminal photosensory regions, forming a parallelogram.
• Internal domain linkages were identified that accelerate the reversion of the active Pfr state to the inactive Pr state, reducing Pfr stability.

Conclusions:

• The unique dimeric structure of PhyB provides insights into plant light signal perception and transduction.
• Structural asymmetry suggests distinct signaling potentials for each protomer.
• The dynamic structure facilitates conformation-dependent interactions with signaling partners, mediating photoperception.