Both phytochrome A and phyB interact with PHYTOCHROME-INTERACTING FACTORs through an evolutionary conserved...

Area of Science:

• Plant Biology
• Photoreceptor Signaling
• Molecular Evolution

Background:

• Phytochromes (phyA, phyB) are key red/far-red light photoreceptors regulating plant development.
• Phytochromes interact with PHYTOCHROME-INTERACTING FACTORs (PIFs) via specific binding motifs.
• The interaction of phyB's N-terminal photosensory module (phyB^PSM) with APB is known, but APA's interaction with phyA^PSM is unclear.

Purpose of the Study:

• To elucidate the interaction mechanisms between phytochromes (phyA, phyB) and PIFs.
• To investigate the role of APA and APB motifs in phytochrome-PIF interactions.
• To determine the evolutionary conservation of these interactions.

Main Methods:

• Investigated phytochrome-PIF interactions using biochemical assays.
• Characterized binding interfaces involving photosensory module (PSM) and output module (OPM).
• Compared interactions across different plant species, including Arabidopsis and Marchantia.

Main Results:

• Both phyA and phyB interact with APA via the phytochrome output module (phy^OPM).
• phyB also interacts with APB through its photosensory module (phyB^PSM).
• The phy^OPM-APA interaction is ancient, conserved in Arabidopsis and Marchantia, and promotes PIF3 degradation independently of light.

Conclusions:

• The phy^OPM-APA interaction is a conserved, ancient mechanism for phytochrome-PIF signaling.
• Light-dependent phy-APA interaction arises from competition between Pr-phy^PSM and APA for phy^OPM.
• This study reveals novel insights into the molecular basis and evolution of phytochrome signaling pathways.