PHYTOCHROME INTERACTING FACTOR 7 moderates the activity and the cytosolic-nuclear shuttling of PHYTOCHROME A

In nature, plants sense and navigate complex vegetative environments using the phytochrome (phy) photoreceptor-signaling system. The canopy adaptation strategy, elicited by phyA, and the shade avoidance syndrome, regulated by phyB, allow plants to adapt to diverse forms of vegetation shade. The phyA High Irradiance Response (HIR) mode, involving photocycle- coupled nuclear shuttling, is essential for detecting persistent far-red rich conditions typical of canopy or occlusive shade. Our research identifies PHYTOCHROME INTERACTION FACTOR 7 (PIF7) as a critical regulator of phyA function. We demonstrate PIF7ox can effectively block phyA action. In persistent shade, PIF7 and phyA both accumulate and interact within nuclear bodies, with binding facilitated through the prion-like domain of PIF7 and the C-terminal PAS-PAS domain of phyA. PIF7 also interacts with FHY1 and FHL chaperones, interfering with phyA cytosolic-nuclear shuttling. This strategic molecular targeting by PIF7 provides an effective strategy for modulating the phyA HIR in response to shade signals.