PHYTOCHROME INTERACTING FACTOR 7 moderates the activity of phytochrome A in persistent canopy shade conditions

In nature, plants perceive and respond to complex vegetative environments through the phytochrome (phy) photoreceptor-signaling system. The Canopy Adaptation Strategy, elicited by phyA, together with the Shade Avoidance Syndrome, regulated by phyB, enables plants to adapt to diverse forms of vegetation shade. The phyA High Irradiance Response mode, which involves photocycle-coupled nuclear shuttling, is essential for sensing sustained far-red-rich conditions typical of canopy or occlusive shade. Our research identifies PHYTOCHROME INTERACTING FACTOR 7 (PIF7) as a key regulator of phyA function. We show that PIF7 overexpression (PIF7ox) effectively suppresses phyA action. Under persistent shade, PIF7 and phyA both accumulate and associate within nuclear photobodies, with this interaction mediated by the C-terminal domain of PIF7 and the PAS-PAS domain of phyA. PIF7 also interacts with FAR-RED ELONGATED HYPOCOTYL 1 (FHY1) and FHY1-LIKE transport facilitators, thereby interfering with phyA cytosolic-nuclear shuttling. This coordinated molecular targeting by PIF7 constitutes an effective strategy for modulating phyA function under persistent shade conditions.