Shining Light on Plant Growth: Recent Insights into Phytochrome Interacting Factors

Abstract Light serves as a pivotal environmental cue regulating various aspects of plant growth and development, including seed germination, seedling de-etiolation, and shade avoidance. Within this regulatory framework, the basic helix-loop-helix transcription factors known as PHYTOCHROME INTERACTING FACTORS (PIFs) play an essential role in orchestrating responses to light stimuli. Phytochromes, acting as red/far-red light receptors, initiate a cascade leading to the degradation of PIFs (except PIF7), thereby triggering transcriptional reprogramming to facilitate photomorphogenesis. Recent research has unveiled multiple post-translational modifications that regulate the abundance and/or activity of PIFs, including phosphorylation, dephosphorylation, ubiquitination, deubiquitination and SUMOylation. Moreover, intriguing findings indicate that PIFs can influence chromatin modifications. These include modulation of Histone 3 Lysine-9 acetylation (H3K9ac), as well as occupancy of histone variants such as H2A.Z (associated with gene repression) and H3.3 (associated with gene activation), thereby intricately regulating downstream gene expression in response to environmental cues. This review summarizes recent advances in understanding PIFs' role in regulating various signaling pathways with a major focus on photomorphogenesis.