Multi-level modulation of light signaling by GIGANTEA regulates both the output and pace of the circadian clock ($) (Devel Cell)

The daily cycle of light and dark controls many facets of plant growth and development, but these cycles depend on and are most efficient when integrated with the rhythms of the circadian clock. Nohales et al. have identified a key mechanism that directly links the regulation of light-responsive genes and the regulation of the clock. GIGANTEA (GI) is a plant-specific protein that has been shown genetically to contribute to light and clock signaling but whose biochemical function has been difficult to determine. Here, the authors show that GI directly binds to the promoter regions of numerous genes, perhaps indirectly through interactions with other transcription factors. The authors also show that GI interacts with PIF proteins, modulating their stability and activity. Finally, they show that “modulation of PIF activity by GI is not only required to adequately phase output rhythms such as growth but also for proper clock progression and light input.”  (Summary by Mary Williams) Devel. Cell 10.1016/j.devcel.2019.04.030