PIFs dark vs light

PIFs bind active phytochrome (Pfr) and are targeted to the proteasome in response to light. In the dark: PIF transcription factors activate genes involved in hypocotyl elongation. Light-activated phytochrome B moves to the nucleus where it binds PIF transcription factors. PIF proteins are targeted for degradation and hypocotyl elongation is inhibited. PIFs act to upregulate expression of auxin (IAA) biosynthesis genes, YUCCA (YUC).