FIGURE 3.

Nuclear factor Y regulates hypocotyl elongation through PIF4. At dawn, Phytochrome interacting factor 4 (PIF4) is degraded by the 26S proteasome. At dusk, the transcription level of PIF4 is repressed by evening complex (ELF4-ELF3-LUX). Therefore, NF-YB9/LEC1 cannot be recruited to the promoter of IAA19. At midnight, the transcription level of PIF4 increases along with decreased abundance of the ELF4-ELF3-LUX complex. Meanwhile, NF-YB9/LEC1 is recruited to the promoter of IAA19 through its interaction with PIF4, thus increasing the transcription level of IAA19 and promotes hypocotyl elongation.