Fig. 8.

A proposed working model for UGT76F1-mediated auxin homeostasis in regulating light- and temperature-dependent seedling growth. IPyA is the major precursor for IAA biosynthesis in plants. YUCs promote the conversion from IPyA to IAA, whereas UGT76F1 antagonizes the role of YUCs through glucosylating IPyA to form its sugar conjugates. Acting as the pivotal integrator in light- and temperature-signaling pathways, PIF4 can transcriptionally regulate the expression of both YUCs (28, 50) and UGT76F1 (this study) through directly binding to their promoters, maintaining a trade-off between IAA biosynthesis and IPyA-Glc formation at the IPyA watershed and thereby fine-tuning the auxin homeostasis and the light- and temperature-dependent adaptation growth of seedlings.