HECT E3 ligase UPL3 targets PIF1 for degradation to promote light-induced seed germination

Prof. Shangwei Zhong published a paper in Science Bulletin with his collaborator.

Protein degradation via the ubiquitin-26S proteasome system is essential for cellular signal transduction. Seed germination, a critical stage in the plant life cycle, is intricately regulated by environmental signals. In Arabidopsis, light induces seed germination primarily by reducing the protein levels of the key transcription factor PHYTOCHROME-INTERACTING FACTOR 1 (PIF1), although the underlying mechanisms remain elusive. Here, we demonstrate that the HECT E3 ligase UBIQUITIN PROTEIN LIGASE 3 (UPL3) directly targets PIF1 for proteasomal degradation. Our results show that UPL3 facilitates light-induced seed germination by mediating the degradation of PIF1. UPL3 physically interacts with PIF1, driving its polyubiquitination and subsequent degradation. Importantly, UPL3 selectively interacts with the photoactive form of photoreceptor phyB, and the activated phyB enhances the UPL3–PIF1 interaction, accelerating PIF1 degradation in response to light. This study uncovers a mechanism by which a HECT E3 ligase, in conjunction with photoreceptor activation, mediates rapid protein degradation of PIF1, thereby promoting timely seed germination under favorable light conditions.