Seed germination marks the beginning of the plant life cycle, acting as a pivotal determinant of agricultural production and crop yield. Buried in the soil, seeds must keenly sense external cues to determine the optimal timing for germination, a process in which light serves as a crucial environmental signal. Previous studies have identified the transcription factor PHYTOCHROME-INTERACTING FACTOR 1 (PIF1) as a core repressor of seed germination. PIF1 undergoes rapid degradation upon light exposure, yet the precise molecular mechanism by which light promotes PIF1 degradation to initiate seed germination has remained unclear.
Recently, the research group of Prof. Hui Shi from Capital Normal University, in collaboration with the research group of Prof. Shangwei Zhong at Peking University, published a paper online in Science Bulletin titled “HECT E3 ligase UPL3 targets PIF1 for degradation to promote light-induced seed germination”. This study reveals a critical role for the HECT-type E3 ubiquitin ligase UBIQUITIN PROTEIN LIGASE 3 (UPL3) in the light-induced seed germination signaling pathway. It elucidates the molecular mechanism by which the photoreceptor phytochrome B (phyB) enhances the interaction between UPL3 and PIF1, thereby accelerating PIF1 degradation and initiating seed germination upon light exposure.
The research team identified UPL3, a HECT-family member, as the E3 ubiquitin ligase responsible for mediating PIF1 degradation. The study demonstrates that UPL3 physically interacts with PIF1 and catalyzes its polyubiquitination, thereby driving PIF1 degradation through the 26S proteasome pathway. Phenotypic analyses confirmed that loss of UPL3 function leads to abnormal accumulation of PIF1 protein and significantly delayed seed germination under light, whereas normal UPL3 expression is essential for light-induced germination. Further investigation revealed that UPL3 selectively interacts with the activated form of phyB, and that activated phyB promotes the UPL3-PIF1 interaction, accelerating PIF1 degradation in seeds upon light exposure. This study uncovers a rapid PIF1 degradation mechanism that is coordinated by a HECT family E3 ubiquitin ligase and photoreceptor activation, ensuring timely seed germination under favorable light conditions. These findings comprehensively elucidate the key molecular mechanisms within the light-regulated seed germination signaling pathway, providing promising genetic targets and theoretical support for molecular design breeding aimed at enhancing crop seed vigor and improving germination uniformity.
Prof. Hui Shi from Capital Normal University and Prof. Shangwei Zhong from Prof. Hui Shi from Capital Normal University and Prof. Shangwei Zhong from Peking University are the corresponding authors of this paper. Dr. Sheng Xu is the first author, and Dr. Xing Shen and Ph.D. student Yixuan Fan are co-authors. This study was supported by the National Key Research and Development Program of China and the National Natural Science Foundation of China. Special thanks go to the State Key Laboratory of Gene Function and Modulation Research, the Peking University-Tsinghua University Joint Center for Life Sciences, the Mass Spectrometry Platform at the Peking University PHOENIX Center, and the Optical Imaging Core Facility of the National Center for Protein Sciences at Peking University for their strong support of this project.
Science Bulletin
Experimental study