On April 17, 2020, Chair Professor Xingwang Deng from Department of Biology, led his research group to publish a paper in Plant Communications. The article, entitled “A positive feedback loop of BBX11-BBX21-HY5 promotes photomorphogenic development in Arabidopsis”, shows a new mechanism of light signaling transduction. Post-doc Xianhai Zhao and Senior Research Assistant Dr. Yueqin Heng from the Institute of Plant and Food Science, Department of Biology, are the co-first authors; Professor Xing Wang Deng at SUSTech and Professor Dongqing Xu at Nanjing Agricultural University are the co-corresponding authors of the paper. Post-doc Xuncheng Wang at Peking University is co-author.

Light is not only the major energy source for plants, but also acts as one of the most essential environmental factors affecting various physiological and developmental processes in plants. Light-mediated seedling development is modulated by a group of components including various photoreceptors, E3 ubiquitin ligase, and transcription factors at the molecular level. controls light-mediated seedling development. Recent studies have revealed that multiple B-BOX-CONTAINING PROTEINS (BBXs) play critical roles in COP1-HY5 regulatory network that precisely mediates light-mediated seedling development.

A working model depicting the positive feedback regulation of photomorphogenesis by BBX11-BBX21-HY5

Light triggers the rapid transcriptomic changes in one third of genes expression, ultimately leading to the promotion of seedling development. A group of transcription factors directly mediate the light-controlled transcriptional reprogramming. In this study, the team found a previously unidentified positive regulator of light signaling, BBX11, which contains two tandem conserved B-box domains in N-terminal region.  BBX11 synergistically works together with BBX21 and HY5 to mediate photomorphogenic development in plants. All of BBX11, BBX21 and HY5 are degraded in darkness, and accumulate in the light. Both BBX21 and HY5 are ubiquitinated by COP1, subsequently are subjected to 26S proteasome system for degradation in darkness. However, COP1 stabilized BBX11, rather than promoting its degradation. This fact suggests that yet unidentified component(s) might promote the degradation of BBX11 in etiolated seedlings.

Further analysis showed that BBX11 binds to the HY5 promoter to activate its transcription, while both BBX21 and HY5 associate with promoter region of BBX11 and positively regulate its expression. In conclusion, the team reveals that a positive feedback regulation consisting of BBX11, BBX21 and HY5 in promoting photomorphogenesis, and thus provides a transcriptional regulatory mechanism in maintaining normal development in response to light in plants.

This work was supported by the Southern University of Science and Technology, National Natural Science Foundation of China, Peking University-Tsinghua Life Science Joint Center and China Postdoctoral Science Foundation.

Link to paper: https://doi.org/10.1016/j.xplc.2020.100045