On April 2, 2026, a research team led by Professor Bojian Zhong from the School of Life Sciences published a paper in Plant Communications entitled “Functional evolution and rewiring of the UVR8-BES1/BIM1 module underpin refined UV-B responses during plant terrestrialization”. The study reveals that, during their transition from aquatic to terrestrial environments, green plants adapted to UV-B radiation through the stepwise assembly of the UV-B signaling module UVR8-BES1/BIM1 and the rewiring of its regulatory network. The findings offer new insight into the adaptive evolution of plants in response to complex environmental conditions.
Plant terrestrialization occurred approximately 480 million years ago. The high intensity and strong fluctuations of UV-B radiation in terrestrial environments posed major challenges to the survival and adaptation of early land plants. UVR8 serves as a UV-B-specific photoreceptor in green plants. In the model plant Arabidopsis thaliana, UVR8 interacts with BES1 and BIM1, two core transcription factors in the brassinosteroid (BR) signaling pathway. This interaction forms the UVR8-BES1/BIM1 module, which is crucial for the coordinated regulation of UV-B signaling and endogenous growth. However, the origin of this module in green plants, the establishment of its protein-protein interactions, and the rewiring of its downstream regulatory network have remained unclear.
To address these questions, the researchers combined AlphaFold2-based structural prediction with FoldMason alignment to reconstruct the evolutionary history of UVR8, BES1, and BIM1 across green plants. The results showed that UVR8 and BIM1 originated in the common ancestor of green plants, whereas BES1 first emerged in the common ancestor of streptophytes. The study also demonstrated that structure-based phylogenetic analysis can substantially improve the accuracy of ortholog identification in ancient green plant lineages. Through computational predictions and experimental validation, they found that the UVR8-BIM1 interaction had already been established in green algae and has remained highly conserved across green plants. In bryophytes, BES1 participates indirectly in UV-B signaling through BIM1. In vascular plants, BES1 acquired the ability to interact directly with UVR8, thereby completing the stepwise assembly of the UVR8-BES1/BIM1 module. By integrating cross-species comparative analyses of UV-B-responsive transcriptomes with DAP-seq and regulatory network inference, the researchers revealed extensive reprogramming of the UV-B-responsive transcriptional network during plant terrestrialization. In Marchantia polymorpha, BIM1 functions as a major regulator of UV-B responses, while BES1 acts a cofactor. In A. thaliana, BES1 has evolved into a core regulatory factor that integrates UV-B and BR signaling, in part through an expanded DNA-binding repertoire.
Taken together, the study systematically delineates the evolutionary trajectory of the UVR8-BES1/BIM1 module in terms of structural evolution, interaction assembly, and regulatory network remodeling. The study reveals that the stepwise assembly of this module constituted a key evolutionary innovation underlying plant adaptation to the terrestrial light environment and provides a new evolutionary framework for understanding the integration of light and hormone signaling in green plants.
Dr. Chengjuan Cao, a postdoctoral researcher at the College of Life Sciences, Nanjing Normal University, is the first author of the paper. Professor Bojian Zhong and Associate Professor Zhenhua Zhang are the co-corresponding authors. Professor Hongtao Liu of Shenzhen University provided important support for this study. This research was supported by the National Natural Science Foundation of China and the Natural Science Foundation of Jiangsu Province.
Original paper link: https://doi.org/10.1016/j.xplc.2026.101842