Origin And Evolution Of UVR8 And Its Signaling Pathway In Green Plants

The UV-B radiation(280-315 nm)varies drastically during the transition from aquatic environments to land,and it serves as a vital information signal for plant photomorphogenesis.During the plant terrestrialization,plants have evolved the ability to perceive and transduce UV-B signal,adjusting their growth,metabolism and developments.The major components of UV-B perception,signal transduction and UV-B responses have been extensively studied in Arabidopsis thaliana,and UV RESISTANCE LOCUS 8(UVR8)has been characterized as the exclusive UV-B photoreceptor in green plants.However,the origin and evolution of UVR8-mediated signaling pathway remains largely unknown.In this study,we selected hundreds of high-quality genomes and transcriptomes to investigate the origin and evolution of the major components of UVR8-mediated signaling pathway(UVR8,RUP,COP1,SPAs,HY5,HYH,BES1,BIM1,WRKY36,MYB73,MYB77,MYB13 and PIFs).We took advantage of phylogenetic analysis,domain analysis,motif analysis,positive selection analysis and co expression analysis in this study.We found the UVR8-COP1/SPA-HY5-RUP signaling pathway originated in chlorophytes,and UVR8-BES1/BIM1,UVR8-WRKY36-HY5 and UVR8-MYB73/MYB77 signaling pathway originated in charophytes.UVR8 presented a conservative evolutionary route during the plant evolution,and the evolutionary history of negative regulators or transcription factors were different with the evolution of green plants.We identified that UVR8 experienced significant positive selection in the ancestral branch of chlorophytes and the ancestral branch of streptophytes,and RUP experienced significant positive selection in the ancestral branch of streptophytes.Our results characterized the origins and evolution of the discovered UVR8-mediated signaling pathways in Viridiplantae by genomic and phylogenetic approaches.The adaptative modifications(increase in copy number and positive Darwinian selection)on components of UVR8-mediated signaling pathways largely coincide with the terrestrialization of plants.During the transition from deep sea to shallow water,and from aquatic to terrestrial environments,UV light was a crucial environmental stress for green plants.Our study has greatly advanced our understanding of molecular evolution and adaptive mechanisms underlying the plant UV-B acclimation.