| The circadian clock is a self-sustaining 24 h timekeeper which enables plants to anticipate periodic environmental changes and optimize the biological activities for most beneficial time during the day/night cycle,thereby increasing the utilization efficiency of energy and improving the adaptability of plants.The sustained circadian rhythm in plants relies on the network of transcription and translation feedback loops(TTFLs)of transcription factors at the core of the oscillator.Transcription factors PSEUDO-RESPONSE REGULATORS(PRRs)regulate the components of the core loops,and they are also key players in the circadian clock output pathway.Over the past years,Chromatin immunoprecipitation(ChIP)has become an indispensable method to uncover the clock network through identifications of circadian transcription factors binding sites on a genome-wide scale.In recent years,feedback loops study of Arabidopsis thaliana(At)circadian rhythm genes were characterized and integrated the circadian core loops model through a genetic approach.However,much of the existing knowledge about plant circadian clock was gained from Arabidopsis,and the architecture of crop circadian clock remains poorly understood.Besides,recent works suggested that circadian clock transcription factor always control important agricultural relevant traits in crops.Therefore,understanding the genome binding profiles of crop circadian transcription factor(TFs)may potentially benefit in crop improvement.In this study,our research focuses on the circadian clock genes of Arabidopsis and Oryza sativa(Os).First,to find the possible downstream output pathway for the Arabidopsis circadian clock.We generated transgenic lines of PRR5,PRR7,and PRR9.Then we used ChIP-seq data which already published to analyze the occupancy of circadian transcription factors.We found the new target genes B-BOX DOMAIN PROTEIN 28(BBX28)and BBX29,which were downstream of PRRs.Through ChIP-qPCR,we confirmed TIMING OF CAB EXPRESSION 1(TOC1),PRR5,and PRR9 can bind the promoter of BBX28 and BBX29.Also,we used the rice circadian clock transcription factor gene OsTOC1 transgenic lines for ChIP-seq and ChIP-qPCR experiments.The OsTOC1 binding site of the rice genome and the motif sequence G-box were obtained.OsTOC1 downstream gene OsTOC1,PRR37,PRR73,PRR95,LATE ELONGATED HYPOCOTYL(LHY),GIGANTEA(GI),and four CONSTANS-like(CO-like)family genes were identified by ChIP-qPCR.These demonstrate the important role of OsTOC1 in maintaining the rhythm of the rice circadian clock.These results on rice and Arabidopsis are beneficial for further research in the circadian clock. |
