Molecular Mechanism Of Rice Mediator Subunit OsMED25 In Regulating Brassinosteroid Signaling

Rice(Oryza sativa L.)is one of the most important food crops and rice plant architecture is crucial for grain yield.Leaf inclination is one of influencing factor that regulate plant architecture,etect leaves contribute to capture more light energy and increase crop yield.Brassinosteroids(BRs)could regulate plant growth,development,and adaptation.As well as it plays an important role in regulating plant architecture.It accompanies with a sort of transcriptional regulation during phytohormone signaling pathway.Mediator serves as a bridge between gene-specific transcription factors and the RNA polymerase machinery,functioning as important component to regulate transcription process.However,the study on rice mediator has been less reported.In this study,we found that OsMED25 could effect leaf angle.The phenotype and BRs sensitivity showed that OsMED25 act as a positive regulator involved in BR signaling.The genetics and biochemical analysis revealed that OsMED25 interact with OsBZR1 and affect transcriptional activity of OsBZR1 target genes,and then involve in rice BR signaling.The main results are as follows:1.The phenotype of OsMED25-RNAi and osmed25 mutants conferred compacted plant architecture and erect leaf inclination compared with wild type plants at seedling and heading stage.As well as the heading time of mutants was significantly later than control.2.The sensitivity to different concentrations of 24-epi BL for OsMED25-RNAi and osmed25 mutants decreased compared with wild type plants in term of leaf inclination and root length.The relative expression of BRs biosynthetic gene in mutants was increased compared with wild type plants to different degree.3.OsMED25-RNAi can largely suppress the enhanced BR signaling phenotype of Osbzr1-D.At the same time the BR sensitivity of OsMED25-RNAi Osbzr1-D double mutants approached OsMED25-RNAi mutants and the biosynthetic gene expression level in OsMED25-RNAi Osbzr1-D plant was approximated to Nipponbare.It suggests that functional OsMED25 is indispensable for leaf inclination regulated by OsBZR1.4.Bi FC assay and LCI assay confirmed that OsMED25 interact with OsBZR1 in vivo.In addition,OsMED25 interact with OsBZR1 through its ACID domain.5.OsMED25 could be recruited to OsD2 promoter region of OsBZR1 target gene,as well as OsMED25 works with OsBZR1 and impairs its transcriptional activity to OsD2 significantly.6.By comparative analysis of the RNA-sequence data in Nipponbare,Osbzr1-D and OsMED25-RNAi Osbzr1-D double mutants,1195 different expression genes were co-upregulated by OsMED25 and OsBZR1.978 different expression genes were codownregulated by OsMED25 and OsBZR1.OsMED25 can significantly affect expression of around 45% OsBZR1-regulated genes,which supporting the notion that OsMED25 affect OsBZR1 regulating target genes.