The Mechanism Of Br Regulates Rice Tillering

Brassinosteroids(BRs)are a class of important plant hormones that regulate plant growth development in several aspects.Tiller is a particular type of branch in grass family of monocotyledon,also an important agronomic trait which firmly associates with rice yield.It was early found that BR-deficient mutants d2-2,dll,BR-perceptional mutant d61-2 and signal mutant showed dwarf and low tillering phenotype since these mutants were identified involved in BR biosynthesis and signaling pathway.But it was unclear that whether BR controls rice tillering and if so the mechanism of BR regulating rice tillering needs to be elucidated.The research in this paper is aimed to figure out that whether BR regulates rice tilering and shed light on the possible mechanism of BR regulating rice tillering.First,we did tiller phenotyping of BR-deficient mutants d2-2,d11,BR-perceptional mutant d61-2,BR signal mutants dlt,rla1 and 35S::GSK2,35S::GSK2-RNAi,D3::bzr1-d,D3::BZR1-RNAi transgenic plants,compared with wild type at maturation stage,tiller number of BR signal enhanced transgenic plants dramatically increased and significantly decreased in BR signal attenuated mutants and transgenic plants,the results indicated that BR indeed promotes rice tiller.Then we performed kinetic analyses of buds outgrowth,and found that buds outgrowth of BR signal enhanced transgenic plants was faster than wild type,but much slower in BR signal attenuated mutants and transgenic plants compared with wild type,these results demonstrate that BR promotes rice tiller mainly through accelerating tiller buds outgrowth.Next,we identified the key gene FC1 that negatively controls tiller buds outgrowth expression level in buds of above mutants and transgenic plants,qRT-PCR assay showed that FC1 expression was remarkably decreased in BR signal enhanced transgenic plants,and notably increased in BR-deficient mutants,signal mutants and BR signal disruption transgenic plants.Finally,we verified that OsBZR1 can directly bind to FC1 promoter and inhibit its transcription by ChIP,EMSA and LUC experiment.It was preliminary revealed the mechanism of BR positively regulating tillering in rice,we shed light on BR positively regulating tiller buds outgrowth mainly through OsBZR1 inhibiting FC1 transcription.