title: Antagonistic HLH/bHLH transcription factors mediate brassinosteroid regulation of cell elongation and plant development in rice and Arabidopsis.
abstract: In rice (Oryza sativa), brassinosteroids (BRs) induce cell elongation at the adaxial side of the lamina joint to promote leaf bending. We identified a rice mutant (ili1-D) showing an increased lamina inclination phenotype similar to that caused by BR treatment. The ili1-D mutant overexpresses an HLH protein homologous to Arabidopsis thaliana Paclobutrazol Resistance1 (PRE1) and the human Inhibitor of DNA binding proteins. Overexpression and RNA interference suppression of ILI1 increase and reduce, respectively, rice laminar inclination, confirming a positive role of ILI1 in leaf bending. ILI1 and PRE1 interact with basic helix-loop-helix (bHLH) protein IBH1 (ILI1 binding bHLH), whose overexpression causes erect leaf in rice and dwarfism in Arabidopsis. Overexpression of ILI1 or PRE1 increases cell elongation and suppresses dwarf phenotypes caused by overexpression of IBH1 in Arabidopsis. Thus, ILI1 and PRE1 may inactivate inhibitory bHLH transcription factors through heterodimerization. BR increases the RNA levels of ILI1 and PRE1 but represses IBH1 through the transcription factor BZR1. The spatial and temporal expression patterns support roles of ILI1 in laminar joint bending and PRE1/At IBH1 in the transition from growth of young organs to growth arrest. These results demonstrate a conserved mechanism of BR regulation of plant development through a pair of antagonizing HLH/bHLH transcription factors that act downstream of BZR1 in Arabidopsis and rice.
authors.affiliation: Key Laboratory of Photosynthesis and Environmental Molecular Biology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
authors.forename: Li-Ying
authors.initials: LY
authors.lastname: Zhang
authors.forename: Ming-Yi
authors.initials: MY
authors.lastname: Bai
authors.forename: Jinxia
authors.initials: J
authors.lastname: Wu
authors.forename: Jia-Ying
authors.initials: JY
authors.lastname: Zhu
authors.forename: Hao
authors.initials: H
authors.lastname: Wang
authors.forename: Zhiguo
authors.initials: Z
authors.lastname: Zhang
authors.forename: Wenfei
authors.initials: W
authors.lastname: Wang
authors.forename: Yu
authors.initials: Y
authors.lastname: Sun
authors.forename: Jun
authors.initials: J
authors.lastname: Zhao
authors.forename: Xuehui
authors.initials: X
authors.lastname: Sun
authors.forename: Hongjuan
authors.initials: H
authors.lastname: Yang
authors.forename: Yunyuan
authors.initials: Y
authors.lastname: Xu
authors.forename: Soo-Hwan
authors.initials: SH
authors.lastname: Kim
authors.forename: Shozo
authors.initials: S
authors.lastname: Fujioka
authors.forename: Wen-Hui
authors.initials: WH
authors.lastname: Lin
authors.forename: Kang
authors.initials: K
authors.lastname: Chong
authors.forename: Tiegang
authors.initials: T
authors.lastname: Lu
authors.forename: Zhi-Yong
authors.initials: ZY
authors.lastname: Wang
mesh_terms: D017360:Arabidopsis / Q000166:cytology / Q000235:genetics / Q000254:growth & development*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D049108:Cell Enlargement; D004268:DNA-Binding Proteins; D018506:Gene Expression Regulation, Plant; D008855:Microscopy, Electron, Scanning; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism; D012275:Oryza / Q000166:cytology / Q000235:genetics / Q000254:growth & development*; D010802:Phylogeny; D010937:Plant Growth Regulators / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics; D036226:Seedlings / Q000254:growth & development / Q000648:ultrastructure; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein; D013256:Steroids / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D010937:Plant Growth Regulators; D010940:Plant Proteins; D018749:RNA, Plant; D013256:Steroids; D014157:Transcription Factors; C454444:BZR1 protein, Arabidopsis; C582892:IBH1 protein, Arabidopsis; C513126:PRE1 protein, Arabidopsis