Antagonistic HLH/bHLH transcription factors mediate brassinosteroid regulation of cell elongation and plant development in rice and Arabidopsis

Plant Cell. 2009 Dec;21(12):3767-80. doi: 10.1105/tpc.109.070441. Epub 2009 Dec 15.


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / cytology
  • Arabidopsis / genetics
  • Arabidopsis / growth & development*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Basic Helix-Loop-Helix Transcription Factors / genetics
  • Basic Helix-Loop-Helix Transcription Factors / metabolism*
  • Cell Enlargement
  • DNA-Binding Proteins
  • Gene Expression Regulation, Plant
  • Microscopy, Electron, Scanning
  • Mutation
  • Nuclear Proteins / metabolism
  • Oryza / cytology
  • Oryza / genetics
  • Oryza / growth & development*
  • Phylogeny
  • Plant Growth Regulators / metabolism*
  • Plant Proteins / genetics
  • Plant Proteins / metabolism
  • RNA, Plant / genetics
  • Seedlings / growth & development
  • Seedlings / ultrastructure
  • Sequence Alignment
  • Sequence Analysis, Protein
  • Steroids / metabolism
  • Transcription Factors / metabolism


  • Arabidopsis Proteins
  • BZR1 protein, Arabidopsis
  • Basic Helix-Loop-Helix Transcription Factors
  • DNA-Binding Proteins
  • IBH1 protein, Arabidopsis
  • Nuclear Proteins
  • PRE1 protein, Arabidopsis
  • Plant Growth Regulators
  • Plant Proteins
  • RNA, Plant
  • Steroids
  • Transcription Factors