Chemical genetics reveal the novel transmembrane protein BIL4, which mediates plant cell elongation in brassinosteroid signaling

Biosci Biotechnol Biochem. 2009 Feb;73(2):415-21. doi: 10.1271/bbb.80752. Epub 2009 Feb 7.


Steroid hormones are conserved between animals and plants as signaling molecules to control growth and development. Plant steroid hormones, brassinosteroids (BRs), appear to play an important role in plant cell elongation. BRs bind to leucine-rich repeat kinase BRASSINOSTEROID-INSENSITIVE 1 (BRI1) localized to the plasma membrane, activate transcription factors in collaboration with cytosolic kinases and phosphatases, and regulate BR-responsive gene expression, but the details regarding the BR signaling pathway from perception to nuclear events remain unknown. In this study we used chemical genetics to identify an evolutionarily conserved transmembrane protein, Brz-insensitive-long hypocotyls 4 (BIL4), and demonstrated its role as a critical component of plant cell elongation occurring upon BR signaling. A dominant mutation, bil4-1D, showed cell elongation in the presence of the BR-specific inhibitor Brz. Brz suppresses expression of the BIL4 gene in wild-type plants, and overexpression of BIL4 in bil4-1D suppresses the BR deficiency caused by Brz. Our results indicate that BIL4 mediates cell elongation on BR signaling.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Arabidopsis / cytology*
  • Arabidopsis / drug effects
  • Arabidopsis / genetics*
  • Arabidopsis / metabolism
  • Arabidopsis Proteins / chemistry
  • Arabidopsis Proteins / genetics*
  • Arabidopsis Proteins / isolation & purification
  • Arabidopsis Proteins / metabolism*
  • Cell Enlargement* / drug effects
  • Gene Expression Regulation, Plant / drug effects
  • Genes, Plant
  • Membrane Proteins / chemistry
  • Membrane Proteins / genetics*
  • Membrane Proteins / isolation & purification
  • Membrane Proteins / metabolism*
  • Molecular Sequence Data
  • Mutation
  • Plant Growth Regulators / chemistry
  • Plant Growth Regulators / metabolism
  • RNA, Messenger / metabolism
  • Signal Transduction*
  • Steroids / chemistry
  • Steroids / metabolism*
  • Triazoles / chemistry
  • Triazoles / pharmacology


  • Arabidopsis Proteins
  • BIL4 protein, Arabidopsis
  • Membrane Proteins
  • Plant Growth Regulators
  • RNA, Messenger
  • Steroids
  • Triazoles