Structural Basis for LEAFY Floral Switch Function and Similarity With Helix-Turn-Helix Proteins

EMBO J. 2008 Oct 8;27(19):2628-37. doi: 10.1038/emboj.2008.184. Epub 2008 Sep 11.

Abstract

The LEAFY (LFY) protein is a key regulator of flower development in angiosperms. Its gradually increased expression governs the sharp floral transition, and LFY subsequently controls the patterning of flower meristems by inducing the expression of floral homeotic genes. Despite a wealth of genetic data, how LFY functions at the molecular level is poorly understood. Here, we report crystal structures for the DNA-binding domain of Arabidopsis thaliana LFY bound to two target promoter elements. LFY adopts a novel seven-helix fold that binds DNA as a cooperative dimer, forming base-specific contacts in both the major and minor grooves. Cooperativity is mediated by two basic residues and plausibly accounts for LFY's effectiveness in triggering sharp developmental transitions. Our structure reveals an unexpected similarity between LFY and helix-turn-helix proteins, including homeodomain proteins known to regulate morphogenesis in higher eukaryotes. The appearance of flowering plants has been linked to the molecular evolution of LFY. Our study provides a unique framework to elucidate the molecular mechanisms underlying floral development and the evolutionary history of flowering plants.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Arabidopsis / anatomy & histology
  • Arabidopsis / physiology*
  • Arabidopsis Proteins / chemistry*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Crystallography, X-Ray
  • DNA / metabolism
  • Dimerization
  • Flowers / physiology*
  • Helix-Turn-Helix Motifs*
  • Macromolecular Substances / chemistry
  • Macromolecular Substances / metabolism
  • Models, Molecular
  • Molecular Sequence Data
  • Nucleic Acid Conformation
  • Promoter Regions, Genetic
  • Protein Binding
  • Protein Conformation
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Transcription Factors / chemistry*
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*

Substances

  • Arabidopsis Proteins
  • LFY protein, Arabidopsis
  • Macromolecular Substances
  • Transcription Factors
  • DNA