The shade avoidance syndrome in Arabidopsis: a fundamental role for atypical basic helix-loop-helix proteins as transcriptional cofactors

Plant J. 2011 Apr;66(2):258-67. doi: 10.1111/j.1365-313X.2011.04485.x. Epub 2011 Feb 16.

Abstract

The shade avoidance syndrome (SAS) refers to a set of plant responses aimed at anticipating eventual shading by potential competitors. The SAS is initiated after perception of nearby vegetation as a reduction in the red to far-red ratio (R:FR) of the incoming light. Low R:FR light is perceived by the phytochromes, triggering dramatic changes in gene expression that, in seedlings, eventually result in an increased hypocotyl elongation to overgrow competitors. This response is inhibited by genes such as PHYTOCHROME RAPIDLY REGULATED 1 (PAR1), PAR2 and LONG HYPOCOTYL IN FR 1 (HFR1), which are transcriptionally induced by low R:FR. Although PAR1/PAR2 and HFR1 proteins belong to different groups of basic helix-loop-helix (bHLH) transcriptional regulators, they all lack a typical basic domain required for binding to E-box and G-box motifs in the promoter of target genes. By overexpressing derivatives of PAR1 and HFR1 we show that these proteins are actually transcriptional cofactors that do not need to bind DNA to directly regulate transcription. We conclude that protein-protein interactions involving the HLH domain of PAR1 and HFR1 are a fundamental aspect of the mechanism by which these proteins regulate gene expression, most likely through interaction with true transcription factors that do bind to the target genes and eventually unleash the observed SAS responses.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / genetics
  • Arabidopsis / metabolism
  • Arabidopsis / radiation effects*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Basic Helix-Loop-Helix Transcription Factors / genetics
  • Basic Helix-Loop-Helix Transcription Factors / metabolism*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • Gene Expression Regulation, Plant
  • Hypocotyl / radiation effects
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Plants, Genetically Modified / genetics
  • Plants, Genetically Modified / metabolism
  • Plants, Genetically Modified / radiation effects
  • Transcription, Genetic
  • Transgenes

Substances

  • Arabidopsis Proteins
  • Basic Helix-Loop-Helix Transcription Factors
  • DNA-Binding Proteins
  • HFR1 protein, Arabidopsis
  • Nuclear Proteins
  • PAR1 protein, Arabidopsis
  • PAR2 protein, Arabidopsis