Regulatory switch enforced by basic helix-loop-helix and ACT-domain mediated dimerizations of the maize transcription factor R

Que Kong, Sitakanta Pattanaik, Antje Feller, Joshua R Werkman, Chenglin Chai, Yongqin Wang, Erich Grotewold, Ling Yuan

Research output: Contribution to journalArticlepeer-review


The maize R2R3-MYB regulator C1 cooperates with the basic helix-loop-helix (bHLH) factor R to activate the expression of anthocyanin biosynthetic genes coordinately. As is the case for other bHLH factors, R harbors several protein-protein interaction domains. Here we show that not the classical but rather a briefly extended R bHLH region forms homodimers that bind canonical G-box DNA motifs. This bHLH DNA-binding activity is abolished if the C-terminal ACT (aspartokinase, chorismate, and TyrA) domain is licensed to homodimerize. Then the bHLH remains in the monomeric form, allowing it to interact with R-interacting factor 1 (RIF1). In this configuration, the R-RIF1 complex is recruited to the promoters of a subset of anthocyanin biosynthetic genes, such as A1, through the interaction with its MYB partner C1. If, however, the ACT domain remains monomeric, the bHLH region dimerizes and binds to G-boxes present in several anthocyanin genes, such as Bz1. Our results provide a mechanism by which a dimerization domain in a bHLH factor behaves as a switch that permits distinct configurations of a regulatory complex to be tethered to different promoters. Such a combinatorial gene regulatory framework provides one mechanism by which genes lacking obviously conserved cis-regulatory elements are regulated coordinately.

Original languageEnglish
Pages (from-to)E2091-7
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number30
StatePublished - Jul 24 2012


  • Anthocyanins/biosynthesis
  • Basic Helix-Loop-Helix Transcription Factors/chemistry
  • Biosynthetic Pathways/genetics
  • Chromatin Immunoprecipitation
  • Dimerization
  • Electrophoretic Mobility Shift Assay
  • Gene Expression Regulation, Plant/genetics
  • Models, Molecular
  • Nuclear Proteins/chemistry
  • Plant Proteins/chemistry
  • Protein Structure, Tertiary
  • Recombinant Proteins/metabolism
  • Two-Hybrid System Techniques
  • Zea mays/chemistry


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