Regulatory switch enforced by basic helix-loop-helix and ACT-domain mediated dimerizations of the maize transcription factor R.
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.
Department of Plant and Soil Sciences, University of Kentucky, Lexington, KY 40546, USA.
Que
Q
Kong
Sitakanta
S
Pattanaik
Antje
A
Feller
Joshua R
JR
Werkman
Chenglin
C
Chai
Yongqin
Y
Wang
Erich
E
Grotewold
Ling
L
Yuan
D000872:Anthocyanins / Q000096:biosynthesis; D051792:Basic Helix-Loop-Helix Proteins / Q000737:chemistry*; D053898:Biosynthetic Pathways / Q000235:genetics / Q000502:physiology*; D047369:Chromatin Immunoprecipitation; D019281:Dimerization; D024202:Electrophoretic Mobility Shift Assay; D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology*; D008958:Models, Molecular; D009687:Nuclear Proteins / Q000737:chemistry*; D010940:Plant Proteins / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism; D020798:Two-Hybrid System Techniques; D003313:Zea mays / Q000737:chemistry*
D000872:Anthocyanins; D051792:Basic Helix-Loop-Helix Proteins; D009687:Nuclear Proteins; D010940:Plant Proteins; D011994:Recombinant Proteins; C085200:R protein, Zea mays