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

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 109; no. 30; pp. E2091 - E2097
• Main Authors: Kong, Que, Pattanaik, Sitakanta, Feller, Antje, Werkman, Joshua R, Chai, Chenglin, Wang, Yongqin, Grotewold, Erich, Yuan, Ling
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 24.07.2012; National Acad Sciences
• Series: PNAS Plus
• Subjects: anthocyanins; Anthocyanins - biosynthesis; aspartate kinase; Basic Helix-Loop-Helix Transcription Factors - chemistry; Binding sites; Biological Sciences; Biosynthetic Pathways - genetics; Biosynthetic Pathways - physiology; chorismic acid; Chromatin Immunoprecipitation; corn; Deoxyribonucleic acid; Dimerization; DNA; Electrophoretic Mobility Shift Assay; Gene expression; Gene Expression Regulation, Plant - genetics; Gene Expression Regulation, Plant - physiology; Genes; Models, Molecular; Nuclear Proteins - chemistry; nucleotide motifs; Plant Proteins - chemistry; PNAS Plus; Protein Structure, Tertiary; protein-protein interactions; Proteins; Recombinant Proteins - metabolism; regulator genes; transcription factors; Two-Hybrid System Techniques; Zea mays - chemistry
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1205513109

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.