title: A triantagonistic basic helix-loop-helix system regulates cell elongation in Arabidopsis.
abstract: In plants, basic helix-loop-helix (bHLH) transcription factors play important roles in the control of cell elongation. Two bHLH proteins, PACLOBTRAZOL RESISTANCE1 (PRE1) and Arabidopsis ILI1 binding bHLH1 (IBH1), antagonistically regulate cell elongation in response to brassinosteroid and gibberellin signaling, but the detailed molecular mechanisms by which these factors regulate cell elongation remain unclear. Here, we identify the bHLH transcriptional activators for cell elongation (ACEs) and demonstrate that PRE1, IBH1, and the ACEs constitute a triantagonistic bHLH system that competitively regulates cell elongation. In this system, the ACE bHLH transcription factors directly activate the expression of enzyme genes for cell elongation by interacting with their promoter regions. IBH1 negatively regulates cell elongation by interacting with the ACEs and thus interfering with their DNA binding. PRE1 interacts with IBH1 and counteracts the ability of IBH1 to affect ACEs. Therefore, PRE1 restores the transcriptional activity of ACEs, resulting in induction of cell elongation. The balance of triantagonistic bHLH proteins, ACEs, IBH1, and PRE1, might be important for determination of the size of plant cells. The expression of IBH1 and PRE1 is regulated by brassinosteroid, gibberellins, and developmental phase dependent factors, indicating that two phytohormones and phase-dependent signals are integrated by this triantagonistic bHLH system.
authors.affiliation: Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8562, Japan.
authors.forename: Miho
authors.initials: M
authors.lastname: Ikeda
authors.forename: Sumire
authors.initials: S
authors.lastname: Fujiwara
authors.forename: Nobutaka
authors.initials: N
authors.lastname: Mitsuda
authors.forename: Masaru
authors.initials: M
authors.lastname: Ohme-Takagi
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics* / Q000378:metabolism; D060406:Brassinosteroids / Q000378:metabolism; D018548:Cotyledon / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D018744:DNA, Plant / Q000235:genetics; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D005875:Gibberellins / Q000378:metabolism; D018546:Hypocotyl / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D008954:Models, Biological; D020411:Oligonucleotide Array Sequence Analysis; D010641:Phenotype; D010937:Plant Growth Regulators / Q000378:metabolism; D018515:Plant Leaves / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D030821:Plants, Genetically Modified; D011485:Protein Binding; D036226:Seedlings / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D020798:Two-Hybrid System Techniques
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D060406:Brassinosteroids; D018744:DNA, Plant; D005875:Gibberellins; D010937:Plant Growth Regulators; D014157:Transcription Factors; C582892:IBH1 protein, Arabidopsis; C513126:PRE1 protein, Arabidopsis