title: FLOWERING BHLH transcriptional activators control expression of the photoperiodic flowering regulator CONSTANS in Arabidopsis.
abstract: Many plants monitor day-length changes throughout the year and use the information to precisely regulate the timing of seasonal flowering for maximum reproductive success. In Arabidopsis thaliana, transcriptional regulation of the CONSTANS (CO) gene and posttranslational regulation of CO protein are crucial mechanisms for proper day-length measurement in photoperiodic flowering. Currently, the CYCLING DOF FACTOR proteins are the only transcription factors known to directly regulate CO gene expression, and the mechanisms that directly activate CO transcription have remained unknown. Here we report the identification of four CO transcriptional activators, named FLOWERING BHLH 1 (FBH1), FBH2, FBH3, and FBH4. All FBH proteins are related basic helix-loop-helix-type transcription factors that preferentially bind to the E-box cis-elements in the CO promoter. Overexpression of all FBH genes drastically elevated CO levels and caused early flowering regardless of photoperiod, whereas CO levels were reduced in the fbh quadruple mutants. In addition, FBH1 is expressed in the vascular tissue and bound near the transcription start site of the CO promoter in vivo. Furthermore, FBH homologs in poplar and rice induced CO expression in Arabidopsis. These results indicate that FBH proteins positively regulate CO transcription for photoperiodic flowering and that this mechanism may be conserved in diverse plant species. Our results suggest that the diurnal CO expression pattern is generated by a concert of redundant functions of positive and negative transcriptional regulators.
authors.affiliation: Department of Biology, University of Washington, Seattle, WA 98195-1800, USA.
authors.forename: Shogo
authors.initials: S
authors.lastname: Ito
authors.forename: Young Hun
authors.initials: YH
authors.lastname: Song
authors.forename: Anna R
authors.initials: AR
authors.lastname: Josephson-Day
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Miller
authors.forename: Ghislain
authors.initials: G
authors.lastname: Breton
authors.forename: Richard G
authors.initials: RG
authors.lastname: Olmstead
authors.forename: Takato
authors.initials: T
authors.lastname: Imaizumi
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000502:physiology*; D017124:Conserved Sequence; D004268:DNA-Binding Proteins / Q000502:physiology*; D035264:Flowers / Q000254:growth & development; D018506:Gene Expression Regulation, Plant / Q000502:physiology*; D017343:Genes, Plant; D017930:Genes, Reporter; D008969:Molecular Sequence Data; D012275:Oryza / Q000235:genetics; D017440:Photoperiod; D030821:Plants, Genetically Modified; D032107:Populus / Q000235:genetics; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000235:genetics; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D015534:Trans-Activators / Q000235:genetics / Q000502:physiology*; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic
chemical_list: D029681:Arabidopsis Proteins; C092776:CONSTANS protein, Arabidopsis; D004268:DNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D015534:Trans-Activators; D014157:Transcription Factors