title: Bell-like homeodomain selectively regulates the high-irradiance response of phytochrome A.
abstract: Plant responses mediated by phytochrome A display a first phase saturated by transient light signals and a second phase requiring sustained excitation with far-red light (FR). These discrete outcomes, respectively so-called very-low-fluence response (VLFR) and high-irradiance response (HIR), are appropriate in different environmental and developmental contexts but the mechanisms that regulate the switch remain unexplored. Promoter analysis of a light-responsive target gene revealed a motif necessary for HIR but not for VLFR. This motif is required for binding of the Bell-like homeodomain 1 (BLH1) to the promoter in in vitro and in yeast 1-hybrid experiments. Promoter substitutions that increased BLH1 binding also enhanced HIR. blh1 mutants showed reduced responses to continuous FR and to deep canopy shadelight, but they retained normal responses to pulsed FR or red light and unfiltered sunlight. BLH1 enhanced BLH1 expression and its promotion by FR. We conclude that BLH1 specifically regulates HIR and not VLFR of phytochrome A.
authors: Fundación Instituto Leloir, Instituto de Investigaciones Bioquímicas Buenos Aires, Consejo Nacional de Investigaciones Cientificas y Técnicas and Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, C1405BWE Buenos Aires, Argentina.
authors: Roberto J
authors: RJ
authors: Staneloni
authors: María José
authors: MJ
authors: Rodriguez-Batiller
authors: Danilo
authors: D
authors: Legisa
authors: María R
authors: MR
authors: Scarpin
authors: Adamantia
authors: A
authors: Agalou
authors: Pablo D
authors: PD
authors: Cerdán
authors: Annemarie H
authors: AH
authors: Meijer
authors: Pieter B F
authors: PB
authors: Ouwerkerk
authors: Jorge J
authors: JJ
authors: Casal
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D020869:Gene Expression Profiling; D018398:Homeodomain Proteins / Q000378:metabolism*; D008027:Light; D009154:Mutation / Q000235:genetics; D051942:Phytochrome A / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding / Q000528:radiation effects; D014026:Nicotiana; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; C543640:BLH1 protein, Arabidopsis; D018398:Homeodomain Proteins; D051942:Phytochrome A; D014157:Transcription Factors