title: BR-dependent phosphorylation modulates PIF4 transcriptional activity and shapes diurnal hypocotyl growth.
abstract: Signaling by the hormones brassinosteroid (BR) and gibberellin (GA) is critical to normal plant growth and development and is required for hypocotyl elongation in response to dark and elevated temperatures. Active BR signaling is essential for GA promotion of hypocotyl growth and suppresses the dwarf phenotype of GA mutants. Cross-talk between these hormones occurs downstream from the DELLAs, as GA-induced destabilization of these GA signaling repressors is not affected by BRs. Here we show that the light-regulated PIF4 (phytochrome-interacting factor 4) factor is a phosphorylation target of the BR signaling kinase BRASSINOSTEROID-INSENSITIVE 2 (BIN2), which marks this transcriptional regulator for proteasome degradation. Expression of a mutated PIF41A protein lacking a conserved BIN2 phosphorylation consensus causes a severe elongated phenotype and strongly up-regulated expression of the gene targets. However, PIF41A is not able to suppress the dwarf phenotype of the bin2-1 mutant with constitutive activation of this kinase. PIFs were shown to be required for the constitutive BR response of bes1-D and bzr1-1D mutants, these factors acting in an interdependent manner to promote cell elongation. Here, we show that bes1-D seedlings are still repressed by the inhibitor BRZ in the light and that expression of the nonphosphorylatable PIF41A protein makes this mutant fully insensitive to brassinazole (BRZ). PIF41A is preferentially stabilized at dawn, coinciding with the diurnal time of maximal growth. These results uncover a main role of BRs in antagonizing light signaling by inhibiting BIN2-mediated destabilization of the PIF4 factor. This regulation plays a prevalent role in timing hypocotyl elongation to late night, before light activation of phytochrome B (PHYB) and accumulation of DELLAs restricts PIF4 transcriptional activity.
authors.affiliation: Centro Nacional de Biotecnología-Consejo Superior de Investigaciones Científicas, 28049 Madrid, Spain.
authors.forename: Stella
authors.initials: S
authors.lastname: Bernardo-García
authors.affiliation: Centro Nacional de Biotecnología-Consejo Superior de Investigaciones Científicas, 28049 Madrid, Spain.
authors.forename: Miguel
authors.initials: M
authors.lastname: de Lucas
authors.affiliation: Centro Nacional de Biotecnología-Consejo Superior de Investigaciones Científicas, 28049 Madrid, Spain.
authors.forename: Cristina
authors.initials: C
authors.lastname: Martínez
authors.affiliation: Centro Nacional de Biotecnología-Consejo Superior de Investigaciones Científicas, 28049 Madrid, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Espinosa-Ruiz
authors.affiliation: Centro Nacional de Biotecnología-Consejo Superior de Investigaciones Científicas, 28049 Madrid, Spain.
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Davière
authors.affiliation: Centro Nacional de Biotecnología-Consejo Superior de Investigaciones Científicas, 28049 Madrid, Spain sprat@cnb.csic.es.
authors.forename: Salomé
authors.initials: S
authors.lastname: Prat
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism*; D060406:Brassinosteroids / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D005875:Gibberellins / Q000378:metabolism; D018546:Hypocotyl / Q000235:genetics / Q000254:growth & development*; D008027:Light; D009154:Mutation; D010641:Phenotype; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D055550:Protein Stability / Q000528:radiation effects; D015398:Signal Transduction
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D060406:Brassinosteroids; D005875:Gibberellins; D046988:Proteasome Endopeptidase Complex; D011494:Protein Kinases; C459466:PIF4 protein, Arabidopsis; C497729:PIF5 protein, Arabidopsis; C448985:At4g18710 protein, Arabidopsis
keywords: brassinosteroid; gibberellin; plant growth; signal integration
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