title: Interaction of shade avoidance and auxin responses: a role for two novel atypical bHLH proteins.
abstract: Plants sense the presence of potentially competing nearby individuals as a reduction in the red to far-red ratio of the incoming light. In anticipation of eventual shading, a set of plant responses known as the shade avoidance syndrome (SAS) is initiated soon after detection of this signal by the phytochrome photoreceptors. Here we analyze the function of PHYTOCHROME RAPIDLY REGULATED1 (PAR1) and PAR2, two Arabidopsis thaliana genes rapidly upregulated after simulated shade perception. These genes encode two closely related atypical basic helix-loop-helix proteins with no previously assigned function in plant development. Using reverse genetic approaches, we show that PAR1 and PAR2 act in the nucleus to broadly control plant development, acting as negative regulators of a variety of SAS responses, including seedling elongation and photosynthetic pigment accumulation. Molecularly, PAR1 and PAR2 act as direct transcriptional repressors of two auxin-responsive genes, SMALL AUXIN UPREGULATED15 (SAUR15) and SAUR68. Additional results support that PAR1 and PAR2 function in integrating shade and hormone transcriptional networks, rapidly connecting phytochrome-sensed light changes with auxin responsiveness.
authors.affiliation: Laboratori de Genètica Molecular Vegetal Consorci CSIC-IRTA, Departament de Genètica Molecular, Barcelona, Spain.
authors.forename: Irma
authors.initials: I
authors.lastname: Roig-Villanova
authors.forename: Jordi
authors.initials: J
authors.lastname: Bou-Torrent
authors.forename: Anahit
authors.initials: A
authors.lastname: Galstyan
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Carretero-Paulet
authors.forename: Sergi
authors.initials: S
authors.lastname: Portolés
authors.forename: Manuel
authors.initials: M
authors.lastname: Rodríguez-Concepción
authors.forename: Jaime F
authors.initials: JF
authors.lastname: Martínez-García
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000494:pharmacology; D000220:Adaptation, Biological; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000033:anatomy & histology / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics* / Q000378:metabolism; D003513:Cycloheximide / Q000494:pharmacology; D018744:DNA, Plant / Q000235:genetics; D003907:Dexamethasone / Q000494:pharmacology; D005938:Glucocorticoids / Q000494:pharmacology; D006540:Herbicides / Q000494:pharmacology; D007210:Indoleacetic Acids / Q000378:metabolism; D008969:Molecular Sequence Data; D010641:Phenotype; D030821:Plants, Genetically Modified / Q000033:anatomy & histology / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D017422:Sequence Analysis, DNA; D013472:Sunlight
chemical_list: D015084:2,4-Dichlorophenoxyacetic Acid; D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D003513:Cycloheximide; D018744:DNA, Plant; D003907:Dexamethasone; D005938:Glucocorticoids; D006540:Herbicides; D007210:Indoleacetic Acids; D011500:Protein Synthesis Inhibitors; C524961:PAR1 protein, Arabidopsis; C524962:PAR2 protein, Arabidopsis; C086789:SAUR-AC1 protein, Arabidopsis