title: A Negative Feedback Loop between PHYTOCHROME INTERACTING FACTORs and HECATE Proteins Fine-Tunes Photomorphogenesis in Arabidopsis.
abstract: The phytochrome interacting factors (PIFs), a small group of basic helix-loop-helix transcription factors, repress photomorphogenesis both in the dark and light. Light signals perceived by the phytochrome family of photoreceptors induce rapid degradation of PIFs to promote photomorphogenesis. Here, we show that HECATE (HEC) proteins, another small group of HLH proteins, antagonistically regulate PIFs to promote photomorphogenesis. HEC1 and HEC2 heterodimerize with PIF family members. PIF1, HEC1, and HEC2 genes are spatially and temporally coexpressed, and HEC2 is localized in the nucleus. hec1, hec2, and hec3 single mutants and the hec1 hec2 double mutant showed hyposensitivity to light-induced seed germination and accumulation of chlorophyll and carotenoids, hallmark processes oppositely regulated by PIF1. HEC2 inhibits PIF1 target gene expression by directly heterodimerizing with PIF1 and preventing DNA binding and transcriptional activation activity of PIF1. Conversely, PIFs directly activate the expression of HEC1 and HEC2 in the dark, and light reduces the expression of these HECs possibly by degrading PIFs. HEC2 is partially degraded in the dark through the ubiquitin/26S-proteasome pathway and is stabilized by light. HEC2 overexpression also reduces the light-induced degradation of PIF1. Taken together, these data suggest that PIFs and HECs constitute a negative feedback loop to fine-tune photomorphogenesis in Arabidopsis thaliana.
authors.affiliation: Department of Molecular Biosciences and The Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712.
authors.forename: Ling
authors.initials: L
authors.lastname: Zhu
authors.affiliation: Department of Molecular Biosciences and The Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712.
authors.forename: Ruijiao
authors.identifier: 0000-0002-2218-9161
authors.initials: R
authors.lastname: Xin
authors.affiliation: Department of Molecular Biosciences and The Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712.
authors.forename: Qingyun
authors.initials: Q
authors.lastname: Bu
authors.affiliation: Department of Molecular Biosciences and The Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712.
authors.forename: Hui
authors.initials: H
authors.lastname: Shen
authors.affiliation: Department of Molecular Biosciences and The Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Dang
authors.affiliation: Department of Molecular Biosciences and The Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712 huq@austin.utexas.edu.
authors.forename: Enamul
authors.identifier: 0000-0001-7692-5139
authors.initials: E
authors.lastname: Huq
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D046988:Proteasome Endopeptidase Complex; D014157:Transcription Factors; C587998:HECATE1 protein, Arabidopsis; C508068:At2g20180 protein, Arabidopsis