title: Phytochromes promote seedling light responses by inhibiting four negatively-acting phytochrome-interacting factors.
abstract: PIF3 is a phytochrome-interacting basic helix-loop-helix transcription factor that negatively regulates light responses, including hypocotyl elongation, cotyledon opening, and hypocotyl negative gravitropism. However, the role of PIF3 in chlorophyll biosynthesis has not been clearly defined. Here, we show that PIF3 also negatively regulates chlorophyll biosynthesis by repressing biosynthetic genes in the dark. Consistent with the gene expression patterns, the etiolated pif3 mutant accumulated a higher amount of protochlorophyllide and was bleached severely when transferred into light. The photobleaching phenotype of pif3 could be suppressed by the gun5 mutation and mimicked by overexpression of GUN5. When 4 negative phytochrome-interacting protein genes (PIF1, PIF3, PIF4, and PIF5) were mutated, the resulting quadruple mutant seedlings displayed constitutive photomorphogenic phenotypes, including short hypocotyls, open cotyledons, and disrupted hypocotyl gravitropism in the dark. Microarray analysis further confirmed that the dark-grown quadruple mutant has a gene expression pattern similar to that of red light-grown WT. Together, our data indicate that 4 phytochrome-interacting proteins are required for skotomorphogenesis and phytochromes activate photomorphogenesis by inhibiting these factors.
authors.affiliation: Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea.
authors.forename: Jieun
authors.initials: J
authors.lastname: Shin
authors.forename: Keunhwa
authors.initials: K
authors.lastname: Kim
authors.forename: Hyojin
authors.initials: H
authors.lastname: Kang
authors.forename: Ismayil S
authors.initials: IS
authors.lastname: Zulfugarov
authors.forename: Gabyong
authors.initials: G
authors.lastname: Bae
authors.forename: Choon-Hwan
authors.initials: CH
authors.lastname: Lee
authors.forename: Doheon
authors.initials: D
authors.lastname: Lee
authors.forename: Giltsu
authors.initials: G
authors.lastname: Choi
mesh_terms: D017360:Arabidopsis / Q000033:anatomy & histology / Q000235:genetics / Q000254:growth & development*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism; D002734:Chlorophyll / Q000096:biosynthesis* / Q000235:genetics; D003624:Darkness; D020869:Gene Expression Profiling; D009024:Morphogenesis / Q000235:genetics; D009154:Mutation; D038761:Photobleaching; D010788:Photosynthesis / Q000235:genetics; D010834:Phytochrome / Q000378:metabolism*; D036226:Seedlings / Q000033:anatomy & histology / Q000235:genetics / Q000254:growth & development
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D002734:Chlorophyll; D010834:Phytochrome; C508068:At2g20180 protein, Arabidopsis; C116162:PIF3 protein, Arabidopsis; C459466:PIF4 protein, Arabidopsis; C497729:PIF5 protein, Arabidopsis