title: Independent and interdependent functions of LAF1 and HFR1 in phytochrome A signaling.
abstract: Several positive regulators of phytochrome A signaling--e.g., LAF1, HFR1, and HY5--operate downstream from the photoreceptor, but their relative sites of action in the transduction pathway are unknown. Here, we show that HFR1RNAi/laf1 or hfr1-201/LAF1RNAi generated by RNA interference (RNAi) has an additive phenotype under FR light compared with the single mutants, hfr1-201 or laf1. This result indicates that LAF1 and HFR1 function in largely independent pathways. LAF1, an R2R3-MYB factor, interacts with HFR1, a basic helix-loop-helix (bHLH) factor, and this interaction is abolished by the R97A mutation in the LAF1 R2R3 domain. Polyubiquitinations of LAF1 and HFR1 by the COP1 E3 ligase in vitro are inhibited by LAF1/HFR1 association. Consistent with this result, endogenous HFR1 is less stable in laf1 compared with wild type, and similarly, LAF1-3HA expressed from a transgene is also less stable in hfr1-201 than wild type. In transgenic plants, HFR1 levels are significantly elevated upon induced expression of LAF1 but not LAF1(R97A). Moreover, induced expression of LAF1 but not LAF1(R97A) delays post-translational HFR1 degradation in FR light. Constitutive coexpression of HFR1 and LAF1 but not HFR1 and LAF1 (R97A) confers FR hypersensitivity in double transgenic plants. Our results show that in addition to their independent functions in phyA signaling, LAF1 and HFR1 also cooperate post-translationally to stabilize each other through inhibition of ubiquitination by COP1, thereby enhancing phyA photoresponses.
authors: Laboratory of Plant Molecular Biology, The Rockefeller University, New York, New York 10065, USA.
authors: In-Cheol
authors: IC
authors: Jang
authors: Seong Wook
authors: SW
authors: Yang
authors: Jun-Yi
authors: JY
authors: Yang
authors: Nam-Hai
authors: NH
authors: Chua
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D018744:DNA, Plant / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D017343:Genes, Plant; D005816:Genetic Complementation Test; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D018462:Photobiology; D051942:Phytochrome A / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011499:Protein Processing, Post-Translational; D034622:RNA Interference; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D018744:DNA, Plant; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D051942:Phytochrome A; D011994:Recombinant Proteins; D015534:Trans-Activators; D025801:Ubiquitin; D044767:Ubiquitin-Protein Ligases; C414438:At1g02340 protein, Arabidopsis; C438763:LAF1 protein, Arabidopsis; C497973:PHYA protein, Arabidopsis; C471983:AT2G32950 protein, Arabidopsis
references: Nat Rev Mol Cell Biol. 2002 Feb;3(2):85-93
references: 11836510
references: Proc Natl Acad Sci U S A. 2000 Dec 5;97(25):13579-84
references: 11095727
references: Genes Dev. 1999 Aug 1;13(15):2017-27
references: 10444599
references: Curr Biol. 2005 Dec 6;15(23):2125-30
references: 16332538
references: Plant Cell. 2006 May;18(5):1274-91
references: 16603655
references: Trends Plant Sci. 2005 Feb;10(2):63-70
references: 15708343
references: Genes Dev. 2003 Nov 1;17(21):2642-7
references: 14597662
references: Plant Cell Physiol. 2006 Aug;47(8):1023-34
references: 16861711
references: J Biol Chem. 1993 Sep 15;268(26):19626-31
references: 8366106
references: Genes Dev. 2001 Jan 1;15(1):90-103
references: 11156608
references: Plant Cell. 1998 Jan;10(1):19-33
references: 9477570
references: Exp Cell Res. 2005 Oct 1;309(2):419-28
references: 16055116
references: Genes Dev. 2000 Aug 1;14(15):1958-70
references: 10921909
references: Genes Dev. 2005 Jul 1;19(13):1532-43
references: 15998807
references: EMBO J. 2002 Mar 15;21(6):1339-49
references: 11889039
references: Plant J. 1998 Dec;16(6):735-43
references: 10069079
references: Development. 2003 Oct;130(20):4859-69
references: 12917293
references: Curr Opin Plant Biol. 2003 Oct;6(5):453-62
references: 12972046
references: Genes Dev. 2001 Oct 1;15(19):2613-25
references: 11581165
references: Plant Physiol. 2003 Dec;133(4):1592-604
references: 14645728
references: Genes Dev. 2000 Feb 1;14(3):257-71
references: 10673498
references: Plant J. 1998 Oct;16(2):263-76
references: 9839469
references: Plant Cell. 2005 Mar;17(3):804-21
references: 15705947
references: Plant Cell. 1994 Apr;6(4):487-500
references: 8205001
references: Genes Dev. 2001 Nov 15;15(22):2980-90
references: 11711433
references: Genes Dev. 1992 May;6(5):864-75
references: 1577278
references: J Biol Chem. 2006 Dec 8;281(49):37636-45
references: 17015446
references: Genes Dev. 1997 Nov 15;11(22):2983-95
references: 9367981
references: Plant Cell. 2000 Nov;12(11):2061-74
references: 11090209
references: Plant J. 2004 Oct;40(1):22-34
references: 15361138
references: Plant J. 2002 Jun;30(6):711-9
references: 12061902
references: Genes Dev. 2000 May 15;14(10):1269-78
references: 10817761
references: Genes Dev. 2005 Mar 1;19(5):593-602
references: 15741320
references: Plant J. 2005 Aug;43(3):356-70
references: 16045472
references: Science. 2000 Dec 15;290(5499):2105-10
references: 11118137
references: Cell. 2005 Nov 4;123(3):409-21
references: 16269333
references: Trends Plant Sci. 2003 Apr;8(4):172-8
references: 12711229
references: Nature. 2003 Jun 26;423(6943):995-9
references: 12827204
references: Genes Dev. 2000 Sep 15;14(18):2377-91
references: 10995393
references: Plant Cell Physiol. 2001 Nov;42(11):1193-200
references: 11726703
references: Plant Physiol. 2000 Sep;124(1):39-45
references: 10982420