Independent and interdependent functions of LAF1 and HFR1 in phytochrome A signaling.
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.
Jang
In-Cheol
IC
Laboratory of Plant Molecular Biology, The Rockefeller University, New York, New York 10065, USA.
Yang
Seong Wook
SW
Yang
Jun-Yi
JY
Chua
Nam-Hai
NH
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
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
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