Aux/IAA proteins are phosphorylated by phytochrome in vitro.
Auxin/indole-3-acetic acid (Aux/IAA) genes encode short-lived transcription factors that are induced as a primary response to the plant growth hormone IAA or auxin. Gain-of-function mutations in Arabidopsis genes, SHY2/IAA3, AXR3/IAA17, and AXR2/IAA7 cause pleiotropic phenotypes consistent with enhanced auxin responses, possibly by increasing Aux/IAA protein stability. Semidominant mutations shy2-1D, shy2-2, axr3-1, and axr2-1 induce ectopic light responses in dark-grown seedlings. Because genetic studies suggest that the shy2-1D and shy2-2 mutations bypass phytochrome requirement for certain aspects of photomorphogenesis, we tested whether SHY2/IAA3 and related Aux/IAA proteins interact directly with phytochrome and whether they are substrates for its protein kinase activity. Here we show that recombinant Aux/IAA proteins from Arabidopsis and pea (Pisum sativum) interact in vitro with recombinant phytochrome A from oat (Avena sativa). We further show that recombinant SHY2/IAA3, AXR3/IAA17, IAA1, IAA9, and Ps-IAA4 are phosphorylated by recombinant oat phytochrome A in vitro. Deletion analysis of Ps-IAA4 indicates that phytochrome A phosphorylation occurs on the N-terminal half of the protein. Metabolic labeling and immunoprecipitation studies with affinity-purified antibodies to IAA3 demonstrate increased in vivo steady-state levels of mutant IAA3 in shy2-2 plants and phosphorylation of the SHY2-2 protein in vivo. Phytochrome-dependent phosphorylation of Aux/IAA proteins is proposed to provide one molecular mechanism for integrating auxin and light signaling in plant development.
Colón-Carmona
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A
Department of Vegetable Crops, University of California, One Shields Avenue, Davis, California 95616, USA.
Chen
D L
DL
Yeh
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KC
Abel
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D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D018532:Pisum sativum / Q000235:genetics / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D010834:Phytochrome / Q000235:genetics / Q000378:metabolism*; D051942:Phytochrome A; D010937:Plant Growth Regulators; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D011233:Precipitin Tests; D011494:Protein Kinases / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
C503841:ARF1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; C497973:PHYA protein, Arabidopsis; D010750:Phosphoproteins; D051942:Phytochrome A; D010937:Plant Growth Regulators; D010940:Plant Proteins; D011994:Recombinant Proteins; C117994:SHY2 protein, Arabidopsis; D014157:Transcription Factors; D010834:Phytochrome; D011494:Protein Kinases