AUX/IAA proteins are active repressors, and their stability and activity are modulated by auxin.
Aux/IAA genes are early auxin response genes that encode short-lived nuclear proteins with four conserved domains, referred to as I, II, III, and IV. Arabidopsis Aux/IAA proteins repressed transcription on auxin-responsive reporter genes in protoplast transfection assays. Mutations in domain II resulted in increased repression, whereas mutations in domains I and III partially relieved repression. Aux/IAA proteins fused to a heterologous DNA binding domain were targeted to promoters of constitutively expressed reporter genes and actively repressed transcription in an auxin-responsive and dose-dependent manner. In comparison with an unfused luciferase protein, luciferase fused to Aux/IAA proteins displayed less luciferase activity, which further decreased in the presence of auxin in transfected protoplasts. Domain II mutations increased and domain I mutations decreased luciferase activity with the fusion proteins. These results suggested that Aux/IAA proteins function as active repressors by dimerizing with auxin response factors bound to auxin response elements and that early auxin response genes are regulated by auxin-modulated stabilities of Aux/IAA proteins.
Tiwari
S B
SB
Department of Biochemistry, 117 Schweitzer Hall, University of Missouri, Columbia, Missouri 65211, USA.
Wang
X J
XJ
Hagen
G
G
Guilfoyle
T J
TJ
D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics; D018552:Daucus carota / Q000235:genetics / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D007210:Indoleacetic Acids / Q000378:metabolism / Q000494:pharmacology*; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D008954:Models, Biological; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism; D011523:Protoplasts / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism
D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D008156:Luciferases