PT  - JOURNAL ARTICLE
AU  - Tiwari, Shiv B.
AU  - Wang, Xiao-Jun
AU  - Hagen, Gretchen
AU  - Guilfoyle, Tom J.
TI  - AUX/IAA Proteins Are Active Repressors, and Their Stability and Activity Are Modulated by Auxin
AID  - 10.1105/tpc.010289
DP  - 2001 Dec 01
TA  - The Plant Cell
PG  - 2809--2822
VI  - 13
IP  - 12
4099  - http://www.plantcell.org/content/13/12/2809.short
4100  - http://www.plantcell.org/content/13/12/2809.full
SO  - Plant Cell2001 Dec 01; 13
AB  - 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.