Aux/IAA Proteins Contain a Potent Transcriptional Repression Domain

Abstract

Aux/IAA proteins are short-lived nuclear proteins that repress expression of primary/early auxin response genes in protoplast transfection assays. Repression is thought to result from Aux/IAA proteins dimerizing with auxin response factor (ARF) transcriptional activators that reside on auxin-responsive promoter elements, referred to as AuxREs. Most Aux/IAA proteins contain four conserved domains, designated domains I, II, III, and IV. Domain II and domains III and IV play roles in protein stability and dimerization, respectively. A clear function for domain I had not been established. Results reported here indicate that domain I in Aux/IAA proteins is an active repression domain that is transferable and dominant over activation domains. An LxLxL motif within domain I is important for conferring repression. The dominance of Aux/IAA repression domains over activation domains in ARF transcriptional activators provides a plausible explanation for the repression of auxin response genes via ARF-Aux/IAA dimerization on auxin-responsive promoters

Identical Amino Acid Substitutions in the Repression Domain of Auxin/Indole-3-Acetic Acid Proteins Have Contrasting Effects on Auxin Signaling

“…where L is Leu and x is any of several different amino acids) motif similar to the so-called ethylene response factorassociated amphiphilic repression (EAR) repression domain (Tiwari et al, 2004). Supporting evidence for domain I being a repression domain came from experiments that demonstrated this domain's interaction with the TOPLESS (TPL) corepressor (Szemenyei et al, 2008).…”

“…VP16-IAA17mImII) resulted in constitutive activation of an auxin-responsive reporter gene (Tiwari et al, 2003). Furthermore, the wild-type domain I of IAA17 was shown to be an active, portable repression domain that could alleviate activation by VP16, while a domain I mutant of IAA17 could not (Tiwari et al, 2004).…”

“…To address whether IAA19 might contain a cryptic activation domain that could function if the repression domain becomes defective, effector genes encoding a yeast GALACTOSE4 DNA-binding domain (GD) fused to the VP16 activation domain alone, IAA19mImII-1, or VP16-IAA19mImII-1 were tested using a GAL4 UPSTREAM ACTIVATION SEQUENCE promoter:GUS (GAL4:GUS) reporter gene in transfected Arabidopsis protoplasts. The GAL4 system has been described previously by Tiwari et al (2001Tiwari et al ( , 2003Tiwari et al ( , 2004). Supplemental Figure S4 shows that while transfection of effector constructs encoding GD-VP16 or GD-VP16-IAA19mImII-1 strongly induced expression of the GAL4:GUS reporter gene in an auxin-independent manner, transfection of effector constructs encoding only GD or GD-IAA19mImII-1 failed to induce reporter gene expression.…”

The MYB182 Protein Down-Regulates Proanthocyanidin and Anthocyanin Biosynthesis in Poplar by Repressing Both Structural and Regulatory Flavonoid Genes

“…This suggests that additional mechanisms are important. Nevertheless, the C2 region with the core EAR motif is considered to be the predominant transcriptional repression motif in plants (Ohta et al, 2001;Hiratsu et al, 2003;Tiwari et al, 2004). In tobacco ERF3 (NtERF3), where the EAR motif was first characterized, deletion mutations within the EAR motif eliminated its ability to repress transcription (Ohta et al, 2001).…”

The Arabidopsis transcription factor bZIP11 activates auxin-mediated transcription by recruiting the histone acetylation machinery

“…To control these various responses, coordinated regulation of auxin-induced genes is required, which is primarily mediated by cis-acting auxinresponsive elements (AuxREs) [5][6][7] , which are bound by auxin response factors (ARFs) [8][9][10] . Via protein-protein interaction, ARF-mediated transcription is repressed by AUX/IAA proteins 11,12 . These repressors exert their function by interaction with the Groucho/Tup type corepressor TOPLESS that is thought to recruit histone deacetylases (HDACs) to target promoters 13,14 leading to transcriptionally inactive, tightly packed chromatin 15 .…”