Auxin modulates the degradation rate of Aux/IAA proteins

Zenser, Nathan; Ellsmore, Amanda; Leasure, Colin D.; Callis, Judy

doi:10.1073/pnas.211312798

Cited by 253 publications

(180 citation statements)

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“…Significant advances toward linking Aux/IAA protein degradation and auxin signaling have been made. Auxin treatment increases the instability of the pea IAA6 (PSIAA6):luciferase (LUC) and Arabidopsis IAA1:LUC fusion proteins (Zenser et al, 2001(Zenser et al, , 2003, suggesting that auxin directly modulates the degradation rate of Aux/IAA proteins. Biochemical and genetic studies have shown that IAA7/AXR2 and IAA17/AXR3 proteins are targeted for ubiquitinmediated proteolysis by the SCF TIR1 ubiquitin ligase complex.…”

Section: Introductionmentioning

confidence: 99%

Functional Genomic Analysis of theAUXIN/INDOLE-3-ACETIC ACIDGene Family Members inArabidopsis thaliana [W]

et al. 2005

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Auxin regulates various aspects of plant growth and development. The AUXIN/INDOLE-3-ACETIC ACID (Aux/IAA) genes encode short-lived transcriptional repressors that are targeted by the TRANSPORT INHIBITOR RESPONSE1/AUXIN RECEPTOR F-BOX proteins. The Aux/IAA proteins regulate auxin-mediated gene expression by interacting with members of the AUXIN RESPONSE FACTOR protein family. Aux/IAA function is poorly understood; herein, we report the identification and characterization of insertion mutants in 12 of the 29 Aux/IAA family members. The mutants show no visible developmental defects compared with the wild type. Double or triple mutants of closely related Aux/IAA genes, such as iaa8-1 iaa9-1 or iaa5-1 iaa6-1 iaa19-1, also exhibit wild-type phenotypes. Global gene expression analysis reveals that the molecular phenotypes of auxin-treated and untreated light-grown seedlings are unaffected in the iaa17-6 and iaa5-1 iaa6-1 iaa19-1 mutants. By contrast, similar analysis with the gain-of-function axr3-1/iaa17-1 mutant seedlings reveals dramatic changes in basal and auxin-induced gene expression compared with the wild type. Expression of several type-A ARABIDOPSIS RESPONSE REGULATOR genes and a number of genes involved in cell wall biosynthesis and degradation is repressed in axr3-1/iaa17-1. The data suggest extensive functional redundancy among Aux/IAA gene family members and that enhanced stability of the AXR3/IAA17 protein severely alters the molecular phenotype, resulting in developmental defects.

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Section: Introductionmentioning

confidence: 99%

Functional Genomic Analysis of theAUXIN/INDOLE-3-ACETIC ACIDGene Family Members inArabidopsis thaliana [W]

et al. 2005

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“…These diverse effects are mediated partly by the ability of auxin to regulate the expression of numerous genes by controlling the abundance of transcriptional repressor proteins of the Aux͞IAA family (2)(3)(4)(5).…”

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Auxin-induced SCF ^TIR1 –Aux/IAA interaction involves stable modification of the SCF ^TIR1 complex

Kepinski

Leyser

2004

Proc. Natl. Acad. Sci. U.S.A.

160

104

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The plant hormone auxin can regulate gene expression by destabilizing members of the Aux͞IAA family of transcriptional repressors. Auxin-induced Aux͞IAA degradation requires the proteinubiquitin ligase SCF TIR1 , with auxin acting to enhance the interaction between the Aux͞IAAs and SCF TIR1 . SKP1, Cullin, and an F-box-containing protein (SCF)-mediated degradation is an important component of many eukaryotic signaling pathways. In all known cases to date, the interaction between the targets and their cognate SCFs is regulated by signal-induced modification of the target. The mechanism by which auxin promotes the interaction between SCF TIR1 and Aux͞IAAs is not understood, but current hypotheses propose auxin-induced phosphorylation, hydroxylation, or proline isomerization of the Aux͞IAAs. We found no evidence to support these hypotheses or indeed that auxin induces any stable modification of Aux͞IAAs to increase their affinity for SCF TIR1 . Instead, we present data suggesting that auxin promotes the SCF TIR1 -Aux͞IAA interaction by affecting the SCF component, TIR1, or proteins tightly associated with it.

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“…This SCF TIR complex mediates a proteolytic pathway responsible for the degradation of AUX/IAA repressors and ultimately impinges on gene expression including its own. Auxin increases the degradation rate of AUX/IAA proteins (16) and promotes the interaction between AUX/IAA and TIR proteins (9). However, probably due to gene redundancy and complex feedback control of AUX/IAA expression, loss of function of any specific AUX/IAA gene has little, if any, phenotype.…”

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confidence: 99%

Yokonolide B, a Novel Inhibitor of Auxin Action, Blocks Degradation of AUX/IAA Factors

Hayashi

Jones

Ogino

et al. 2003

Journal of Biological Chemistry

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Yokonolide B (YkB; also known as A82548A), a spiroketal-macrolide, was isolated from Streptomyces diastatochromogenes B59 in a screen for inhibitors of ␤-glucoronidase expression under the control of an auxin-responsive promoter in Arabidopsis. YkB inhibits the expression of auxin-inducible genes as shown using native and synthetic auxin promoters as well as using expression profiling of 8,300 Arabidopsis gene probes but does not affect expression of an abscisic acid-and a gibberellin A 3 -inducible gene. The mechanism of action of YkB is to block AUX/IAA protein degradation; however, YkB is not a general proteasome inhibitor. YkB blocks auxin-dependent cell division and auxin-regulated epinastic growth mediated by auxin-binding protein 1. Gain of function mutants such as shy2-2, slr1, and axr2-1 encoding AUX/IAA transcriptional repressors and loss of function mutants encoding components of the ubiquitin-proteolytic pathway such as axr1-3 and tir1-1, which display increased AUX/IAAs protein stability, are less sensitive to YkB, although axr1 and tir1 mutants were sensitive to MG132, a general proteasome inhibitor, consistent with a site of action downstream of AXR1 and TIR. YkB-treated seedlings displayed similar phenotypes as dominant AUX/IAA mutants. Taken together, these results indicate that YkB acts to block AUX/IAA protein degradation upstream of AXR and TIR, links a shared element upstream of AUX/IAA protein stability to auxin-induced cell division/elongation and to auxin-binding protein 1, and provides a new tool to dissect auxin signal transduction.Auxin controls cell division, elongation, and differentiation and therefore, through its action at the level of the cell, exerts profound effects on growth and development throughout the life of the plant (1). Consistent with the diverse effects of auxin on growth and development is that the expression patterns of a number of genes are dramatically and rapidly altered by auxin application (2), suggesting that auxin ultimately regulates cell growth by controlling the profile of expressed genes. AUX/IAA genes comprise a 34-member gene family in Arabidopsis that is one of three known gene families that are regulated by auxin and implicated to play essential roles in auxin signaling (3, 4).The molecular and genetic studies on auxin signaling have revealed that auxin specifically enhances the transcription of many AUX/IAA genes within minutes without requiring de novo protein synthesis, suggesting that AUX/IAA genes are primary auxin-response genes (5, 6). AUX/IAA genes encode short lived nuclear proteins capable of heterodimerization with auxin-responsive factors (7) and are thought to act by negatively regulating the expression of early auxin-responsive genes including other members of the AUX/IAA family (3).Studies on Arabidopsis mutants with altered responses to auxin such as iaa3/shy2-2, iaa7/axr2-1, iaa17/axr3, iaa14/slr1, tir1, and axr1 revealed that the turnover rate of AUX/IAA proteins is in some way important in various developmental processes including ...

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Auxin modulates the degradation rate of Aux/IAA proteins

Cited by 253 publications

References 33 publications

Functional Genomic Analysis of theAUXIN/INDOLE-3-ACETIC ACIDGene Family Members inArabidopsis thaliana [W]

Functional Genomic Analysis of theAUXIN/INDOLE-3-ACETIC ACIDGene Family Members inArabidopsis thaliana [W]

Auxin-induced SCF ^TIR1 –Aux/IAA interaction involves stable modification of the SCF ^TIR1 complex

Yokonolide B, a Novel Inhibitor of Auxin Action, Blocks Degradation of AUX/IAA Factors

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Auxin modulates the degradation rate of Aux/IAA proteins

Cited by 253 publications

References 33 publications

Functional Genomic Analysis of theAUXIN/INDOLE-3-ACETIC ACIDGene Family Members inArabidopsis thaliana [W]

Functional Genomic Analysis of theAUXIN/INDOLE-3-ACETIC ACIDGene Family Members inArabidopsis thaliana [W]

Auxin-induced SCF TIR1 –Aux/IAA interaction involves stable modification of the SCF TIR1 complex

Yokonolide B, a Novel Inhibitor of Auxin Action, Blocks Degradation of AUX/IAA Factors

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Auxin-induced SCF ^TIR1 –Aux/IAA interaction involves stable modification of the SCF ^TIR1 complex