IAA17/AXR3: Biochemical Insight into an Auxin Mutant Phenotype

Ouellet, François; Overvoorde, Paul J.; Theologis, Athanasios

doi:10.2307/3871343

Cited by 98 publications

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“…Each mutant gene acts to disrupt various auxin-regulated growth processes. Two of the mutations, axr2-1 and axr3-1, act to stabilize their respective proteins, and it is likely that the others have the same effect (Worley et al, 2000;Ouellet et al, 2001). Our recent results indicate that members of the Aux/ IAA family of proteins interact directly with SCF TIR1 (Gray et al, 2001).…”

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AXR1-ECR1–Dependent Conjugation of RUB1 to the Arabidopsis Cullin AtCUL1 Is Required for Auxin Response

et al. 2002

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Mutations in the AXR1 gene result in a reduction in auxin response and diverse defects in auxin-regulated growth and development. In a previous study, we showed that AXR1 forms a heterodimer with the ECR1 protein. This enzyme activates the ubiquitin-related protein RUB1 in vitro. Furthermore, we showed that the Skp1-Cul1/Cdc53-F-box (SCF) subunit AtCUL1 is modified by RUB1 in vivo. In this report, we demonstrate that the formation of RUB-AtCUL1 is dependent on AXR1 and ECR1 in vivo. The expression of AXR1 and ECR1 is restricted to zones of active cell division and cell elongation, consistent with their role in growth regulation. These results provide strong support for a model in which RUB conjugation of AtCUL1 affects the function of SCF E3s that are required for auxin response. INTRODUCTIONIndole-3-acetic acid (IAA or auxin) is an important regulator of plant growth and development. Auxin is implicated in many growth processes, ranging from embryogenesis to floral development (Davies, 1995). In addition, auxin plays a principal role in the control of cell division and elongation (Evans, 1984;Gray et al., 1998Gray et al., , 1999. Despite the importance of this hormone, the molecular mechanisms of auxin action are poorly defined. In an attempt to elucidate these mechanisms, several groups have taken a genetic approach by screening for Arabidopsis mutants with defects in auxin response (Hobbie et al., 1994). One of the mutants recovered in these screens, called axr1 , has a pleiotropic phenotype related to decreased auxin response. Mutant plants have reduced apical dominance, fewer lateral roots and root hairs, low fertility, and reduced gravitropic response (Lincoln et al., 1990). In addition, members of the Aux/IAA and SAUR families of auxin-regulated genes are not expressed normally in the mutant, suggesting that AXR1 functions in auxin signal transduction (Abel et al., 1995;Timpte et al., 1995).AXR1 encodes a subunit of a heterodimeric RUB-activating enzyme (del Pozo et al., 1998). Biochemical studies suggest that a protein called ECR1 is the second subunit in this enzyme (del Pozo et al., 1998). RUB (or NEDD8 in humans) is a small ubiquitin-related protein that is conjugated to cellular proteins via a pathway similar to the ubiquitin conjugation pathway. At present, the only known targets of RUB modification are members of the cullin family (del Pozo et al., 1998;Lammer et al., 1998;Osaka et al., 1998;del Pozo and Estelle, 1999;Liakopoulos et al., 1999;Wada et al., 1999). Cullins are subunits of an E3-ubiquitin ligase complex called the Skp1-Cul1/Cdc53-F-box (SCF). The other subunits of the complex are SKP1, RBX1, and an F-box protein (Patton et al., 1998;Kamura et al., 1999). The SCF promotes the transfer of ubiquitin from a ubiquitin-conjugating enzyme (E2) to a target protein. The function of RUB modification of cullin is unknown. Unlike ubiquitination, RUB modification of the cullin does not affect its metabolic stability. Instead, genetic and biochemical evidence suggests that RUB modification regulate...

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AXR1-ECR1–Dependent Conjugation of RUB1 to the Arabidopsis Cullin AtCUL1 Is Required for Auxin Response

et al. 2002

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“…IAA12 differs from the other four IAA proteins exam- ined in having an LxLxLxLxL motif in domain I and is discussed separately below. Each IAA protein also contained a Ser substitution for the first Pro in the GWPP motif of domain II to increase its stability compared with wild-type proteins (Worley et al, 2000;Gray et al, 2001;Ouellet et al, 2001;Ramos et al, 2001). The CaMV 35S promoter was used to drive expression of the mutant IAA proteins in stably transformed Arabidopsis ecotype Columbia (Col-0) plants, and transformed lines are referred to as 35S: IAAmImII with the specific IAA protein indicated (e.g.…”

Section: Constitutive Expression Of Closely Related Iaa Repressors Wimentioning

confidence: 99%

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

Tiwari

Hagen

et al. 2011

Plant Physiology

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Auxin/indole-3-acetic acid (Aux/IAA) proteins function as repressors of auxin response gene expression when auxin concentrations in a cell are low. At elevated auxin concentrations, these repressors are destroyed via the ubiquitin-proteasome pathway, resulting in derepression/activation of auxin response genes. Most Aux/IAA repressors contain four conserved domains, with one of these being an active, portable repression domain (domain I) and a second being an auxin-dependent instability domain (domain II). Here, we have analyzed the effects of amino acid substitutions in the repression domain of selected Aux/IAA proteins. We show that stabilized versions of Aux/IAA proteins with amino acid substitutions in domain I display contrasting phenotypes when expressed in transformed Arabidopsis (Arabidopsis thaliana) plants. An alanine-forleucine substitution in the LxLxL (where L is leucine and x is another amino acid) repression domain of IAA3, IAA6, or IAA19 confers enhanced auxin response gene expression and "high-auxin" phenotypes when expressed from the 35S or IAA19 promoter (as tested with IAA19) in transformed Arabidopsis plants. In marked contrast, a single alanine-for-leucine substitution in domain I of IAA12 or IAA17 confers repression of auxin response genes and "low-auxin" phenotypes. These results point to intrinsic differences in the repression domain(s) of IAA proteins and suggest that some IAA proteins have stronger or more complex repression domains than others.

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“…Dominant mutations in domain II of AUX/IAA as defined by iaa3/shy2-2, iaa7/ axr2-1, iaa14/slr1, and iaa17/axr3 alleles confer resistance to ubiquitin-mediated degradation (10,11). AXR1 is a subunit of the heterodimeric Nedd8/RUB1-activating enzyme that mediates the first step in the conjugation of the ubiquitin-like modification Nedd8/RUB1 to the cullin subunit of Skp1/Cullin/Fbox (SCF) 1 -type E3s (12,13), and TIR1 encodes an F-box protein interacting with the Skp1 and Cdc53 (Cullin) proteins to form ubiquitin ligase complexes called SCFs (14,15).…”

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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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IAA17/AXR3: Biochemical Insight into an Auxin Mutant Phenotype

Cited by 98 publications

References 0 publications

AXR1-ECR1–Dependent Conjugation of RUB1 to the Arabidopsis Cullin AtCUL1 Is Required for Auxin Response

AXR1-ECR1–Dependent Conjugation of RUB1 to the Arabidopsis Cullin AtCUL1 Is Required for Auxin Response

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

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

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