Distinct functions of TIR1 and AFB1 receptors in auxin signalling (original) (raw)
Related papers
The F-box protein TIR1 is an auxin receptor
Nature, 2005
The plant hormone auxin regulates diverse aspects of plant growth and development. Recent studies indicate that auxin acts by promoting the degradation of the Aux/IAA transcriptional repressors through the action of the ubiquitin protein ligase SCF TIR1 . The nature of the signalling cascade that leads to this effect is not known. However, recent studies indicate that the auxin receptor and other signalling components involved in this response are soluble factors. Using an in vitro pull-down assay, we demonstrate that the interaction between transport inhibitor response 1 (TIR1) and Aux/IAA proteins does not require stable modification of either protein. Instead auxin promotes the Aux/IAA-SCF TIR1 interaction by binding directly to SCF TIR1 . We further show that the loss of TIR1 and three related F-box proteins eliminates saturable auxin binding in plant extracts. Finally, TIR1 synthesized in insect cells binds Aux/IAA proteins in an auxindependent manner. Together, these results indicate that TIR1 is an auxin receptor that mediates Aux/IAA degradation and auxin-regulated transcription.
Plant Development Is Regulated by a Family of Auxin Receptor F Box Proteins
Developmental Cell, 2005
The Aux/IAA proteins (29 members in Arabidopsis) Indiana University are small nuclear proteins that possess four conserved Bloomington, Indiana 47405 domains (I through IV). Domains III and IV are similar in 2 ZMBP sequence to the ARF dimerization domain. In yeast Entwicklungsgenetik two-hybrid tests and in vitro, this sequence promotes Universitat Tubingen the formation of diverse homo-and heterodimers D-72076 Tubingen among the Aux/IAAs and between Aux/IAAs and ARFs. Federal Republic of Germany Domain I is a transferable repressor domain that is dominant over the activation function of an ARF protein (Tiwari et al., 2004). Domain II contains a degron in-Summary volved in auxin-dependent degradation of these proteins (Gray et al., 2001; Ramos et al., 2001; Zenser et The plant hormone auxin has been implicated in virtual., 2001). Mutations within domain II act to stabilize ally every aspect of plant growth and development. the affected protein and result in a decrease in auxin Auxin acts by promoting the degradation of transcripresponse as well as diverse defects in growth and detional regulators called Aux/IAA proteins. Aux/IAA velopment (Gray et al., 2001; Liscum and Reed, 2002; degradation requires TIR1, an F box protein that has Ouellet et al., 2001; Ramos et al., 2001; Tiwari et al., been shown to function as an auxin receptor. How-2001). The most severe mutant, bdl/iaa12, has defects ever, loss of TIR1 has a modest effect on auxin rein embryogenesis that result in seedling lethality (Hasponse and plant development. Here we show that mann et al., 1999; Hamann et al., 2002). three additional F box proteins, called AFB1, 2, and 3, The biological functions of the ARFs and Aux/IAAs also regulate auxin response. Like TIR1, these proare complex. However, a number of lines of evidence teins interact with the Aux/IAA proteins in an auxinindicate that the Aux/IAAs function as transcriptional dependent manner. Plants that are deficient in all four repressors by binding to activating ARFs (Kim et al., proteins are auxin insensitive and exhibit a severe 1997; Ulmasov et al., 1997; Ulmasov et al., 1999a; Ulembryonic phenotype similar to the mp/arf5 and bdl/ masov et al., 1999b). Although an interaction between iaa12 mutants. Correspondingly, all TIR1/AFB proa particular pair of Aux/IAA and ARF proteins has not teins interact with BDL, and BDL is stabilized in triple been directly demonstrated in vivo, genetic studies mutant plants. Our results indicate that TIR1 and the suggest that MSG2/IAA19 and NPH4/ARF7 interact AFB proteins collectively mediate auxin responses during hypocotyl growth and lateral root development throughout plant development. while BDL/IAA12 represses MP/ARF5 function during embryogenesis (Hamann et al., 2002; Tatematsu et al., 2004). Introduction Auxin stimulates degradation of the Aux/IAA proteins, suggesting that auxin acts, at least in part, by The plant hormone indole-3-acetic acid (IAA or auxin) promoting the removal of these transcriptional represhas been implicated in diverse aspects of plant growth sors from the cell (Dharmasiri and Estelle, 2004; Leyser, and development (Davies, 1995). Recent studies of 2002; Ouellet et al., 2001; Tiwari et al., 2001; Zenser et auxin signaling have focused on transcriptional regulaal., 2001). The F box protein TIR1 has been shown to tion by members of the ARF and Aux/IAA protein famidirectly interact with the Aux/IAA proteins and promote lies (Leyser, 2002). The ARF proteins (23 members in their degradation (Dharmasiri et al., 2003; Gray et al., Arabidopsis) each contain conserved DNA binding and 2001
Selective auxin agonists induce specific AUX/IAA protein degradation to modulate plant development
Proceedings of the National Academy of Sciences, 2019
Auxin phytohormones control most aspects of plant development through a complex and interconnected signaling network. In the presence of auxin, AUXIN/INDOLE-3-ACETIC ACID (AUX/IAA) transcriptional repressors are targeted for degradation by the SKP1-CULLIN1-F-BOX (SCF) ubiquitin-protein ligases containing TRANSPORT INHIBITOR RESISTANT 1/AUXIN SIGNALING F-BOX (TIR1/AFB). CULLIN1-neddylation is required for SCF TIR1/AFB functionality, as exemplified by mutants deficient in the NEDD8-activating enzyme subunit AUXIN-RESISTANT 1 (AXR1). Here, we report a chemical biology screen that identifies small molecules requiring AXR1 to modulate plant development. We selected four molecules of interest, RubNeddin 1 to 4 (RN1 to -4), among which RN3 and RN4 trigger selective auxin responses at transcriptional, biochemical, and morphological levels. This selective activity is explained by their ability to consistently promote the interaction between TIR1 and a specific subset of AUX/IAA proteins, sti...
Mechanism of auxin perception by the TIR1 ubiquitin ligase
Nature, 2007
Auxin is a pivotal plant hormone that controls many aspects of plant growth and development. Perceived by a small family of F-box proteins including transport inhibitor response 1 (TIR1), auxin regulates gene expression by promoting SCF ubiquitin-ligase-catalysed degradation of the Aux/IAA transcription repressors, but how the TIR1 F-box protein senses and becomes activated by auxin remains unclear. Here we present the crystal structures of the Arabidopsis TIR1-ASK1 complex, free and in complexes with three different auxin compounds and an Aux/IAA substrate peptide. These structures show that the leucine-rich repeat domain of TIR1 contains an unexpected inositol hexakisphosphate co-factor and recognizes auxin and the Aux/IAA polypeptide substrate through a single surface pocket. Anchored to the base of the TIR1 pocket, auxin binds to a partially promiscuous site, which can also accommodate various auxin analogues. Docked on top of auxin, the Aux/IAA substrate peptide occupies the rest of the TIR1 pocket and completely encloses the hormone-binding site. By filling in a hydrophobic cavity at the protein interface, auxin enhances the TIR1-substrate interactions by acting as a 'molecular glue'. Our results establish the first structural model of a plant hormone receptor.
Auxin receptors: a new role for F-box proteins
Current Opinion in Cell Biology, 2006
The plant hormone auxin regulates transcription by promoting the degradation of a family of transcriptional repressors called Aux/IAA proteins. Genetic and biochemical studies have shown that this degradation is dependent on a ubiquitin protein ligase called SCF TIR1 . In the presence of auxin, the F-box protein TIR1 binds to the Aux/IAA proteins, resulting in their ubiquitination and degradation. Recent attention has focused on the nature of the auxin receptor and upstream signaling events involved in this process. Now, two recent papers demonstrate that auxin binds directly to TIR1 and promotes the interaction with the Aux/IAA proteins. Furthermore, TIR1 functions together with at least three other related F-box protein/receptors to mediate the auxin response throughout plant growth and development.
Auxin-Binding Protein 1 is a negative regulator of the SCFTIR1/AFB pathway
Nature Communications, 2013
Auxin is a major plant hormone that controls most aspects of plant growth and development. Auxin is perceived by two distinct classes of receptors: transport inhibitor response 1 (TIR1, or auxin-related F-box (AFB)) and auxin/indole-3-acetic acid (AUX/IAA) coreceptors, that control transcriptional responses to auxin, and the auxin-binding protein 1 (ABP1), that controls a wide variety of growth and developmental processes. To date, the mode of action of ABP1 is still poorly understood and its functional interaction with TIR1/AFB-AUX/IAA coreceptors remains elusive. Here we combine genetic and biochemical approaches to gain insight into the integration of these two pathways. We find that ABP1 is genetically upstream of TIR1/AFBs; ABP1 knockdown leads to an enhanced degradation of AUX/IAA repressors, independently of its effects on endocytosis, through the SCF TIR1/AFB E3 ubiquitin ligase pathway. Combining positive and negative regulation of SCF ubiquitin-dependent pathways might be a common mechanism conferring tight control of hormone-mediated responses.
Short title: Intruding selectively within plant auxin perception
Auxin phytohormones control most aspects of plant development through a complex and interconnected signaling network. In the presence of auxin, AUXIN/INDOLE-3ACETIC ACID (AUX/IAA) transcriptional repressors are targeted for degradation by the SKP1-CULLIN1-F-BOX (SCF) ubiquitin-protein ligases containing TRANSPORT INHIBITOR RESISTANT 1/AUXIN SIGNALING F-BOX (TIR1/AFB). CULLIN1-neddylation is required for SCF TIR1/AFB functionality as exemplified by mutants deficient in the NEDD8-activating enzyme subunit AUXINRESISTANT 1 (AXR1). Here, we report a chemical biology screen that identifies small molecules requiring AXR1 to modulate plant development. We selected four molecules of interest, RubNeddin1 to 4 (RN1 to 4), among which RN3 and RN4 trigger selective auxin responses at transcriptional, biochemical and morphological levels. This selective activity is explained by their ability to consistently promote the interaction between TIR1 and a specific subset of AUX/IAA proteins, stimulati...
Genes & Development, 1999
The plant hormone auxin regulates diverse aspects of plant growth and development. We report that in Arabidopsis, auxin response is dependent on a ubiquitin-ligase (E3) complex called SCF TIR1 . The complex consists of proteins related to yeast Skp1p and Cdc53p called ASK and AtCUL1, respectively, as well as the F-box protein TIR1. Mutations in either ASK1 or TIR1 result in decreased auxin response. Further, overexpression of TIR1 promotes auxin response suggesting that SCF TIR1 is limiting for the response. These results provide new support for a model in which auxin action depends on the regulated proteolysis of repressor proteins.
Complex regulation of the TIR1/AFB family of auxin receptors
Proceedings of the National Academy of Sciences, 2009
Auxin regulates most aspects of plant growth and development. The hormone is perceived by the TIR1/AFB family of F-box proteins acting in concert with the Aux/IAA transcriptional repressors. Arabidopsis plants that lack members of the TIR1/AFB family are auxin resistant and display a variety of growth defects. However, little is known about the functional differences between individual members of the family. Phylogenetic studies reveal that the TIR1/AFB proteins are conserved across land plant lineages and fall into four clades. Three of these subgroups emerged prior to separation of angiosperms and gynosperms while the last emerged before the monocot-eudicot split.