1 Genetic analysis of auxin signaling : A long road to a short pathway (original) (raw)
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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
A molecular basis for auxin action
Seminars in Cell & Developmental Biology, 1999
The plant hormone auxin is central in the regulation of growth and development, however, the molecular basis for its action has remained enigmatic. In the absence of a molecular model, the wide range of responses elicited by auxin have been difficult to explain. Recent advances using molecular genetic approaches in Arabidopsis have led to the isolation of a number of key genes involved in auxin action. Of particular importance are genes involved in channelling polar auxin transport through the plant. In addition a model for auxin signal transduction, centred on regulated protein degradation, has been developed.
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.
Distinct functions of TIR1 and AFB1 receptors in auxin signalling
Auxin is the major plant hormone regulating growth and development (Friml, 2022). Forward genetic approaches in the model plantArabidopsis thalianahave identified major components of auxin signalling and established the canonical mechanism mediating transcriptional and thus developmental reprogramming. In this textbook view, TRANSPORT INHIBITOR RESPONSE 1 (TIR1)/AUXIN-SIGNALING F-BOX (AFBs) are auxin receptors, which act as F-box subunits determining the substrate specificity of the Skp1-Cullin1-F box protein (SCF) type E3 ubiquitin ligase complex. Auxin acts as a “molecular glue” increasing the affinity between TIR1/AFBs and the Aux/IAA repressors. Subsequently, Aux/IAAs are ubiquitinated and degraded, thus releasing auxin transcription factors from their repression making them free to mediate transcription of auxin response genes (Yuet al., 2022). Nonetheless, accumulating evidence suggests existence of rapid, non-transcriptional responses downstream of TIR1/AFBs such as auxin-ind...
Points of regulation for auxin action
Plant Cell Reports, 2003
There have been few examples of the application of our growing knowledge of hormone action to crop improvement. In this review we discuss what is known about the critical points regulating auxin action. We examine auxin metabolism, transport, perception and signalling and identify genes and proteins that might be keys to regulation, particularly the rate-limiting steps in various pathways. Certain mutants show that substrate flow in biosynthesis can be limiting. To date there is little information available on the genes and proteins of catabolism. There have been several auxin transport proteins and some elegant transport physiology described recently, and the potential for using transport proteins to manage free indole-3-acetic acid (IAA) concentrations is discussed. Free IAA is very mobile, and so while it may be more practical to control auxin action through managing the receptor and signalling pathways, the candidate genes and proteins through which this can be done remain largely unknown. From the available evidence, it is clear that the reason for so few commercial applications arising from the control of auxin action is that knowledge is still limited.
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.
Auxin perception and downstream events
Current Opinion in Plant Biology, 2016
Auxin responses have been arbitrarily divided into two categories: genomic and non-genomic effects. Genomic effects are largely mediated by SCF TIR1/AFB-Aux/IAA auxin receptor complexes whereas it has been postulated that AUXIN BINDING PROTEIN 1 (ABP1) controls the nongenomic effects. However, the roles of ABP1 in auxin signaling and plant development were recently called into question. In this paper, we present recent progress in understanding the SCF TIR1/AFB-Aux/IAA pathway. In more detail, we discuss the current understanding of ABP1 research and provide an updated view of ABP1-related genetic materials. Further, we propose a model in which auxin efflux carriers may play a role in auxin perception and we briefly describe recent insight on processes downstream of auxin perception.
The AXR1 and AUX1 genes of Arabidopsis function in separate auxin-response pathways
The Plant Journal, 1995
The recessive mutations auxl and axrl of Arabidopsis confer resistance to the plant hormone auxin. The axrl mutants display a variety of morphological defects. In contrast, the only morphological defect observed in auxl mutants is a loss of root gravitropism. To learn more about the function of these genes in auxin response, the expression of the auxin-regulated gene SAUR-ACI in mutant and wild-type plants has been examined. It has been found that axrl plants display a pronounced deficiency in auxin-induced accumulation of SAUR-AC1 mRNA in seedlings as well as rosette leaves and mature roots. In contrast, the auxl mutation has a modest effect on auxin induction of SAUR-AC1. To determine if the AUXI and AXR1 genes interact to facilitate auxin response, plants which are homozygous for both auxl and axrl mutations have been constructed and characterized. The two mutations are addItive in their effects on auxin response, suggesting that each mutation confers resistance by a different mechanism. However, the morphology of double mutant plants indicates that there is an interaction between the AXR1 and AUX1 genes. In mature plants, the auxl-7 mutation acts to partially suppress the morphological defects conferred by the axr1-12 mutation. This suppression is not accompanied by an increase in auxin response, as measured by SAUR-AC1 expression, suggesting that the interaction between the AUX1 and AXRI genes is indirect.
G3 (Bethesda, Md.), 2016
The plant hormone auxin is perceived by a family of F-box proteins called the TIR1/AFBs. Phylogenetic studies reveal that these proteins fall into four clades in flowering plants called TIR1, AFB2, AFB4, and AFB6 (Parry et al. 2009). Genetic studies indicate that members of the TIR1 and AFB2 groups act as positive regulators of auxin signaling by promoting the degradation of the Aux/IAA transcriptional repressors (Dharmasiri et al. 2005; Parry et al. 2009). In this report, we demonstrate that both AFB4 and AFB5 also function as auxin receptors based on in vitro assays. We also provide genetic evidence that AFB4 and AFB5 are targets of the picloram family of auxinic herbicides in addition to indole-3-acetic acid. In contrast to previous studies we find that null afb4 alleles do not exhibit obvious defects in seedling morphology or auxin hypersensitivity. We conclude that AFB4 and AFB5 act in a similar fashion to other members of the family but exhibit a distinct auxin specificity.