Auxin-binding Protein Research Articles

Auxin binding proteins ABP1 and ABP4 are involved in the light- and auxin-induced down-regulation of phytochrome gene PHYB in maize (Zea mays L.) mesocotyl

Previous research in maize suggested a possible involvement of auxin-binding proteins (ABPs) in light signaling during maize seedling development. To obtain more information about the interaction of auxin and light signaling, we investigated the gene expression of phytochrome B (PHYB) and phytochrome A (PHYA) in loss-of-function mutants in ABP1 and ABP4 genes in maize (Zea mays L.). We studied how expression of the PHYB and PHYA genes in mesocotyl is regulated by white light (WL), and whether exogenous auxin NAA influences the expression of the phytochrome genes. We found that knockout of ABP1 or ABP4 results in essentially reduced expression of PHYB gene in dark-grown mesocotyl. WL reduced PHYB expression in WT but not in the ABPs knockout seedlings. The data indicate that ABP1 and ABP4 are positively involved in PHYB expression in etiolated mesocotyl. Our results also indicate that in etiolated mesocotyl, ABP1 and ABP4 mediate the inhibitory effect of exogenous auxin on level of PHYB transcript. In contrast, in our experimental conditions, WL does not reduce expression of PHYA. Our results further suggest that ABP1 and ABP4 are not likely involved in the expression of PHYA gene and neither in auxin-induced suppression of PHYA transcript accumulation. Our results support the existence of cross-talk between auxin and light signaling and indicate for the first time that ABP1, ABP4 and PHYB genes could share common signaling pathway(s).

Fine mapping of Rscmv2, a major gene for resistance to sugarcane mosaic virus in maize

Sugarcane mosaic virus (SCMV) is one of the most devastating virus diseases in maize. In our previous study, two dominant complementary genes, Rscmv1 and Rscmv2, were identified in the resistant inbred line Siyi to confer resistance against SCMV. In this study, we report on the fine mapping of Rscmv2 and prediction of candidate genes. We developed a near-isogenic mapping population comprising 9,856 individuals segregating at Rscmv2, but not the Rscmv1 region. Combining the screening of the recombinants in the Rscmv2 region with 16 newly developed molecular markers, we fine-mapped Rscmv2 to an interval of 196.5 kb. Two overlapping bacterial artificial chromosomes covering this region were analyzed to identify putative candidate genes. Two predicted genes, encoding an auxin-binding protein and a Rho GTPase-activating protein, respectively, can be suggested as candidate genes for Rscmv2. The information from fine-mapping Rscmv2 can contribute to map-based cloning of this gene and molecular-assisted breeding in maize resistance breeding programs.

The Interaction and Integration of Auxin Signaling Components

IAA, a naturally occurring auxin, is a simple signaling molecule that regulates many diverse steps of plant development. Auxin essentially coordinates plant development through transcriptional regulation. Auxin binds to TIR1/AFB nuclear receptors, which are F-box subunits of the SCF ubiquitin ligase complex. The auxin signal is then modulated by the quantitative and qualitative responses of the Aux/IAA repressors and the auxin response factor (ARF) transcription factors. The specificity of the auxin-regulated gene expression profile is defined by several factors, such as the expression of these regulatory proteins, their post-transcriptional regulation, their stability and the affinity between these regulatory proteins. Auxin-binding protein 1 (ABP1) is a candidate protein for an auxin receptor that is implicated in non-transcriptional auxin signaling. ABP1 also affects TIR1/AFB-mediated auxin-responsive gene expression, implying that both the ABP1 and TIR1/AFB signaling machineries coordinately control auxin-mediated physiological events. Systematic approaches using the comprehensive mapping of the expression and interaction of signaling modules and computational modeling would be valuable for integrating our knowledge of auxin signals and responses.

Modulation of AUXIN-BINDING PROTEIN 1 gene expression in maize and the teosintes by transposon insertions in its promoter

Auxin plays crucial roles in plant development. Auxin-binding protein 1 (ABP1) is an auxin receptor required to coordinate cell division and expansion during postembryonic shoot development, and differential auxin responses during root growth. While ABP1 is encoded by a single gene in maize, multiple gene copies exist in teosinte, the wild relatives of maize. We have previously shown that some of the differences between these genes are caused by multiple transposon insertions in the promoter. Here we show that the different ABP1 promoter types confer differential gene expression levels on a firefly luciferase reporter gene. We also discovered a negative regulatory sequence upstream of the conserved transcriptional start site. When this sequence is insulated by an Ac-like transposon or deleted in natural ABP1 gene variants, expression levels are enhanced. Promoters combining both a MITE and a solo-LTR showed small but significant increase in expression compared to those containing only one insertion. This increase seems to be additive, suggesting that it may be due to enhancer sequences present within these transposons. Our results point to a potential role of the ABP1-associated transposons in the modulation of ABP1 gene expression.

Distribution and change patterns of free IAA, ABP 1 and PM H +-ATPase during ovary and ovule development of Nicotiana tabacum L.

Auxin plays key roles in flower induction, embryogenesis, seed formation and seedling development, but little is known about whether auxin regulates the development of ovaries and ovules before pollination. In the present report, we measured the content of free indole-3-acetic (IAA) in ovaries of Nicotiana tabacum L., and localized free IAA, auxin binding protein 1 (ABP1) and plasma membrane (PM) H +-ATPase in the ovaries and ovules. The level of free IAA in the developmental ovaries increased gradually from the stages of ovular primordium to the functional megaspore, but slightly decreased when the embryo sacs formed. Immunoenzyme labeling clearly showed that both IAA and ABP1 were distributed in the ovules, the edge of the placenta, vascular tissues and the ovary wall, while PM H +-ATPase was mainly localized in the ovules. By using immunogold labeling, the subcellular distributions of IAA, ABP1 and PM H +-ATPase in the ovules were also shown. The results suggest that IAA, ABP1 and PM H +-ATPase may play roles in the ovary and ovule initiation, formation and differentiation.

옥신 호르몬 결합단백질 ABP57 유전자를 이용한 작물의 형질개선

Auxin is a group of small natural and synthetic molecules having diverse regulatory functions in plant growth and development. In this review, two auxin binding proteins identified by biochemical experiments to measure their auxin binding activities and biochemical functions are described. ABP1, a 22 kDa auxin binding protein, shows strong auxin binding affinity and possibly plays an important role in plant development, although its biochemical function are still unclear. ABP57, a 57 kDa soluble protein from rice shoots, has both of IAA binding activity and the plasma membrane proton pump activation. Although it is yet to be accomplished, the improvement of agronomic traits using auxin binding proteins is worth to be considered, since auxin is known to be related to such a diverse crop traits.

AUXIN BINDING PROTEIN1: the outsider.

AUXIN BINDING PROTEIN1 (ABP1) is one of the first characterized proteins that bind auxin and has been implied as a receptor for a number of auxin responses. Early studies characterized its auxin binding properties and focused on rapid electrophysiological and cell expansion responses, while subsequent work indicated a role in cell cycle and cell division control. Very recently, ABP1 has been ascribed a role in modulating endocytic events at the plasma membrane and RHO OF PLANTS-mediated cytoskeletal rearrangements during asymmetric cell expansion. The exact molecular function of ABP1 is still unresolved, but its main activity apparently lies in influencing events at the plasma membrane. This review aims to connect the novel findings with the more classical literature on ABP1 and to point out the many open questions that still separate us from a comprehensive model of ABP1 action, almost 40 years after the first reports of its existence.

AUXIN-BINDING-PROTEIN1, the second auxin receptor: what is the significance of a two-receptor concept in plant signal transduction?

Since we are living in the 'age of transcription', awareness of aspects other than transcription in auxin signal transduction seems to have faded. One purpose of this review is to recall these other aspects. The focus will also be on the time scales of auxin responses and their potential or known dependence on either AUXIN BINDING PROTEIN 1 (ABP1) or on TRANSPORT-INHIBITOR-RESISTANT1 (TIR1) as a receptor. Furthermore, both direct and indirect evidence for the function of ABP1 as a receptor will be reviewed. Finally, the potential functions of a two-receptor system for auxin and similarities to other two-receptor signalling systems in plants will be discussed. It is suggested that such a functional arrangement is a property of plants which strengthens tissue autonomy and overcomes the lack of nerves or blood circulation which are responsible for rapid signal transport in animals.

Expression and Subcellular Localization of Arabidopsis thaliana Auxin-Binding Protein 1 (ABP1)

Expression of Arabidopsis thalianaABP1 (AUXIN-BINDING PROTEIN 1) was studied using a promoter:GUS approach. Two promoter regions were analyzed. The 1585-bp promoter region upstream of the translation start site (PABP1) showed different activity compared to the promoter region that included, in addition, the first two introns and three exons of the transcribed ABP1 sequence (PABP1i1,2), indicating that cis elements were present downstream of the start codon. PABP1i1,2-driven β-glucuronidase activity was highest in growing leaves, in the root meristem, in vascular tissues, and in hydathodes. ABP1 promoter activities overlapped largely but not completely with that of DR5, which is a marker for the ARF-AuxRE-dependent auxin response. Subcellular ABP1 localization was studied using a constitutively overexpressed EGFP-ABP1 fusion protein. Results confirmed predominant localization to the endoplasmic reticulum as was concluded previously.

Cell-cycle control as a target for calcium, hormonal and developmental signals: the role of phosphorylation in the retinoblastoma-centred pathway

During the life cycle of plants, both embryogenic and post-embryogenic growth are essentially based on cell division and cell expansion that are under the control of inherited developmental programmes modified by hormonal and environmental stimuli. Considering either stimulation or inhibition of plant growth, the key role of plant hormones in the modification of cell division activities or in the initiation of differentiation is well supported by experimental data. At the same time there is only limited insight into the molecular events that provide linkage between the regulation of cell-cycle progression and hormonal and developmental control. Studies indicate that there are several alternative ways by which hormonal signalling networks can influence cell division parameters and establish functional links between regulatory pathways of cell-cycle progression and genes and protein complexes involved in organ development. An overview is given here of key components in plant cell division control as acceptors of hormonal and developmental signals during organ formation and growth. Selected examples are presented to highlight the potential role of Ca(2+)-signalling, the complex actions of auxin and cytokinins, regulation by transcription factors and alteration of retinoblastoma-related proteins by phosphorylation. Auxins and abscisic acid can directly influence expression of cyclin, cyclin-dependent kinase (CDK) genes and activities of CDK complexes. D-type cyclins are primary targets for cytokinins and over-expression of CyclinD3;1 can enhance auxin responses in roots. A set of auxin-activated genes (AXR1-ARGOS-ANT) controls cell number and organ size through modification of CyclinD3;1 gene expression. The SHORT ROOT (SHR) and SCARECROW (SCR) transcriptional factors determine root patterning by activation of the CYCD6;1 gene. Over-expression of the EBP1 gene (plant homologue of the ErbB-3 epidermal growth factor receptor-binding protein) increased biomass by auxin-dependent activation of both D- and B-type cyclins. The direct involvement of auxin-binding protein (ABP1) in the entry into the cell cycle and the regulation of leaf size and morphology is based on the transcriptional control of D-cyclins and retinoblastoma-related protein (RBR) interacting with inhibitory E2FC transcriptional factor. The central role of RBRs in cell-cycle progression is well documented by a variety of experimental approaches. Their function is phosphorylation-dependent and both RBR and phospho-RBR proteins are present in interphase and mitotic phase cells. Immunolocalization studies showed the presence of phospho-RBR protein in spots of interphase nuclei or granules in mitotic prophase cells. The Ca(2+)-dependent phosphorylation events can be accomplished by the calcium-dependent, calmodulin-independent or calmodulin-like domain protein kinases (CDPKs/CPKs) phosphorylating the CDK inhibitor protein (KRP). Dephosphorylation of the phospho-RBR protein by PP2A phosphatase is regulated by a Ca(2+)-binding subunit.

The heterozygous abp1/ABP1 insertional mutant has defects in functions requiring polar auxin transport and in regulation of early auxin‐regulated genes

AUXIN-BINDING PROTEIN 1 (ABP1) is not easily accessible for molecular studies because the homozygous T-DNA insertion mutant is embryo-lethal. We found that the heterozygous abp1/ABP1 insertion mutant has defects in auxin physiology-related responses: higher root slanting angles, longer hypocotyls, agravitropic roots and hypocotyls, aphototropic hypocotyls, and decreased apical dominance. Heterozygous plants flowered earlier than wild-type plants under short-day conditions. The length of the main root, the lateral root density and the hypocotyl length were little altered in the mutant in response to auxin. Compared to wild-type plants, transcription of early auxin-regulated genes (IAA2, IAA11, IAA13, IAA14, IAA19, IAA20, SAUR9, SAUR15, SAUR23, GH3.5 and ABP1) was less strongly up-regulated in the mutant by 0.1, 1 and 10 μm IAA. Surprisingly, ABP1 was itself an early auxin-up-regulated gene. IAA uptake into the mutant seedlings during auxin treatments was indistinguishable from wild-type. Basipetal auxin transport in young roots was slower in the mutant, indicating a PIN2/EIR1 defect, while acropetal transport was indistinguishable from wild-type. In the eir1 background, three of the early auxin-regulated genes tested (IAA2, IAA13 and ABP1) were more strongly induced by 1 μm IAA in comparison to wild-type, but eight of them were less up-regulated in comparison to wild-type. Similar but not identical disturbances in regulation of early auxin-regulated genes indicate tight functional linkage of ABP1 and auxin transport regulation. We hypothesize that ABP1 is involved in the regulation of polar auxin transport, and thus affects local auxin concentration and early auxin gene regulation. In turn, ABP1 itself is under the transcriptional control of auxin.

12. Design and synthesis of specific ligand to auxin binding protein 1 and its biological activity

12. Design and synthesis of specific ligand to auxin binding protein 1 and its biological activity

An analysis of sequence variability in eight genes putatively involved in drought response in sunflower (Helianthus annuus L.)

With the aim to study variability in genes involved in ecological adaptations, we have analysed sequence polymorphisms of eight unique genes putatively involved in drought response by isolation and analysis of allelic sequences in eight inbred lines of sunflower of different origin and phenotypic characters and showing different drought response in terms of leaf relative water content (RWC). First, gene sequences were amplified by PCR on genomic DNA from a highly inbred line and their products were directly sequenced. In the absence of single nucleotide polymorphisms, the gene was considered as unique. Then, the same PCR reaction was performed on genomic DNAs of eight inbred lines to isolate allelic variants to be compared. The eight selected genes encode a dehydrin, a heat shock protein, a non-specific lipid transfer protein, a z-carotene desaturase, a drought-responsive-element-binding protein, a NAC-domain transcription regulator, an auxin-binding protein, and an ABA responsive-C5 protein. Nucleotide diversity per synonymous and non-synonymous sites was calculated for each gene sequence. The π (a)/π (s) ratio range was usually very low, indicating strong purifying selection, though with locus-to-locus differences. As far as non-coding regions, the intron showed a larger variability than the other regions only in the case of the dehydrin gene. In the other genes tested, in which one or more introns occur, variability in the introns was similar or even lower than in the other regions. On the contrary, 3'-UTRs were usually more variable than the coding regions. Linkage disequilibrium in the selected genes decayed on average within 1,000bp, with large variation among genes. A pairwise comparison between genetic distances calculated on the eight genes and the difference in RWC showed a significant correlation in the first phases of drought stress. The results are discussed in relation to the function of analysed genes, i.e. involved in gene regulation and signal transduction, or encoding enzymes and defence proteins.

The Arabidopsis Cell Cycle F-Box Protein SKP2A Binds to Auxin

Arabidopsis thaliana S-Phase Kinase-Associated Protein 2A (SKP2A) is an F-box protein that regulates the proteolysis of cell cycle transcription factors. The plant hormone auxin regulates multiple aspects of plant growth and development, including cell division. We found that auxin induces the ubiquitin-dependent degradation of SKP2A both in vivo and in vitro, suggesting that this hormone acts as a signal to trigger SKP2A proteolysis. In this article, we show that auxin binds directly and specifically to SKP2A. By TIR1-based superposition and docking analyzes, we identified an auxin binding site in SKP2A. Mutations in this binding site reduce the ability of SKP2A to bind to auxin and generate nondegradable SKP2A forms. In addition, these non-auxin binding proteins are unable to promote E2FC/DPB degradation in vivo or to induce cell division in the root meristem. Auxin binds to TIR1 to promote its interaction with the auxin/indole-3-acetic acid target proteins. Here, we show that auxin also enhanced the interaction between SKP2A and DPB. Finally, a mutation in SKP2A leads to auxin-resistant root growth, an effect that is additive with the tir1-1 phenotype. Thus, our data indicate that SKP2A is an auxin binding protein that connects auxin signaling with cell division.

Cloning and sequence analysis of auxin-binding proteins gene cDNA of <I>Nicotiana tabacum</I> WS38

Nicotiana tabacum WS38 ABP1 cDNA coding sequence was cloned by RT-PCR with the primers that were designed according to reported Nicotiana tabacum ABP1 amino acid sequence in GenBank. The sequence analysis showed that the length of the cDNA was 564 bp. Information analysis indicated that the open reading frame can encode 188 amino acids polypeptide with the 98.4% homology with the reported ABP1. It also demonstrated that the ABP1 in Nicotiana tabacum varied in different cultivars and there was some single nucleic acid polymorphasim with WS38 and NK326.

Shaping Up with Auxin

AUXIN BINDING PROTEIN 1 mediates rapid auxin responses in roots and leaves.

Endoplasmic Reticulum: The Rising Compartment in Auxin Biology

Plants have evolved outstanding capacities to adapt their development and physiology to changes in the environment. The availability, distribution, and activity of endogenous signals, plant hormones, underlie and coordinate these responses (Santner and Estelle, 2009). Auxin, one such signaling molecule, affects a multitude of developmental processes (Woodward and Bartel, 2005; Leyser, 2006; Vanneste and Friml, 2009). The differential distribution of auxin within tissues is essential for many adaptive responses, including embryo and leaf patterning, root and stem elongation, lateral root initiation, leaf expansion, tropisms, regenerative growth, and vascular tissue formation (Vanneste and Friml, 2009). The best characterized auxin signaling pathway operates in the nucleus (Mockaitis and Estelle, 2008). In this pathway, auxin is perceived by and promotes the interaction of TIR1/AFB and Aux/IAA coreceptor proteins (Dharmasiri et al., 2005; Kepinski and Leyser, 2005; Tan et al., 2007), and downstream signaling is mediated by ubiquitination and proteosome-mediated degradation of Aux/IAA transcriptional repressors (Gray et al., 2001; dos Santos Maraschin et al., 2009), which themselves regulate the activity of ARF transcription factors (Tiwari et al., 2004; Guilfoyle and Hagen, 2007). Ultimately, this mechanism leads to complex transcriptional reprogramming in response to auxin. The large number of different Aux/IAA and ARF proteins means that different combinations can be expressed in different cell types, allowing the pathway to produce a multitude of different developmental and physiological responses to auxin (Mockaitis and Estelle, 2008; Vanneste and Friml, 2009). In addition to this nuclear signaling pathway, the observation of rapid cellular responses to auxin suggests the existence of another, presumably nontranscriptional, signaling pathway that might be related to the action of auxin-binding protein1 (ABP1). ABP1 was identified on the basis of its ability to bind to natural and synthetic auxins with high affinity, and has been found in various monocot and dicot species (Napier et al., 2002). However, despite decades of studies, its mode of action remains unclear (Badescu and Napier, 2006; Schenck et al., 2010). The majority of ABP1 is detected in the endoplasmic reticulum (ER), but its physiological effects, mainly relating to cell expansion and division, have been attributed to the smaller apoplastic pool of the protein (Napier et al., 2002; Perrot-Rechenmann, 2010). In theory, auxin could be perceived at several different subcellular destinations, including the nucleus, ER, and extracellular compartment. The final output of auxin signaling is therefore likely to be influenced not only by the overall cellular auxin content, but also by the relative distribution of auxin among different subcellular compartments. Thus subcellular auxin distribution may represent an important regulatory level in the complex action of auxin.

ABP1 Mediates Auxin Inhibition of Clathrin-Dependent Endocytosis in Arabidopsis

Spatial distribution of the plant hormone auxin regulates multiple aspects of plant development. These self-regulating auxin gradients are established by the action of PIN auxin transporters, whose activity is regulated by their constitutive cycling between the plasma membrane and endosomes. Here, we show that auxin signaling by the auxin receptor AUXIN-BINDING PROTEIN 1 (ABP1) inhibits the clathrin-mediated internalization of PIN proteins. ABP1 acts as a positive factor in clathrin recruitment to the plasma membrane, thereby promoting endocytosis. Auxin binding to ABP1 interferes with this action and leads to the inhibition of clathrin-mediated endocytosis. Our study demonstrates that ABP1 mediates a nontranscriptional auxin signaling that regulates the evolutionarily conserved process of clathrin-mediated endocytosis and suggests that this signaling may be essential for the developmentally important feedback of auxin on its own transport.

Cell Surface- and Rho GTPase-Based Auxin Signaling Controls Cellular Interdigitation in Arabidopsis

Auxin is a multifunctional hormone essential for plant development and pattern formation. A nuclear auxin-signaling system controlling auxin-induced gene expression is well established, but cytoplasmic auxin signaling, as in its coordination of cell polarization, is unexplored. We found a cytoplasmic auxin-signaling mechanism that modulates the interdigitated growth of Arabidopsis leaf epidermal pavement cells (PCs), which develop interdigitated lobes and indentations to form a puzzle-piece shape in a two-dimensional plane. PC interdigitation is compromised in leaves deficient in either auxin biosynthesis or its export mediated by PINFORMED 1 localized at the lobe tip. Auxin coordinately activates two Rho GTPases, ROP2 and ROP6, which promote the formation of complementary lobes and indentations, respectively. Activation of these ROPs by auxin occurs within 30 s and depends on AUXIN-BINDING PROTEIN 1. These findings reveal Rho GTPase-based auxin-signaling mechanisms, which modulate the spatial coordination of cell expansion across a field of cells.

Auxin Paves the Way for Planar Morphogenesis

The coordinated growth of epidermal cells in plant leaves creates the characteristic jigsaw puzzle appearance of the pavement cells. Now, Xu et al. (2010) report that AUXIN-BINDING PROTEIN 1 mediates auxin activation of two GTPase pathways that antagonistically control planar morphogenesis of leaf epidermal cells to create this distinctive pattern.