Auxin concentration gradients are informative for the transduction of many developmental cues, triggering downstream gene expression and other responses. The generation of auxin gradients depends significantly on cell-to-cell auxin transport, which is supported by the activities of auxin efflux and influx carriers. However, at the level of individual plant cell, the co-ordination of auxin efflux and influx largely remains uncharacterized. We addressed this issue by analyzing the contribution of canonical PIN-FORMED (PIN) proteins to the carrier-mediated auxin efflux in Nicotiana tabacum L., cv. Bright Yellow (BY-2) tobacco cells. We show here that a majority of canonical NtPINs are transcribed in cultured cells and in planta. Cloning of NtPIN genes and their inducible overexpression in tobacco cells uncovered high auxin efflux activity of NtPIN11, accompanied by auxin starvation symptoms. Auxin transport parameters after NtPIN11 overexpression were further assessed using radiolabelled auxin accumulation and mathematical modelling. Unexpectedly, these experiments showed notable stimulation of auxin influx, which was accompanied by enhanced transcript levels of genes for a specific auxin influx carrier and by decreased transcript levels of other genes for auxin efflux carriers. A similar transcriptional response was observed upon removal of auxin from the culture medium, which resulted in decreased auxin efflux. Overall, our results revealed an auxin transport-based homeostatic mechanism for the maintenance of endogenous auxin levels. OPEN RESEARCH BADGES: This article has earned an Open Data Badge for making publicly available the digitally-shareable data necessary to reproduce the reported results. The data is available at http://osf.io/ka97b/.
- MeSH
- Biological Transport MeSH
- Cell Line MeSH
- Phylogeny MeSH
- Homeostasis MeSH
- Indoleacetic Acids metabolism MeSH
- Membrane Transport Proteins genetics metabolism MeSH
- Arabidopsis Proteins genetics metabolism MeSH
- Plant Growth Regulators metabolism MeSH
- Plant Proteins genetics metabolism MeSH
- Nicotiana genetics physiology MeSH
- Models, Theoretical MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
To maintain the activity of meristems is an absolute requirement for plant growth and development, and the role of the plant hormones auxin and cytokinin in apical meristem function is well established. Only little attention has been given, however, to the function of the reactive oxygen species (ROS) gradient along meristematic tissues and its interplay with hormonal regulatory networks. The interdependency between auxin-related, cytokinin-related and ROS-related circuits controls primary growth and development while modulating plant morphology in response to detrimental environmental factors. Because ROS interaction with redox-active compounds significantly affects the cellular redox gradient, the latter constitutes an interface for crosstalk between hormone and ROS signalling pathways. This review focuses on the mechanisms underlying ROS-dependent interactions with redox and hormonal components in shoot and root apical meristems which are crucial for meristems maintenance when plants are exposed to environmental hardships. We also emphasize the importance of cell type and the subcellular compartmentalization of ROS and redox networks to obtain a holistic understanding of how apical meristems adapt to stress.
Auxin (indole-3-acetic acid, IAA) plays fundamental roles as a signalling molecule during numerous plant growth and development processes. The formation of local auxin gradients and auxin maxima/minima, which is very important for these processes, is regulated by auxin metabolism (biosynthesis, degradation, and conjugation) as well as transport. When studying auxin metabolism pathways it is crucial to combine data obtained from genetic investigations with the identification and quantification of individual metabolites. Thus, to facilitate efforts to elucidate auxin metabolism and its roles in plants, we have developed a high-throughput method for simultaneously quantifying IAA and its key metabolites in minute samples (<10 mg FW) of Arabidopsis thaliana tissues by in-tip micro solid-phase extraction and fast LC-tandem MS. As a proof of concept, we applied the method to a collection of Arabidopsis mutant lines and identified lines with altered IAA metabolite profiles using multivariate data analysis. Finally, we explored the correlation between IAA metabolite profiles and IAA-related phenotypes. The developed rapid analysis of large numbers of samples (>100 samples d-1) is a valuable tool to screen for novel regulators of auxin metabolism and homeostasis among large collections of genotypes.
- MeSH
- Arabidopsis genetics metabolism MeSH
- Chromatography, Liquid MeSH
- Solid Phase Extraction MeSH
- Indoleacetic Acids metabolism MeSH
- Multivariate Analysis MeSH
- Mutation * MeSH
- Plant Proteins analysis MeSH
- Tandem Mass Spectrometry MeSH
- High-Throughput Nucleotide Sequencing methods MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Arabidopsis PIN2 protein directs transport of the phytohormone auxin from the root tip into the root elongation zone. Variation in hormone transport, which depends on a delicate interplay between PIN2 sorting to and from polar plasma membrane domains, determines root growth. By employing a constitutively degraded version of PIN2, we identify brassinolides as antagonists of PIN2 endocytosis. This response does not require de novo protein synthesis, but involves early events in canonical brassinolide signaling. Brassinolide-controlled adjustments in PIN2 sorting and intracellular distribution governs formation of a lateral PIN2 gradient in gravistimulated roots, coinciding with adjustments in auxin signaling and directional root growth. Strikingly, simulations indicate that PIN2 gradient formation is no prerequisite for root bending but rather dampens asymmetric auxin flow and signaling. Crosstalk between brassinolide signaling and endocytic PIN2 sorting, thus, appears essential for determining the rate of gravity-induced root curvature via attenuation of differential cell elongation.
- MeSH
- Arabidopsis drug effects metabolism MeSH
- Biological Transport drug effects MeSH
- Brassinosteroids metabolism pharmacology MeSH
- Endocytosis drug effects MeSH
- Gravitropism drug effects physiology MeSH
- Plant Roots drug effects metabolism MeSH
- Indoleacetic Acids metabolism MeSH
- Meristem drug effects metabolism MeSH
- Arabidopsis Proteins metabolism MeSH
- Plant Growth Regulators metabolism pharmacology MeSH
- Signal Transduction MeSH
- Steroids, Heterocyclic metabolism pharmacology MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
AtNHX5 and AtNHX6 are endosomal Na+ ,K+ /H+ antiporters that are critical for growth and development in Arabidopsis, but the mechanism behind their action remains unknown. Here, we report that AtNHX5 and AtNHX6, functioning as H+ leak, control auxin homeostasis and auxin-mediated development. We found that nhx5 nhx6 exhibited growth variations of auxin-related defects. We further showed that nhx5 nhx6 was affected in auxin homeostasis. Genetic analysis showed that AtNHX5 and AtNHX6 were required for the function of the endoplasmic reticulum (ER)-localized auxin transporter PIN5. Although AtNHX5 and AtNHX6 were colocalized with PIN5 at ER, they did not interact directly. Instead, the conserved acidic residues in AtNHX5 and AtNHX6, which are essential for exchange activity, were required for PIN5 function. AtNHX5 and AtNHX6 regulated the pH in ER. Overall, AtNHX5 and AtNHX6 may regulate auxin transport across the ER via the pH gradient created by their transport activity. H+ -leak pathway provides a fine-tuning mechanism that controls cellular auxin fluxes.
- MeSH
- Arabidopsis genetics growth & development metabolism MeSH
- Endoplasmic Reticulum metabolism MeSH
- Homeostasis MeSH
- Immunoprecipitation MeSH
- Hydrogen-Ion Concentration MeSH
- Indoleacetic Acids metabolism MeSH
- Membrane Transport Proteins metabolism MeSH
- Sodium-Hydrogen Exchangers metabolism MeSH
- Promoter Regions, Genetic genetics MeSH
- Arabidopsis Proteins metabolism MeSH
- Genes, Plant MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Being sessile organisms, plants have evolved mechanisms allowing them to control their growth and development in response to environmental changes. This occurs by means of complex interacting signalling networks that integrate diverse environmental cues into co-ordinated and highly regulated responses. Auxin is an essential phytohormone that functions as a signalling molecule, driving both growth and developmental processes. It is involved in numerous biological processes ranging from control of cell expansion and cell division to tissue specification, embryogenesis, and organ development. All these processes require the formation of auxin gradients established and maintained through the combined processes of biosynthesis, metabolism, and inter- and intracellular directional transport. Environmental conditions can profoundly affect the plant developmental programme, and the co-ordinated shoot and root growth ought to be fine-tuned to environmental challenges such as temperature, light, and nutrient and water content. The key role of auxin as an integrator of environmental signals has become clear in recent years, and emerging evidence implicates auxin biosynthesis as an essential component of the overall mechanisms of plants tolerance to stress. In this review, we provide an account of auxin's role as an integrator of environmental signals and, in particular, we highlight the effect of these signals on the control of auxin production.
Polar auxin transport plays a pivotal role in plant growth and development. PIN-FORMED (PIN) auxin efflux carriers regulate directional auxin movement by establishing local auxin maxima, minima, and gradients that drive multiple developmental processes and responses to environmental signals. Auxin has been proposed to modulate its own transport by regulating subcellular PIN trafficking via processes such as clathrin-mediated PIN endocytosis and constitutive recycling. Here, we further investigated the mechanisms by which auxin affects PIN trafficking by screening auxin analogs and identified pinstatic acid (PISA) as a positive modulator of polar auxin transport in Arabidopsis (Arabidopsis thaliana). PISA had an auxin-like effect on hypocotyl elongation and adventitious root formation via positive regulation of auxin transport. PISA did not activate SCFTIR1/AFB signaling and yet induced PIN accumulation at the cell surface by inhibiting PIN internalization from the plasma membrane. This work demonstrates PISA to be a promising chemical tool to dissect the regulatory mechanisms behind subcellular PIN trafficking and auxin transport.
- MeSH
- Arabidopsis drug effects metabolism MeSH
- Biological Transport drug effects MeSH
- Cell Membrane drug effects metabolism MeSH
- Endocytosis * drug effects MeSH
- Phenotype MeSH
- Phenylacetates pharmacology MeSH
- Gravitropism drug effects MeSH
- Hypocotyl drug effects growth & development MeSH
- Plant Roots drug effects growth & development MeSH
- Indoleacetic Acids metabolism MeSH
- Arabidopsis Proteins metabolism MeSH
- Signal Transduction MeSH
- Plant Shoots metabolism MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
BACKGROUND: Auxin binding protein 1 (ABP1) is a putative auxin receptor and its function is indispensable for plant growth and development. ABP1 has been shown to be involved in auxin-dependent regulation of cell division and expansion, in plasma-membrane-related processes such as changes in transmembrane potential, and in the regulation of clathrin-dependent endocytosis. However, the ABP1-regulated downstream pathway remains elusive. METHODOLOGY/PRINCIPAL FINDINGS: Using auxin transport assays and quantitative analysis of cellular morphology we show that ABP1 regulates auxin efflux from tobacco BY-2 cells. The overexpression of ABP1can counterbalance increased auxin efflux and auxin starvation phenotypes caused by the overexpression of PIN auxin efflux carrier. Relevant mechanism involves the ABP1-controlled vesicle trafficking processes, including positive regulation of endocytosis of PIN auxin efflux carriers, as indicated by fluorescence recovery after photobleaching (FRAP) and pharmacological manipulations. CONCLUSIONS/SIGNIFICANCE: The findings indicate the involvement of ABP1 in control of rate of auxin transport across plasma membrane emphasizing the role of ABP1 in regulation of PIN activity at the plasma membrane, and highlighting the relevance of ABP1 for the formation of developmentally important, PIN-dependent auxin gradients.
- MeSH
- Alzheimer Disease diagnosis metabolism MeSH
- Fluorodeoxyglucose F18 diagnostic use MeSH
- Cell Physiological Phenomena * MeSH
- Glucose metabolism MeSH
- Cognitive Dysfunction diagnosis metabolism MeSH
- Middle Aged MeSH
- Humans MeSH
- Longitudinal Studies MeSH
- Brain Mapping * MeSH
- Follow-Up Studies MeSH
- Neural Networks, Computer MeSH
- Neuroimaging * MeSH
- Positron-Emission Tomography MeSH
- Aged, 80 and over MeSH
- Aged MeSH
- Case-Control Studies MeSH
- Check Tag
- Middle Aged MeSH
- Humans MeSH
- Male MeSH
- Aged, 80 and over MeSH
- Aged MeSH
- Female MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
The phenylpropanoid 3,4-(methylenedioxy)cinnamic acid (MDCA) is a plant-derived compound first extracted from roots of Asparagus officinalis and further characterized as an allelochemical. Later on, MDCA was identified as an efficient inhibitor of 4-COUMARATE-CoA LIGASE (4CL), a key enzyme of the general phenylpropanoid pathway. By blocking 4CL, MDCA affects the biosynthesis of many important metabolites, which might explain its phytotoxicity. To decipher the molecular basis of the allelochemical activity of MDCA, we evaluated the effect of this compound on Arabidopsis thaliana seedlings. Metabolic profiling revealed that MDCA is converted in planta into piperonylic acid (PA), an inhibitor of CINNAMATE-4-HYDROXYLASE (C4H), the enzyme directly upstream of 4CL. The inhibition of C4H was also reflected in the phenolic profile of MDCA-treated plants. Treatment of in vitro grown plants resulted in an inhibition of primary root growth and a proliferation of lateral and adventitious roots. These observed growth defects were not the consequence of lignin perturbation, but rather the result of disturbing auxin homeostasis. Based on DII-VENUS quantification and direct measurement of cellular auxin transport, we concluded that MDCA disturbs auxin gradients by interfering with auxin efflux. In addition, mass spectrometry was used to show that MDCA triggers auxin biosynthesis, conjugation, and catabolism. A similar shift in auxin homeostasis was found in the c4h mutant ref3-2, indicating that MDCA triggers a cross talk between the phenylpropanoid and auxin biosynthetic pathways independent from the observed auxin efflux inhibition. Altogether, our data provide, to our knowledge, a novel molecular explanation for the phytotoxic properties of MDCA.
- MeSH
- Trans-Cinnamate 4-Monooxygenase antagonists & inhibitors metabolism MeSH
- Arabidopsis drug effects genetics metabolism MeSH
- Benzoates metabolism pharmacology MeSH
- Biosynthetic Pathways drug effects MeSH
- Cinnamates chemistry metabolism pharmacology MeSH
- Phenylpropionates chemistry metabolism pharmacology MeSH
- Plants, Genetically Modified MeSH
- Mass Spectrometry MeSH
- Homeostasis drug effects MeSH
- Coenzyme A Ligases antagonists & inhibitors metabolism MeSH
- Microscopy, Confocal MeSH
- Plant Roots drug effects genetics metabolism MeSH
- Indoleacetic Acids metabolism MeSH
- Lignin biosynthesis MeSH
- Seedlings drug effects genetics growth & development metabolism MeSH
- Dose-Response Relationship, Drug MeSH
- Publication type
- Journal Article MeSH
Plant growth and development are critically influenced by unpredictable abiotic factors. To survive fluctuating changes in their environments, plants have had to develop robust adaptive mechanisms. The dynamic and complementary actions of the auxin and cytokinin pathways regulate a plethora of developmental processes, and their ability to crosstalk makes them ideal candidates for mediating stress-adaptation responses. Other crucial signaling molecules responsible for the tremendous plasticity observed in plant morphology and in response to abiotic stress are reactive oxygen species (ROS). Proper temporal and spatial distribution of ROS and hormone gradients is crucial for plant survival in response to unfavorable environments. In this regard, the convergence of ROS with phytohormone pathways acts as an integrator of external and developmental signals into systemic responses organized to adapt plants to their environments. Auxin and cytokinin signaling pathways have been studied extensively. Nevertheless, we do not yet understand the impact on plant stress tolerance of the sophisticated crosstalk between the two hormones. Here, we review current knowledge on the function of auxin and cytokinin in redirecting growth induced by abiotic stress in order to deduce their potential points of crosstalk.
- MeSH
- Biological Transport MeSH
- Cytokinins metabolism MeSH
- Adaptation, Physiological MeSH
- Stress, Physiological * MeSH
- Plant Physiological Phenomena * MeSH
- Gene Regulatory Networks MeSH
- Indoleacetic Acids metabolism MeSH
- Gene Expression Regulation, Plant MeSH
- Plant Growth Regulators metabolism MeSH
- Plants genetics metabolism MeSH
- Signal Transduction MeSH
- Publication type
- Journal Article MeSH
- Review MeSH
