Auxin Derivatives Research Articles

Photoswitchable Auxin-Inducible Degron System for Conditional Protein Degradation with Spatiotemporal Resolution.

The auxin-inducible degron (AID) system degrades target proteins rapidly in a controllable manner. Although this is a highly versatile technique for studying protein functionality, protein degradation with spatiotemporal resolution is not currently possible. Herein we describe a photoswitchable AID using a light-active auxin derivative for reversible and site-specific protein degradation with temporal resolution.

In situ separation and visualization of isomeric auxin derivatives in Arabidopsis by ion mobility mass spectrometry imaging.

In situ separation and visualization of synthetic and naturally occurring isomers from heterogeneous plant tissues, especially when they share similar molecular structures, are a challenging task. In this study, we combined the ion mobility separation with desorption electrospray ionization mass spectrometry imaging (DESI-IM-MSI) to achieve a direct separation and visualization of two synthetic auxin derivatives, auxinole and its structural isomer 4pTb-MeIAA, as well as endogenous auxins from Arabidopsis samples. Distinct distribution of these synthetic isomers and endogenous auxins in Arabidopsis primary roots and hypocotyls was achieved in the same imaging analysis from both individually treated and cotreated samples. We also observed putative metabolites of synthetic auxin derivatives, i.e. auxinole amino acid conjugates and hydrolysed 4pTb-MeIAA product - 4pTb-IAA, based on their unique drifting ion intensity patterns. Furthermore, DESI-IM-MSI-revealed abundance of endogenous auxins and synthetic isomers was validated by liquid chromatography-mass spectrometry (LC-MS). Our results demonstrate that DESI-IM-MSI could be used as a robust technique for detecting endogenous and exogenous isomers and provide a spatiotemporal evaluation of hormonomics profiles in plants.

New fluorescent auxin derivatives: anti-auxin activity and accumulation patterns in Arabidopsis thaliana

AbstractAuxin belongs among major phytohormones and governs multiple aspects of plant growth and development. The establishment of auxin concentration gradients, determines, among other processes, plant organ positioning and growth responses to environmental stimuli.Herein we report the synthesis of new NBD- or DNS-labelled IAA derivatives and the elucidation of their biological activity, fluorescence properties and subcellular accumulation patterns in planta. These novel compounds did not show auxin-like activity, but instead antagonized physiological auxin effects. The DNS-labelled derivatives FL5 and FL6 showed strong anti-auxin activity in roots and hypocotyls, which also occurred at the level of gene transcription as confirmed by quantitative PCR analysis. The auxin antagonism of our derivatives was further demonstrated in vitro using an SPR-based binding assay. The NBD-labelled compound FL4 with the best fluorescence properties proved to be unsuitable to study auxin accumulation patterns in planta. On the other hand, the strongest anti-auxin activity possessing compounds FL5 and FL6 could be useful to study binding mechanisms to auxin receptors and for manipulations of auxin-regulated processes.

The Natural Alternatives: The Impact of Plant Extracts on Snowbush (Breynia disticha Forst.) Cuttings’ Morpho-Physiological and Biochemical Characteristics

The utilization of cuttings remains a prevalent method for vegetative propagation in various plant species. Synthetic rooting hormones have conventionally been employed to enhance the rooting process; however, their high cost and potential environmental risks have necessitated the exploration of natural alternative compounds. In this study, the efficacy of natural plant extracts (pure honey, aloe extract, willow extract, moringa extract, and cinnamon powder) and synthetic auxin derivatives (indole-3-butyric acid and α-naphthaleneacetic acid) at a concentration of 2000 ppm was compared for their influence on rooting and vegetative growth of snowbush (Breynia disticha) cuttings, a significant ornamental and medicinal shrub. Results demonstrated that while the synthetic hormones produced the highest survival percentages and root number, the roots were consistently short, thick, friable, and largely void of secondary roots. Conversely, the alternative natural plant extracts, particularly aloe extract, exhibited promising outcomes, showcasing good rooting percentage and root number, significantly increased root length, and fresh and dry root weight. Furthermore, aloe extract demonstrated the potential to enhance shoot length and alter the chemical constituents of the cuttings. The highest values of total phenols and nitrogen percentage were recorded with cuttings treated with indole-3-butyric acid, followed by cuttings treated with aloe extract. While using aloe extract, we recorded the highest values of total carbohydrates, phosphorus, and potassium percentages. Notably, the highest endogenous levels of indole acetic acid and gibberellic acid, along with the lowest abscisic acid concentration in cutting tissues, were associated with the highest rooting percentage observed with indole-3-butyric acid, followed by the use of aloe extract. We hypothesized that natural plant extracts, specifically aloe extract, have potential as a viable alternative for synthetic auxins in promoting successful rooting and vegetative growth in snowbush cuttings. Further research is warranted to explore the underlying mechanisms and optimize the application of these natural compounds in vegetative propagation techniques.

Probing into the unique relationship between a soil bacterium, Pseudomonas putida AKMP7 and Arabidopsis thaliana: A case of “conditional pathogenesis”

Plant growth-promoting rhizobacteria (PGPR) are beneficial soil bacteria that colonise the rhizosphere and help plants in growth, development, and stress tolerance. While there is a significant body of research elucidating their benefits to plants, studies on the “abnormal” or “unexpected” behavior of these bacteria are almost non-existent. One such study from our laboratory has previously reported a unique situation in which a certain strain of drought and thermo-tolerant PGPR, namely, Pseudomonas putida AKMP7, becomes pathogenic towards Arabidopsis thaliana under drought conditions, but not under normal (well-watered) conditions. In this study, we have probed deeper into this phenomenon of “conditional pathogenesis”. We found that, AKMP7 imparts an enhancement in plant growth under well-watered conditions, while, causing a deterioration in plant health under drought conditions. In an attempt to understand the underlying reasons for this phenomenon, we analysed the phytohormones released by Pseudomonas putida AKMP7 using LC-ESI-MS/MS technique. We identified that AKMP7 releases zeatin (a cytokinin), the auxin derivative -indole acetamide and amino acid-conjugates of auxin (indole-3-acetyl-L-alanine, indole-3-acetyl-L-phenylalanine and indole-3-acetyl-L-aspartate) in the growth medium. By treating the plants with commercially obtained forms of these phytohormones, individually or in combination with AKMP7, we identified that zeatin and auxin derivative indole acetamide can play a crucial role in the conditional pathogenesis exhibited by this bacterium on A. thaliana under drought conditions. Our work lays a foundation for further understanding the precise molecular mechanisms involved in this unique phenomenon of conditional/opportunistic pathogenesis.

A heterochiral diphenylalanine auxin derivative empowers remarkable mechanical integrity with promising Antiinflammatory and Antimicrobial Performances

A proteolytically stable, biocompatible hydrogel has been developed with a heterochiral diphenylalanine auxin derivative that displayed excellent mechanical integrity & pharmacological properties at room temperature at physiological pH.

Nicotiana benthamiana as a Transient Expression Host to Produce Auxin Analogs.

Plant secondary metabolites have applications for the food, biofuel, and pharmaceutical industries. Recent advances in pathway elucidation and host expression systems now allow metabolic engineering of plant metabolic pathways to produce “new-to-nature” derivatives with novel biological activities, thereby amplifying the range of industrial uses for plant metabolites. Here we use a transient expression system in the model plant Nicotiana benthamiana to reconstitute the two-step plant-derived biosynthetic pathway for auxin (indole acetic acid) to achieve accumulation up to 500 ng/g fresh mass (FM). By expressing these plant-derived enzymes in combination with either bacterial halogenases and alternative substrates, we can produce both natural and new-to-nature halogenated auxin derivatives up to 990 ng/g FM. Proteins from the auxin synthesis pathway, tryptophan aminotransferases (TARs) and flavin-dependent monooxygenases (YUCs), could be transiently expressed in combination with four separate bacterial halogenases to generate halogenated auxin derivatives. Brominated auxin derivatives could also be observed after infiltration of the transfected N. benthamiana with potassium bromide and the halogenases. Finally, the production of additional auxin derivatives could also be achieved by co-infiltration of TAR and YUC genes with various tryptophan analogs. Given the emerging importance of transient expression in N. benthamiana for industrial scale protein and product expression, this work provides insight into the capacity of N. benthamiana to interface bacterial genes and synthetic substrates to produce novel halogenated metabolites.

Screening of Aspergillus, Bacillus and Trichoderma strains and influence of substrates on auxin and phytases production through solid-state fermentation

Abstract Crop inoculation with microorganisms is an agricultural technique that has been used to stimulate plant growth and development by different mechanisms, such as the production of P solubilizing enzymes, the phytases, and indole-3-acetic acid (IAA). The aim of the present study is to produce phytases and IAA via solid-state fermentation (SSF) and to correlate biomolecule yield with the characteristics of SSF substrate, such as porosity, water retention, dry mass, electrical conductivity, pH, crude protein, lipids, hemicellulose, cellulose, and lignin for process optimization. Microorganisms belonging to genera Aspergillus, Trichoderma, and Bacillus were cultivated in soybean and wheat bran, in cassava bagasse and in maize and sorghum distiller dried grains with solubles (DDGS). The strains B. subtilis (D), T. atroviride (IOC 4503), and Aspergillus niger (01) produced IAA from tryptophan as shown by LC-MS/MS. All tested microbial genera produced auxins and phytases. The highest indole derivative levels and phytase activity were observed in combinations such as wheat bran/B. subtilis (D) and maize DDGS/T. atroviride, respectively. There were not strong correlations among substrate property, phytase activity and Aspergillus indole compound levels, but there was strong negative correlation between Trichoderma indole derivative and lignin levels. The auxin content in genus Bacillus had strong negative correlation to lignin and strong positive correlation to pH and hemicellulose; therefore, the production of auxin derivatives by genera Trichoderma and Bacillus was improved by substrates presenting low lignin content. In addition, substrates with neutral pH and higher hemicellulose content were recommended to Bacillus.

Isolation and Structure Identification of Novel Brominated Diketopiperazines from Nocardia ignorata-A Lichen-Associated Actinobacterium.

Actinobacteria are well known for their potential in biotechnology and their production of metabolites of interest. Lichens are a promising source of new bacterial strains, especially Actinobacteria, which afford a broad chemical diversity. In this context, the culture medium of the actinobacterium Nocardia ignorata, isolated from the terrestrial lichen Collema auriforme, was studied. The strain was cultivated in a BioFlo 115 bioreactor, and the culture medium was extracted using an XAD7HP resin. Five known diketopiperazines: cyclo (l-Pro-l-OMet) (1), cyclo (l-Pro-l-Tyr) (2), cyclo (d-Pro-l-Tyr) (3), cyclo (l-Pro-l-Val) (4), cyclo (l-Pro-l-Leu) (5), and one auxin derivative: indole-carboxaldehyde (8) were isolated, along with two new brominated diketopiperazines: cyclo (d-Pro-l-Br-Tyr) (6) and cyclo (l-Pro-l-Br-Tyr) (7). Structure elucidation was performed using HRMS and 1D and 2D NMR analysis, and the synthesis of compounds 6 and 7 was carried out in order to confirm their structure.

The function of ABCB transporters in auxin transport

Plant ATP-binding cassette (ABC) transporters consist of largest family members among many other membrane transporters and have been implicated in various functions such as detoxification, disease resistance and transport of diverse substrates. Of the ABC-B/multi-drug resistance/P-glycoprotein (ABCB/MDR/PGP) subfamily, at least five members have been reported to mediate cellular transport of auxin or auxin derivatives. Although single mutant phenotypes of these genes are milder than PIN-FORMED (PIN) mutants, those ABCBs significantly contribute for the directional auxin movement in the tissue-level auxin-transporting assay. Uniformly localized ABCB proteins in the plasma membrane (PM) are generaly found in different plant species and stably retained regardless of internal and external signals. This implies that these ABCB proteins may play as basal auxin transporters.

Chemical stimulation of the Arabidopsis thaliana root using multi-laminar flow on a microfluidic chip

In this article, we developed a "plant on a chip" microfluidic platform that can control the local chemical environment around live roots of Arabidopsis thaliana with high spatial resolution using multi-laminar flow. We characterized the flow profile around the Arabidopsis root, and verified that the shear forces within the device ( approximately 10 dyne cm(-2)) did not impede growth of the roots. Our platform was able to deliver stimuli to the root at a spatial resolution of 10-800 microm. Further, the platform was validated by exposing desired regions of the root with a synthetic auxin derivative, 2,4-dichlorophenoxyacetic acid (2,4-D), and its inhibitor N-1-naphthylphthalamic acid (NPA). The response to the stimuli was observed using a DR5::GFP Arabidopsis line, where GFP expression is coupled to the auxin response regulator DR5. GFP expression in the root matched the position of the flow-focused stream containing 2,4-D. When the regions around the 2,4-D stimulus were exposed to the auxin transport inhibitor NPA, the active and passive transport mechanisms of auxin could be differentiated, as NPA blocks active cell-to-cell transport of auxin. Finally, we demonstrated that local 2,4-D stimulation in a approximately 10 microm root segment enhanced morphological changes such as epidermal hair growth. These experiments were proof-of-concept and agreed with the results expected based on known root biology, demonstrating that this "root on a chip" platform can be used to test how root development is affected by any chemical component of interest, including nitrogen, phosphate, salts, and other plant hormones.

Synthesis of Plant Auxin Derivatives and Their Effects on Ceratopteris richardii

In this experiment, organic chemistry laboratory students synthesized derivatives of their own design of the plant auxins indole-3-acetic acid (IAA) and 1-naphthalene acetic acid (NAA). Their syntheses varied from making ester to amide derivatives. After optimizing their synthesis, the organic chemistry student groups shared their products with a student group from the biochemistry�cell biology lab. The biochemistry�cell biology students compared the development of Ceratopteris richardii gametophytes on three types of sterile medium: medium without hormones, medium with 10-5 M NAA, and medium with 10-4 M of an auxin derivative synthesized in the organic chemistry lab. The organic syntheses were performed over a four-week period, and observations of C. richardii gametophytes were done for a two week period, after which the gametophyte measurements where analyzed quantitatively using Microsoft Excel. The project terminated in a poster session presented by both the organic chemistry and biochemistry�cell biology classes during which the students discussed their results and compared any structure activity relationships that were evident. Results from this bioassay of auxin derivatives typically fall into four groups: (i) there is an effect on gametophyte growth similar to that of known auxins, (ii) there is no effect on the growth of the gametophyte, (iii) there is a novel effect on gametophyte growth, or (iv) the auxin derivative is lethal to the gametophyte.

Auxins as Signals in Arbuscular Mycorrhiza Formation

Plant hormones such as auxin derivatives are likely signals during the establishment of an arbuscular mycorrhizal (AM) symbiosis. Although reports on auxin levels during AM in different plant species are contradictory, the contribution of auxins to the establishment of an AM symbiosis might be an important factor especially for the development of lateral roots which are the preferred infection sites for the fungi. In addition to evidence that different auxins could be elevated after colonization with AM fungi, there are also overlapping gene expression patterns between auxin-treated and AM-inoculated roots that provide further clues on auxin-triggered colonization events. Using an auxin-inducible promoter-reporter system it was shown that the reporter was strongly induced in AM colonized roots, although co-localization with AM fungi was not observed. Our data are discussed in frame of a model together with other plant hormones which might be involved in the AM colonization processes.

ChemInform Abstract: New Dimethylaminoalkyl Substituted Auxin Derivatives.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Earthworm humic matter produces auxin-like effects on Daucus carota cell growth and nitrate metabolism

While earthworms are known to improve plant growth by improving the structure of the soil, recent work has suggested that earthworms also produced humic substances endowed with hormone-like activity. Suspensions of Daucus carota (carrot) cells were treated with auxin derivatives (2,4-D=2,4-dichlorophenoxyacetic acid, IAA=indole-3-acetic acid and NAA=1-naphthylacetic acid) and a humic substance of low molecular weight (HEf), obtained from the faeces of the earthworms Nicodrilus caliginosus and Allolobophora rosea, which have auxin-like activity. HEf, at a concentration of 200 μg C l −l, caused an increase in carrot cell growth, determined by packed cell volumes, similar to that of 2,4-D, and morphological changes induced by HEf were similar to those induced by IAA. Humic matter and the tested auxin derivatives stimulated carrot cell glutamate dehydrogenase (GDH), glutamine synthetase (GS) and malic dehydrogenase (MDH) to various extents. When carrot cells were treated with HEf or IAA, GDH and MDH isoenzymes separated by isoelectrofocusing showed similar polymorphism. The addition of HEf or auxin derivatives to carrot cells caused an increase in free amino acids belonging to the oxaloacetate and α-ketoglutarate pathways. Our results showed that HEf affects nitrate metabolism, has auxin-like activity, was strongly acidic and had elevated peptide, carbohydrate and aliphatic C contents. Our work has confirmed that the effective materials in the HEf were highly acidic and of low molecular weight. We conclude that, in addition to the already well established modes of action, earthworms are important in humogenesis because their faeces contained humic substances that can influence plant growth via physiological effects.

The effects of auxin derivatives on the root growth of several plants.

The effects of auxin derivatives on the root growth of several plants.

Enhanced suppression of plant growth through production of L-tryptophan-derived compounds by deleterious rhizobacteria

Plant-growth-suppressive activity of deleterious rhizobacteria (DRB) may be due to production of metabolites absorbed through roots. Auxins produced in high concentrations in the rhizosphere by DRB contribute to reduced root growth. Selected DRB able to produce excessive amounts of auxin compounds for suppression of weed seedling growth may be effective for biological control of weeds. The objectives to this study were to assess the ability of DRB originating from weed seedlings to synthesize auxins from L-tryptophan (L-TRP), determine effects of DRB with or without L-TRP on seedling root growth, and characterize auxins produced from L-TRP using high performance liquid chromatography (HPLC). Auxins expressed as indole-3-acetic acid (IAA)-equivalents were produced by 22.8% of the DRB tested based on a colorimetric method. Under laboratory conditions, a DRB isolate classified as Enterobacter taylorae with high auxin-producing potential (72 mg L−1 IAA-equivalents) inhibited root growth of field bindweed (Convolvulus arvensis L.) by 90.5% when combined with 10−5M L-TRP compared with non-treated control. Auxin derivatives produced by E. taylorae from L-TRP in broth culture after 24 h incubation identified by HPLC included IAA (102 μg L−1), indole-3-aldehyde (IALD; 0.4 μg L−1), and indole-3-lactic acid (ILA; 7.6 μg L−1). Results suggest that providing L-TRP with selected auxin-producing DRB to increase phytotoxic activity against emerging weed seedlings may be a practical biological control strategy.

Metabolism of tryptophan in soil

Production of auxins in soil is stimulated by the addition of l-tryptophan ( l-Trp) as a precursor. Metabolism of l-Trp results in the formation of many products including niacin (kynurenine pathway) and serotonin (hydroxylation) in addition to auxins and is regulated by two distinct enzymes, L-TRP-2,3-dioxygenase (TDO) and indole-2,3-dioxygenase (IDO). The roles of IDO and TDO in l-Trp metabolism and indole-3-acetic acid (IAA) formation in soil were studied by the use of bactericides and specific enzyme inhibitors. The addition of a broad spectrum bactericide, chloramphenicol, to soil resulted in a significant decrease of l-Trp catabolism and stimulated hydroxylation of l-Trp. There was no evidence in this work to support the view that l-Trp is transformed through extracellular reactions in soil. Inhibition of TDO by the addition of benzaldehyde and norharman (a potent inhibitor of TDO and IDO) also reduced l-Trp catabolism in soil. Although IAA was detected in all soils treated with bactericides or enzyme inhibitors, production of this secondary metabolite (IAA) was not reduced by blocking the kynurenine pathway or hydroxylation. Auxins were not detected in soils tested with the addition of intermediates of the TDO and IDO pathways (kynurenine and 5-hydroxytryptophan, respectively). Incubation of d-TRP as a possible auxin precursor in California soils resulted in a significant decrease in metabolism compared with l-Trp additions as measured by CO 2 evolution and HPLC analysis. Rhizosphere bacteria isolated from lettuce ( Lactuca sativa) were found to produce more IAA derived from l-Trp after they had been cultured on a medium containing l-alanine, l-asparagine and l-lysine compared with cultures that had been exposed to l-Trp or nutrient agar and then gron on a l-TRP supplemented minimal salts liquid medium. A soil which had extremely low yields of l-TRP-derived IAA increased production of auxin derivatives, including TRP-derived IAA, when incubated for 1 week with the amino acids, l-lysine, l-asparagine and l-alanine. The results suggest that synthesis of IAA in soil may not be the result of direct catabolism of l-Trp but may be linked to the cometabolism of l-Trp by the broad specificity of l-aminotransferases present in soil.

特集 植物細胞膜 原形質膜におけるオーキシン受容体

Auxin is a plant hormone that regulates cell growth and cell differentiation. Auxin moves basipetally from the shoot apex to the basal region along a polar axis of plant. This movement has been believed to be performed through a cell-to-cell transport mediated by specific carriers located in the plasmalemma. Recently, evidence indicating that the plasmalemma of plant cells is one of the targeting sites of auxin has been reported. Exogenously applied antibodies raised against a microsomal auxin-binding protein inhibit cellular responses to auxin, and membrane-impermeable auxin derivatives mimic free auxins in cellular responses. In addition, several enzymic functions found in plasmalemma have been reported to be regulated directly by auxin. These findings indicate that both the auxin receptor and the signaltransduction machinery, in addition to the auxinflux carries, locate in the plasmalemma of plant cells.

On-line solid-phase extraction of soil auxins produced from exogenously-applied tryptophan with ion-suppression reverse-phase HPLC analysis

The isolation and purification of plant hormones such as auxins from biological matrices has long been complicated by the need to use liquid-liquid solvent partitioning to isolate and concentrate the neutral, basic and acidic auxin compounds from matrix interferences. To eliminate this solvent partitioning step, a column switching method was devised for use with on-line solid phase extraction and separation by ion-suppression reverse-phase high performance liquid chromatography (IS-HPLC) with ultra-violet (UV) detection (280 nm). The on-line purification of auxins with isocratic HPLC separation is applicable to neutral, basic and acidic auxins and auxin conjugates in a single 40-minute analysis. The method allows direct injection of aliquots from 5 to 100 μl with the same precision as loop injection. The method also allows for the analysis of tryptophan and its transformed intermediates into secondary auxin products in a single chromatographic run. Bacterial fermentation broths and soil extracts were analyzed by this method to monitor the conversion of exogenously-applied tryptophan into auxin derivatives.