Indole-3-pyruvic Acid Research Articles

Yucasin is a potent inhibitor of YUCCA, a key enzyme in auxin biosynthesis

Indole-3-acetic acid (IAA), an auxin plant hormone, is biosynthesized from tryptophan. The indole-3-pyruvic acid (IPyA) pathway, involving the tryptophan aminotransferase TAA1 and YUCCA (YUC) enzymes, was recently found to be a major IAA biosynthetic pathway in Arabidopsis. TAA1 catalyzes the conversion of tryptophan to IPyA, and YUC produces IAA from IPyA. Using a chemical biology approach with maize coleoptiles, we identified 5-(4-chlorophenyl)-4H-1,2,4-triazole-3-thiol (yucasin) as a potent inhibitor of IAA biosynthesis in YUC-expressing coleoptile tips. Enzymatic analysis of recombinant AtYUC1-His suggested that yucasin strongly inhibited YUC1-His activity against the substrate IPyA in a competitive manner. Phenotypic analysis of Arabidopsis YUC1 over-expression lines (35S::YUC1) demonstrated that yucasin acts in IAA biosynthesis catalyzed by YUC. In addition, 35S::YUC1 seedlings showed resistance to yucasin in terms of root growth. A loss-of-function mutant of TAA1, sav3-2, was hypersensitive to yucasin in terms of root growth and hypocotyl elongation of etiolated seedlings. Yucasin combined with the TAA1 inhibitor l-kynurenine acted additively in Arabidopsis seedlings, producing a phenotype similar to yucasin-treated sav3-2 seedlings, indicating the importance of IAA biosynthesis via the IPyA pathway in root growth and leaf vascular development. The present study showed that yucasin is a potent inhibitor of YUC enzymes that offers an effective tool for analyzing the contribution of IAA biosynthesis via the IPyA pathway to plant development and physiological processes.

Molecular Mechanisms of Ethylene–Auxin Interaction

During the century-long history of plant hormone research, the focus in this area has shifted from the original physiological experiments to molecular, genetic, biochemical, and, more recently, genomic approaches. During this journey, we have learned about the many effects these natural compounds have on plant growth and development at the morphological and molecular levels. We have also uncovered how these molecules are sensed by the plant cell and how they trigger signaling cascades that relay information to the nucleus, ultimately culminating in a transcriptional cascade.

Genetic aspects of auxin biosynthesis and its regulation

Auxin is an essential plant hormone that controls nearly every aspect of a plant's life, from embryo development to organ senescence. In the last decade the key genes involved in auxin transport, perception, signaling and response have been identified and characterized, but the elucidation of auxin biosynthesis has proven to be especially challenging. In plants, a significant amount of indole-3-acetic acid (IAA), the predominant biologically active form of auxin, is synthesized via a simple two-step route where indole-3-pyruvic acid (IPyA) produced from l-tryptophan by tryptophan aminotransferases (TAA1/TAR) is converted to IAA by the YUC family of flavin monooxygenases. The TAA1/TAR and YUC gene families constitute the first complete auxin biosynthetic pathway described in plants. Detailed characterization of these genes' expression patterns suggested a key role of local auxin biosynthesis in plant development. This has prompted an active search for the molecular mechanisms that regulate the spatiotemporal activity of the IPyA route. In addition to the TAA1/TAR and YUC-mediated auxin biosynthesis, several alternative routes of IAA production have been postulated to function in plants, but their biological significance is yet to be demonstrated. Herein, we take a genetic perspective to describe the current view of auxin biosynthesis and its regulation in plants, focusing primarily on Arabidopsis.

Disturbed Local Auxin Homeostasis Enhances Cellular Anisotropy and Reveals Alternative Wiring of Auxin-ethylene Crosstalk in Brachypodium distachyon Seminal Roots

Observations gained from model organisms are essential, yet it remains unclear to which degree they are applicable to distant relatives. For example, in the dicotyledon Arabidopsis thaliana (Arabidopsis), auxin biosynthesis via indole-3-pyruvic acid (IPA) is essential for root development and requires redundant TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS 1 (TAA1) and TAA1-RELATED (TAR) genes. A promoter T-DNA insertion in the monocotyledon Brachypodium distachyon (Brachypodium) TAR2-LIKE gene (BdTAR2L) severely down-regulates expression, suggesting reduced tryptophan aminotransferase activity in this mutant, which thus represents a hypomorphic Bdtar2l allele (Bdtar2lhypo). Counterintuitive however, Bdtar2lhypo mutants display dramatically elongated seminal roots because of enhanced cell elongation. This phenotype is also observed in another, stronger Bdtar2l allele and can be mimicked by treating wild type with L-kynerunine, a specific TAA1/TAR inhibitor. Surprisingly, L-kynerunine-treated as well as Bdtar2l roots display elevated rather than reduced auxin levels. This does not appear to result from compensation by alternative auxin biosynthesis pathways. Rather, expression of YUCCA genes, which are rate-limiting for conversion of IPA to auxin, is increased in Bdtar2l mutants. Consistent with suppression of Bdtar2lhypo root phenotypes upon application of the ethylene precursor 1-aminocyclopropane-1-carboxylic-acid (ACC), BdYUCCA genes are down-regulated upon ACC treatment. Moreover, they are up-regulated in a downstream ethylene-signaling component homolog mutant, Bd ethylene insensitive 2-like 1, which also displays a Bdtar2l root phenotype. In summary, Bdtar2l phenotypes contrast with gradually reduced root growth and auxin levels described for Arabidopsis taa1/tar mutants. This could be explained if in Brachypodium, ethylene inhibits the rate-limiting step of auxin biosynthesis in an IPA-dependent manner to confer auxin levels that are sub-optimal for root cell elongation, as suggested by our observations. Thus, our results reveal a delicate homeostasis of local auxin and ethylene activity to control cell elongation in Brachypodium roots and suggest alternative wiring of auxin-ethylene crosstalk as compared to Arabidopsis.

Indole-3-acetic acid biosynthetic pathway and aromatic amino acid aminotransferase activities inPantoea dispersastrain GPK

This investigation deals with the production of IAA by a bacterial isolate Pantoea dispersa strain GPK (PDG) identified by 16S rRNA gene sequence analysis. HPLC and Mass spectral analysis of metabolites from bacterial spent medium revealed that, IAA production by PDG is Trp-dependent and follows indole-3-pyruvic acid (IPyA) pathway. Substrate specificity study of aromatic amino acid aminotransferase (AAT) showed high activities, only when tryptophan (Trp) and α-ketoglutarate (α-kg) were used as substrates. AAT is highly specific for Trp and α-kg as amino group donor and acceptor, respectively. The effect of exogenous IAA on bacterial growth was established. Low concentration of exogenous IAA induced the growth, whereas high concentration decreased the growth of bacterium. PDG treatment significantly increased the root length, shoot length and dry mass of the chickpea and pigeon pea plants.

Overexpression of Arabidopsis YUCCA6 in Potato Results in High-Auxin Developmental Phenotypes and Enhanced Resistance to Water Deficit

Indole-3-acetic acid (IAA), a major plant auxin, is produced in both tryptophan-dependent and tryptophan-independent pathways. A major pathway in Arabidopsis thaliana generates IAA in two reactions from tryptophan. Step one converts tryptophan to indole-3-pyruvic acid (IPA) by tryptophan aminotransferases followed by a rate-limiting step converting IPA to IAA catalyzed by YUCCA proteins. We identified eight putative StYUC (Solanum tuberosum YUCCA) genes whose deduced amino acid sequences share 50%-70% identity with those of Arabidopsis YUCCA proteins. All include canonical, conserved YUCCA sequences: FATGY motif, FMO signature sequence, and FAD-binding and NADP-binding sequences. In addition, five genes were found with ~50% amino acid sequence identity to Arabidopsis tryptophan aminotransferases. Transgenic potato (Solanum tuberosum cv. Jowon) constitutively overexpressing Arabidopsis AtYUC6 displayed high-auxin phenotypes such as narrow downward-curled leaves, increased height, erect stature, and longevity. Transgenic potato plants overexpressing AtYUC6 showed enhanced drought tolerance based on reduced water loss. The phenotype was correlated with reduced levels of reactive oxygen species in leaves. The results suggest a functional YUCCA pathway of auxin biosynthesis in potato that may be exploited to alter plant responses to the environment.

Indole-3-Acetic Acid Biosynthesis in Fusarium delphinoides Strain GPK, a Causal Agent of Wilt in Chickpea

Fusarium delphinoides (Ascomycota; Nectriaceae) is an indole-3-acetic acid (IAA) producing plant pathogen and a causal agent of wilt in chickpea. The IAA biosynthetic pathway in F. delphinoides strain GPK (FDG) was examined by analyzing metabolic intermediates and by feeding experiments. Gas chromatograph (GC) analysis of FDG culture filtrates showed the presence of metabolic intermediates of indole-3-pyruvic acid (IPyA), indole-3-acetamide (IAM), and tryptamine (TRA) pathways. The different IAA biosynthetic pathways were further confirmed by identifying the presence of different enzymes of these pathways. Substrate specificity study of aromatic amino acid aminotransferase revealed that the enzyme is highly specific for tryptophan (Trp) and α-ketoglutarate (α-kg) as amino group donor and acceptor, respectively. Furthermore, the concentration-dependent effect of exogenous IAA on fungal growth was established. Low concentration of exogenous IAA increases the fungal growth and at high concentration it decreases the growth of FDG.

Coupling Reaction of Indolepyruvic Acid by StaD and Its Product: Implications for Biosynthesis of Indolocarbazole and Violacein

Coupling Reaction of Indolepyruvic Acid by StaD and Its Product: Implications for Biosynthesis of Indolocarbazole and Violacein

The pathway of auxin biosynthesis in plants

The plant hormone auxin, which is predominantly represented by indole-3-acetic acid (IAA), is involved in the regulation of plant growth and development. Although IAA was the first plant hormone identified, the biosynthetic pathway at the genetic level has remained unclear. Two major pathways for IAA biosynthesis have been proposed: the tryptophan (Trp)-independent and Trp-dependent pathways. In Trp-dependent IAA biosynthesis, four pathways have been postulated in plants: (i) the indole-3-acetamide (IAM) pathway; (ii) the indole-3-pyruvic acid (IPA) pathway; (iii) the tryptamine (TAM) pathway; and (iv) the indole-3-acetaldoxime (IAOX) pathway. Although different plant species may have unique strategies and modifications to optimize their metabolic pathways, plants would be expected to share evolutionarily conserved core mechanisms for auxin biosynthesis because IAA is a fundamental substance in the plant life cycle. In this review, the genes now known to be involved in auxin biosynthesis are summarized and the major IAA biosynthetic pathway distributed widely in the plant kingdom is discussed on the basis of biochemical and molecular biological findings and bioinformatics studies. Based on evolutionarily conserved core mechanisms, it is thought that the pathway via IAM or IPA is the major route(s) to IAA in plants.

Plant‐derived auxin plays an accessory role in symptom development upon Rhodococcus fascians infection

The biotrophic phytopathogen Rhodococcus fascians has a profound impact on plant development, mainly through its principal virulence factors, a mix of synergistically acting cytokinins that induce shoot formation. Expression profiling of marker genes for several auxin biosynthesis routes and mutant analysis demonstrated that the bacterial cytokinins stimulate the auxin biosynthesis of plants via specific targeting of the indole-3-pyruvic acid (IPA) pathway, resulting in enhanced auxin signaling in infected tissues. The double mutant tryptophan aminotransferase 1-1 tryptophan aminotransferase related 2-1 (taa1-1 tar2-1) of Arabidopsis (Arabidopsis thaliana), in which the IPA pathway is defective, displayed a decreased responsiveness towards R. fascians infection, although bacterial colonization and virulence gene expression were not impaired. These observations implied that plant-derived auxin was employed to reinforce symptom formation. Furthermore, the increased auxin production and, possibly, the accumulating bacterial cytokinins in infected plants modified the polar auxin transport so that new auxin maxima were repetitively established and distributed, a process that is imperative for symptom onset and maintenance. Based on these findings, we extend our model of the mode of action of bacterial and plant signals during the interaction between R. fascians and Arabidopsis.

Development and Validation of a Reversed-Phase Liquid Chromatography Method for the Simultaneous Determination of Indole-3-Acetic Acid, Indole-3-Pyruvic Acid, and Abscisic Acid in Barley (Hordeum vulgare L.).

A simple, sensitive, precise, and specific reverse HPLC method was developed and validated for the determination of plant hormones in barley (Hordeum vulgare L.). The method includes extraction in aqueous organic solvent followed by solid-phase extraction, sample evaporation, and reversed-phase HPLC analysis in a general purpose UV-visible (abscisic acid (ABA)) and fluorescence detection (indole-3-acetic acid (IAA) and indole-3-pyruvic acid (IPA)), high-performance liquid chromatography system. The separation was carried out on Zorbax Eclipse XDB C8 column (150 × 4.6 mm I.D) with a mobile phase composed of methanol and 1% acetic acid (60 : 40 v/v) in isocratic mode at a flow rate of 1 ml min−1. The detection was monitored at 270 nm (ABA) and at 282 nm (Ex) and 360 nm (Em) (IAA, IPA). The developed method was validated in terms of accuracy, precision, linearity, limit of detection, limit of quantification, and robustness. The determined validation parameters are in the commonly acceptable ranges for that kind of analysis.

Protocol: High-throughput and quantitative assays of auxin and auxin precursors from minute tissue samples

BackgroundThe plant hormone auxin, indole-3-acetic acid (IAA), plays important roles in plant growth and development. The signaling response to IAA is largely dependent on the local concentration of IAA, and this concentration is regulated by multiple mechanisms in plants. Therefore, the precise quantification of local IAA concentration provides insights into the regulation of IAA and its biological roles. Meanwhile, pathways and genes involved in IAA biosynthesis are not fully understood, so it is necessary to analyze the production of IAA at the metabolite level for unbiased studies of IAA biosynthesis.ResultsWe have developed high-throughput methods to quantify plant endogenous IAA and its biosynthetic precursors including indole, tryptophan, indole-3-pyruvic acid (IPyA), and indole-3-butyric acid (IBA). The protocol starts with homogenizing plant tissues with stable-labeled internal standards added, followed by analyte purification using solid phase extraction (SPE) tips and analyte derivatization. The derivatized analytes are finally analyzed by selected reaction monitoring on a gas chromatograph-mass spectrometer (GC-MS/MS) to determine the precise abundance of analytes. The amount of plant tissue required for the assay is small (typically 2–10 mg fresh weight), and the use of SPE tips is simple and convenient, which allows preparation of large sets of samples within reasonable time periods.ConclusionsThe SPE tips and GC-MS/MS based method enables high-throughput and accurate quantification of IAA and its biosynthetic precursors from minute plant tissue samples. The protocol can be used for measurement of these endogenous compounds using isotope dilution, and it can also be applied to analyze IAA biosynthesis and biosynthetic pathways using stable isotope labeling. The method will potentially advance knowledge of the role and regulation of IAA.

The Arabidopsis YUCCA1 Flavin Monooxygenase Functions in the Indole-3-Pyruvic Acid Branch of Auxin Biosynthesis

The effects of auxins on plant growth and development have been known for more than 100 years, yet our understanding of how plants synthesize this essential plant hormone is still fragmentary at best. Gene loss- and gain-of-function studies have conclusively implicated three gene families, CYTOCHROME P450 79B2/B3 (CYP79B2/B3), YUCCA (YUC), and TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS1/TRYPTOPHAN AMINOTRANSFERASE-RELATED (TAA1/TAR), in the production of this hormone in the reference plant Arabidopsis thaliana. Each of these three gene families is believed to represent independent routes of auxin biosynthesis. Using a combination of pharmacological, genetic, and biochemical approaches, we examined the possible relationships between the auxin biosynthetic pathways defined by these three gene families. Our findings clearly indicate that TAA1/TARs and YUCs function in a common linear biosynthetic pathway that is genetically distinct from the CYP79B2/B3 route. In the redefined TAA1-YUC auxin biosynthetic pathway, TAA1/TARs are required for the production of indole-3-pyruvic acid (IPyA) from Trp, whereas YUCs are likely to function downstream. These results, together with the extensive genetic analysis of four pyruvate decarboxylases, the putative downstream components of the TAA1 pathway, strongly suggest that the enzymatic reactions involved in indole-3-acetic acid (IAA) production via IPyA are different than those previously postulated, and a new and testable model for how IAA is produced in plants is needed.

The main auxin biosynthesis pathway in Arabidopsis

The phytohormone auxin plays critical roles in the regulation of plant growth and development. Indole-3-acetic acid (IAA) has been recognized as the major auxin for more than 70 y. Although several pathways have been proposed, how auxin is synthesized in plants is still unclear. Previous genetic and enzymatic studies demonstrated that both TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS (TAA) and YUCCA (YUC) flavin monooxygenase-like proteins are required for biosynthesis of IAA during plant development, but these enzymes were placed in two independent pathways. In this article, we demonstrate that the TAA family produces indole-3-pyruvic acid (IPA) and the YUC family functions in the conversion of IPA to IAA in Arabidopsis (Arabidopsis thaliana) by a quantification method of IPA using liquid chromatography-electrospray ionization-tandem MS. We further show that YUC protein expressed in Escherichia coli directly converts IPA to IAA. Indole-3-acetaldehyde is probably not a precursor of IAA in the IPA pathway. Our results indicate that YUC proteins catalyze a rate-limiting step of the IPA pathway, which is the main IAA biosynthesis pathway in Arabidopsis.

Improved growth performance of the mangrove Avicennia marina seedlings using a 1-aminocyclopropane-1-carboxylic acid deaminase-producing isolate of Pseudoalteromonas maricaloris

Out of 62 bacterial isolates obtained from the mangrove Avicenniamarina rhizosphere that grows along the Abu Dhabi coast, United Arab Emirates (UAE), an isolate of Pseudoalteromonas maricaloris (Wild type strain) (WT) produced relatively high levels of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase in vitro. Application of this WT strain under greenhouse conditions to A. marina seedlings significantly (P < 0.05), reduced endogenous levels of ACC in the roots and shoots, and significantly (P < 0.05) increased the levels of in planta endogenous plant growth regulators (PGRs) including indole-3-acetic acid (IAA), indole-3-pyruvic acid (IPYA), putrescine (Put), spermidine (Spd) and spermine (Spm) in roots and shoots compared with control mangrove seedlings. WT application has also significantly (P < 0.05) increased photosynthetic pigment contents, photosynthetic carbon assimilation, plant water use efficiency and promoted mangrove seedlings growth characteristics including increased dry weight and length of roots and shoots, total leaf area and the number of the side branches compared with control mangrove seedlings. In comparison, an ACC deaminase non-producing mutant strain (NPM) failed to reduce endogenous levels of ACC in the roots and shoots and also failed to increase endogenous PGRs and photosynthetic pigments and did not promote seedling growth. Both WT and NPM strains were incapable of producing in vitro detectable levels of IAA, IPYA, Gibberellic acid (GA3), zeatin (Z), Put, Spd and Spm in the culture filtrates. This study demonstrated for the first time the ability of ACC deaminase-producing bacteria to promote mangrove growth under greenhouse conditions. P. maricaloris has potential as biological inoculants to promote the growth of mangrove seedlings in afforestation programs in nutrient impoverished sediments in hyper-saline coastal areas in the UAE.

Bactérias produtoras de auxinas isoladas de raízes de Cattleya walkeriana, orquídea Brasileira ameaçada de extinção, e sua função na aclimatização

Bactérias produtoras de auxinas habitam raízes de orquídeas e podem trazer benefícios para a planta hospedeira. Plantas dessa família são multiplicadas em condições assimbióticas in vitro e pouco se conhece sobre a função desses microrganismos para a aclimatização ex vitro. Quatro rizobactérias isoladas da espécie Cattleya walkeriana foram avaliadas por sua capacidade de promoção do crescimento e sobrevivência de plântulas germinadas in vitro durante a aclimatização. Essas rizobactérias foram identificadas como Bacillus, Burkholderia, Enterobacter e Curtobacterium, com base no sequenciamento do gene 16S rRNA. A presença de compostos indólicos no sobrenadante filtrado de culturas líquidas foi quantificada por ensaios colorimétricos e cromatografia líquida de alta eficiência (CLAE). Ácidos 3-indol lático (AIL) e indol-3-acetaldeído (AIAld) foram encontrados em grande quantidade, exceto na cultura de Enterobacter sp., em que ácido 3-indol acético (AIA) e ácido 3-indol pirúvico (AIP) prevaleceram. As rizobactérias foram inoculadas em plântulas germinadas in vitro, aclimatizadas em casa de vegetação durante 90 dias e avaliadas quanto à sua capacidade de promover o crescimento. Burkholderia sp. e Curtobacterium sp. proporcionaram a menor eficiência para o crescimento, enquanto Bacillus sp. e Enterobacter sp. favoreceram incrementos em todas as características avaliadas e ampliaram a percentagem de sobrevivência. Este trabalho elucida a função de rizobactérias produtoras de auxinas e seus benefícios para a promoção de crescimento de uma orquídea brasileira germinada em condições assimbióticas durante a aclimatização - condição que confere alta letalidade e limitante para a propagação de orquídeas.

Indole-3-acetic acid biosynthesis in the biocontrol strain Pseudomonas fluorescens Psd and plant growth regulation by hormone overexpression

Pseudomonas fluorescens is an important biological component of agricultural soils that bestows a number of direct and indirect beneficial attributes to the plants. We analyzed the biocontrol strain P. fluorescens Psd for indole-3-acetic acid (IAA) biosynthesis and studied the effect of its consequent manipulation on its plant-growth-promoting (PGP) potential. While the indole pyruvic acid (IPyA) pathway commonly associated with PGP bacteria was lacking, the indole acetamide (IAM) pathway generally observed in phytopathogens was expressed in strain Psd. Overexpression of IAM pathway genes iaaM-iaaH, from Pseudomonas syringae subsp. savastanoi drastically increased IAA levels and showed a detrimental effect on sorghum root development. On the other hand, heterologous expression of the indole-3-pyruvate decarboxylase/phenylpyruvate decarboxylase gene ( ipdC/ppdC) of the IPyA pathway from the PGP bacterium Azospirillum brasilense SM led to enhancement of the IAA level. A more favorable effect of this recombinant strain on sorghum root growth and development suggests that metabolic engineering could be used to generate strains with improved PGP function.

Functional characterization of the CKRC1/TAA1 gene and dissection of hormonal actions in the Arabidopsis root

Cytokinin (CK) influences many aspects of plant growth and development, and its function often involves intricate interactions with other phytohormones such as auxin and ethylene. However, the molecular mechanisms underlying the role of CK and its interactions with other growth regulators are still poorly understood. Here we describe the isolation and characterization of the Arabidopsis CK-induced root curling 1 (ckrc1) mutant. CKRC1 encodes a previously identified tryptophan aminotransferase (TAA1) involved in the indole-3-pyruvic acid (IPA) pathway of indole-3-acetic acid (IAA) biosynthesis. The ckrc1 mutant exhibits a defective root gravitropic response (GR) and an increased resistance to CK in primary root growth. These defects can be rescued by exogenous auxin or IPA. Furthermore, we show that CK up-regulates CKRC1/TAA1 expression but inhibits polar auxin transport in roots in an AHK3/ARR1/12-dependent and ethylene-independent manner. Our results suggest that CK regulates root growth and development not only by down-regulating polar auxin transport, but also by stimulating local auxin biosynthesis.

Sugar–Hormone Cross-Talk in Seed Development: Two Redundant Pathways of IAA Biosynthesis Are Regulated Differentially in the Invertase-Deficient miniature1 (mn1) Seed Mutant in Maize

The miniature1 (mn1) seed phenotype is a loss-of-function mutation at the Mn1 locus that encodes a cell wall invertase; its deficiency leads to pleiotropic changes including altered sugar levels and decreased levels of IAA throughout seed development. To understand the molecular details of such a sugar-hormone relationship, we have initiated studies on IAA biosynthesis genes in developing seeds of maize. Two tryptophan-dependent pathways of IAA biosynthesis, tryptamine (TAM) and indole-3-pyruvic acid (IPA), are of particular interest. We report on molecular isolation and characterization of an endosperm-specific ZmTARelated1 (ZmTar1) gene of the IPA branch; we have also reported recently on ZmYuc1 gene in the TAM branch. Comparative gene expression analyses here have shown that (1) the ZmTar1 transcripts were approximately 10-fold higher levels than the ZmYuc1; (2) although both genes showed the highest level of expression at 8-12 d after pollination (DAP) coincident with an early peak in IAA levels, the two showed highly divergent (antagonistic) response at 12 and 16 DAP but similar patterns at 20 and 28 DAP in the Mn1 and mn1 endosperm. The Western blot analyses for the ZmTAR1 protein, however, displayed disconcordant protein/transcript expression patterns. Overall, these data report novel observations on redundant trp-dependent pathways of auxin biosynthesis in developing seeds of maize, and suggest that homeostatic control of IAA in this important sink is highly complex and may be regulated by both sucrose metabolism and developmental signals.

L-Tryptophan catabolism by Rubrivivax benzoatilyticus JA2 occurs through indole 3-pyruvic acid pathway

Rubrivivax benzoatilyticus JA2 utilizes L: -tryptophan as the sole source of nitrogen for growth, and it has a doubling time of approximately 11 h (compared to 8 h with ammonium chloride). With cell free extracts in the presence of 2-oxoglutarate, indole-3-pyruvic acid, indole-3-acetaldehyde, indole-3-acetic acid, isatin, benzaldehyde, gallic acid and pyrogallol were identified using high performance liquid chromatography (HPLC) and liquid chromatography-mass spectroscopy (LC-MS) analysis. The conversion of L: -tryptophan into indole 3-pyruvic acid and glutamate by an enzyme aminotransferase was confirmed and the catabolism of indole-3-pyruvic acid via side chain oxidation followed by ring oxidation, gallic acid and pyrogallol were confirmed as metabolites. In addition, the proposed pathway sequential conversion of indole-3-pyruvic acid to the end product of pyrogallol was identified, including an enzymatic step that would convert isatin to benzaldehyde by an enzyme yet to be identified. At this stage of the study, the enzyme tryptophan aminotransferase in R. benzoatilyticus JA2 was demonstrated.