RESUMEN
Major results of the authors' findings on the implementation of biotechnological potential of aerobic methylobacteria and methanotrophs for obtaining forage proteins, biopolymers (polybutyrate and polysaccharides), enzymes (oxidoreductases), and bioprotectors (ectoin), as well as for degrading toxic C1 and Cn compounds have been reviewed. Unique features of the structural and functional organization of the metabolism of extremophilic (tolerant) methylotrophs are discussed, with a view for their prospective use in various fields of modern biotechnology, including biocatalysis and nanotechnology.
Asunto(s)
Methylobacterium/enzimología , Aminoácidos Diaminos/biosíntesis , Biodegradación Ambiental , Biopolímeros/biosíntesis , Butiratos/metabolismo , Carbono/metabolismo , Citocininas/biosíntesis , Contaminantes Ambientales/metabolismo , Formaldehído/metabolismo , Ácidos Indolacéticos/biosíntesis , Methylobacterium/metabolismo , Oxidorreductasas/biosíntesis , Valeratos/metabolismoRESUMEN
Bacteria associated with the roots of greenhouse tropical orchids were shown to produce indole-3-acetic acid (IAA) and to excrete it into the culture liquid. The presence and activity of IAA were demonstrated colorimetrically, by thin-layer chromatography, and by biotests. The associated bacteria varied in their ability to excrete indole compounds (1-28 microg/ml nutrient broth). Addition of tryptophan to the growth medium enhanced phytohormone production. Upon addition of 200 microg/ml tryptophan, the bacteria isolated from Dendrobium moschatum roots (Sphingomonas sp. 18, Microbacterium sp. 23, Mycobacterium sp. 1, Bacillus sp. 3, and Rhizobium sp. 5) produced 50.2, 53.1, 92.9, 37.6, and 60.4 microg IAA/ml respectively, while the bacteria isolated from Acampe papillosa roots (Sphingomonas sp. 42, Rhodococcus sp. 37, Cellulomonas sp. 23, Pseudomonas sp. 24, and Micrococcus luteus) produced 69.4, 49.6, 53.9, 31.0, and 39.2 microg IAA/ml. Auxin production depended on cultivation conditions and on the growth phase of the bacterial cultures. Treatment of kidney bean cuttings with bacterial culture liquid promoted formation of a "root brush" with location height 7.4- to 13.4-fold greater than the one in the control samples. The ability of IAA-producing associated bacteria to act as stimulants of the host plant root development is discussed.
Asunto(s)
Bacterias/metabolismo , Ácidos Indolacéticos/biosíntesis , Orchidaceae/microbiología , Raíces de Plantas/microbiología , Ácidos Indolacéticos/metabolismo , Phaseolus/microbiología , Phaseolus/fisiología , Reguladores del Crecimiento de las Plantas/biosíntesis , Raíces de Plantas/fisiología , Simbiosis , Triptófano/metabolismoRESUMEN
AIM: To isolate and characterize groundnut-associated bacterial isolates for growth promotion of groundnut in field. METHODS AND RESULTS: Three hundred and ninety-three groundnut-associated bacteria, representing the geocarposphere, phylloplane and rhizosphere, and endophytes were applied as seed treatment in greenhouse. Maximum increase in plant biomass (up to 26%) was observed following treatment with a rhizosphere isolate identified as Bacillus firmis GRS 123, and two phylloplane isolates Bacillus megaterium GPS 55 and Pseudomonas aeruginosa GPS 21. There was no correlation between the production of L-tryptophan-derived auxins and growth promotion by the test isolates. Actively growing cells and peat formulations of GRS 123 and GPS 55, and actively growing cells of GPS 21, significantly increased the plant growth and pod yield (up to 19%) in field. Rifampicin-resistant mutants of GRS 123 and GPS 21 colonized the ecto- and endorhizospheres of groundnut, respectively, up to 100 days after sowing (DAS), whereas GPS 55 was recovered from both the habitats at 100 DAS. CONCLUSION: Seed bacterization with phylloplane isolates promoted groundnut growth indicating the possibility of isolating rhizosphere beneficial bacteria from different habitats. SIGNIFICANCE AND IMPACT OF THE STUDY: Identification of phylloplane bacteria as effective plant growth-promoting rhizobacteria (PGPR) broadens the spectrum of PGPR available for field application.
Asunto(s)
Arachis/crecimiento & desarrollo , Arachis/microbiología , Bacterias/aislamiento & purificación , Bacterias/metabolismo , Antibacterianos/farmacología , Arachis/efectos de los fármacos , Bacillus/clasificación , Bacillus/aislamiento & purificación , Bacillus/metabolismo , Bacterias/clasificación , Biomasa , Farmacorresistencia Bacteriana , India , Ácidos Indolacéticos/biosíntesis , Fosfatos/metabolismo , Raíces de Plantas/microbiología , Pseudomonas aeruginosa/clasificación , Pseudomonas aeruginosa/aislamiento & purificación , Pseudomonas aeruginosa/metabolismo , Rifampin/farmacologíaRESUMEN
The role and metabolism of indole-3-acetic acid in gram-negative bacteria is well documented, but little is known about indole-3-acetic acid biosynthesis and regulation in gram-positive bacteria. The phytopathogen Rhodococcus fascians, a gram-positive organism, incites diverse developmental alterations, such as leafy galls, on a wide range of plants. Phenotypic analysis of a leafy gall suggests that auxin may play an important role in the development of the symptoms. We show here for the first time that R. fascians produces and secretes the auxin indole-3-acetic acid. Interestingly, whereas noninfected-tobacco extracts have no effect, indole-3-acetic acid synthesis is highly induced in the presence of infected-tobacco extracts when tryptophan is not limiting. Indole-3-acetic acid production by a plasmid-free strain shows that the biosynthetic genes are located on the bacterial chromosome, although plasmid-encoded genes contribute to the kinetics and regulation of indole-3-acetic acid biosynthesis. The indole-3-acetic acid intermediates present in bacterial cells and secreted into the growth media show that the main biosynthetic route used by R. fascians is the indole-3-pyruvic acid pathway with a possible rate-limiting role for indole-3-ethanol. The relationship between indole-3-acetic acid production and the symptoms induced by R. fascians is discussed.
Asunto(s)
Ácidos Indolacéticos/biosíntesis , Plantas/microbiología , Rhodococcus/metabolismo , Rhodococcus/patogenicidad , Ácidos Indolacéticos/metabolismo , Indoles/metabolismo , Cinética , Enfermedades de las Plantas/etiología , Enfermedades de las Plantas/microbiología , Plantas/metabolismo , Plásmidos/genética , Rhodococcus/genética , Nicotiana/metabolismo , Nicotiana/microbiología , Virulencia/genéticaRESUMEN
The role of ethylene and auxin in stigma-to-ovule signalling was investigated in maize (Zea mays L.). Maturation of the egg cells in an ear was stimulated before actual fertilization by the application of fresh pollen grains or quartz sand to fully receptive stigmas. Ethylene emission by maize ears increased in response to those treatments. Silks and ovaries were involved in ethylene synthesis after pollen or sand was shed over the silks. The content of ethylene precursor [1-aminocyclopropane-1-carboxylic acid (ACC)] increased in both pistil parts soon after pollination. ACC rise was delayed by 4 h in the ovaries, and by 8 h in the silks after mock-pollination with sand. The auxin level increased rapidly in the silks and ovaries after pollination, and it was very high in the pollinated silks due to the high indole-3-acetic acid (IAA) content of pollen grains. IAA rise also appeared in the silks and ovaries after treatment with sand but it was delayed by 8 h. Application of ACC (10 microM) or IAA (6 microM) solutions to non-pollinated silks stimulated maturation of the egg cells. Moreover, the response of the egg cells to pollination was cancelled by l-alpha-(2-aminoethoxyvinyl)-glycine, alpha-aminoisobutyric acid or 2,3,5-triiodobenzoic acid applied to the silks before pollination. Thus ethylene synthesis and polar auxin transport in the silks pollinated with fresh pollen were necessary to evoke accelerated differentiation of the egg cells in maize ovules. Differences in pistil responses found between true- and mock-pollination suggest that signalling pathways are at least partially different for the reception of pollen grains and sand crystals on maize stigma.
Asunto(s)
Etilenos/biosíntesis , Flores/crecimiento & desarrollo , Ácidos Indolacéticos/biosíntesis , Oocitos/crecimiento & desarrollo , Zea mays/embriología , Zea mays/metabolismo , Aminoácidos Cíclicos/metabolismo , Aminoácidos Cíclicos/farmacología , Aminobutiratos/farmacología , Diferenciación Celular/efectos de los fármacos , Diferenciación Celular/genética , Fertilización/efectos de los fármacos , Fertilización/genética , Flores/citología , Flores/metabolismo , Ácidos Indolacéticos/metabolismo , Oocitos/efectos de los fármacos , Oocitos/metabolismo , Polen/genética , Semillas/efectos de los fármacos , Semillas/crecimiento & desarrollo , Semillas/metabolismo , Ácidos Triyodobenzoicos/farmacologíaRESUMEN
A study was made of cell division activity and hormonal status in roots of 4 day old wheat seedling treated with wheat germ agglutinin (WGA). The revealed stimulating effect of WGA on mitotic index (MI) and cell area in root extension zone was specific for this lectin, because gliadin, taken as a control protein, caused no changes in growth parameters. Phytolectins (phytohemagglutinin and concanavalin A) possessing properties of mitogens rendered no such essential influence on cell growth of wheat. Immunoassay has shown that WGA-treatment leads to accumulation of auxins and cytokinins in roots. This suggest participation of WGA in regulation of MI of meristem cells in roots of seedlings during their interaction with phytohormones.
Asunto(s)
Triticum/efectos de los fármacos , Aglutininas del Germen de Trigo/farmacología , División Celular/efectos de los fármacos , Citocininas/biosíntesis , Ácidos Indolacéticos/biosíntesis , Índice Mitótico , Reguladores del Crecimiento de las Plantas/metabolismo , Raíces de Plantas/efectos de los fármacos , Plantones/efectos de los fármacos , Triticum/crecimiento & desarrollo , Triticum/metabolismoRESUMEN
BACKGROUND: The DefH9-iaaM gene fusion which is expressed specifically in placenta/ovules and promotes auxin-synthesis confers parthenocarpic fruit development to eggplant, tomato and tobacco. Transgenic DefH9-iaaM eggplants and tomatoes show increased fruit production due mainly to an improved fruit set. However, the weight of the fruits is also frequently increased. RESULTS: DefH9-iaaM strawberry and raspberry plants grown under standard cultivation conditions show a significant increase in fruit number and size and fruit yield. In all three Rosaceae species tested, Fragaria vesca, Fragaria x ananassa and Rubus idaeus, DefH9-iaaM plants have an increased number of flowers per inflorescence and an increased number of inflorescences per plant. This results in an increased number of fruits per plant. Moreover, the weight and size of transgenic fruits was also increased. The increase in fruit yield was approximately 180% in cultivated strawberry, 140% in wild strawberry, and 100% in raspberry. The DefH9-iaaM gene is expressed in the flower buds of all three species. The total IAA (auxin) content of young flower buds of strawberry and raspberry expressing the DefH9-iaaM gene is increased in comparison to untransformed flower buds. The DefH9-iaaM gene promotes parthenocarpy in emasculated flowers of both strawberry and raspberry. CONCLUSIONS: The DefH9-iaaM gene is expressed and biologically active in Rosaceae. The DefH9-iaaM gene can be used, under cultivation conditions that allow pollination and fertilization, to increase fruit productivity significantly in Rosaceae species. The finding that the DefH9-iaaM auxin-synthesizing gene increases the number of inflorescences per plant and the number of flowers per inflorescence indicates that auxin plays a role in plant fecundity in these three perennial Rosaceae species.
Asunto(s)
Fragaria/genética , Frutas/genética , Genes de Plantas/genética , Ácidos Indolacéticos/biosíntesis , Southern Blotting , Fertilidad/genética , Fertilidad/fisiología , Flores/genética , Flores/metabolismo , Fragaria/crecimiento & desarrollo , Fragaria/metabolismo , Frutas/crecimiento & desarrollo , Frutas/metabolismo , Tamaño de los Órganos , Plantas Modificadas Genéticamente , ARN Mensajero/genética , ARN Mensajero/metabolismo , ARN de Planta/genética , ARN de Planta/metabolismoRESUMEN
Immature seeds of some dicotyledonous plants contain IAGlc synthase catalysing the synthesis of 1-O-IAGlc. This enzyme activity is comparable with 1-O-IAGlc synthase activity investigated earlier in liquid endosperm of Zea mays. Polyclonal antibodies against maize 1-O-IAGlc synthase cross-react with partially purified 1-O-IAGlc synthase from immature pea and rape seeds. Single immunoreactive bands were observed at a locus corresponding to 45.7 kDa and 43.7 kDa from pea and rape enzyme preparations, respectively, unlike that from the 50 kDa molecular mass of the maize enzyme. It was also observed that some high molecular weight compounds of pea seeds are labelled in vivo by [(14)C] IAA, and unlabelled 1-O-IAGlc inhibits that labelling. In immature pea seeds 43-49.8% of the IAA-modified high molecular weight compounds, obtained after ultracentrifugation, was found in the soluble fraction and 50.1-57% in the insoluble fraction. Ester-linked IAA accounted for about 6-9% and 38-45.6% in soluble and insoluble material, respectively, estimated after hydrolysis in 1 N NaOH. Enzymatic hydrolysis of IAA-labelled high molecular weight compounds gives free IAA and compound(s) corresponding to IAGlc isomers. These results suggest that 1-O-IAGlc synthesized in legume seeds may be used for the modification of some high molecular weight compounds.
Asunto(s)
Fabaceae/enzimología , Glucósidos/metabolismo , Glucosiltransferasas/metabolismo , Ácidos Indolacéticos/biosíntesis , Indoles/metabolismo , Semillas/enzimología , Brassica rapa/enzimología , Ácidos Indolacéticos/metabolismo , Cinética , Pisum sativum/enzimología , Phaseolus/enzimología , Proteínas de Plantas/metabolismo , Especificidad de la Especie , Zea mays/enzimologíaRESUMEN
We report characterization of SUPERROOT1 (SUR1) as the C-S lyase in glucosinolate biosynthesis. This is evidenced by selective metabolite profiling of sur1, which is completely devoid of aliphatic and indole glucosinolates. Furthermore, following in vivo feeding with radiolabeled p-hydroxyphenylacetaldoxime to the sur1 mutant, the corresponding C-S lyase substrate accumulated. C-S lyase activity of recombinant SUR1 heterologously expressed in Escherichia coli was demonstrated using the C-S lyase substrate djenkolic acid. The abolishment of glucosinolates in sur1 indicates that the SUR1 function is not redundant and thus SUR1 constitutes a single gene family. This suggests that the "high-auxin" phenotype of sur1 is caused by accumulation of endogenous C-S lyase substrates as well as aldoximes, including indole-3-acetaldoxime (IAOx) that is channeled into the main auxin indole-3-acetic acid (IAA). Thereby, the cause of the "high-auxin" phenotype of sur1 mutant resembles that of two other "high-auxin" mutants, superroot2 (sur2) and yucca1. Our findings provide important insight to the critical role IAOx plays in auxin homeostasis as a key branching point between primary and secondary metabolism, and define a framework for further dissection of auxin biosynthesis.
Asunto(s)
Arabidopsis/enzimología , Glucosinolatos/biosíntesis , Ácidos Indolacéticos/fisiología , Indoles/metabolismo , Liasas/metabolismo , Oximas/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Escherichia coli/genética , Escherichia coli/metabolismo , Regulación Enzimológica de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Ácidos Indolacéticos/biosíntesis , Liasas/genética , Familia de Multigenes , MutaciónRESUMEN
Some microorganisms found in the soil are able to produce substances which regulate plant growth. In this study, we show the presence of a substance associated with auxin activity, identified as indole-3-butyric acid (IBA), in Azospirillum brasilense UAP 154 growth medium. A. brasilense was grown and indolic compounds were extracted from the supernatant. These were then analyzed by high performance liquid chromatography (HPLC), gas chromatography and gas chromatography mass spectrometry. The retention time was similar to those of the authentic IBA standard. The compound obtained from HPLC was collected and applied to maize seedlings (Zea mays), inducing biological activity along the roots, similar to that induced by an authentic IBA standard.
Asunto(s)
Azospirillum brasilense/metabolismo , Ácidos Indolacéticos/biosíntesis , Indoles/metabolismo , Azospirillum brasilense/crecimiento & desarrollo , Cromatografía Líquida de Alta Presión , Medios de Cultivo , Cromatografía de Gases y Espectrometría de Masas , Ácidos Indolacéticos/química , Ácidos Indolacéticos/aislamiento & purificación , Ácidos Indolacéticos/farmacología , Indoles/química , Indoles/aislamiento & purificación , Indoles/farmacología , Raíces de Plantas/efectos de los fármacos , Raíces de Plantas/crecimiento & desarrollo , Zea mays/efectos de los fármacos , Zea mays/crecimiento & desarrolloRESUMEN
Agrobacterium tumefaciens-induced plant tumors accumulate considerable concentrations of free auxin. To determine possible mechanisms by which high auxin concentrations are maintained, we examined the pattern of auxin and flavonoid distribution in plant tumors. Tumors were induced in transformants of Trifolium repens (L.), containing the beta-glucuronidase ( GUS)-fused auxin-responsive promoter ( GH3) or chalcone synthase ( CHS2) genes, and in transformants of Arabidopsis thaliana (L.) Heynh., containing the GUS-fused synthetic auxin response element DR5. Expression of GH3::GUS and DR5::GUS was strong in proliferating metabolically active tumors, thus suggesting high free-auxin concentrations. Immunolocalization of total auxin with indole-3-acetic acid antibodies was consistent with GH3::GUS expression indicating the highest auxin concentration in the tumor periphery. By in situ staining with diphenylboric acid 2-aminoethyl ester, by thin-layer chromatography, reverse-phase high-performance liquid chromatography, and two-photon laser-scanning microscopy spectrometry, tumor-specific flavones, isoflavones and pterocarpans were detected, namely 7,4'-dihydroxyflavone (DHF), formononetin, and medicarpin. DHF was the dominant flavone in high free-auxin-accumulating stipules of Arabidopsis leaf primordia. Flavonoids were localized at the sites of strongest auxin-inducible CHS2::GUS expression in the tumor that was differentially modulated by auxin in the vascular tissue. CHS mRNA expression changes corresponded to the previously analyzed auxin concentration profile in tumors and roots of tumorized Ricinus plants. Application of DHF to stems, apically pretreated with alpha-naphthaleneacetic acid, inhibited GH3::GUS expression in a fashion similar to 1-N-naphthyl-phthalamic acid. Tumor, root and shoot growth was poor in inoculated tt4(85) flavonoid-deficient CHS mutants of Arabidopsis. It is concluded that CHS-dependent flavonoid aglycones are possibly endogenous regulators of the basipetal auxin flux, thereby leading to free-auxin accumulation in A. tumefaciens-induced tumors. This, in turn, triggers vigorous proliferation and vascularization of the tumor tissues and suppresses their further differentiation.
Asunto(s)
Arabidopsis/crecimiento & desarrollo , Flavonoides/biosíntesis , Ácidos Indolacéticos/biosíntesis , Tumores de Planta/etiología , Rhizobium/patogenicidad , Trifolium/crecimiento & desarrollo , Aciltransferasas/genética , Aciltransferasas/metabolismo , Arabidopsis/genética , Arabidopsis/microbiología , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Flavonoides/farmacología , Regulación Enzimológica de la Expresión Génica/efectos de los fármacos , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Glucuronidasa/metabolismo , Hibridación Fluorescente in Situ , Isoflavonas/biosíntesis , Mutación , Ftalimidas/farmacología , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Pterocarpanos/biosíntesis , ARN Mensajero/genética , ARN Mensajero/metabolismo , Trifolium/genética , Trifolium/microbiologíaRESUMEN
The effect of 16 different day (DT) and night (NT) temperature combinations (DT and NT 12, 17, 22 and 27 degrees C) on rosette leaf growth, flower stem elongation and flowering time in Arabidopsis thaliana Ler was investigated. Final leaf length decreased with increasing NT due to a combination of reduced elongation period and reduced elongation rate. Final stem length increased with increasing DT due to increased elongation rate, and decreased with increasing NT due to a decrease in elongation period. Under NT 27 degrees C, however, stem elongation rate increased greatly, resulting in the same final stem length as under NT 12 degrees C. The transition to flowering was accelerated by increasing NT. A linear regression analysis was performed to clarify the relationship between final leaf length, final stem length and flowering time with DIF (DT minus NT) and/or ADT (average daily temperature). For all three variables, the effect of DIF depended on ADT and vice versa. The relationship of final stem length with DIF also depended on the temperature range. Increased cell volume in flower stems developing at DT/NT 22/12 degrees C gave rise to longer and thicker stems compared with stems developing at DT/NT 12/22 degrees C. GC-MS analysis (gas chromatography-mass spectrometry) showed that the endogenous level of IAA was 56 % higher in stems grown under DT/NT 22/12 degrees C compared with DT/NT 12/22 degrees C. Of the 12 gibberellins analysed, however, only the level of non-bioactive GA29 was affected by the temperature treatment.
Asunto(s)
Arabidopsis/metabolismo , Flores/crecimiento & desarrollo , Giberelinas/biosíntesis , Ácidos Indolacéticos/biosíntesis , Hojas de la Planta/crecimiento & desarrollo , Adaptación Fisiológica/fisiología , Arabidopsis/anatomía & histología , Arabidopsis/crecimiento & desarrollo , Tamaño de la Célula/fisiología , Hojas de la Planta/anatomía & histología , Tallos de la Planta/anatomía & histología , Tallos de la Planta/crecimiento & desarrollo , Temperatura , Factores de TiempoRESUMEN
There have been few examples of the application of our growing knowledge of hormone action to crop improvement. In this review we discuss what is known about the critical points regulating auxin action. We examine auxin metabolism, transport, perception and signalling and identify genes and proteins that might be keys to regulation, particularly the rate-limiting steps in various pathways. Certain mutants show that substrate flow in biosynthesis can be limiting. To date there is little information available on the genes and proteins of catabolism. There have been several auxin transport proteins and some elegant transport physiology described recently, and the potential for using transport proteins to manage free indole-3-acetic acid (IAA) concentrations is discussed. Free IAA is very mobile, and so while it may be more practical to control auxin action through managing the receptor and signalling pathways, the candidate genes and proteins through which this can be done remain largely unknown. From the available evidence, it is clear that the reason for so few commercial applications arising from the control of auxin action is that knowledge is still limited.
Asunto(s)
Ácidos Indolacéticos/biosíntesis , Plantas/metabolismo , Transporte Biológico , Regulación del Desarrollo de la Expresión Génica , Homeostasis , Ácidos Indolacéticos/metabolismo , Desarrollo de la Planta , Plantas/genética , Transducción de Señal/fisiologíaRESUMEN
The synthesis of plant growth hormone auxin, indole-3-acetic acid (IAA), is not only confined to flowering plants. Yeasts and other fungi are also known to produce this hormone and in many cases at higher levels than plants. The main concern of this study was to determine the physical and chemical conditions necessary for optimal biosynthesis of this hormone by Lentinus sajor-caju. Glucose was determined to be superior to sucrose as carbon and energy source. The synthesis of IAA in a nitrogen-free medium or in a medium with low external phosphate was substantially reduced. Light exposed and non-agitated cultures grown in dark had also reduced levels of IAA compared to agitated cultures grown in dark. The highest (0.18 mg ml-1) IAA level was determined in cultures grown in glucose containing medium (pH 7.5) on a rotary shaker (150 rpm) at 30 degrees C in dark. The biological activity of IAA obtained from the extra-cellular culture of Lentinus sajor-caju was determined using oat coleptile growth test.
Asunto(s)
Ácidos Indolacéticos/biosíntesis , Ácidos Indolacéticos/metabolismo , Lentinula/metabolismo , Avena/crecimiento & desarrollo , Biomasa , Cotiledón/crecimiento & desarrollo , Medios de Cultivo , Oscuridad , Glucosa/metabolismo , Concentración de Iones de Hidrógeno , Ácidos Indolacéticos/farmacología , Lentinula/crecimiento & desarrollo , Luz , Micelio/crecimiento & desarrollo , Sacarosa/metabolismo , TemperaturaRESUMEN
The answer to the simple question of how plants make auxin has proven to be inordinately complex. Recent in planta studies in Arabidopsis have uncovered additional complexity in auxin biosynthesis. Two distinct pathways from tryptophan to the intermediate indoleacetaldoxime were identified. Genic, as well as functional redundancy, appear to be characteristic for auxin biosynthesis and plants might have evolved many different solutions for making and regulating auxin.
Asunto(s)
Arabidopsis/metabolismo , Ácidos Indolacéticos/biosíntesis , Triptófano/metabolismo , Arabidopsis/citología , Arabidopsis/enzimología , Arabidopsis/genética , Regulación de la Expresión Génica de las Plantas , Ácidos Indolacéticos/química , Estructura Molecular , Triptófano/químicaRESUMEN
Higher plants assimilate inorganic sulfate into cysteine, which is subsequently converted to methionine, and into a variety of other sulfur-containing organic compounds. To resist sulfur deficiency, plants must demonstrate physiological flexibility: the expression of an extensive set of genes and gene regulators that act in the affected pathways or signalling cascades must be delicately tuned in response to environmental challenges. To elucidate this network of interactions, we have applied an array hybridisation/transcript profiling method to Arabidopsis plants subjected to 6, 10 and 13 days of constitutive and induced sulfur starvation. The temporal expression behaviour of approximately 7200 non-redundant genes was analysed simultaneously. The experiment was designed in a way to identify statistically significant changes of gene expression based on sufficient numbers of repeated hybridisations performed with five uniform pools of plant material. The expression profiles were processed to select differentially expressed genes. Among the 1507 sulfur-responsive clones implicated in this way, 632 genes responded specifically to sulfur deficiency by significant over-expression. The sulfur-responsive genes were grouped according to functional categories or biosynthetic pathways. As expected, genes of the sulfur assimilation pathway were altered in expression. Furthermore, genes involved in flavonoid, auxin, and jasmonate biosynthesis pathways were upregulated in conditions of sulfur deficiency. Based on the correlative analysis of gene expression patterns, we suggest that a complex co-ordination of systematic responses to sulfur depletion is provided via integration of flavonoid, auxin and jasmonate pathway elements. Plait concept for transduction of specificity via the main non-specific signalling stream is proposed.
Asunto(s)
Proteínas de Arabidopsis/genética , Arabidopsis/genética , Perfilación de la Expresión Génica , Azufre/deficiencia , Adaptación Fisiológica/genética , Adaptación Fisiológica/fisiología , Aminoácidos Sulfúricos/metabolismo , Arabidopsis/metabolismo , Proteínas de Arabidopsis/metabolismo , Ciclopentanos/metabolismo , Cisteína/metabolismo , Flavonoides/biosíntesis , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Genes de Plantas/genética , Ácidos Indolacéticos/biosíntesis , Metionina/metabolismo , Oxilipinas , Fenotipo , Transducción de Señal/genética , Transducción de Señal/fisiología , Azufre/metabolismo , Azufre/farmacologíaRESUMEN
The major regulatory shoot signal is auxin, whose synthesis in young leaves has been a mystery. To test the leaf-venation hypothesis [R. Aloni (2001) J Plant Growth Regul 20: 22-34], the patterns of free-auxin production, movement and accumulation in developing leaf primordia of DR5::GUS-transformed Arabidopsis thaliana (L.) Heynh. were visualized. DR5::GUS expression was regarded to reflect sites of free auxin, while immunolocalization with specific monoclonal antibodies indicated total auxin distribution. The mRNA expression of key enzymes involved in the synthesis, conjugate hydrolysis, accumulation and basipetal transport of auxin, namely indole-3-glycerol-phosphate-synthase, nitrilase, IAA-amino acid hydrolase, chalcone synthase and PIN1 as an essential component of the basipetal IAA carrier, was investigated by reverse transcription-polymerase chain reaction. Near the shoot apex, stipules were the earliest sites of high free-auxin production. During early stages of primordium development, leaf apical dominance was evident from strong beta-glucuronidase activity in the elongating tip, possibly suppressing the production of free auxin in the leaf tissues below it. Hydathodes, which develop in the tip and later in the lobes, were apparently primary sites of high free-auxin production, the latter supported by auxin-conjugate hydrolysis, auxin retention by the chalcone synthase-dependent action of flavonoids and also by the PIN1-component of the carrier-mediated basipetal transport. Trichomes and mesophyll cells were secondary sites of free-auxin production. During primordium development there are gradual shifts in sites and concentrations of free-auxin production occurring first in the tip of a leaf primordium, then progressing basipetally along the margins, and finally appearing also in the central regions of the lamina. This developmental pattern of free-auxin production is suggested to control the basipetal maturation sequence of leaf development and vascular differentiation in Arabidopsis leaves.
Asunto(s)
Arabidopsis/crecimiento & desarrollo , Proteínas Bacterianas , Ácidos Indolacéticos/biosíntesis , Hojas de la Planta/crecimiento & desarrollo , Aciltransferasas/genética , Aciltransferasas/metabolismo , Amidohidrolasas/genética , Amidohidrolasas/metabolismo , Aminohidrolasas/genética , Aminohidrolasas/metabolismo , Arabidopsis/genética , Arabidopsis/metabolismo , Transporte Biológico , Diferenciación Celular , Extensiones de la Superficie Celular/metabolismo , Regulación Enzimológica de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Glucuronidasa/genética , Glucuronidasa/metabolismo , Inmunohistoquímica , Indol-3-Glicerolfosfato Sintasa/genética , Indol-3-Glicerolfosfato Sintasa/metabolismo , Morfogénesis , Peptidilprolil Isomerasa de Interacción con NIMA , Isomerasa de Peptidilprolil/genética , Isomerasa de Peptidilprolil/metabolismo , Hojas de la Planta/metabolismo , Raíces de Plantas/crecimiento & desarrollo , Raíces de Plantas/metabolismo , Brotes de la Planta/crecimiento & desarrollo , Brotes de la Planta/metabolismoRESUMEN
Ethylene or its precursor 1-aminocyclopropane-1-carboxylic acid (ACC) can stimulate hypocotyl elongation in light-grown Arabidopsis seedlings. A mutant, designated ACC-related long hypocotyl 1 (alh1), that displayed a long hypocotyl in the light in the absence of the hormone was characterized. Etiolated alh1 seedlings overproduced ethylene and had an exaggerated apical hook and a thicker hypocotyl, although no difference in hypocotyl length was observed when compared with wild type. Alh1 plants were less sensitive to ethylene, as reflected by reduction of ACC-mediated inhibition of hypocotyl growth in the dark and delay in flowering and leaf senescence. Alh1 also had an altered response to auxin, whereas auxin levels in whole alh1 seedlings remained unaffected. In contrast to wild type, alh1 seedlings showed a limited hypocotyl elongation when treated with indole-3-acetic acid. Alh1 roots had a faster response to gravity. Furthermore, the hypocotyl elongation of alh1 and of ACC-treated wild type was reverted by auxin transport inhibitors. In addition, auxin up-regulated genes were ectopically expressed in hypocotyls upon ACC treatment, suggesting that the ethylene response is mediated by auxins. Together, these data indicate that alh1 is altered in the cross talk between ethylene and auxins, probably at the level of auxin transport.
Asunto(s)
Arabidopsis/genética , Etilenos/farmacología , Ácidos Indolacéticos/farmacología , Aminoácidos Cíclicos/metabolismo , Arabidopsis/efectos de los fármacos , Arabidopsis/metabolismo , Mapeo Cromosómico , Oscuridad , Etilenos/biosíntesis , Gravitropismo/fisiología , Sensación de Gravedad/fisiología , Hipocótilo/genética , Hipocótilo/crecimiento & desarrollo , Ácidos Indolacéticos/biosíntesis , Luz , Mutación , Fenotipo , Raíces de Plantas/genética , Raíces de Plantas/fisiología , Transducción de Señal/efectos de los fármacos , Transducción de Señal/genéticaRESUMEN
The plant hormone auxin regulates many aspects of plant growth and development. Although several auxin biosynthetic pathways have been proposed, none of these pathways has been precisely defined at the molecular level. Here we provide in planta evidence that the two Arabidopsis cytochrome P450s, CYP79B2 and CYP79B3, which convert tryptophan (Trp) to indole-3-acetaldoxime (IAOx) in vitro, are critical enzymes in auxin biosynthesis in vivo. IAOx is thus implicated as an important intermediate in auxin biosynthesis. Plants overexpressing CYP79B2 contain elevated levels of free auxin and display auxin overproduction phenotypes. Conversely, cyp79B2 cyp79B3 double mutants have reduced levels of IAA and show growth defects consistent with partial auxin deficiency. Together with previous work on YUCCA, a flavin monooxygenase also implicated in IAOx production, and nitrilases that convert indole-3-acetonitrile to auxin, this work provides a framework for further dissecting auxin biosynthetic pathways and their regulation.