RESUMEN
Brassinosteroids (BRs) are plant steroids that have growth-promoting capacities, which are partly enabled by an ability to induce biosynthesis of gibberellins (GAs), a second class of plant hormones. In addition, BRs can also activate GA catabolism; here we show that in Arabidopsis (Arabidopsis thaliana) the basic helix-loop-helix transcription factor CESTA (CES) and its homologues BRASSINOSTEROID-ENHANCED EXPRESSION (BEE) 1 and 3 contribute to this activity. CES and the BEEs are BR-regulated at the transcriptional and posttranslational level and participate in different physiological processes, including vegetative and reproduction development, shade avoidance, and cold stress responses. We show that CES/BEEs can induce the expression of the class III GA 2-oxidase GA2ox7 and that this activity is increased by BRs. In BR signaling - and CES/BEE-deficient mutants, GA2ox7 expression decreased, yielding reduced levels of GA110, a product of GA2ox7 activity. In plants that over-express CES, GA2ox7 expression is hyper-responsive to BR, GA110 levels are elevated and amounts of bioactive GA are reduced. We provide evidence that CES directly binds to the GA2ox7 promoter and is activated by BRs, but can also act by BR-independent means. Based on these results, we propose a model for CES activity in GA catabolism where CES can be recruited for GA2ox7 induction not only by BR, but also by other factors.
Asunto(s)
Proteínas de Arabidopsis , Arabidopsis , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/metabolismo , Brasinoesteroides/metabolismo , Regulación de la Expresión Génica de las Plantas , Oxigenasas de Función Mixta/genética , Oxigenasas de Función Mixta/metabolismo , Reguladores del Crecimiento de las Plantas/metabolismoRESUMEN
Bioactive gibberellins (GAs) are central regulators of plant growth and development, including seed development. GA homeostasis is achieved via complex biosynthetic and catabolic pathways, whose exact activities remain to be elucidated. Here, we isolated two cDNAs from mature or imbibed cucumber seeds with high sequence similarity to known GA 3-oxidases. We found that one enzyme (designated here CsGA3ox5) has GA 3-oxidation activity. However, the second enzyme (designated CsGA1ox/ds) performed multiple reactions, including 1ß-oxidation and 9,11-desaturation of GAs, but was lacking the 3-oxidation activity. CsGA1ox/ds overexpression in Arabidopsis plants resulted in severely dwarfed plants that could be rescued by the exogenous application of bioactive GA4, confirming that CsGA1ox/ds catabolizes GAs. Substitution of three amino acids in CsGA1ox/ds, Phe93, Pro106, and Ser202, with those typically conserved among GA 3-oxidases, Tyr93, Met106, and Thr202, respectively, conferred GA 3-oxidase activity to CsGA1ox/ds and thereby augmented its potential to form bioactive GAs in addition to catabolic products. Accordingly, overexpression of this amino acid-modified GA1ox/ds variant in Arabidopsis accelerated plant growth and development, indicating that this enzyme variant can produce bioactive GAs in planta Furthermore, a genetically modified GA3ox5 variant in which these three canonical GA 3-oxidase amino acids were changed to the ones present in CsGA1ox/ds was unable to convert GA9 to GA4, highlighting the importance of these three conserved amino acids for GA 3-oxidase activity.
Asunto(s)
Oxigenasas de Función Mixta/metabolismo , Proteínas de Plantas/metabolismo , Arabidopsis/crecimiento & desarrollo , Arabidopsis/metabolismo , Cucumis sativus/metabolismo , Giberelinas/metabolismo , Oxigenasas de Función Mixta/clasificación , Oxigenasas de Función Mixta/genética , Mutagénesis , Fenotipo , Filogenia , Proteínas de Plantas/clasificación , Proteínas de Plantas/genética , Plantas Modificadas Genéticamente/crecimiento & desarrollo , Plantas Modificadas Genéticamente/metabolismoRESUMEN
Many developmental processes in plants are regulated by GA hormones. GA homeostasis is achieved via complex biosynthetic and catabolic pathways. GA catabolic enzymes include GA 2-oxidases that are classified into three classes. Members of class III GA 2-oxidases typically act on GA precursors containing a C20-skeleton. Here, we identified two further members of this class of GA 2-oxidases, namely AtGA2ox9 and AtGA2ox10, in the Arabidopsis (Arabidopsis thaliana) genome. Both genes encode enzymes that have functional similarities to AtGA2ox7 and AtGA2ox8, which are class III GA 2-oxidases that 2ß-hydroxylate C20-GAs. Previously unknown for GA 2-oxidases, AtGA2ox9 performs 2α-hydroxylation of C19-GAs and harbors putative desaturating activity of C20-GAs. Additionally, AtGA2ox9 and AtGA2ox10 exhibit GA 20-oxidase activity. AtGA2ox9 oxidizes carbon-20 to form tricarboxylic acid C20-GAs, whereas AtGA2ox10 produces C19-GA9 AtGA2ox9 transcript levels increase after cold treatment and AtGA2ox10 is expressed mainly in the siliques of Arabidopsis plants. Atga2ox9 loss-of-function mutants are more sensitive to freezing temperatures, whereas Atga2ox10 loss-of-function mutants produce considerably more seeds per silique than wild-type plants. We conclude that in Arabidopsis, AtGA2ox9 contributes to freezing tolerance and AtGA2ox10 regulates seed production.
Asunto(s)
Arabidopsis/enzimología , Arabidopsis/metabolismo , Oxigenasas de Función Mixta/metabolismo , Arabidopsis/genética , Flores/genética , Flores/metabolismo , Congelación , Regulación de la Expresión Génica de las Plantas/genética , Regulación de la Expresión Génica de las Plantas/fisiología , Giberelinas/metabolismo , Oxigenasas de Función Mixta/genéticaRESUMEN
Gibberellin (GA) hormones regulate the development of plants and their responses to environmental signals. The final part of GA biosynthesis is catalyzed by multifunctional 2-oxoglutarate-dependent dioxygenases, which are encoded by multigene families. According to their enzymatic properties and physiological functions, GA-oxidases are classified as anabolic or catabolic enzymes. Together they allow complex regulation of the GA biosynthetic pathway, which adapts the specific hormonal needs of a plant during development and interaction with its environment. In this review, we combine recent advances in enzymatic characterization of the multifunctional GA-oxidases, in particular, from cucumber and Arabidopsis that have been most comprehensively investigated.
Asunto(s)
Dioxigenasas/metabolismo , Giberelinas/metabolismo , Reguladores del Crecimiento de las Plantas/biosíntesis , Proteínas de Plantas/metabolismo , Reguladores del Crecimiento de las Plantas/metabolismo , Plantas/enzimología , Plantas/metabolismoRESUMEN
Asexual and sexual reproduction occur jointly in many angiosperms. Stolons (elongated stems) are used for asexual reproduction in the crop species potato (Solanum tuberosum) and strawberry (Fragaria spp), where they produce tubers and clonal plants, respectively. In strawberry, stolon production is essential for vegetative propagation at the expense of fruit yield, but the underlying molecular mechanisms are unknown. Here, we show that the stolon deficiency trait of the runnerless (r) natural mutant in woodland diploid strawberry (Fragaria vesca) is due to a deletion in the active site of a gibberellin20-oxidase (GA20ox) gene, which is expressed primarily in the axillary meristem dome and primordia and in developing stolons. This mutation, which is found in all r mutants, goes back more than three centuries. When FveGA20ox4 is mutated, axillary meristems remain dormant or produce secondary shoots terminated by inflorescences, thus increasing the number of inflorescences in the plant. The application of bioactive gibberellin (GA) restored the runnering phenotype in the r mutant, indicating that GA biosynthesis in the axillary meristem is essential for inducing stolon differentiation. The possibility of regulating the runnering-flowering decision in strawberry via FveGA20ox4 provides a path for improving productivity in strawberry by controlling the trade-off between sexual reproduction and vegetative propagation.
Asunto(s)
Diploidia , Flores/fisiología , Fragaria/enzimología , Fragaria/genética , Oxigenasas de Función Mixta/metabolismo , Arabidopsis/genética , Biocatálisis , Segregación Cromosómica/genética , Cruzamientos Genéticos , Eliminación de Gen , Regulación de la Expresión Génica de las Plantas , Sitios Genéticos , Giberelinas/metabolismo , Homocigoto , Meristema/fisiología , Fenotipo , Plantas Modificadas Genéticamente , ARN Mensajero/genética , ARN Mensajero/metabolismoRESUMEN
Gibberellins (GAs) are hormones that control many aspects of plant development, including flowering. It is well known that stamen is the source of GAs that regulate male and bisexual flower development. However, little is known about the role of GAs in female flower development. In cucumber, high levels of GA precursors are present in ovaries and high levels of bioactive GA4 are identified in sepals/petals, reflecting the expression of GA 20-oxidase and 3-oxidase in these organs, respectively. Here, we show that the biologically inactive precursor GA9 moves from ovaries to sepal/petal tissues where it is converted to the bioactive GA4 necessary for female flower development. Transient expression of a catabolic GA 2-oxidase from pumpkin in cucumber ovaries decreases GA9 and GA4 levels and arrests the development of female flowers, and this can be restored by application of GA9 to petals thus confirming its function. Given that bioactive GAs can promote sex reversion of female flowers, movement of biologically inactive precursors, instead of the hormone itself, might help to maintain floral organ identity, ensuring fruit and seed production.
Asunto(s)
Cucumis sativus/crecimiento & desarrollo , Flores/crecimiento & desarrollo , Flores/metabolismo , Giberelinas/metabolismo , Oxigenasas de Función Mixta/metabolismo , Cucurbita/enzimología , Cucurbita/genética , Giberelinas/genética , Desarrollo de la Planta/genética , Desarrollo de la Planta/fisiología , Plantas Modificadas Genéticamente/genética , Transducción de SeñalRESUMEN
Flowering in plants is a dynamic and synchronized process where various cues including age, day length, temperature and endogenous hormones fine-tune the timing of flowering for reproductive success. Arabidopsis thaliana is a facultative long day (LD) plant where LD photoperiod promotes flowering. Arabidopsis still flowers under short-day (SD) conditions, albeit much later than in LD conditions. Although factors regulating the inductive LD pathway have been extensively investigated, the non-inductive SD pathway is much less understood. Here, we identified a key basic helix-loop-helix transcription factor called NFL (NO FLOWERING IN SHORT DAY) that is essential to induce flowering specifically under SD conditions in Arabidopsis. nfl mutants do not flower under SD conditions, but flower similar to the wild type under LD conditions. The no-flowering phenotype in SD is rescued either by exogenous application of gibberellin (GA) or by introducing della quadruple mutants in the nfl background, suggesting that NFL acts upstream of GA to promote flowering. NFL is expressed at the meristematic regions and NFL is localized to the nucleus. Quantitative RT-PCR assays using apical tissues showed that GA biosynthetic genes are downregulated and the GA catabolic and receptor genes are upregulated in the nfl mutant compared with the wild type, consistent with the perturbation of the endogenous GA biosynthetic and catabolic intermediates in the mutant. Taken together, these data suggest that NFL is a key transcription factor necessary for promotion of flowering under non-inductive SD conditions through the GA signaling pathway.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/fisiología , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/metabolismo , Flores/fisiología , Fotoperiodo , Arabidopsis/efectos de los fármacos , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/genética , Núcleo Celular/efectos de los fármacos , Núcleo Celular/metabolismo , Frío , Epistasis Genética/efectos de los fármacos , Flores/efectos de los fármacos , Regulación del Desarrollo de la Expresión Génica/efectos de los fármacos , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Prueba de Complementación Genética , Giberelinas/biosíntesis , Giberelinas/metabolismo , Giberelinas/farmacología , Meristema/efectos de los fármacos , Meristema/metabolismo , Modelos Biológicos , Mutación/genética , Especificidad de Órganos/efectos de los fármacos , Especificidad de Órganos/genética , Fenotipo , Transporte de Proteínas/efectos de los fármacos , Reacción en Cadena en Tiempo Real de la Polimerasa , Fracciones Subcelulares/efectos de los fármacos , Fracciones Subcelulares/metabolismo , Factores de TiempoRESUMEN
Plant growth and development are highly regulated processes that are coordinated by hormones including the brassinosteroids (BRs), a group of steroids with structural similarity to steroid hormones of mammals. Although it is well understood how BRs are produced and how their signals are transduced, BR targets, which directly confer the hormone's growth-promoting effects, have remained largely elusive. Here, we show that BRs regulate the biosynthesis of gibberellins (GAs), another class of growth-promoting hormones, in Arabidopsis thaliana. We reveal that Arabidopsis mutants deficient in BR signaling are severely impaired in the production of bioactive GA, which is correlated with defective GA biosynthetic gene expression. Expression of the key GA biosynthesis gene GA20ox1 in the BR signaling mutant bri1-301 rescues many of its developmental defects. We provide evidence that supports a model in which the BR-regulated transcription factor BES1 binds to a regulatory element in promoters of GA biosynthesis genes in a BR-induced manner to control their expression. In summary, our study underscores a role of BRs as master regulators of GA biosynthesis and shows that this function is of major relevance for the growth and development of vascular plants.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Brasinoesteroides/metabolismo , Giberelinas/biosíntesis , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Proteínas de Arabidopsis/genética , Proteínas de Unión al ADN , Flores/genética , Flores/crecimiento & desarrollo , Flores/metabolismo , Regulación del Desarrollo de la Expresión Génica/efectos de los fármacos , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Giberelinas/farmacología , Hipocótilo/genética , Hipocótilo/crecimiento & desarrollo , Hipocótilo/metabolismo , Immunoblotting , Oxigenasas de Función Mixta/genética , Oxigenasas de Función Mixta/metabolismo , Mutación , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Reguladores del Crecimiento de las Plantas/metabolismo , Reguladores del Crecimiento de las Plantas/farmacología , Plantas Modificadas Genéticamente , Regiones Promotoras Genéticas/genética , Unión Proteica , Proteínas Quinasas/genética , Proteínas Quinasas/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Transducción de Señal/genéticaRESUMEN
Ent-kaurenoic acid oxidase (KAO), a class of cytochrome P450 monooxygenases of the subfamily CYP88A, catalyzes the conversion of ent-kaurenoic acid (KA) to gibberellin (GA) GA12 , the precursor of all GAs, thereby playing an important role in determining GA concentration in plants. Past work has demonstrated the importance of KAO activity for growth in various plant species. In Arabidopsis, this enzyme is encoded by two genes designated KAO1 and KAO2. In this study, we used various approaches to determine the physiological roles of KAO1 and KAO2 throughout plant development. Analysis of gene expression pattern reveals that both genes are mainly expressed in germinating seeds and young developing organs, thus suggesting functional redundancy. Consistent with this, kao1 and kao2 single mutants are indistinguishable from wild-type plants. By contrast, the kao1 kao2 double mutant exhibits typical non-germinating GA-dwarf phenotypes, similar to those observed in the severely GA-deficient ga1-3 mutant. Phenotypic characterization and quantitative analysis of endogenous GA contents of single and double kao mutants further confirm an overlapping role of KAO1 and KAO2 throughout Arabidopsis development.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/enzimología , Regulación de la Expresión Génica de las Plantas , Giberelinas/metabolismo , Oxigenasas de Función Mixta/metabolismo , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Proteínas de Arabidopsis/genética , Regulación Enzimológica de la Expresión Génica , Germinación , Giberelinas/análisis , Oxigenasas de Función Mixta/genética , Mutación , FenotipoRESUMEN
Hormones play pivotal roles in regulating plant development, growth, and stress responses, and cross-talk among different hormones fine-tunes various aspects of plant physiology. Jasmonic acid (JA) is important for plant defense against herbivores and necrotic fungi and also regulates flower development; in addition, Arabidopsis mutants over-producing JA usually have stunted stems and wound-induced jasmonates suppress Arabidopsis growth, suggesting that JA is also involved in stem elongation. Gibberellins (GAs) promote stem and leaf growth and modulate seed germination, flowering time, and the development of flowers, fruits, and seeds. However, little is known about the interaction between the JA and GA pathways. Two calcium-dependent protein kinases, CDPK4 and CDPK5, are important suppressors of JA accumulation in a wild tobacco species, Nicotiana attenuata. The stems of N. attenuata silenced in CDPK4 and CDPK5 (irCDPK4/5 plants) had dramatically increased levels of JA and exhibited stunted elongation and had very high contents of secondary metabolites. Genetic analysis indicated that the high JA levels in irCDPK4/5 stems accounted for the suppressed stem elongation and the accumulation of secondary metabolites. Supplementation of GA(3) to irCDPK4/5 plants largely restored normal stem growth to wild-type levels. Measures of GA levels indicated that over-accumulation of JA in irCDPK4/5 stems inhibited the biosynthesis of GAs. Finally, we show that JA antagonizes GA biosynthesis by strongly inhibiting the transcript accumulation of GA20ox and possibly GA13ox, the key genes in GA production, demonstrating that high JA levels antagonize GA biosynthesis in stems.
Asunto(s)
Acetatos/farmacología , Ciclopentanos/metabolismo , Ciclopentanos/farmacología , Giberelinas/biosíntesis , Nicotiana/efectos de los fármacos , Oxilipinas/metabolismo , Oxilipinas/farmacología , Tallos de la Planta/crecimiento & desarrollo , Anatomía Transversal , Regulación Enzimológica de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Silenciador del Gen , Genes de Plantas , Prueba de Complementación Genética , Giberelinas/antagonistas & inhibidores , Giberelinas/farmacología , Reguladores del Crecimiento de las Plantas/metabolismo , Reguladores del Crecimiento de las Plantas/farmacología , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Tallos de la Planta/efectos de los fármacos , Tallos de la Planta/enzimología , Polinización , Regiones Promotoras Genéticas , Proteínas Quinasas/genética , Proteínas Quinasas/metabolismo , Nicotiana/enzimología , Nicotiana/genética , Nicotiana/crecimiento & desarrollo , Transcripción GenéticaRESUMEN
Transplastomic tobacco (Nicotiana tabacum) plants expressing ß-glucosidase (Bgl-1) show modified development. They flower 1 month earlier with an increase in biomass (1.9-fold), height (1.5-fold), and leaf area (1.6-fold) than untransformed plants. Trichome density on the upper and lower leaf surfaces of BGL-1 plants increase by 10- and 7-fold, respectively, harboring 5-fold more glandular trichomes (as determined by rhodamine B staining), suggesting that BGL-1 lines produce more sugar esters than control plants. Gibberellin (GA) levels were investigated because it is a known regulator of flowering time, plant height, and trichome development. Both GA(1) and GA(4) levels are 2-fold higher in BGL-1 leaves than in untransformed plants but do not increase in other organs. In addition, elevated levels of other plant hormones, including zeatin and indole-3-acetic acid, are observed in BGL-1 lines. Protoplasts from BGL-1 lines divide and form calli without exogenous hormones. Cell division in protoplasts is enhanced 7-fold in the presence of exogenously applied zeatin-O-glucoside conjugate, indicating the release of active hormones from their conjugates. Whitefly (Bemisia tabaci) and aphid (Myzus persicae) populations in control plants are 18 and 15 times higher than in transplastomic lines, respectively. Lethal dose to kill 50% of the test population values of 26.3 and 39.2 µg per whitefly and 23.1 and 35.2 µg per aphid for BGL-1 and untransformed control exudates, respectively, confirm the enhanced toxicity of transplastomic exudates. These data indicate that increase in sugar ester levels in BGL-1 lines might function as an effective biopesticide. This study provides a novel strategy for designing plants for enhanced biomass production and insect control by releasing plant hormones or sugar esters from their conjugates stored within their chloroplasts.
Asunto(s)
Áfidos/fisiología , Biomasa , Cloroplastos/enzimología , Nicotiana/parasitología , Reguladores del Crecimiento de las Plantas/metabolismo , Sacarosa/metabolismo , beta-Glucosidasa/metabolismo , Animales , Células Cultivadas , Cloroplastos/genética , Cloroplastos/ultraestructura , Segregación Cromosómica/genética , Ésteres/metabolismo , Vectores Genéticos/genética , Mutagénesis Insercional/genética , Fenotipo , Hojas de la Planta/enzimología , Hojas de la Planta/parasitología , Hojas de la Planta/ultraestructura , Proteínas de Plantas/metabolismo , Plantas Modificadas Genéticamente , Protoplastos/citología , Protoplastos/metabolismo , Nicotiana/enzimología , Nicotiana/genética , Nicotiana/ultraestructura , Transformación Genética , Transgenes/genética , Trichoderma/enzimologíaRESUMEN
Gibberellin (GA) signalling during pumpkin male flower development is highly regulated, including biosynthetic, perception, and transduction pathways. GA 20-oxidases, 3-oxidases, and 2-oxidases catalyse the final part of GA synthesis. Additionally, 7-oxidase initiates this part of the pathway in some cucurbits including Cucurbita maxima L. (pumpkin). Expression patterns for these GA-oxidase-encoding genes were examined by competitive reverse transcription-PCR (RT-PCR) and endogenous GA levels were determined during pumpkin male flower development. In young flowers, GA20ox3 transcript levels are high in stamens, followed by high levels of the GA precursor GA(9). Later, just before flower opening, transcript levels for GA3ox3 and GA3ox4 increase in the hypanthium and stamens, respectively. In the stamen, following GA3ox4 expression, bioactive GA(4) levels rise dramatically. Accordingly, catabolic GA2ox2 and GA2ox3 transcript levels are low in developing flowers, and increase in mature flowers. Putative GA receptor GID1b and DELLA repressor GAIPb transcript levels do not change in developing flowers, but increase sharply in mature flowers. Emasculation arrests floral development completely and leads to abscission of premature flowers. Application of GA(4) (but not of its precursors GA(12)-aldehyde or GA(9)) restores normal growth of emasculated flowers. These results indicate that de novo GA(4) synthesis in the stamen is under control of GA20ox3 and GA3ox4 genes just before the rapid flower growth phase. Stamen-derived bioactive GA is essential and sufficient for male flower development, including the petal and the pedicel growth.
Asunto(s)
Cucurbita/metabolismo , Flores/crecimiento & desarrollo , Giberelinas/biosíntesis , Cucurbita/enzimología , Cucurbita/genética , Cucurbita/crecimiento & desarrollo , Flores/enzimología , Flores/genética , Flores/metabolismo , Regulación del Desarrollo de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Datos de Secuencia Molecular , Oxidorreductasas/genética , Oxidorreductasas/metabolismo , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Especificidad de la EspecieRESUMEN
Brassinosteroids (BRs) are required for various aspects of plant growth and development, but also participate in stress responses. The hormones convey their activity through transcriptional regulation and posttranslational modification of transcription factors and one class are basic helix-loop-helix (bHLH) proteins of the BR Enhanced Expression (BEE) subfamily, which in Arabidopsis thaliana include BEE1-3 and CESTA (CES). CES and the BEEs promote the expression of different BR-responsive genes, including genes encoding gibberellin (GA) biosynthetic and catabolizing enzymes, as well as cold-responsive genes. Interestingly, in terms of an application, CES could promote both fruit growth and cold stress tolerance when over-expressed in A. thaliana and here it was investigated, if this function is conserved in the fruit crop Solanum lycopersicum (cultivated tomato). Based on amino acid sequence similarity and the presence of regulatory motifs, a CES orthologue of S. lycopersicum, SlCES, was identified and the effects of its over-expression were analysed in tomato. This showed that SlCES, like AtCES, was re-localized to nuclear bodies in response to BR signaling activation and that it effected GA homeostasis, with related phenotypes, when over-expressed. In addition, over-expression lines showed an increased chilling tolerance and had altered fruit characteristics. The possibilities and potential limitations of a gain of SlCES function as a breeding strategy for tomato are discussed.
RESUMEN
The consequences of altered abscisic acid (ABA) sensitivity in gray poplar (Populus x canescens [Ait.] Sm.) development were examined by ectopic expression of the Arabidopsis (Arabidopsis thaliana) mutant abi1 (for abscisic acid insensitive1) gene. The expression resulted in an ABA-insensitive phenotype revealed by a strong tendency of abi1 poplars to wilt, impaired responsiveness of their stomata to ABA, and an ABA-resistant bud outgrowth. These plants therefore required cultivation under very humid conditions to prevent drought stress symptoms. Morphological alterations became evident when comparing abi1 poplars with poplars expressing Arabidopsis nonmutant ABI1 or wild-type plants. abi1 poplars showed increased stomatal size, enhanced shoot growth, and retarded leaf and root development. The increased stomatal size and its reversion to the size of wild-type plants by exogenous ABA indicate a role for ABA in regulating stomatal development. Enhanced shoot growth and retarded leaf and root development support the hypothesis that ABA acts independently from drought stress as a negative regulator of growth in shoots and as a positive regulator of growth in leaves and roots. In shoots, we observed an interaction of ABA with ethylene: abi1 poplars exhibited elevated ethylene production, and the ethylene perception inhibitor Ag(+) antagonized the enhanced shoot growth. Thus, we provide evidence that ABA acts as negative regulator of shoot growth in nonstressed poplars by restricting ethylene production. Furthermore, we show that ABA has a role in regulating shoot branching by inhibiting lateral bud outgrowth.
Asunto(s)
Ácido Abscísico/farmacología , Proteínas de Arabidopsis/genética , Arabidopsis/genética , Mutación/genética , Fosfoproteínas Fosfatasas/genética , Estomas de Plantas/crecimiento & desarrollo , Populus/crecimiento & desarrollo , Populus/genética , Arabidopsis/efectos de los fármacos , Proteínas de Arabidopsis/metabolismo , Medios de Cultivo/farmacología , Etilenos/metabolismo , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Genes de Plantas/genética , Fosfoproteínas Fosfatasas/metabolismo , Brotes de la Planta/efectos de los fármacos , Brotes de la Planta/crecimiento & desarrollo , Estomas de Plantas/efectos de los fármacos , Plantas Modificadas Genéticamente , Populus/efectos de los fármacos , Transformación Genética/efectos de los fármacos , Agua/fisiologíaRESUMEN
Plants are able to sense a rise in temperature of several degrees, and appropriately adapt their metabolic and growth processes. To this end, plants produce various signalling molecules that act throughout the plant body. Here, we report that root-derived GA12, a precursor of the bioactive gibberellins, mediates thermo-responsive shoot growth in Arabidopsis. Our data suggest that root-to-shoot translocation of GA12 enables a flexible growth response to ambient temperature changes.
Asunto(s)
Arabidopsis/metabolismo , Giberelinas/metabolismo , Reguladores del Crecimiento de las Plantas/metabolismo , Raíces de Plantas/metabolismo , Brotes de la Planta/crecimiento & desarrollo , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Regulación de la Expresión Génica de las Plantas , Raíces de Plantas/genética , Raíces de Plantas/crecimiento & desarrollo , Brotes de la Planta/genética , Brotes de la Planta/metabolismo , TemperaturaRESUMEN
Bahiagrass (Paspalum notatum Flugge) is a prime candidate for molecular improvement of turf quality. Its persistence and low input characteristics made it the dominant utility turfgrass along highways in the south-eastern USA. However, the comparatively poor turf quality due to reduced turf density and prolific production of unsightly inflorescences currently limits the widespread use of bahiagrass as residential turf. Alteration of endogenous gibberellin (GA) levels by application of growth regulators or transgenic strategies has modified plant architecture in several crops. GA catabolizing AtGA2ox1 was subcloned under the control of the constitutive maize ubiquitin promoter and Nos 3'UTR. A minimal AtGA2ox1 expression cassette lacking vector backbone sequences was stably introduced into apomictic bahiagrass by biolistic gene transfer as confirmed by Southern blot analysis. Expression of AtGA2ox1 in bahiagrass as indicated by reverse transcription-polymerase chain reaction and Northern blot analysis resulted in a significant reduction of endogenous bioactive GA(1) levels compared to wild type. Interestingly, transgenic plants displayed an increased number of vegetative tillers which correlated with the level of AtGA2ox1 expression and enhanced turf density under field conditions. This indicates that GAs contribute to signalling the outgrowth of axillary buds in this perennial grass. Transgenic plants also showed decreased stem length and delayed flowering under controlled environment and field conditions. Consequently, turf quality following weekly mowing was improved in transgenic bahiagrass. Transgene expression and phenotype were transmitted to seed progeny. Argentine bahiagrass produces seeds asexually by apomixis, which reduces the risk of unintended transgene dispersal by pollen and results in uniform progeny.
Asunto(s)
Arabidopsis/genética , Giberelinas/metabolismo , Oxigenasas de Función Mixta/metabolismo , Paspalum/metabolismo , Plantas Modificadas Genéticamente/metabolismo , Expresión Génica , Oxigenasas de Función Mixta/genética , Paspalum/genética , Paspalum/crecimiento & desarrollo , Plantas Modificadas Genéticamente/crecimiento & desarrollo , Transformación GenéticaRESUMEN
Touch can lead to a reduction in plant growth and a delay in flowering time. Touch-induced changes in plant morphology, termed thigmomorphogenesis, have been shown to depend on the phytohormone jasmonate(1). However, touch-induced phenotypes are also reminiscent of plants deficient in the phytohormone gibberellin(2). Here we assess the effect of touch on wild-type Arabidopsis plants and mutants deficient in gibberellin signalling. We show that touch leads to stunted growth and delayed flowering in wild-type plants, as expected. These touch-induced changes in morphology are accompanied by a reduction in gibberellin levels, and can be reversed through the application of a bioactive form of gibberellin. We further show that touch induces the expression of AtGA2ox7, which encodes an enzyme involved in gibberellin catabolism. Arabidopsis ga2ox7 loss-of-function mutants do not respond to touch, suggesting that this gene is a key regulator of thigmomorphogenesis. We conclude that touch-induced changes in Arabidopsis morphology depend on gibberellin catabolism. Given that AtGA2ox7 helps to confer resistance to salt stress, and that touch can increase plant resistance to pathogens, we suggest that gibberellin catabolism could be targeted to improve plant resistance to abiotic and biotic stress.
RESUMEN
Brassinosteroids (BRs) are plant steroid hormones with structural similarity to mammalian sex steroids and ecdysteroids from insects. The BRs are synthesized from sterols and are essential regulators of cell division, cell elongation and cell differentiation. In this work we show that voriconazole, an antifungal therapeutic drug used in human and veterinary medicine, severely impairs plant growth by inhibiting sterol-14α-demethylation and thereby interfering with BR production. The plant growth regulatory properties of voriconazole and related triazoles were identified in a screen for compounds with the ability to alter BR homeostasis. Voriconazole suppressed growth of the model plant Arabidopsis thaliana and of a wide range of both monocotyledonous and dicotyledonous plants. We uncover that voriconazole toxicity in plants is a result of a deficiency in BRs that stems from an inhibition of the cytochrome P450 CYP51, which catalyzes a step of BR-dependent sterol biosynthesis. Interestingly, we found that the woodland strawberry Fragaria vesca, a member of the Rosaceae, is naturally voriconazole resistant and that this resistance is conferred by the specific CYP51 variant of F. vesca. The potential of voriconazole as a novel tool for plant research is discussed.
Asunto(s)
Vías Biosintéticas/efectos de los fármacos , Brasinoesteroides/metabolismo , Resistencia a Medicamentos/genética , Variación Genética , Pirimidinas/farmacología , Esterol 14-Desmetilasa/genética , Esteroles/biosíntesis , Triazoles/farmacología , Arabidopsis/efectos de los fármacos , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Fragaria/efectos de los fármacos , Fragaria/genética , Fragaria/crecimiento & desarrollo , Fragaria/metabolismo , Metaboloma , Fenotipo , Pirimidinas/química , Triazoles/química , VoriconazolRESUMEN
Cucurbits have been used widely to elucidate gibberellin (GA) biosynthesis. With the recent availability of the genome sequence for the economically important cucurbit Cucumis sativus, sequence data became available for all genes potentially involved in GA biosynthesis for this species. Sixteen cDNAs were cloned from root and shoot of 3-d to 7-d old seedlings and from mature seeds of C. sativus. Two cDNAs code for GA 7-oxidases (CsGA7ox1, and -2), five for GA 20-oxidases (CsGA20ox1, -2, -3, -4, and -5), four for GA 3-oxidases (CsGA3ox1, -2, -3, and -4), and another five for GA 2-oxidases (CsGA2ox1, -2, -3, -4, and -5). Their enzymatic activities were investigated by heterologous expression of the cDNAs in Escherichia coli and incubation of the cell lysates with (14)C-labelled, D2-labelled, or unlabelled GA-substrates. The two GA 7-oxidases converted GA12-aldehyde to GA12 efficiently. CsGA7ox1 converted GA12 to GA14, to 15α-hydroxyGA12, and further to 15α-hydroxyGA14. CsGA7ox2 converted GA12 to its 12α-hydroxylated analogue GA111. All five GA 20-oxidases converted GA12 to GA9 as a major product, and to GA25 as a minor product. The four GA 3-oxidases oxidized the C19-GA GA9 to GA4 as the only product. In addition, three of them (CsGA3ox2, -3, and -4) converted the C20-GA GA12 to GA14. The GA 2-oxidases CsGA2ox1, -2, -3, and -4 oxidized the C19-GAs GA9 and GA4 to GA34 and GA51, respectively. CsGA2ox2, -3, and -4 converted GA51 and GA34 further to respective GA-catabolites. In addition to C19-GAs, CsGA2ox4 also converted the C20-GA GA12 to GA110. In contrast, CsGA2ox5 oxidized only the C20 GA12 to GA110 as the sole product. As shown for CsGA20ox1 and CsGA3ox1, similar reactions were catalysed with 13-hydroxlyated GAs as substrates. It is likely that these enzymes are also responsible for the biosynthesis of 13-hydroxylated GAs in vivo that occur at low levels in cucumber.