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At least 325 records · Page 18Linked to original sources
PubMed1994

Cloning of two gibberellin-regulated cDNAs from Arabidopsis thaliana by subtractive hybridization: expression of the tonoplast water channel, gamma-TIP, is increased by GA3.

The Arabidopsis ga1 mutant has very low levels of endogenous, active gibberellins and thus has an extreme dwarf phenotype; application of GA3 induces stem elongation and flower development. To test the hypothesis that GA action in this system involves changes in gene expression, we have cloned mRNAs whose abundance changes following GA application. A subtraction cloning scheme for the isolation of differentially regulated cDNAs was established, involving hybridization of single-stranded cDNA to biotinylated mRNA. cDNA populations enriched up to 150-fold in GA-regulated sequences were produced and cDNA libraries generated. Screening of these libraries has isolated two clones that identify mRNAs of ca. 1100 and 750 bases whose abundance is markedly increased 24 h after GA application. One of these clones encodes the vegetative form of the Arabidopsis tonoplast intrinsic protein (gamma-TIP), a water channel protein, the expression of which has recently been shown to be correlated with regions of cell expansion. The second clone is expressed only in the inflorescence and encodes a proline- and glycine-rich protein that may be a cell wall component.

Arabidopsis↗
PubMed1995

Endogenous gibberellin levels influence in-vitro shoot regeneration in Arabidopsis thaliana (L.) Heynh.

The regeneration of shoot buds from callus cells in vitro is an important technique in modern plant genetic manipulation. Whilst it is clear that genetic factors play a major role in determining the ability of callus cells to become organized into regenerating shoot buds, the precise nature of these factors remains unknown. Here we show that callus derived from mutants of Arabidopsis thaliana which have reduced levels of endogenous bioactive gibberellins (GAs), or reduced responsivity to GAs, regenerates shoot buds more readily than does callus derived from wild-type controls. In addition, exogenous GA reduces, and exogenous paclobutrazol (a GA-bio-synthesis inhibitor) increases, the frequency of shoot bud regeneration from wild-type callus. These results show that GA levels play a role in regulating shoot bud regeneration from callus, and suggest that variation in endogenous GA levels or responsivity may account for a major component of the genetic variation in shoot bud regeneration frequency described in other species.

Arabidopsis↗
PubMed1995

Isolation and preliminary characterization of gas1-1, a mutation causing partial suppression of the phenotype conferred by the gibberellin-insensitive (gai) mutation in Arabidopsis thaliana (L.) Heyhn.

The semi-dominant gai mutation of arabidopsis confers a dark-green dwarf phenotype resembling that of gibberellin (GA)-deficient mutants. In contrast to GA-deficient mutants, gai mutants do not respond to GA treatments and accumulate higher levels of bioactive GAs than are found in wild-type controls. The gai mutation thus alters the responses of plant cells to GA, indicating that the GAI (wild-type) gene product is involved in GA reception and/or signal transduction. Here we describe the isolation and preliminary characterization of a mutation, gas1-1, which is not linked to gai and which partially suppresses the effect of the gai mutation. Double mutant, gai gas1-1, homozygotes are less severely dwarfed and lighter green than gai GAS1 controls. However, comparisons of the effects of treatments with exogenous GA demonstrate that gas1-1 does not increase the GA responsiveness of the gai mutant. Thus the gas1-1 mutation appears to reduce the GA-dependency of plant growth, and identifies a gene (GAS1) whose product is a candidate GA signal-transduction component.

Arabidopsis↗
PubMed1996

Feed-back regulation of gibberellin biosynthesis and gene expression in Pisum sativum L.

Treatment of tall and dwarf (3 beta-hydroxylase impaired) genotypes of pea (Pisum sativum L.) with the synthetic, highly active gibberellin (GA), 2,2-dimethyl GA4, reduced the shoot contents of C19-GAs, including GA1, and increased the concentration of the C20-GA, GA19. In shoots of the slender (la crys) mutant, the content of C19-GAs was lower and GA19 content was higher than in those of the tall line. Metabolism of GA19 and GA20 in leaves of a severe (na) GA-deficient dwarf mutant was reduced by GA treatment. The results suggest feed-back regulation of the 20-oxidation and 3 beta-hydroxylation reactions. Feed-back regulation of GA 20-oxidation was studied further using a cloned GA 20-oxidase cDNA from pea. The cDNA, Ps074, was isolated using polymerase chain reaction with degenerate oligonucleotide primers based on pumpkin and Arabidopsis 20-oxidase sequences. After expression of this cDNA clone in Escherichia coli, the product oxidized GA12 to GA15, GA24 and the C19-GA, GA9, which was the major product. The 13-hydroxylated substrate GA53 was similarly oxidized, but less effectively than GA12, giving mainly GA44 with low yields of GA19 and GA20. Ps074 hybridized to polyadenylated RNA from expanding shoots of pea. Amounts of this transcript were less in the slender genotype than in the tall line and were reduced in GA-deficient genotypes by treatment with GA3, suggesting that there is feed-back regulation of GA 20-oxidase gene expression.

Amino Acid Sequence↗
PubMed2004

Isolation of gibberellin metabolic pathway genes from barley and comparative mapping in barley, wheat and rice.

Gene sequences encoding gibberellin (GA) biosynthetic and catabolic enzymes were isolated from "Himalaya" barley. These genes account for most of the enzymes required for the core pathway of GA biosynthesis as well as for the first major catabolic enzyme. By means of DNA gel blot analysis, we mapped coding sequences to chromosome arms in barley and wheat using barley-wheat chromosome addition lines, nulli-tetrasomic substitution and ditelosomic lines of wheat. These same sequences were used to identify closely related sequences from rice, which were mapped in silico, thereby allowing their syntenic relationship with map locations in barley and wheat to be investigated. Determination of the chromosome arm locations for GA metabolic genes provides a framework for future studies investigating possible identity between GA metabolic genes and dwarfing genes in barley and wheat.

Amino Acid Sequence↗
PubMed2004

Gibberellin biosynthesis in fungi: genes, enzymes, evolution, and impact on biotechnology.

Gibberellins (GAs) constitute a large family of tetracyclic diterpenoid carboxylic acids, some members of which function as growth hormones in higher plants. As well as being phytohormones, GAs are also present in some fungi and bacteria. In recent years, GA biosynthetic genes from Fusarium fujikuroi and Arabidopsis thaliana have been cloned and well characterised. Although higher plants and the fungus both produce structurally identical GAs, there are important differences indicating that GA biosynthetic pathways have evolved independently in higher plants and fungi. The fact that horizontal gene transfer of GA genes from the plant to the fungus can be excluded, and that GA genes are obviously missing in closely related Fusarium species, raises the question of the origin of fungal GA biosynthetic genes. Besides characterisation of F. fujikuroi GA pathway genes, much progress has been made in the molecular analysis of regulatory mechanisms, especially the nitrogen metabolite repression controlling fungal GA biosynthesis. Basic research in this field has been shown to have an impact on biotechnology. Cloning of genes, construction of knock-out mutants, gene amplification, and regulation studies at the molecular level are powerful tools for improvement of production strains. Besides increased yields of the final product, GA3, it is now possible to produce intermediates of the GA biosynthetic pathway, such as ent-kaurene, ent-kaurenoic acid, and GA14, in high amounts using different knock-out mutants. This review concentrates mainly on the fungal biosynthetic pathway, the genes and enzymes involved, the regulation network, the biotechnological relevance of recent studies, and on evolutionary aspects of GA biosynthetic genes.

Biotechnology↗
PubMed1999

Biosynthesis of gibberellins in Gibberella fujikuroi: biomolecular aspects.

Gibberellins (GAs) are a large family of isoprenoid plant hormones hormones, some of which are bioactive growth regulators, controlling seed germination, stem elongation, and flowering. The rice pathogen Gibberella fujikuroi (mating population C) is able to produce large amounts of GAs, especially the bioactive compounds gibberellic acid (GA3) and its precursors, GA4 and GA7. The main steps of the biosynthetic pathway have long been established from the identification of intermediates in wild-type G. fujikuroi and mutant strains. However, the genetics of the fungus have been rather under-developed, and molecular genetic studies of the GA pathway started just recently. The progress in researching GA biosynthesis in the last 2 years resulted primarily from development of the molecular tools, e.g. transformation systems for the fungus, and cloning the genes encoding GA biosynthesis enzymes, such as the bifunctional ent-copalyl diphosphate/kaurene synthase and several cytochrome P450 monooxygenases. The availability of these genes opened new horizons both for detailed study of the pathway and the regulation mechanisms at the molecular level, and for modern strain improvement programs. This review gives a short overview of the well-known physiological and biochemical studies and concentrates mainly on the new molecular genetic data from GA research, including new information on the regulation of GA biosynthesis.

Aerobiosis↗
PubMed2002

Inhibition of growth of microcultured Hancornia speciosa shoots by 3beta-hydroxylated gibberellins and one of their C-3 deoxy precursors.

Gibberellins (GAs) A(1), A(3), A(4) and A(7), all 3beta-hydroxylated, growth-active GAs, significantly inhibited shoot elongation and the formation of nodes in in vitro-grown Hancornia speciosa, as did GA(20), a 3-deoxy precursor of GA(1). Ancymidol, an early-stage inhibitor of GA biosynthesis, significantly retarded shoot elongation without affecting the formation of nodes. Co-application of ancymidol and GA(1 )did not overcome the ancymidol-induced growth retardation. Trinexapac-ethyl, which can inhibit 3beta-hydroxylation (GA activation) and 2beta-hydroxylation (GA inactivation), gave no significant response on either shoot elongation or node formation, while two isomers of 16,17-dihydro GA(5), also inhibitors of GA 3beta-hydroxylation, significantly inhibited both shoot growth and the formation of nodes. These unusual results may indicate a unique metabolism for GAs in microcultured shoots of H. speciosa.

Apocynaceae↗
PubMed2006

Gibberellins and antheridiogen on sex in Blechnum spicant L.

The role of gibberellins (GAs) in determining sex in the gametophyte of the fern Blechnum spicant L. was studied through (a) the effect of exogenous GA(4+7) and GA3 (b) quantitation of the endogenous levels of GA1, GA3, GA4, GA7, GA9, and GA20 in male and female gametophytes, and (c) the effect of flurprimidol, a GAs biosynthesis inhibitor of the steps of oxidation of ent-kaureno to ent-kaurenoic acid. Our results show that GA(4+7) had a slight effect of inducing either male or female sexual organs, antheridia and archegonia, respectively. The endogenous GAs content was not significantly different between sexes, but the GA4, GA7, and GA20 levels were raised above those of the other GAs in both sexes. Neither antheridiogen biosynthesis nor antheridia formation was inhibited by flurprimidol. Gametophytes regenerated from homogenized mature gametophytes (HG) show a different physiological behavior than spore-derived gametophytes. In the first case, gametophytes are males and synthesize antheridiogen before they attain maturity, in contrast to what occurs in spore-derived gametophytes which are females and synthesize antheridiogen when mature.

Abscisic Acid↗
PubMed2002

Molecular analysis of the barley ( Hordeum vulgare L.) gene encoding the protein kinase PKABA1 capable of suppressing gibberellin action in aleurone layers.

Abscisic acid (ABA) induces the expression of a gene encoding a protein kinase, PKABA1, in wheat ( Triticum aestivum L.). Transient expression of the cDNA encoding this kinase suppresses the gibberellin (GA)-induced expression of alpha-amylase genes in barley ( Hordeum vulgare L.) aleurone layers. We have cloned the cDNA and genomic sequences for the barley PKABA1 (HvPKABA1) to further study its role in regulating the GA-inducible gene expression in barley seeds. The amino acid sequence deduced from the cDNA shows 97% identity with that of wheat PKABA1. RNA blot analysis indicated that ABA induced, but GA suppressed, the expression of HvPKABA1 in barley seeds. Transient expression of HvPKABA1 also suppressed the GA-inducible alpha-amylase gene expression. These results suggest that HvPKABA1 is probably involved in the signal transduction pathway from ABA to suppress the GA-inducible gene expression. Southern blot analysis showed that HvPKABA1 is likely a single-copy gene in barley. The sequence of the genomic clone reveals that HvPKABA1 consists of eight introns, the first one being more than 6 kb long. The mapped transcription start site of this gene suggests that it may have a TATA-less promoter.

Abscisic Acid↗
PubMed2004

Molecular analysis of the 5'-upstream region of a gibberellin-inducible cytosolic glutamine synthetase gene (GS1b) expressed in pine vascular tissue.

The promoter region of the cytosolic glutamine synthetase GS1b gene was isolated from the conifer Pinus sylvestris L. (Scots pine). The 1,171-bp stretch of sequence lying immediately upstream of the transcriptional start site was sufficient to drive the expression of a reporter gene in a manner consistent with the expression pattern of the native GS1b gene. Computer analysis of putative cis elements in this promoter region revealed the presence of an AT box, an AC motif similar to those found in other genes expressed in the vascular tissue, and a gibberellin (GA)-responsive element. Consistent with the latter finding, GS1b gene expression was induced by exogenously supplied gibberellic acid (GA3) in germinating pine embryos and pine seedlings. In order to examine if the putative GA-response element found in the GS1b promoter could function in the regulation of GS1b expression, a series of deletions of the upstream gene region were fused to the uidA reporter gene, and transient expression analyzed either in untreated or in GA3-treated pine (Pinus pinaster Ait.) protoplasts. Deletion analysis revealed that sequences containing the GA-responsive element, located between -1005 and -724 bp were essential for the increased promoter activity observed in response to GA3. Furthermore, electrophoretic-mobility-shift assays showed that pine nuclear proteins bind to a 22-bp sequence that contains the GA-response element, located between -768 and -747 bp relative to the transcription start site.

5' Flanking Region↗
PubMed2004

Pleiotropic effects of the male sterile33 (ms33) mutation in Arabidopsis are associated with modifications in endogenous gibberellins, indole-3-acetic acid and abscisic acid.

Earlier, we reported that mutation in the Male Sterile33 (MS33) locus in Arabidopsis thaliana causes inhibition of stamen filament growth and a defect in the maturation of pollen grains [Fei and Sawhney (1999) Physiol Plant 105:165-170; Fei and Sawhney (2001) Can J Bot 79:118-129]. Here we report that the ms33 mutant has other pleiotropic effects, including aberrant growth of all floral organs and a delay in seed germination and in flowering time. These defects could be partially or completely restored by low temperature or by exogenous gibberellin A4 (GA4), which in all cases was more effective than GA3. Analysis of endogenous GAs showed that in wild type (WT) mature flowers GA4 was the major GA, and that relative to WT the ms33 flowers had low levels of the growth active GAs, GA1 and GA4, and very reduced levels of GA9, GA24 and GA15, precursors of GA4. This suggests that mutation in the MS33 gene may suppress the GA biosynthetic pathway that leads to GA4 via GA9 and the early 13-H C20 GAs. WT flowers also possessed a much higher level of indole-3-acetic acid (IAA), and a lower level of abscisic acid (ABA), relative to ms33 flowers. Low temperature induced partial restoration of male fertility in the ms33 flowers and this was associated with partial increase in GA4. In contrast, in WT flowers GA1 and GA4 were very much reduced by low temperature. Low temperature also had little effect on IAA or ABA levels of ms33 flowers, but did reduce (>2-fold) IAA levels in WT flowers. The double mutants, ms33 aba1-1 (an ABA-deficient mutant), and ms33 spy-3 (a GA signal transduction mutant) had flower phenotypes similar to ms33. Together, the data suggest that the developmental defects in the ms33 mutant are unrelated to ABA levels, but may be causally associated with reduced levels of IAA, GA1 and GA4, compared to WT flowers.

Abscisic Acid↗
PubMed2004

The brassinosteroid growth response in pea is not mediated by changes in gibberellin content.

The objective of this study was to increase our understanding of the relationship between brassinosteroids (BRs) and gibberellins (GAs) by examining the effects of BR deficiency on the GA biosynthesis pathway in several tissue types of pea (Pisum sativum L.). It was suggested recently that, in Arabidopsis, BRs act as positive regulators of GA 20-oxidation, a key step in GA biosynthesis [Bouquin et al. (2001) Plant Physiol 127:450-458]. However, this may not be the case in pea as GA20 levels were consistently higher in all shoot tissues of BR-deficient (lk and lkb) and BR-response (lka) mutants. The application of brassinolide (BL) to lkb plants reduced GA20 levels, and metabolism studies revealed a reduced conversion of GA19 to GA20 in epi-BL-treated lkb plants. These results indicate that BRs actually negatively regulate GA20 levels in pea. Although GA20 levels are affected by BR levels, this does not result in consistent changes in the level of the bioactive GA, GA1. Therefore, even though a clear interaction exists between endogenous BR levels and the level of GA20, this interaction may not be biologically significant. In addition to the effect of BRs on GA levels, the effect of altered GA1 levels on endogenous BR levels was examined. There was no significant difference in BR levels between the GA mutants and the wild type (wt), indicating that altered GA1 levels have no effect on BR levels in pea. It appears that the BR growth response is not mediated by changes in bioactive GA levels, thus providing further evidence that BRs are important regulators of stem elongation.

Arabidopsis↗
PubMed2005

Function and transcript analysis of gibberellin-biosynthetic enzymes in wheat.

The enzymes gibberellin (GA) 20-oxidase and 3-oxidase are major sites of regulation in GA biosynthesis. We have characterised one member of each of the gene families encoding these enzymes that are highly expressed in elongating stems and in developing and germinating grains of wheat and are therefore likely to have prominent developmental roles in these tissues. We mapped the three homoeologues of the GA 20-oxidase gene TaGA20ox1 to chromosomes 5BL, 5DL and 4AL. TaGA20ox1 is expressed mainly in the nodes and ears of the elongating stem, and also in developing and germinating embryos. Expression in the nodes, ears and germinating embryos is predominantly from the A and D genomes. Each homoeologous cDNA encodes a functional enzyme that catalyses the multi-step conversions of GA12-GA9, and GA53-GA20. Time course and enzyme kinetic studies indicate that the initial oxidation steps from GA12 and GA53 to the free alcohol forms of GA15 and GA44, respectively, occur rapidly but that subsequent steps occur more slowly. The intermediate GA19 has an especially low affinity for the enzyme, consistent with its accumulation in wheat tissues. The three homoeologous cDNAs for the 3-oxidase gene TaGA3ox2 encode functional enzymes, one of which was shown to possess low levels of 2beta-hydroxylase, 2,3-desaturase, 2,3-epoxidase and even 13-hydroxylase activities in addition to 3beta-hydroxylase activity. In contrast to TaGA20ox1, TaGA3ox2 is expressed in internodes, as well as nodes and the ear of the elongating stem. It is also highly expressed in developing and germinated embryos.

Chromosome Mapping↗
PubMed2005

Interactions between ethylene, gibberellin and abscisic acid regulate emergence and growth rate of adventitious roots in deepwater rice.

Growth of adventitious roots is induced in deepwater rice (Oryza sativa L.) when plants become submerged. Ethylene which accumulates in flooded plant parts is responsible for root growth induction. Gibberellin (GA) is ineffective on its own but acts in a synergistic manner together with ethylene to promote the number of penetrating roots and the growth rate of emerged roots. Studies with the GA biosynthesis inhibitor paclobutrazol revealed that root emergence was dependent on GA activity. Abscisic acid (ABA) acted as a competitive inhibitor of GA activity. Root growth rate on the other hand was dependent on GA concentration and ABA acted as a potent inhibitor possibly of GA but also of ethylene signaling. The results indicated that root emergence and elongation are distinct phases of adventitious root growth that are regulated through different networking between ethylene, GA and ABA signaling pathways. Adventitious root emergence must be coordinated with programmed death of epidermal cells which cover root primordia. Epidermal cell death is also controlled by ethylene, GA and ABA albeit with cell-type specific cross-talk. Different interactions between the same hormones may be a means to ensure proper timing of cell death and root emergence and to adjust the growth rate of emerged adventitious roots.

Abscisic Acid↗
PubMed2005

A phytochrome-dependent embryonic factor modulates gibberellin responses in the embryo and micropylar endosperm of Datura ferox seeds.

The promotion of germination by phytochrome is associated with extensive changes both in the embryo and in the micropylar region of the endosperm (ME) of Datura ferox seeds. These changes require de novo gibberellins (GAs) biosynthesis in the embryo, the site where the light stimulus is perceived. GAs stimulate embryo growth potential and move to ME, promoting the expression of genes related with weakening. We report here that, in addition, phytochrome stimulates the sensitivity of the seeds to gibberellic acid (GA). The phytochrome-induced signal is produced in the embryo and enhances the stimulus by GA of embryo growth potential (EGP) and the promotion of the expression of proteins thought to participate in ME weakening: endo-beta-mannanase (EC 3.2.1.78), endo-beta-mannosidase (EC 3.2.1.25) and expansin. Our results suggest that the cytokinins may be a component of the embryonic signal. Phytochrome also modulates DfPHOR and DfMYB transcript levels in ME. These genes show a high identity with components of GAs signaling identified in other species. Expression of DfPHOR in the ME is apparently regulated by phytochrome through the supply of GAs from the embryo to ME, whereas DfMYB expression is regulated by an embryonic factor with some of the characteristics of the one that modulates seed sensitivity to GAs.

Datura↗
PubMed2006

Transgenic modification of gai or rgl1 causes dwarfing and alters gibberellins, root growth, and metabolite profiles in Populus.

In Arabidopsis and other plants, gibberellin (GA)-regulated responses are mediated by proteins including GAI, RGA and RGL1-3 that contain a functional DELLA domain. Through transgenic modification, we found that DELLA-less versions of GAI (gai) and RGL1 (rgl1) in a Populus tree have profound, dominant effects on phenotype, producing pleiotropic changes in morphology and metabolic profiles. Shoots were dwarfed, likely via constitutive repression of GA-induced elongation, whereas root growth was promoted two- to threefold in vitro. Applied GA(3 )inhibited adventitious root production in wild-type poplar, but gai/rgl1 poplars were unaffected by the inhibition. The concentrations of bioactive GA(1) and GA(4) in leaves of gai- and rgl1-expressing plants increased 12- to 64-fold, while the C(19) precursors of GA(1) (GA(53), GA(44) and GA(19)) decreased three- to ninefold, consistent with feedback regulation of GA 20-oxidase in the transgenic plants. The transgenic modifications elicited significant metabolic changes. In roots, metabolic profiling suggested increased respiration as a possible mechanism of the increased root growth. In leaves, we found metabolite changes suggesting reduced carbon flux through the lignin biosynthetic pathway and a shift towards allocation of secondary storage and defense metabolites, including various phenols, phenolic glucosides, and phenolic acid conjugates.

Arabidopsis Proteins↗