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PubMed2001

Metabolism of gibberellins A1 and A3 in fruits and shoots of Prunus avium.

Isotope-labelled GA metabolites were identified by GC--MS, following HPLC fractionation of extracts derived from fruits or shoots, that had been incubated with [2H]- and [3H]- GA1 or [2H]- and [3H]- GA3. GA1 (1) was converted into GA8 (10) by developing fruits and vegetative shoots of sweet cherry (Prunus avium cv. 'Stella'), while GA3 (4) was converted into GA3-isolactone (17). Other metabolites of each GA were detected but were not identified unequivocally. These included a metabolite of GA1 (1) in fruitlets that was more polar (by reverse phase HPLC) than GA8 (10) and a metabolite of similar polarity to GA87 (6), was obtained after incubating fruitlets with GA3 (4). However, no evidence was obtained to suggest that GA87 (6) was a metabolite of GA3 (4) or that GA85 (2) was a metabolite of GA1 (1) in these tissues, under the conditions used. The pattern of metabolites obtained from vegetative tissues was similar to that from fruitlets. However, the results suggested that GA1 (1) and GA3 (4) were metabolised at a greater rate in shoots from mature trees than in shoots from seedlings, and that GA1 (1) was metabolised more rapidly than GA3 (4) in juvenile and mature shoots. We conclude from these observations that GA3 (4) is not a precursor of GA87 (6) and GA32 (5), also, that GA1 (1) is not a precursor of GA85 (2) and GA86 (3) in developing fruits or in vegetative shoots of sweet cherry.

Gas Chromatography-Mass Spectrometry↗
PubMed2005

The genomic view of genes responsive to the antagonistic phytohormones, abscisic acid, and gibberellin.

We now have the various genomics tools for monocot (Oryza sativa) and a dicot (Arabidopsis thaliana) plant. Plant is not only a very important agricultural resource but also a model organism for biological research. It is important that the interaction between ABA and GA is investigated for controlling the transition from embryogenesis to germination in seeds using genomics tools. These studies have investigated the relationship between dormancy and germination using genomics tools. Genomics tools identified genes that had never before been annotated as ABA- or GA-responsive genes in plant, detected new interactions between genes responsive to the two hormones, comprehensively characterized cis-elements of hormone-responsive genes, and characterized cis-elements of rice and Arabidopsis. In these research, ABA- and GA-regulated genes have been classified as functional proteins (proteins that probably function in stress or PR tolerance) and regulatory proteins (protein factors involved in further regulation of signal transduction). Comparison between ABA and/or GA-responsive genes in rice and those in Arabidopsis has shown that the cis-element has specificity in each species. cis-Elements for the dehydration-stress response have been specified in Arabidopsis but not in rice. cis-Elements for protein storage are remarkably richer in the upstream regions of the rice gene than in those of Arabidopsis.

Abscisic Acid↗
PubMed2001

Gibberellins signal nuclear import of PHOR1, a photoperiod-responsive protein with homology to Drosophila armadillo.

S. tuberosum ssp. andigena potato plants require short days (SD) for tuberization. We have isolated PHOR1 (photoperiod-responsive 1), which shows upregulated expression in induced leaves (SD). PHOR1 encodes an arm repeat protein with homology to the Drosophila segment polarity protein armadillo. Antisense inhibition of PHOR1 produces a semidwarf phenotype similar to that of GA-deficient plants, and the antisense lines show reduced GA responsiveness combined with a higher endogenous GA content than wild-type plants. Feedback regulation of GA biosynthetic genes is also altered in these lines. Conversely, transgenic lines overexpressing PHOR1 show an enhanced response to GA. GA application induces rapid migration of PHOR1-GFP protein to the nucleus. Thus, PHOR1 appears to be a general component of GA signaling pathways that relocalizes to the nucleus in the presence of GA.

Active Transport, Cell Nucleus↗
PubMed2000

Rice gibberellin-insensitive gene homolog, OsGAI, encodes a nuclear-localized protein capable of gene activation at transcriptional level.

This paper reports isolation and properties of a rice gene, OsGAI, a putative homolog of the GAI of Arabidopsis thaliana. OsGAI encodes a polypeptide of 625 amino acids, which shows 53-55% identity to GAI and RGA from A. thaliana, and 85% identity to wheat rht-D1a and maize d8. Genomic DNA blot analysis indicated the OsGAI to be a single-copy gene in the rice genome. RNA blot hybridization showed that OsGAI transcripts increased within 6h upon GA(3) but not ABA application. This GA-induced increment in OsGAI transcripts did not require de novo protein synthesis. High levels of OsGAI transcripts were detected in nodes, internodes, leaf sheaths and ears of adult plants and leaf sheaths of young seedlings, where GA enhances cell elongation and division. Transiently expressed OsGAI-GFP fusion protein located to the nucleus in onion epidermal cells. Transactivation assays clearly indicated that OsGAI protein is a transcriptional activator or a coactivator.

Amino Acid Sequence↗
PubMed2002

Plant meristems: the interplay of KNOX and gibberellins.

KNOX proteins are required for meristem activity in plants. Recent studies have identified potential targets of KNOX proteins, and in doing so suggested a possible mechanism for the generation of different leaf morphologies.

Arabidopsis↗
PubMed2000

Gibberellins 2000.

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Gibberellins↗
PubMed1998

Expression patterns of GASA genes in Arabidopsis thaliana: the GASA4 gene is up-regulated by gibberellins in meristematic regions.

The GASA gene family previously identified in Arabidopsis belongs to a wide-spread class of genes found in mono- and dicotyledonous plants, all structurally related to the original GA-regulated GAST1 gene from tomato. They encode small peptides (97 to 112 residues) of unknown function sharing a 60 amino acid conserved C-terminal domain comprising twelve conserved cysteine residues which define a pattern not related to other known cysteine-rich motifs. Northern blot hybridization analysis revealed sequential expression of three genes during flowering, silique development and seed germination. GASA4 transcripts were detected in flower buds. GASA1 transcripts markedly accumulated in siliques, about five days after pollination, and correlated with the peak of GA biosynthesis at this stage of silique development. GASA3 transcripts accumulated at the end of the maturation stage of the silique, and transcripts were still present in dry seeds but degraded rapidly during imbibition. In addition, the GASA4 gene was again actively transcribed after germination and this expression was shown to be dependent on the presence of GAs in GA-deficient mutants. Immunoblot analysis confirmed the presence of the GASA4 gene product in flower buds, seedlings and roots. We focused on the GASA4 gene and characterized its expression. The upstream region (-890 to +128) was fused to the GUS reporter gene. GASA4/GUS expression was detected in transgenic Arabidopsis primarily in all meristematic regions, including vegetative, inflorescence and floral meristems, as well as primary and lateral root tips. In a GA-deficient background (ga1-3), GUS activity in the vegetative meristem was detected only in the presence of supplied GA. In root and flower meristems, basal GUS activity was slightly enhanced by exogenous GA. Interestingly, GA strongly inhibit GUS activity in expanding cotyledons and leaves in ga1-3 mutants supplied with exogenous GAs, as well as in the wild type. The GA-dependent meristem-specific expression pattern suggests that the GASA4 protein plays a role in dividing cells rather than in elongating cells.

Amino Acid Sequence↗
PubMed1998

Gibberellin and abscisic acid regulate GAST1 expression at the level of transcription.

Both gibberellic acid (GA3) and abscisic acid (ABA) regulate the expression of the GAST1 gene of tomato. Treatment with GA3 increases the abundance of GAST1 RNA while treatment with ABA blocks this effect. In this study, the effects of GA3 and ABA on the rate of transcription of the GAST1 gene and the stability of GAST1 RNA were examined. Nuclear run-on analyses detected an increase in transcription of the GAST1 gene 1 h after GA3 treatment with transcription increasing to a maximum at 9 h after treatment. The half-life of GAST1 RNA in GA3-treated leaves was similar to that in control leaves. In addition, the extent of overexpression of GAST1 RNA in transgenic tomato plants containing the CaMV 35S promoter driving the expression of the GAST1 transcribed region was largely unaffected by GA3. These results suggest that GA3 stimulates the expression of the GAST1 gene by acting only at the level of transcription. ABA treatment dramatically reduced the abundance of GAST1 RNA in gib1 shoots through an effect at the level of transcription and did not appear to affect the stability of this RNA. Midcourse ABA addition to the GA3-incubated shoots reversed the GA3-mediated increase in the transcription of GAST1 gene within 15 min. Transgenic plants that either overexpressed or underexpressed GAST1 RNA exhibited no phenotypic differences from wild type.

Abscisic Acid↗