Yung-Jin Chang

Normalization of reverse transcription quantitative-PCR with housekeeping genes in rice.

Reverse transcription followed by real-time quantitative polymerase chain reaction (RT Q-PCR) is useful for the systematic measurement of plant physiological changes in gene expression. The validity of using 18S rRNA and three housekeeping genes, glyceraldehyde-3-phosphate dehydrogenase, actin, and tubulin, was tested as a reference of RT Q-PCR. Under various growth stages of etiolated seedlings, different cultivars, and various times after UV-irradiation treatment, expression level of 18S rRNA correlated with total RNA suggesting the uniformity of RT Q-PCR efficiencies among samples. Relative expressions of housekeeping genes varied among samples and independently of experimental conditions, up to two-fold, signifying generally constant fraction of mRNA in total RNA. Results indicate 18S rRNA was the most reliable reference gene for RT Q-PCR of total RNA.

Differential expression of three 1-deoxy-D-xylulose-5-phosphate synthase genes in rice

Abstract1-Deoxy-D-xylulose-5-phosphate synthase (DXS) encoded by a multigene family in plants, catalyzes the first step in the methylerythritol 4-phosphate (MEP) pathway. Three rice DXS-related sequences (OsDXS) were identified from available rice databases. The open reading frame of three OsDXS genes (dxs1, dxs2, and dxs3) were amplified against cDNA template. Ratio of their transcript levels in etiolated rice leaf was 9:181:1. While the expression levels were not changed along the growth stages of etiolated culture, UV-irradiation of the etiolated rice induced the expression of dxs3 up to nine-fold compared with that of unirradiated control. In the case of light-illumination, the relative expression of dxs1 based on unilluminated control increased two-fold. The differential expression of three OsDXS genes suggested their distinct and complementary roles in the control of the first step of the MEP pathway in response to environmental stimuli.

Tissue specificity and developmental pattern of amorpha-4,11-diene synthase (ADS) proved by ADS promoter-driven GUS expression in the heterologous plant, Arabidopsis thaliana.

Amorpha-4,11-diene synthase (ADS) of Artemisia annua L. is a sesquiterpene cyclase that catalyzes the conversion of farnesyl diphosphate into amorpha-4,11-diene in the biosynthesis of the antimalarial artemisinin. To explore the mechanisms regulating the tissue-specific and developmental distributions of ADS, a full ADS promoter was generated using PCR, and fused to GUS for introduction into Arabidopsis thaliana. ADSpro::GUS fusion transcripts were organ-specific, mainly present in the anthers and trichomes of the green tissues of the juvenile leaves. This result was consistent with the ADS transcription pattern observed in A. annua as examined by RT-PCR. To determine the subcellular localization of ADS, an open reading frame (ORF) of ADS was fused to the green fluorescent protein (smGFP) gene and introduced into the A. thaliana protoplasts. GFP fluorescence was located exclusively in the cytosol, an indication that ADS is a cytosol-localized protein.

Cloning and characterization of 2-C-methyl-d-erythritol 2,4-cyclodiphosphate synthase (MECS) gene from Ginkgo biloba

Ginkgo biloba contains secondary metabolites with interesting pharmacological properties, including highly modified diterpenoid ginkgolide, potent and selective antagonist of platelet-activating factor. 2-C-Methyl-d-erythritol 2,4-cyclodiphosphate synthase gene (GbMECS) involved in ginkgolide biosynthesis pathway was cloned and characterized from G. biloba embryonic roots, and the full open reading frame was deduced as protein consisting of 238 amino acid residues. Putative mature protein with a 179 residue-long sequence, obtained by deleting N-terminal chloroplast transit peptide region composed of 59 amino acid residues, rescued Esherichia coli NMW26, an E. coli knock-out mutant of ygbB (EcMECS). Transcription levels of GbMECS were two-fold higher in embryo roots compared to leaves. When full-length GbMECS with chloroplast transit peptide sequence was fused to green fluorescent protein gene (GFP), and transiently expressed in Arabidopsis thaliana protoplast, green fluorescence was found in chloroplast, indication of protein transportation into plastid.

cDNA isolation and characterization of (+)-germacrene a synthase fromIxerls dentata form.albiflora Hara

Ixeris dentata form.albiflora Hara, a perennial medicinal herb, accumulates various sesquiterpenes whose first committed step in biosynthesis is the cyclization of farnesyl diphosphate by terpene synthase. To isolate the synthase geneldGAS, we amplified a 184-bp DNA fragment of sesquiterpene synthase gene fromI. dentata genomic DNA, using a homology-based PCR technique. Sequence information derived from the rapid amplification of cDNA ends was used to produce a 1956-bp full-length cDNA sequence. This included a 1755-b open reading frame for 584 amino acids, with a deduced size of 67.1 kDa and a pi of 5.16. The partially purified recombinant synthase had an optimum temperature and pH at 37°C and 7.5 to 8.0, respectively, as well as aKm of 11.0 and 14.9 mM at 25 and 37°C, respectively. The expressed protein was inactive with geranyl diphosphate, but did catalyze the cyclization of farnesyl diphosphate to produce a sesquiterpene that was then identified through GC-MS and NMR analyses as (+)-germacrene A. When 44 residues were deleted from its N-terminal, the mutant lost 90% of its activity, suggesting that additional residues are necessary for full enzymatic activity. Transcript levels were comparable between roots and leaves, but began to decline in leaves near the onset of flowering.

Developmental pattern of Ginkgo biloba levopimaradiene synthase (GbLPS) as probed by promoter analysis in Arabidopsis thaliana

Levopimaradiene synthase (GbLPS) of Ginkgo biloba catalyzes the first committed step in ginkgolide biosynthesis by converting geranylgeranyl diphosphate into levopimaradiene, which subsequently undergoes complex oxidation step and rearrangement of carbon skeleton, leading to formation of ginkgolides. To assess the organ-specificity and developmental characteristics of GbLPS expression, the GbLPS promoter-driven GUS expression in transgenic Arabidopsis was studied. Histological analysis of the transgenic Arabidopsis plant showed that the GUS accumulation was mainly localized in the epidermis of leaves, phloem of the shoots, ovaries and stamens of flowers, and vasculature of roots. These observations correlate with the occurrence of LPS transcripts in roots and male strobili of G. biloba. Treatment of methyl jasmonate on the transformant exhibited significant upregulation of the reporter gene in the roots with little change in leaves and flowers. The present findings support biosynthesis of ginkgolide in the roots of Ginkgo plant and suggest translocation occurs through the phloem.

Point mutation of (+)-germacrene A synthase from Ixeris dentata

Sesquiterpene cyclases catalyze the conversion of common precursor, farnesyl pyrophosphate, into various terpene backbones. X-ray crystallography of tobacco epi-aristolochene synthase has previously proposed a cyclization mechanism wherein the allylic carbocation intermediate is stabilized by the main chain carbonyl oxygens of three consecutive threonine residues. Alignment of amino acid sequences of plant terpene cyclases shows that the first position of the triad is almost invariably threonine or serine. To probe the carbocation-stabilizing role, the amino acid residues of the 433TSA435 triad in (+)-germacrene A synthase from Ixeris dentata were altered by site-directed mutagenesis. Enzyme kinetic measurements of the mutants and GC/MS analysis of the enzyme reaction products indicate that mutations of the triad decreased enzyme catalysis rather than substrate binding but did not affect its structural rearrangement in the catalytic mechanism. This is the first report that the hydroxyl group of threonine at the first position of the triad is required for the cyclase activity.

The high throughput screening of neuropeptide FF2 receptor ligands from Korean herbal plant extracts.

We have screened 356 libraries of Korean herbal plant extracts to find potential anti-obesity drugs. We employed the recently developed fluorescence polarization high throughput screening (FP HTS) assays of human neuropeptide FF (NPFF) receptors in 384-well microtiter plates. The primary hits were cherry-picked from the libraries and further analyzed by secondary displacement curve assays, in vitro GTPgammaS binding assays and cell-based CRE luciferase reporter assays. Agonists of NPFF receptors showed biphasic affinity curves while the antagonist, BIBP 3226, gave a monophasic affinity curve in competitive binding assays. We isolated and characterized two agonists of human NPFF2 receptor, PC 314 with K(i) of 1.42 microM, and PC 315 with K(i) of 2.17 microM from Schizandra chinensis. PC 314 and PC 315 have been characterized as benzoylgomisin Q (M.W. 552) and gomisin G (M.W. 536). We report that PC 314 and PC 315 are the first non-peptide, natural compounds, which bind to human NPFF2 receptors with good affinity. PC 314 and PC 315 inhibit forskolin-stimulated luciferase expression when CHO cells are co-transfected with NPFF2 receptor and CRE reporter vector. They possess the pharmacological and functional profiles of full agonists. The FP HTS system provides a specific, sensitive and reproducible methodology for studying and screening NPFF receptor ligands.

Reverse transcription quantitative-PCR of three genes with high homology encoding 3-hydroxy-methylglutaryl-CoA reductase in rice

Reverse transcription followed by RT Q-PCR is useful for the systematic measurement of changes in gene expression. RT Q-PCR with two pairs of primers for each gene was used for relative expression of three genes with high homology encoding 3-hydroxy-methylglutaryl-CoA reductase (HMGR) in rice. At various growth stages of etiolated seedling and various times after UV-irradiation treatment, RT Q-PCR of each HMGR gene showed a consistent pattern of relative expression with the RT Q-PCR data, using two pairs of primers, giving a high degree of accuracy. Furthermore, the different expression levels of three HMGR genes in a sample were determined by diluting the cDNA concentration. These results indicate that RT Q-PCR with only one pair of primers for a gene can quantify the relative expression and that the high expression level of HMGR2 could be quantified in comparison to the low level of HMGR1 expression.

Metabolic flux analysis of diterpene biosynthesis pathway in rice.

Relative transcript levels of eight rice diterpene cyclases at the branch points of gibberellins and phytoalexins biosynthesis pathway were measured by reverse transcription quantitative PCR. Metabolic flux analysis by the distribution ratio of common substrate showed that UV-irradiation of etiolated rice seedlings decreased the flux for primary metabolism of gibberellins biosynthesis by half (from 62 to 27%) and 41% of geranylgeranyl pyrophosphate was used for induction of pimaradiene intermediate as the major phytoalexin. In comparison, light-illumination used almost all geranylgeranyl pyrophosphate (96%) for gibberellin biosynthesis to stimulate the plant growth and strongly repressed the metabolic flux for phytoalexins biosynthesis.