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N. H. Chua

Publications and source records attributed to N. H. Chua.

8 recordsLinked to original sources
PubMed1995

Expression of the Hevea brasiliensis (H.B.K.) Mull. Arg. 3-Hydroxy-3-Methylglutaryl-Coenzyme A Reductase 1 in Tobacco Results in Sterol Overproduction.

A genomic fragment encoding one (HMGR1) of the three 3-hydroxy-3-methylglutaryl coenzyme A reductases (HMGRs) from Hevea brasiliensis (H.B.K.) Mull. Arg. (M.-L. Chye, C.-T. Tan, N.-H. Chua [1992] Plant Mol Biol 19: 473-484) was introduced into Nicotiana tabacum L. cv xanthi via Agrobacterium transformation to study the influence of the hmg1 gene product on plant isoprenoid biosynthesis. Transgenic plants were morphologically indistinguishable from control wild-type plants and displayed the same developmental pattern. Transgenic lines showed an increase in the level of total sterols up to 6-fold, probably because of an increased expression level of hmg1 mRNA and a corresponding increased enzymatic activity for HMGR, when compared with the level of total sterols from control lines not expressing the hmg1 transgene. In addition to the pathway end products, campesterol, sitosterol, and stigmasterol, some biosynthetic intermediates such as cycloartenol also accumulated in transgenic tissues. Most of the overproduced sterols were detected as steryl-esters and were likely to be stored in cytoplasmic lipid bodies. These data strongly support the conclusion that plant HMGR is a key limiting enzyme in phytosterol biosynthesis.

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PubMed1994

Tissue-Specific Expression of as-1 in Transgenic Tobacco.

When integrated as a transgene in one or a few copies, the -90 35S promoter of cauliflower mosaic virus confers expression in roots with little or no expression in cotyledons and leaves. The responsible cis element, activation sequence-1 (as-1), can bind to the nuclear factor ASF-1 as well as to the transcription factor TGA1a. Here, we show that microinjection of 104 molecules of TGA1a per cotyledon cell activated transgenes containing as-1-linked promoters. Transgenes with promoters linked to the octopine synthase (ocs) element, which also binds TGA1a, responded similarly. The acidic, N-terminal segment of TGA1a is important for transcription activation in vivo because a deletion mutant without the first 80 amino acids was inactive. Finally, we show that the -90 35S-[beta]-glucuronidase (GUS) fusion gene conferred GUS expression in cotyledon cells when injected at 50,000 copies per cell. Collectively, these results provide support for the hypothesis that the undetectable expression of the as-1-linked transgene in cotyledon cells is most likely a result of its inability to compete for a limiting amount of its cognate transcription factor(s), presumably TGA1a or related proteins.

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PubMed1993

Auxin Polar Transport Is Essential for the Establishment of Bilateral Symmetry during Early Plant Embryogenesis.

We used an in vitro culture system to investigate the effects of three auxin polar transport inhibitors (9-hydroxyfluorene-9-carboxylic acid, trans-cinnamic acid, and 2,3,5-triiodobenzoic acid) on the development of early globular to heart-shaped stage embryos of Indian mustard (Brassica juncea) plants. Although the effective concentrations vary with the different inhibitors, all of them induced the formation of fused cotyledons in globular ([less than or equal to]60 [mu]m) but not heart-shaped embryos. Inhibitor-treated Brassica embryos phenocopy embryos of the Arabidopsis pin-formed mutant pin1-1, which has reduced auxin polar transport activity in inflorescence axes, as well as embryos of the Arabidopsis emb30 (gnom) mutant. These results indicate that the polar transport of auxin in early globular embryos is essential for the establishment of bilateral symmetry during plant embryogenesis. Based on these observations, we propose two possible models for the action of auxin during cotyledon formation.

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PubMed1990

Sequence Requirements of the 5-Enolpyruvylshikimate-3-phosphate Synthase 5[prime]-Upstream Region for Tissue-Specific Expression in Flowers and Seedlings.

We have analyzed expression from deletion derivatives of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) 5[prime]-upstream region in transgenic petunia flowers and seedlings. In seedlings, expression was strongest in root cortex cells and in trichomes. High-level expression in petals and in seedling roots was conferred by large (>500 base-pair) stretches of sequence, but was lost when smaller fragments were analyzed individually. This apparent requirement for extensive sequence suggests that combinations of cis-elements that are widely separated control tissue-specific expression from the EPSPS promoter. We have also used the high-level, petal-specific expression of the EPSPS promoter to change petal color in two mutant petunia lines.

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PubMed1989

The Pea rbcS-3A Promoter Mediates Light Responsiveness but not Organ Specificity.

The expression of the pea rbcS-3A gene is responsive to light and restricted to chloroplast-containing cells. Previously, we identified transcriptional elements between -410 and -50 relative to the transcription start site as being sufficient for this regulated expression. Here we investigate the role of the promoter region (-50 to +15) in rbcS-3A expression. We demonstrate an interaction between the promoter and upstream sequences located between -189 and -166, which is important for high level expression. In addition we show that, when the rbcS promoter is driven by a weak test enhancer, it can confer light-responsive but not organ-specific expression upon a bacterial reporter gene.

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PubMed1989

Rice Phytochrome Is Biologically Active in Transgenic Tobacco.

To investigate the mechanisms of phytochrome action in vivo, we have overexpressed rice phytochrome in transgenic tobacco plants. A full-length rice phytochrome cDNA was fused to the cauliflower mosaic virus 35S promoter and transferred to tobacco. The progeny of some of the transgenic plants contain large amounts of rice phytochrome mRNA in green leaves. Extracts prepared from overexpressing plants contain twofold to fivefold more spectrophotometrically detectable phytochrome than extracts from control plants. Species-specific, anti-phytochrome monoclonal antibodies were used in immunoblots to discriminate between rice and tobacco phytochrome apoproteins in fractions eluted from a DEAE-Sepharose column. Red minus far-red difference spectra of the partially purified rice phytochrome from the transgenic plants indicate that the rice phytochrome assembles with chromophore and is photoreversible. Analysis of the circadian pattern of Cab mRNA levels in transgenic plants versus controls demonstrates that the overproduction of rice phytochrome extends the duration of the free-running rhythm of Cab gene expression. The rice phytochrome is, therefore, biologically active in the transgenic tobacco plant, which establishes a system for in vivo functional analysis of phytochrome.

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