Phenotypically normal transgenic T-cyt tobacco plants as a model for the investigation of plant gene expression in response to phytohormonal stress

The tumour-inducing T-DNA gene 4 (T-cyt gene) of the nopaline Ti plasmid pTiC58 was cloned and introduced into tobacco cells by leaf disc transformation using Agrobacterium plasmid vectors. Tobacco shoots exposed to elevated cytokinin levels were unable to develop roots and lacked apical dominance. Using exogenously applied phytohormone manipulations we were able to regenerate morphologically normal transgenic tobacco plants which differed in endogenous cytokinin levels from normal untransformed plants. Although T-cyt gene mRNA levels, as revealed by dot-blot hybridization data, in these rooting plants were only about half those in primary transformed shoots the total amount of cytokinins was much lower than in crown gall tissue or cytokinin-type transformed shoots as reported by others. Nevertheless the cytokinin content in T-cyt plants was about 3 times greater than in control tobacco plants.Elevated cytokinin levels have been shown to change the expression of several plant genes, including some nuclear genes encoding chloroplast proteins. Our results show that the mRNA levels of chloroplast rbcL gene increase in cytokinin-type transgenic tobacco plants as compared with untransformed plants. Data obtained suggest that T-cyt transgenic plants are a good model for studying plant gene activity in different parts of the plant under endogenous cytokinin stress.     

Variability of organ-specific gene expression in transgenic tobacco plants

Variability of expression of introduced marker genes was analysed in a large number of tobacco regenerants from anAgrobacterium-mediated transformation. In spite of standardization of sampling, considerable variation of GUS and NPTII expression was observed between individual transformants at different times of analysis and in different parts of the same plant. Organ-specificity of root versus leaf expression conferred by the par promoter from the haemoglobin gene ofParasponia andersonii in front of thegus gene showed a continuous spectrum. GUS expression in roots was found in 128 out of 140 plants; expression in leaves was found in 46 plants, and was always lower than in the corresponding roots. NPTII expression regulated by the nos promoter also showed a continuous spectrum. Expression levels were generally higher in roots than in leaves. Plants with high GUS expression in leaves showed high NPTII activity as well. A positive correlation between the level of NPTII expression and the numbers of integrated gene copies was noted. Chromosomal position effects and physiological determination are suggested as triggers for the variations. The transformed regenerated tobacco plants were largely comparable to clonal variants.     

Changes in the tissue-specific prevalence of translatable mRNAs in transgenic tobacco shoots containing the T-DNA cytokinin gene

Two-dimensional gel electrophoresis of in vitro translation products was used to examine differences between the steady state RNA populations of an untransformed tobacco plant line and a non-rooting tobacco shoot line transformed with a T _l -DNA segment from Agrobacterium tumefaciens carrying the cytokinin gene (T-cyt). The analysis comprised about 240 translation products representing the more abundant mRNAs. Approximately 8% of the translation products were found to have significantly different concentrations, due to both increases and decreases, when the shoot parts of the transformed and untransformed lines were compared. Only a few of these differences were specific for the comparison of transformed and untransformed shoots. Most of the differences were also observed when the shoot and root parts of the untransformed line were compared. This implies that the shoot or root prevalence of several mRNA species in normal plants is altered in transgenic T-cyt shoots. The observed changes in the mRNA population of transgenic T-cyt shoots are discussed in relation to the transformed phenotype and previously cloned mRNAs showing similar changes in tissue-specific prevalence.     

Expression of a fungal cyanamide hydratase in transgenic soybean detoxifies cyanamide in tissue culture and in planta to provide cyanamide resistance

Embryogenic tissue cultures of soybean were transformed by particle bombardment with a vector pCHZ-II that carries the coding sequence for cyanamide hydratase (Cah), an enzyme that converts toxic cyanamide to urea, from the soil fungus Myrothecium verrucaria. The Cah gene was driven by the constitutive Arabidopsis thaliana actin-2 promoter and terminated with its cognate terminator. This vector also carries the hygromycin phosphotransferase gene (hpt) driven by the potato (Solanum tuberosum) ubiquitin-3 promoter. Twelve individual lines of transgenic plants that were obtained under hygromycin selection expressed Cah mRNA and exhibited resistance to hygromycin in leaf tissue culture, while the untransformed tissues were sensitive. Cah enzyme activity was present in extracts of transformed leaves and embryogenic tissue cultures when measured by a colorimetric assay and the presence of the Cah protein was confirmed by enzyme-linked immunosorbent assay (ELISA). Cah expression detoxified cyanamide in leaf callus and embryogenic cultures as well as in whole plants as shown by cyanamide resistance. The Cah-expressing plants grew and set seeds normally indicating that the Cah enzyme activity did not affect soybean plant metabolism. We also describe a test whereby callus was formed on cultured leaf tissue in the presence of hygromycin or cyanamide only if the hpt or Cah gene was expressed, respectively. This test is a convenient and cost-effective way to follow the marker gene in the primary regenerated plants and subsequent generations, which is particularly reliable for the hpt gene expression using hygromycin.     

Salt stress alleviation in transgenic Vigna mungo L. Hepper (blackgram) by overexpression of the glyoxalase I gene using a novel Cestrum yellow leaf curling virus (CmYLCV) promoter

A reproducible and efficient transformation system utilizing the nodal regions of embryonal axis of blackgram (Vigna mungo L. Hepper) has been established via Agrobacterium tumefaciens. This is a report of genetic transformation of Vigna mungo for value addition of an agronomic trait, wherein the gene of interest, the glyoxalase I driven by a novel constitutive Cestrum yellow leaf curling viral promoter has been transferred for alleviating salt stress. The overexpression of this gene under the constitutive CaMV 35S promoter had earlier been shown to impart salt, heavy metal and drought stress tolerance in the model plant, tobacco. Molecular analyses of four independent transgenic lines performed by PCR, Southern and western blot revealed the stable integration of the transgene in the progeny. The transformation frequency was ca. 2.25% and the time required for the generation of transgenic plants was 10–11 weeks. Exposure of T1 transgenic plants as well as untransformed control plants to salt stress (100 mM NaCl) revealed that the transgenic plants survived under salt stress and set seed whereas the untransformed control plants failed to survive. The higher level of Glyoxalase I activity in transgenic lines was directly correlated with their ability to withstand salt stress. To the best of our knowledge this is the only report of engineering abiotic stress tolerance in blackgram. Prasanna Bhomkar, Chandrama P. Upadhyay are contributed equally. An erratum to this article can be found at     

Transgenic tobacco plants expressingBoRS1 gene fromBrassica oleracea var.acephala show enhanced tolerance to water stress

Water stress is by far the leading environmental stress limiting crop yields worldwide. Genetic engineering techniques hold great promise for developing crop cultivars with high tolerance to water stress. In this study, theBrassica oleracea var.acephala BoRS1 gene was transferred into tobacco throughAgrobacterium- mediated leaf disc transformation. The transgenic status and transgene expression of the transgenic plants was confirmed by polymerase chain reaction (PCR) analysis, Southern hybridization and semi-quantitative one step RT-PCR analysis respectively. Subsequently, the growth status under water stress, and physiological responses to water stress of transgenic tobacco were studied. The results showed that the transgenic plants exhibited better growth status under water stress condition compared to the untransformed control plants. In physiological assessment of water tolerance, transgenic plants showed more dry matter accumulation and maintained significantly higher levels of leaf chlorophyll content along with increasing levels of water stress than the untransformed control plants. This study shows thatBoRS1 is a candidate gene in the engineering of crops for enhanced water stress tolerance.     

The expression of cecropin peptide in transgenic tobacco does not confer resistance to Pseudomonas syringae pv tabaci

Summary We used in vitro growth inhibition assays to demonstrate that synthetic cecropin protein has potent activity against a range of plant pathogenic bacteria. We then prepared transgenic tobacco plants which express cecropin mRNA and protein. We have used Pseudomonas syringae pv tabaci infection of these transgenic tobacco as a model system to evaluate whether the plants which express cecropin protein also have increased tolerance to infection. We found no dramatic difference in disease response between plants which are expressing cecropin protein and control plants which were derived from the transformation with a binary vector which did not carry the gene encoding cecropin protein.     

致病疫霉效应蛋白Pi16275的功能研究

[目的]分析致病疫霉效应蛋白Pi16275的超量表达对病原菌致病性的影响,明确Pi16275的亚细胞定位,筛选Pi16275在植物中的互作靶标蛋白及靶标蛋白在抵御病原菌侵染过程中的作用,初步揭示Pi16275在病原菌侵染植物过程中的作用机制.[方法]利用农杆菌介导的烟草瞬时表达系统在烟草叶片表皮细胞中瞬时表达Pi162...     

Constitutive expression of an inducible lipoxygenase in transgenic tobacco decreases susceptibility to Phytophthora parasitica var. nicotianae

Plant lipoxygenases (LOXs) are key enzymes involved in the generation of fatty acid derivatives, called oxylipins. In tobacco, LOX gene expression and activity are very low in healthy tissues and are highly enhanced in response to infection by Phytophthora parasitica nicotianae and to elicitor treatment. We previously showed, using antisense-LOX1 plants, that expression of the tobacco LOX1 gene is required for the race-cultivar specific resistance of tobacco to Phytophthora parasitica nicotianae. In order to investigate the effect of over-expressing a LOX gene on plant resistance, we transformed tobacco plants with the LOX1 coding sequence fused to the CaMV 35S promoter. Four transgenic lines with enhanced levels of LOX protein and specific activity over control plants were selected for further analysis. These plants were macroscopically indistinguishable from WT plants. Upon stem inoculation, the sense-LOX1 plants displayed a significantly decreased susceptibility to virulent races of Phytophthora parasitica nicotianae, stem lesions being 2- to 3-fold shorter in the transgenic lines than in WT plants. Using a root inoculation assay, the survival rate of sense-LOX1 seedlings was increased about 4-fold compared to their WT counterparts, with 60 to 80% of transgenic plants vs 15 to 20% of WT controls remaining healthy following inoculation with Phytophthora parasitica nicotianae. This is the first demonstration that the over-expression of a LOX gene is sufficient to reduce the susceptibility of a host plant to an oomycete pathogen.     

Stable genetic transformation of embryogenic cultures of <Emphasis Type="Italic">Abies nordmanniana</Emphasis> (nordmann fir) and regeneration of transgenic plants

Summary Stable genetic transformation of embryogenic cultures of Abies nordmanniana (Nordmann fir or Caucasian fir) was achieved using the Biolistic^? transformation technology, followed by regeneration of transgenic plants. Selection of the transgenic tissue was based on the antibiotic resistance induced by the neomycin phosphotransferase II gene (npt II), in combination with the antibiotic geneticin. Six transclones were recovered from a total of 215 bombardments. Expression of the β-glucuronidase gene (uidA) was confirmed by histochemical analysis, and expression of npt II was verified by quantification of NPTII protein by enzyme linked immunosorbent assay (ELISA). Both genes were still expressed in the embryogenic tissue after 5 yr of in vitro culture and in mature somatic embryos and plants produced from these cultures. The integration of npt II was confirmed by Southern hybridization in embryogenic tissue after 5 yr of culture. After 5 yr of growth, uidA was still expressed in needles from the transformed trees.     

Expression of a chimeric CaMV 35S Bacillus thuringiensis insecticidal protein gene in transgenic tobacco

Insecticidal transgenic tobacco plants containing a truncated Bacillus thuringiensis cryIA(b) crystal protein (ICP) gene expressed from the CaMV 35S promoter were analyzed for ICP gene expression under field and greenhouse conditions over the course of a growing season. We present new information on temporal and tissue-specific expression of a CaMV 35S/cryIA(b) gene. Levels of cryIA(b) protein and mRNA were compared in both homozygous and hemizygous lines throughout plant development. Levels of ICP mRNA and protein increased during plant development with a pronounced rise in expression at the time of flowering. Homozygous ICP lines produced higher levels of ICP than the corresponding hemizygous lines. ELISA analysis of different tissues in the tobacco plant showed ICP gene expression in most tissues with a predominance of ICP in older tissue. All transgenic ICP tobacco lines which were studied in the field and greenhouse contained 400 ng to 1 g ICP per gram fresh weight in leaves from the mid-section of the plant at flowering. The amounts of ICP produced by field lines were directly comparable to levels observed in greenhouse-grown plants.     

A rapid immunoprecipitation assay for neomycin phosphotransferase II expression in transformed bacteria and plant tissues

Anti-kanamycin antibodies produced in rabbits, following coupling of the antibiotic to bovine serum albumin, were used to immunoprecipitate radioactively labelled phosphorylated kanamycin from transformed bacterial or plant extracts in a novel assay system, for the detection of neomycin phosphotransferase II (NPTII) activity. Radioactive counts in the immunoprecipitated pellet give a semiquantitative measure of the kanamycin phosphorylation and hence the amount of NPTII activity. This assay is sensitive, uses very small amounts of radioactivity, and is very rapid, allowing many samples to be processed within a few hours. Immunoprecipitated counts from reactions with bacteria carrying a kanamycin resistance gene or from tobacco and Brassica napus plants transformed with NPTII gene-containing vectors were consistently higher than counts from nontransformed controls. Results obtained with this assay correlate well with those from the previously described gel overlay and dot-blot assays, but can be obtained in an appreciably shorter time frame.     

Modification of the cholera toxin B subunit coding sequence to enhance expression in plants

The cholera toxin B subunit (CTB) contains five identical polypeptides and targets glycosphingolipid receptors on eukaryotic cell surfaces. Increased expression of CTB in plants is critical for the development of edible vaccines. In this study, the coding sequence of the CTB gene was optimized, based on the modification of codon usage to that of tobacco plant genes and the removal of mRNA-destabilizing sequences. The synthetic CTB gene was cloned into a plant expression vector and expressed in tobacco plants under the control of the CaMV 35S promoter. The recombinant CTB protein constituted approximately 1.5% of the total soluble protein in transgenic tobacco leaves. This level of CTB production was approximately 15-fold higher than that in tobacco plants that were transformed with the bacterial CTB gene. The recombinant CTB produced by tobacco plants demonstrated strong affinity for GM1-ganglioside, which indicates that the sites required for binding and proper folding of the pentameric CTB structure were conserved. This is the first report on the optimization of the CTB-coding sequence to give a dramatic increase in CTB expression in plants.     

转基因烟草中Bt毒蛋白基因的表达行为

Bt toxin genes were the insecticidal genes most widely used in genetic engineering of pest resistant plant, were of important significance to study their expression behavior in transgenic plants. In this work, a plant expression vector, pBinMoBc, was constructed. It contained the Cry IA(c) gene under control of chimeric OM promoter and the Ω factor. The vector was transferred into tobacco (Nicotiana tabacum L.) plant via Agrobacterium-mediated transformation. ELISA assay showed that the expression levels of the Cry IA(c) gene in transgenic tobacco plants were significantly higher than that in wild-type tobacco plants. The highest could be up to 0.255% of total soluble proteins; the expression level of CryIA(c) gene in transgenic tobacco plant was changeable during the development stages of tobacco plant. Bioassay showed that pBinMoBc transgenic tobacco plants had more notable insecticidal activity than the wild-type tobacco plants. The above results indicated that pBinMoBc was an effective pest-resistent plant expression vector. This study would be very helpful in screening transgenic cotton with high resistance to cotton bollworm (Heliothis armigeva Hubner).     

Expression of the B subunit of <Emphasis Type="Italic">E. coli</Emphasis> heat-labile enterotoxin in tobacco using a herbicide resistance gene as a selection marker

The B subunit of Escherichia coli heat-labile enterotoxin (LTB) has been transformed to plants for use as an edible vaccine. We have developed a simple and reliable Agrobacterium-mediated transformation method to express synthetic LTB gene in N. tabacum using a phosphinothricin acetyltransferase (bar) gene as a selectable marker. The synthetic LTB gene adapted to the coding sequence of tobacco plants was cloned to a plant expression vector under the control of the ubiquitin promoter and transformed to tobacco by Agrobacterium-mediated transformation. Transgenic plants were selected in the medium supplemented with 5 mg l^-1 phosphinothricin (PPT). The amount of LTB protein detected in the transgenic tobacco was approximately 3.3% of the total soluble protein, approximately 300-fold higher than in the plants generated using the native LTB gene under the control of the CaMV 35S promoter. The transgenic plants that were transferred to a greenhouse had harvested seeds that proved to be resistant to herbicide. Thus, the described protocol could provide a useful tool for the transformation of tobacco plants.     

Expression of a synthetic cholera toxin B subunit in tobacco using ubiquitin promoter and bar gene as a selectable marker

A protocol has been developed to produce a cholera toxin B subunit (CTB) in tobacco tolerant to the herbicide phosphinothricin (PPT) by means of in vitro selection. The synthetic CTB subunit gene was altered to modify the codon usage to that of tobacco plant genes. The gene was then cloned into a plant expression vector and was under the control of the ubiquitin promoter and transformed into tobacco plants by Agrobacterium-mediated transformation. Transgenic plantlets were selected in a medium supplemented with 5 mg/L PPT. Polymerase chain reaction analysis confirmed stable integration of the synthetic CTB gene into a chromosomal DNA. A high level of CTB (1.8% of total soluble protein) was expressed in transgenic plants, which was 18-fold higher than that under the control of the expressed CaMV 35S promoter with native gene. The transgenic plants when transferred to a greenhouse proved to be resistant to 2% PPT.