Differential Accumulation of a Transcript Driven by the CaMV 35S Promoter in Transgenic Tobacco

Heterologous mogrosides biosynthesis in cucumber and tomato by genetic manipulation

Mogrosides are widely used as high-value natural zero-calorie sweeteners that exhibit an array of biological activities and allow for vegetable flavour breeding by modern molecular biotechnology. In this study, we developed an In-fusion based gene stacking strategy for transgene stacking and a multi-gene vector harbouring 6 mogrosides biosynthesis genes and transformed it into Cucumis sativus and Lycopersicon esculentum. Here we show that transgenic cucumber can produce mogroside V and siamenoside I at 587 ng/g FW and 113 ng/g FW, respectively, and cultivated transgenic tomato with mogroside III. This study provides a strategy for vegetable flavour improvement, paving the way for heterologous biosynthesis of mogrosides.

Improved growth and tuber quality of transgenic potato plants overexpressing either NHX antiporter, CLC chloride channel, or both

The nutritional enhancement of potato plants (Solanum tuberosum L.,) is highly critical. As it is considered a worldwide basic vegetarian nutrition to maintain health. S. tuberosum is one of the foremost staples and the world's fourth-largest food crop. In advance, its need is increasing because of its high-industrial value and population blast. To improve both potato growth and behavior under harsh environmental conditions, we produced transgenic potato plants overexpressing either VvNHX (a sodium proton antiporter from Vitis vinifera), VvCLC (a chloride channel from Vitis vinifera), or both. Control and transgenic plants were grown in greenhouse and field under non-stressed conditions for 85 days in order to characterize their phenotype and evaluate their agronomical performance. To this aim, the evaluation of plant growth parameters, tuber yields and characteristics (calibers, eye number and color), the chemical composition of tubers, was conducted and compared between the different lines. The obtained results showed that transgenic plants displayed an improved growth (flowering precocity, gain of vigor and better vegetative growth) along with enhanced tuber yields and quality (increased protein and starch contents). Our findings provide then insight into the role played by the VvNHX antiport and the VvCLC channel and a greater understanding of the effect of their overexpression in potato plants.

Detoxification of phenanthrene in Arabidopsis thaliana involves a Dioxygenase For Auxin Oxidation 1 (AtDAO1)

Polycyclic aromatic hydrocarbon (PAH) contamination has a negative impact on ecosystems. PAHs are a large group of toxins with two or more benzene rings that are persistent in the environment. Some PAHs can be cytotoxic, teratogenic, and/or carcinogenic. In the bacterium Pseudomonas, PAHs can be modified by dioxygenases, which increase the reactivity of PAHs. We hypothesize that some plant dioxygenases are capable of PAH biodegradation. Herein, we investigate the involvement of Arabidopsis thaliana At1g14130 in the degradation of phenanthrene, our model PAH. The At1g14130 gene encodes Dioxygenase For Auxin Oxidation 1 (AtDAO1), an enzyme involved in the oxidative inactivation of the hormone auxin. Expression analysis using a β-glucuronidase (GUS) reporter revealed that At1g14130 is prominently expressed in new leaves of plants exposed to media with phenanthrene. Analysis of the oxidative state of gain-of-function mutants showed elevated levels of H₂O₂ after phenanthrene treatments, probably due to an increase in the oxidation of phenanthrene by AtDAO1. Biochemical assays with purified AtDAO1 and phenanthrene suggest an enzymatic activity towards the PAH. Thus, data presented in this study support the hypothesis that an auxin dioxygenase, AtDAO1, from Arabidopsis thaliana contributes to the degradation of phenanthrene and that there is possible toxic metabolite accumulation after PAH exposure.

Sterols are required for the coordinated assembly of lipid droplets in developing seeds

Lipid droplets (LDs) are intracellular organelles critical for energy storage and lipid metabolism. They are typically composed of an oil core coated by a monolayer of phospholipids and proteins such as oleosins. The mechanistic details of LD biogenesis remain poorly defined. However, emerging evidence suggest that their formation is a spatiotemporally regulated process, occurring at specific sites of the endoplasmic reticulum defined by a specific set of lipids and proteins. Here, we show that sterols are required for formation of oleosin-coated LDs in Arabidopsis. Analysis of sterol pathway mutants revealed that deficiency in several ∆⁵-sterols accounts for the phenotype. Importantly, mutants deficient in these sterols also display reduced LD number, increased LD size and reduced oil content in seeds. Collectively, our data reveal a role of sterols in coordinating the synthesis of oil and oleosins and their assembly into LDs, highlighting the importance of membrane lipids in regulating LD biogenesis.

Lipid droplet biogenesis originates at the endoplasmic reticulum and is defined by a specific set of lipids and proteins. Here, the authors show that sterols play an important role in coordinating oil and oleosin biosynthesis for the formation of lipid droplets in plant leaves and seeds.

35S promoter-driven transgenes are variably expressed in different organs of Arabidopsis thaliana and in response to abiotic stress

The cauliflower mosaic virus (CaMV) 35S promoter is known as the most frequently used promoter in plant biotechnology. Although it is widely considered to be a strong constitutive promoter exhibiting high transcriptional activity, the transcriptional stability of CaMV 35S has not been extensively studied. Using the model plant species Arabidopsis thaliana, this study aimed for a comprehensive expression analysis of two widely used plant transgenes, neomycin phosphotransferase II (NPTII) and enhanced green fluorescent protein (EGFP), regulated by a double CaMV 35S promoter depending on the organ type, time of day, plant age, and in response to abiotic stress conditions. Quantitative real-time PCR (qRT-PCR) analysis revealed that the NPTII and EGFP transcript levels were markedly higher in the cotyledons, young leaves, and roots than in the inflorescences, stems, and adult leaves of three independent transgenic A. thaliana lines. The expression of NPTII and EGFP varied during the day and was elevated with the plant age. Drought and cold stress considerably affected the expression of the transgenes, while heat, high salinity, and wounding had no significant effect. This study shows that transgenes driven by a common constitutive promoter can exhibit marked variations in transcriptional activity depending on plant organ, physiological conditions, and in response to abiotic stress. Therefore, to ensure high and stable transgene activity, considerable attention should be given to the transgenic plant material and incubation conditions before harvesting the plant material.

Physiological Conditions and dsRNA Application Approaches for Exogenously induced RNA Interference in Arabidopsis thaliana

Recent studies have revealed that foliar application of double-stranded RNAs (dsRNAs) or small-interfering RNAs (siRNAs) encoding specific genes of plant pathogens triggered RNA interference (RNAi)-mediated silencing of the gene targets. However, a limited number of reports documented silencing of plant endogenes or transgenes after direct foliar RNA application. This study analyzed the importance of physiological conditions (plant age, time of day, soil moisture, high salinity, heat, and cold stresses) and different dsRNA application means (brush spreading, spraying, infiltration, inoculation, needle injection, and pipetting) for suppression of neomycin phosphotransferase II (NPTII) transgene in Arabidopsis thaliana, as transgenes are more prone to silencing. We observed a higher NPTII suppression when dsRNA was applied at late day period, being most efficient at night, which revealed a diurnal variation in dsRNA treatment efficacy. Exogenous NPTII-dsRNA considerably reduced NPTII expression in 4-week-old plants and only limited it in 2- and 6-week-old plants. In addition, a more discernible NPTII downregulation was detected under low soil moisture conditions. Treatment of adaxial and abaxial leaf surfaces by brushes, spraying, and pipetting showed a higher NPTII suppression, while infiltration and inoculation were less efficient. Thus, appropriate plant age, late time of day, low soil moisture, and optimal dsRNA application modes are important for exogenously induced gene silencing.

NaTrxh is an essential protein for pollen rejection in Nicotiana by increasing S-RNase activity

In self-incompatible Solanaceae, the pistil protein S-RNase contributes to S-specific pollen rejection in conspecific crosses, as well as to rejecting pollen from foreign species or whole clades. However, S-RNase alone is not sufficient for either type of pollen rejection. We describe a thioredoxin (Trx) type h from Nicotiana alata, NaTrxh, which interacts with and reduces S-RNase in vitro. Here, we show that expressing a redox-inactive mutant, NaTrxhSS , suppresses both S-specific pollen rejection and rejection of pollen from Nicotiana plumbaginifolia. Biochemical experiments provide evidence that NaTrxh specifically reduces the Cys155 -Cys185 disulphide bond of SC10 -Rnase, resulting in a significant increase of its ribonuclease activity. This reduction and increase in S-RNase activity by NaTrxh helps to explain why S-RNase alone could be insufficient for pollen rejection.

Overexpression of a putative nitrate transporter (StNPF1.11) increases plant height, leaf chlorophyll content and tuber protein content of young potato plants

Nitrate (NO3-) fertilisers are commonly used to improve the yield and quality of most non-legume crops such as potato (Solanum tuberosum L.). Root cells absorb nitrate from the soil using plasma membrane-bound transporters. In this study, we overexpressed a putative nitrate transporter from potato (StNPF1.11) to study its effect on the level of tuber protein content in potato. At 10 weeks after planting, overexpression of StNPF1.11 increased the mean level of protein content of all n = 23 transformants by 42% compared with the wild-type control. The level of chlorophyll content in leaves (from upper and lower plant parts) also increased for several individuals at 10 weeks. Tuber yield (fresh) was not structurally impaired; however, the mean tuber dry matter content of the transformants was reduced by 3-8% at 19 weeks. At 19 weeks, an overall increase in protein content was not clearly observed. Throughout plant development, half of the transformants were taller than the control. A basic understanding of the mechanisms that regulate plant nitrogen uptake, transport and utilisation, enable the development of tools to improve both crop nutrition and crop quality that are needed to enhance the viability and sustainability of future plant production systems.

VpSTS29/STS2 enhances fungal tolerance in grapevine through a positive feedback loop

Accumulation of stilbene phytoalexins stimulates resistance mechanisms against the grapevine fungus Uncinula necator. However, the defensive mechanisms triggered by stilbene synthase (STS) genes, remain largely unknown. Here, we report the function and molecular mechanism of the stilbene synthase gene VpSTS29/STS2 from Vitis pseudoreticulata in the regulation of plant responses to powdery mildew. Stilbene synthesis occurred mainly in root tips and mesophyll cells of transgenic grapevines via transport through the vascular bundles. Overexpression of VpSTS29/STS2 in Vitis vinifera increased the abundance of STSs in mesophyll tissue and resulted in the accumulation of biologically active resveratrol derivatives at the invasion site. Similarly, expression of VpSTS29/STS2 in Arabidopsis increased resistance to Golovinomyces cichoracearum. The VpSTS29/STS2-expressing Arabidopsis lines showed increased piceid accumulation together with more local hypersensitive reactions, inhibition of mycelial growth, and a reduced incidence of pathogens. Transcriptome profiling analyses demonstrated that VpSTS29/STS2-induced defences led to reprograming of global gene expression and activation of salicylic acid (SA) signalling, thus increasing expression of WRKY-MYB transcription factors and other defence response genes. We propose a model for resveratrol-mediated coordination of defence responses in which SA participates in a positive feedback loop.

Promoting scopolamine biosynthesis in transgenic Atropa belladonna plants with pmt and h6h overexpression under field conditions

Atropa belladonna is one of the most important plant sources for producing pharmaceutical tropane alkaloids (TAs). T1 progeny of transgenic A. belladonna, in which putrescine N-methyltransferase (EC. 2.1.1.53) from Nicotiana tabacum (NtPMT) and hyoscyamine 6β-hydroxylase (EC. 1.14.11.14) from Hyoscyamus niger (HnH6H) were overexpressed, were established to investigate TA biosynthesis and distribution in ripe fruits, leaves, stems, primary roots and secondary roots under field conditions. Both NtPMT and HnH6H were detected at the transcriptional level in transgenic plants, whereas they were not detected in wild-type plants. The transgenes did not influence the root-specific expression patterns of endogenous TA biosynthetic genes in A. belladonna. All four endogenous TA biosynthetic genes (AbPMT, AbTRI, AbCYP80F1 and AbH6H) had the highest/exclusive expression levels in secondary roots, suggesting that TAs were mainly synthesized in secondary roots. T1 progeny of transgenic A. belladonna showed an impressive scopolamine-rich chemotype that greatly improved the pharmaceutical value of A. belladonna. The higher efficiency of hyoscyamine conversion was found in aerial than in underground parts. In aerial parts of transgenic plants, hyoscyamine was totally converted to downstream alkaloids, especially scopolamine. Hyoscyamine, anisodamine and scopolamine were detected in underground parts, but scopolamine and anisodamine were more abundant than hyoscyamine. The exclusively higher levels of anisodamine in roots suggested that it might be difficult for its translocation from root to aerial organs. T1 progeny of transgenic A. belladonna, which produces scopolamine at very high levels (2.94-5.13 mg g(-1)) in field conditions, can provide more valuable plant materials for scopolamine production.

From miracle fruit to transgenic tomato: mass production of the taste-modifying protein miraculin in transgenic plants

The utility of plants as biofactories has progressed in recent years. Some recombinant plant-derived pharmaceutical products have already reached the marketplace. However, with the exception of drugs and vaccines, a strong effort has not yet been made to bring recombinant products to market, as cost-effectiveness is critically important for commercialization. Sweet-tasting proteins and taste-modifying proteins have a great deal of potential in industry as substitutes for sugars and as artificial sweeteners. The taste-modifying protein, miraculin, functions to change the perception of a sour taste to a sweet one. This taste-modifying function can potentially be used not only as a low-calorie sweetener but also as a new seasoning that could be the basis of a new dietary lifestyle. However, miraculin is far from inexpensive, and its potential as a marketable product has not yet been fully developed. For the last several years, biotechnological production of this taste-modifying protein has progressed extensively. In this review, the characteristics of miraculin and recent advances in its production using transgenic plants are summarized, focusing on such topics as the suitability of plant species as expression hosts, the cultivation method for transgenic plants, the method of purifying miraculin and future advances required to achieve industrial use.

Characterization of the mannan synthase promoter from guar (Cyamopsis tetragonoloba)

Guar seed gum, consisting primarily of a high molecular weight galactomannan, is the most cost effective natural thickener, having broad applications in the food, cosmetics, paper, pharmaceutical and petroleum industries. The properties of the polymer can potentially be enhanced by genetic modification. Development of suitable endosperm-specific promoters for use in guar is desirable for metabolic engineering of the seed gum. A ~1.6 kb guar mannan synthase (MS) promoter region has been isolated. The MS promoter sequence was fused with the GUS reporter gene and overexpressed in the heterologous species alfalfa (Medicago sativa). The potential strength and specificity of the MS promoter was compared with those of the constitutive 35S promoter and the seed specific β-phaseolin promoter. Quantitative GUS assays revealed that the MS promoter directs GUS expression specifically in endosperm in transgenic alfalfa. Thus, the guar MS promoter could prove generally useful for directing endosperm-specific expression of transgenes in legume species.

Uniform accumulation of recombinant miraculin protein in transgenic tomato fruit using a fruit-ripening-specific E8 promoter

The E8 promoter, a tomato fruit-ripening-specific promoter, and the CaMV 35S promoter, a constitutive promoter, were used to express the miraculin gene encoding the taste-modifying protein in tomato. The accumulation of miraculin protein and mRNA was compared among transgenic tomatoes expressing the miraculin gene driven by these promoters. Recombinant miraculin protein predominantly accumulated in transgenic tomato lines using the E8 promoter (E8-MIR) only at the red fruit stage. The accumulations were almost uniform among all fruit tissues. When the 35S promoter (35S-MIR) was used, miraculin accumulation in the exocarp was much higher than in other tissues, indicating that the miraculin accumulation pattern can be regulated by using different types of promoters. We also discuss the potential of the E8-MIR lines for practical use.

Stability of the MON 810 transgene in maize

We analysed the DNA variability of the transgene insert and its flanking regions in maize MON 810 commercial varieties. Southern analysis demonstrates that breeding, since the initial transformation event more than 10 years ago, has not resulted in any rearrangements. A detailed analysis on the DNA variability at the nucleotide level, using DNA mismatch endonuclease assays, showed the lack of polymorphisms in the transgene insert. We conclude that the mutation rate of the transgene is not significantly different from that observed in the maize endogenous genes. Six SNPs were observed in the 5'flanking region, corresponding to a Zeon1 retrotransposon long terminal repeat. All six SNPs are more than 500 bp upstream of the point of insertion of the transgene and do not affect the reliability of the established PCR-based transgene detection and quantification methods. The mutation rate of the flanking region is similar to that expected for a maize repetitive sequence. We detected low levels of cytosine methylation in leaves of different transgenic varieties, with no significant differences on comparing different transgenic varieties, and minor differences in cytosine methylation when comparing leaves at different developmental stages. There was also a reduction in cryIAb mRNA accumulation during leaf development.

Acute but not chronic exposure to abiotic stress results in transient reduction of expression levels of the transgene driven by the 35S promoter

The transgenic plant performance depends on the stable expression of the integrated transgene. In this paper, we have analyzed the stability of the most frequently used constitutive promoter, the cauliflower mosaic virus (CaMV) 35S promoter. We used several independent Nicotiana tabacum lines transgenic for the luciferase (LUC) or green fluorescence protein (GFP) coding genes driven by the same 35S promoter. As an indication of the expression level, we measured the steady state RNA level, protein level and protein activity. Exposure of plants to an acute single dose of UVC, UVB or X-ray radiation resulted in a decrease of the transgene expression level, whereas exposure to high temperature increased it. In most of the cases, the expression changed at one to two hours post exposure and returned to normal at four hours. By contrast, plants germinated and grown in the presence of a low dose of either UVB radiation or CuSO(4) for two weeks did not show any changes in expression level. We conclude that although the expression level of the transgenes driven by the 35S promoter can be transiently altered by the acute exposure, no substantial changes occur upon constant low exposure.

Enhancement of vitamin B(6) levels in seeds through metabolic engineering

As a versatile cofactor for many enzymes catalyzing important biochemical reactions, vitamin B(6) is required for all cellular organisms. In contrast to bacteria, fungi and plants, which have the ability to synthesize vitamin B(6)de novo, animals have to take up the vitamin from their diet. Plants are the major source of vitamin B(6) for animals. The recent identification of vitamin B(6) biosynthetic enzymes PDX1 and PDX2 in plants makes it possible to regulate the biosynthesis of this important vitamin. In this study, we generated Arabidopsis plants overexpressing the PDX1 and/or PDX2 gene and used a liquid chromatography/mass spectrometry/mass spectrometry method to determine the levels of different forms of vitamin B(6) in these transgenic plants. It was found that expression of the PDX genes under control of the CaMV 35S promoter caused only a limited increase in pyridoxine contents in dry seeds but not in shoots or roots. When using the Arabidopsis seed-specific 12S promoter to drive the expression of the PDX genes, the levels of vitamin B(6) increased more than twofold in transgenic plants. Our work demonstrates that it is feasible to enhance vitamin B(6) content in seeds by metabolic engineering.

Novel plant transformation vectors containing the superpromoter

We developed novel plasmids and T-DNA binary vectors that incorporate a modified and more useful form of the superpromoter. The superpromoter consists of a trimer of the octopine synthase transcriptional activating element affixed to the mannopine synthase2' (mas2') transcriptional activating element plus minimal promoter. We tested a superpromoter-beta-glucuronidaseA fusion gene in stably transformed tobacco (Nicotiana tabacum) and maize (Zea mays) plants and in transiently transformed maize Black Mexican Sweet protoplasts. In both tobacco and maize, superpromoter activity was much greater in roots than in leaves. In tobacco, superpromoter activity was greater in mature leaves than in young leaves, whereas in maize activity differed little among the tested aerial portions of the plant. When compared with other commonly used promoters (cauliflower mosaic virus 35S, mas2', and maize ubiquitin), superpromoter activity was approximately equivalent to those of the other promoters in both maize Black Mexican Sweet suspension cells and in stably transformed maize plants. The addition of a maize ubiquitin intron downstream of the superpromoter did not enhance activity in stably transformed maize.

Molecular farming for antigen (vaccine) production in plants

Genomic and proteomic approaches to the study of fundamental cell mechanisms are rapidly contributing to broaden our knowledge on metabolic pathways for the optimal exploitation of the cell as a factory. In the last few years this knowledge has led to important advances in the large scale production of diagnostic and therapeutic proteins in heterologous hosts (bacteria, yeasts, mammalian and insect cells or transgenic animals and plants), allowing the comparison of the most efficient methods in terms of costs, product quality and safety.

A comparison of constitutive promoters for expression of transgenes in alfalfa (Medicago sativa)

The activity of constitutive promoters was compared in transgenic alfalfa plants using two marker genes. Three promoters, the 35S promoter from cauliflower mosaic virus (CaMV), the cassava vein mosaic virus (CsVMV) promoter, and the sugarcane bacilliform badnavirus (ScBV) promoter were each fused to the beta-glucuronidase (gusA) gene. The highest GUS enzyme activity was obtained using the CsVMV promoter and all alfalfa cells assayed by in situ staining had high levels of enzyme activity. The 35S promoter was expressed in leaves, roots, and stems at moderate levels, but the promoter was not active in stem pith cells, root cortical cells, or in the symbiotic zones of nodules. The ScBV promoter was active primarily in vascular tissues throughout the plant. In leaves, GUS activity driven by the CsVMV promoter was approximately 24-fold greater than the activity from the 35S promoter and 38-fold greater than the activity from the ScBV promoter. Five promoters, the double 35S promoter, figwort mosaic virus (FMV) promoter, CsVMV promoter, ScBV promoter, and alfalfa small subunit Rubisco (RbcS) promoter were used to control expression of a cDNA from Trichoderma atroviride encoding an endochitinase (ech42). Highest chitinase activity in leaves, roots, and root nodules was obtained in plants containing the CsVMV:ech42 transgene. Plants expressing the endochitinase were challenged with Phoma medicaginis var. medicaginis, the causal agent of spring black stem and leaf spot of alfalfa. Although endochitinase activity in leaves of transgenic plants was 50- to 2650-fold greater than activity in control plants, none of the transgenic plants showed a consistent increase in disease resistance compared to controls. The high constitutive levels of both GUS and endochitinase activity obtained demonstrate that the CsVMV promoter is useful for high-level transgene expression in alfalfa.

Inhibition of endogenous trypsin- and chymotrypsin-like activities in transgenic lettuce expressing heterogeneous proteinase inhibitor SaPIN2a

SaPIN2a, a proteinase inhibitor II from American black nightshade (Solanum americanum Mill.) is highly expressed in the phloem and could be involved in regulating proteolysis in the sieve elements. To further investigate the physiological role of SaPIN2a, we have produced transgenic lettuce (Lactuca sativa L.) expressing SaPIN2a from the CaMV35S promoter by Agrobacterium-mediated transformation. Stable integration of the SaPIN2a cDNA and its inheritance in transgenic lines were confirmed by Southern blot analysis and segregation analysis of the R1 progeny. SaPIN2a mRNA was detected in both the R0 and R1 transformants on northern blot analysis but the SaPIN2a protein was not detected on western blot analysis using anti-peptide antibodies against SaPIN2a. Despite an absence of significant inhibitory activity against bovine trypsin and chymotrypsin in extracts of transgenic lettuce, the endogenous trypsin-like activity in each transgenic line was almost completely inhibited, and the endogenous chymotrypsin-like activity moderately inhibited. Our finding that heterogeneously expressed SaPIN2a in transgenic lettuce inhibits plant endogenous protease activity further indicates that SaPIN2a regulates proteolysis, and could be potentially exploited for the protection of foreign protein production in transgenic plants.

A novel procedure for the localization of viral RNAs in protoplasts and whole plants

Analysis of virus spread using co-expressed reporter proteins has provided important details on cell-to-cell and long-distance movement of viruses in plants. However, most viruses cannot tolerate insertion of large non-viral segments or loss of any open-reading frames, procedures required to detect viruses non-evasively. A technique used to localize mRNAs intracellularly in yeast has been modified for detection of viral RNAs in whole plants. The technique makes use of the binding of the coat protein of MS2 bacteriophage (CPMS2) to a 19 base hairpin (hp). A fusion protein, consisting of the CPMS2, green fluorescent protein (GFP), and a nuclear localization signal (NLS), was nuclear-localized upon transient expression in protoplasts. However, addition of the hp to the 3' untranslated region of Turnip crinkle virus (TCV-hp) and co-transfection of the virus and fusion protein construct into protoplasts resulted in the re-location of GFP to the cytoplasm. Neither the insertion of the hp nor the interaction with the fusion protein impaired any viral functions. Transgenic plants expressing the GFP-NLS-CPMS2 fusion protein were generated, and GFP was detected in nuclei of young plant cells. Foci of GFP cytoplasmic fluorescence were detected in TCV-hp-inoculated leaves at 2 days post-inoculation. Later, GFP was detected in young leaves near the midvein and in the base (support) cells of trichomes in the vicinity of secondary and tertiary veins. In older leaves, cytoplasmic GFP could be visualized throughout many of the leaves. This technique should be amenable for detection of any virus with a transformable plant (or animal) host and may also prove useful for localizing properly engineered host RNAs.

Developmental and tissue-specific expression of CaMV 35S promoter in cotton as revealed by GFP

The CaMV 35S promoter is the most commonly used promoter for driving transgene expression in plants. Though it is presumed to be a constitutive promoter, some reports suggest that it is not expressed in all cell types. In addition, the information available on its expression profile in all possible cell and tissue types and during early stages of development is incomplete. We present here a detailed expression profile of this promoter investigated using the green fluorescent protein (GFP) gene as a reporter system in cotton during embryo development, and in all the vegetative and floral cell and tissue types. GFP expression was not detected during the early stages of embryogenesis. The first perceptible GFP expression was observed in a small area at the junction of hypocotyl and cotyledons in embryos at around 13 days after anthesis. The GFP fluorescence progressively became stronger and expanded throughout the cotyledon and hypocotyl as embryo development advanced. After germination, varying levels of promoter activity were observed in all cell and tissue types in the hypocotyl, cotyledon, stem, leaf, petiole, and root. The promoter was also expressed in all floral parts. Although cotton pollen exhibited a low level of greenish autofluorescence, it was possible to discern GFP-dependent fluorescence in some of the pollen from all the T0 plants examined. Developing cotton fibers also exhibited GFP fluorescence suggesting that the 35S promoter was active in these specialized epidermal cells. Thus, we show that the expression of the 35S promoter was developmentally regulated during embryogenesis and that beyond a certain stage during embryogenesis, the promoter was expressed in most cell and tissue types in cotton albeit at different levels.

Changes in fatty acid composition in plant tissues expressing a mammalian delta9 desaturase

Plant tissues expressing a mammalian stearoyl-CoA delta9 desaturase were reported to accumulate delta9 hexadecenoic acid (16:1), normally very minor in most plant tissues. The transgenic plants were thoroughly analyzed for alterations of individual lipids in different subcellular sites. Western blot analysis indicated that the animal desaturase was targeted to the microsomes. The delta9 16:1 was incorporated into both the sn-1 and sn-2 positions of all the major membrane lipids tested, indicating that the endoplasmic reticulum acyltransferases do not exclude unsaturated C16 fatty acids from the sn-2 position. In addition to increases in monounsaturated and decreases in saturated fatty acids, accumulation of 16:1 was accompanied by a reduction in 18:3 in all the lipids tested except phosphatidylglycerol, and increases in 18:2 in phospholipids. Total C16 fatty acid content in the galactolipids of the transgenics was significantly higher than that in the control, but those in the phospholipids were unchanged. In transgenics, delta11 18:1 was detected in the sn-1 position of the lipids tested except phosphatidylinositol and phosphatidylserine. Introduction of the animal desaturase, controlled by a seed-specific phaseolin promoter, into soybean somatic embryo resulted in a significant reduction in saturated fatty acids. Such effects were greater in cotyledons than hypocotyl-radicles. This study demonstrated that the animal desaturase can be used to decrease the levels of saturated fatty acids in a crop plant.

beta-Phaseolin gene activation is a two-step process: PvALF- facilitated chromatin modification followed by abscisic acid-mediated gene activation

We have shown previously that a rotationally and translationally positioned nucleosome is responsible for the absence of transcriptional expression from the phaseolin (phas) gene promoter in leaf tissue and that the repressive chromatin structure is disrupted on transcriptional activation during embryogenesis. To investigate how the chromatin structure is modified, we ectopically expressed PvALF, a putative seed-specific phas activator, in leaf tissue of a tobacco line transgenic for a chimeric phas/uidA construct. DNase I footprinting in vivo revealed that the ectopic expression of PvALF resulted in remodeling of the chromatin architecture over the TATA region of the phas promoter but did not lead to transcriptional activation in the absence of abscisic acid (ABA). Treatment of the transgenic tobacco leaves with ABA in the absence of PvALF neither alleviated the repressive chromatin architecture nor activated transcription. However, in the presence of PvALF, high levels of beta-glucuronidase expression were obtained on exposure of leaves to ABA. These results reveal that expression from the phas promoter involves at least two discrete steps: chromatin potentiation by PvALF followed by ABA-mediated transcriptional activation.

Functional organization of the cassava vein mosaic virus (CsVMV) promoter

Cassava vein mosaic virus (CsVMV) is a pararetrovirus that infects cassava plants in Brazil. A promoter fragment isolated from CsVMV, comprising nucleotides -443 to +72, was previously shown to direct strong constitutive gene expression in transgenic plants. Here we report the functional architecture of the CsVMV promoter fragment. A series of promoter deletion mutants were fused to the coding sequence of uidA reporter gene and the chimeric genes were introduced into transgenic tobacco plants. Promoter activity was monitored by histochemical and quantitative assays of beta-glucuronidase activity (GUS). We found that the promoter fragment is made up of different regions that confer distinct tissue-specific expression of the gene. The region encompassing nucleotides -222 to -173 contains cis elements that control promoter expression in green tissues and root tips. Our results indicate that a consensus as1 element and a GATA motif located within this region are essential for promoter expression in those tissues. Expression from the CsVMV promoter in vascular elements is directed by the region encompassing nucleotides -178 to -63. Elements located between nucleotides -149 and -63 are also required to activate promoter expression in green tissues suggesting a combinatorial mode of regulation. Within the latter region, a 43 bp fragment extending from nucleotide -141 to -99 was shown to interact with a protein factor extracted from nuclei of tobacco seedlings. This fragment showed no sequence homology with other pararetrovirus promoters and hence may contain CsVMV-specific regulatory cis elements.

Sugar Repression of Mannitol Dehydrogenase Activity in Celery Cells

We present evidence that the activity of the mannitol-catabolizing enzyme mannitol dehydrogenase (MTD) is repressed by sugars in cultured celery (Apium graveolens L.) cells. Furthermore, this sugar repression appears to be mediated by hexokinases (HKs) in a manner comparable to the reported sugar repression of photosynthetic genes. Glucose (Glc)-grown cell cultures expressed little MTD activity during active growth, but underwent a marked increase in MTD activity, protein, and RNA upon Glc starvation. Replenishment of Glc in the medium resulted in decreased MTD activity, protein, and RNA within 12 h. Addition of mannoheptulose, a competitive inhibitor of HK, derepressed MTD activity in Glc-grown cultures. In contrast, the addition of the sugar analog 2-deoxyglucose, which is phosphorylated by HK but not further metabolized, repressed MTD activity in mannitol-grown cultures. Collectively, these data suggest that HK and sugar phosphorylation are involved in signaling MTD repression. In vivo repression of MTD activity by galactose (Gal), which is not a substrate of HK, appeared to be an exception to this hypothesis. Further analyses, however, showed that the products of Gal catabolism, Glc and fructose, rather than Gal itself, were correlated with MTD repression.

Expression of two heterologous promoters, Agrobacterium rhizogenes rolC and cauliflower mosaic virus 35S, in the stem of transgenic hybrid aspen plants during the annual cycle of growth and dormancy

We monitored, for the first time, the activity of two model heterologous promoters, the Agrobacterium rhizogenes rolC and the cauliflower mosaic virus (CaMV) 35S, throughout the annual cycle of growth and dormancy in a perennial species, hybrid aspen. Each promoter was fused to the uidA beta-glucuronidase (GUS) reporter gene and the constructs were introduced into the hybrid aspen genome by Agrobacterium-mediated transformation. Both wild-type and transgenic plants were cultivated under different regimes of photoperiod and temperature to induce passage through one growth-dormancy-reactivation cycle, and at intervals GUS staining was assessed in stem sections. In rolC::uidA transformants, GUS activity in rapidly growing current-year shoots was not only tissue-specific, being localized to the phloem, but also cell-specific at the shoot base, where it was present only in the companion cells. However, during the onset of dormancy induced by short photoperiod, GUS activity shifted laterally from the phloem to include the cortex and pith. After subsequent exposure to chilling temperatures to induce the transition between the dormancy stages of rest and quiescence, GUS activity almost disappeared from all stem tissues, but regained its original phloem specificity and intensity after the shoots were reactivated by exposing them to long photoperiod and high temperatures. In contrast, GUS activity in the stem of 35S::uidA transformants was strong in all tissues except for the vascular cambium and xylem, and did not vary in intensity during the growth-dormancy-reactivation cycle. The lateral shift and increased intensity of GUS activity in the stem of rolC::uidA transformants during dormancy induction was shown to be associated with the accumulation of starch, and to be mimicked by incubating stem sections in sucrose, as well as glucose and fructose, but not sorbitol, prior to the GUS assay. Our results demonstrate that the activities of the rolC and 35S promoters varied in very different, unpredictable ways during the annual cycle of growth and dormancy in a perennial species, and indicate that the spatial and temporal variation in rolC promoter activity that we observed in the stem of transgenic hybrid aspen plants is attributable to cellular and seasonal changes in sucrose content.

Protease inhibitors of Manduca sexta expressed in transgenic cotton

To explore the effectiveness of insect derived protease inhibitors in protecting plants against insect feeding, anti-trypsin, anti-chymotrypsin and anti-elastase protease inhibitor (PI) genes from Manduca sexta L. were expressed in transgenic cotton (Gossypium hirsutum L.). From 198 independent transformants, 35 elite lines were further analyzed. Under the control of the 35S promoter of CaMV, PI accumulated to approximately 0.1% of total protein, depending on the tissue analyzed. Using cell-flow cytometry, DNA content/ nuclei of transgenic and non-transformed cotton were identical. On cotton plants expressing PIs, fecundity of Bemisia tabaci (Genn.), the sweetpotato whitefly, was reduced compared to controls. Expression of these protease inhibitors may reduce the developmental rate of B. tabaci and other insects, and provide a strategy for cotton protection.

An S-RNase promoter from Nicotiana alata functions in transgenic N. alata plants but not Nicotiana tabacum

Nicotiana tabacum and Nicotiana alata plants were transformed with genomic clones of two S-RNase alleles from N. alata. Neither the S2 clone, with 1.6 kb of 5' sequence, nor the S6 clone, with 2.8 kb of 5' sequence, were expressed at detectable levels in transgenic N. tabacum plants. In N. alata, expression of the S2 clone was not detected, however the S6 clone was expressed (at low levels) in three out of four transgenic plants. An S6-promoter-GUS fusion gene was also expressed in transgenic N. alata but not N. tabacum. Although endogenous S-RNase genes are expressed exclusively in floral pistils, the GUS fusion was expressed in both styles and leaves.

Expression of soybean nodulin 26 in transgenic tobacco. Targeting to the vacuolar membrane and effects on floral and seed development

Nodulin 26 is an integral membrane protein of the symbiosome membrane of nitrogen-fixing soybean nodules. We expressed a nodulin 26 cDNA in transgenic tobacco (TN26 tobacco) under the control of the cauliflower mosaic virus 35S promoter to study subcellular targeting and the physiological effect(s) of its expression. Based on Northern and Western blots, the expression of nodulin 26 mRNA and protein in transgenic plants is high in apical shoot sections, flowers, and stems, low in mature leaves, and absent in roots. Western blot analysis revealed high levels of transgenic nodulin 26 protein in tonoplast membranes. In contrast, nodulin 26 protein was not found in isolated plasma membranes, the soluble fraction, nor in chloroplast and mitochondria-enriched membrane fractions. About 50-60% of the flowers and pods from TN26 tobacco plants abscised prematurely. Seed capsule size and seed fill per capsule from the remainder of surviving flowers were about 50% of that of control plants. Pollen viability was found to be normal, but flowers from TN26 tobacco plants showed shorter anther filaments compared with control plants. Normal seed production and capsule size was restored by manually crossing the stigmas from TN26 plants with isolated pollen from either transgenic or control plants. Thus, the aberrant filament growth could have resulted in the reproductive defects associated with the plants.

Hormonal Characterization of Transgenic Tobacco Plants Expressing the rolC Gene of Agrobacterium rhizogenes TL-DNA

Transgenic tobacco (Nicotiana tabacum L. cv Wisconsin 38) plants expressing the Agrobacterium rhizogenes rolC gene under the control of the cauliflower mosaic virus 35S RNA promoter were constructed. These plants displayed several morphological alterations reminiscent of changes in indole-3-acetic acid (IAA), cytokinin, and gibberellin (GA) content. However, investigations showed that neither the IAA pool size nor its rate of turnover were altered significantly in the rolC plants. The biggest difference between rolC and wild-type plants was in the concentrations of the cytokinin, isopentenyladenosine (iPA) and the gibberellin GA19. Radio-immunoassay and liquid chromatography-mass spectrometry measurements revealed a drastic reduction in rolC plants of iPA as well as in several other cytokinins tested, suggesting a possible reduction in the synthesis rate of cytokinins. Furthermore, gas chromatography-mass spectrometry quantifications of GA19 showed a 5- to 6-fold increase in rolC plants compared with wild-type plants, indicating a reduced activity of the GA19 oxidase, a proposed regulatory step in the gibberellin biosynthesis. Thus, we conclude that RolC activity in transgenic plants leads to major alterations in the metabolism of cytokinins and gibberellins.

Translation controls the expression level of a chimaeric reporter gene

Transcriptional and translational fusions between the reading frame of the beta-D-glucuronidase gene (gusA) and the 2' as well as the 1' promoter of mannopine synthase (mas), a TR locus of Agrobacterium tumefaciens, were made. The expression of these constructs was studied in the transgenic F1 offspring of independent tobacco transformants at the protein level by assaying for GUS activity and western blot analysis of the GUS protein and at the steady-state mRNA level. In leaves, stems and roots no correlation was found between steady-state levels of GUS mRNA and enzyme activity. In older tissues significantly higher GUS activities were found. This is explained by the stable character of the GUS protein together with an accumulation of protein upon ageing. Three to ten times higher GUS activities were found for in vitro grown plants than for greenhouse-grown plants of the same offspring, despite similar levels of GUS mRNA. Roots from in vitro grown plants display three to ten times higher GUS activities than stems and leaves. In transgenic plants grown in vitro, containing a translational fusion with two AUGs in phase, the initiation of translation in leaf material occurred at both AUGs. Initiation of translation at the first AUG, however, was ten times more frequent. In contrast, initiation in roots from in vitro grown plants occurred exclusively at the second AUG.

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 microgram 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.

Agrobacterium-mediated transformation of tomatillo (Physalis ixocarpa) and tissue specific and developmental expression of the CaMV 35S promoter in transgenic tomatillo plants

A protocol for the Agrobacterium-mediated transformation of tomatillo was developed. Up to 40 transgenic plants could be obtained in experiments using 60 cotyledon expiants. The transformed nature of the regenerated plants was confirmed by NPT II and Southern blot hybridization analysis. Using the b-glucuronidase system the tissue specific and developmental patterns of expression of the Cauliflower Mosaic Virus 35S promoter were determined in transgenic tomatillo plants. It was found that this promoter is developmentally regulated during fruit and seed formation.

Effects of Elevated Cytosolic Glutathione Reductase Activity on the Cellular Glutathione Pool and Photosynthesis in Leaves under Normal and Stress Conditions

Tobacco (Nicotiana tabacum var Samsun) was transformed using the bacterial gor gene coding for the enzyme glutathione reductase. Transgenic plants were selected by their kanamycin resistence and expression of the bacterial gor gene. After separation by isoelectric focusing techniques, leaf extracts from transgenic plants having both native and bacterial glutathione reductase activity gave, in addition to the six bands of the native enzyme, two further closely running isoenzymes. These additional bands originating from the expression of the bacterial gor gene were nonchloroplastic. Leaves from transgenic plants had two- to 10-fold higher glutathione reductase activity than non-transgenic controls. The amount of extractable glutathione reductase activity obtained in transgenic plants was dependent on leaf age and the conditions to which leaves were exposed. Both light and exposure to methylviologen increased leaf glutathione reductase activity. Elevated levels of cytosolic glutathione reductase activity in transgenic plants had no effect on the amount or reduction state of the reduced glutathione/oxidized glutathione pool under optimal conditions or oxidative conditions induced by methylviologen. The glutathione pool was unaltered despite the oxidation-dependent loss of CO(2) assimilation and oxidation of enzymes involved in photosynthesis. However, the reduction state of the ascorbate pool was greater in transgenic plants relative to nontransgenic controls following illumination of methylviologen-treated leaf discs. Therefore, we conclude that in the natural state glutathione reductase is present in tobacco at levels above those required for maximal operation of the ascorbate-glutathione pathway.

'Phytoantibodies': a general vector for the expression of immunoglobulin domains in transgenic plants

Sequences encoding the immunoglobulin heavy-chain variable (VH) domains were engineered in a new general purpose vector to transform plants via Agrobacterium. The expression of an isolated VH domain (IVD) after introduction into the plant genome has been monitored by northern, western and immunohistochemical analysis. Immunoblotting showed that the polypeptide was stably expressed and accounted for up to 1% of the soluble protein fraction. It is therefore proposed that single immunoglobulin domains of suitable specificity expressed in plants may constitute an effective system to inhibit the activity of molecules involved in plant pathology or plant development.

Characterization of Tobacco Expressing Functional Oat Phytochrome : Domains Responsible for the Rapid Degradation of Pfr Are Conserved between Monocots and Dicots

Constitutive expression of a chimeric oat phytochrome gene in tobacco (Nicotiana tabacum) results in the accumulation of a functional 124-kilodalton photoreceptor that markedly alters the phenotype of light-grown tobacco (Keller et al. [1989] EMBO J 8: 1005-1012). Here, we provide a detailed phenotypic and biochemical characterization of homozygous tobacco expressing high levels of oat phytochrome. Phenotypic changes include a substantial inhibition of stem elongation, decreased apical dominance, increased leaf chlorophyll content, and delayed leaf senescence. Oat phytochrome synthesized in tobacco is indistinguishable from that present in etiolated oats, having photoreversible difference spectrum maxima at 665 and 730 nanometers, exhibiting negligible dark reversion of phytochrome-far red-absorbing form (Pfr) to phytochrome-red-absorbing form (Pr), and existing as a dimer with an apparent size of approximately 300 kilodaltons. Heterodimers between the oat and tobacco chromoproteins were detected. Endogenous tobacco phytochrome and transgenically expressed oat phytochrome are rapidly degraded in vivo upon photoconversion of Pr to Pfr. Breakdown of both oat and tobacco Pfr is associated with the accumulation of ubiquitin-phytochrome conjugates, suggesting that degradation occurs via the ubiquitin-dependent proteolytic pathway. This result indicates that the factors responsible for selective recognition of Pfr by the ubiquitin pathway are conserved between monocot and dicot phytochromes. More broadly, it demonstrates that the domain(s) within a plant protein responsible for its selective breakdown can be recognized by the degradation machinery of heterologous species.

Cytokinin content and tissue distribution in plants transformed by a reconstructed isopentenyl transferase gene

The cytokinin gene, isopentenyl transferase (ipt), was placed under the control of a heat-inducible promoter from the Drosophila melanogaster hsp70 gene and introduced into Nicotiana plumbaginifolia by cocultivation with Agrobacterium tumefaciens. Transformants were analyzed for organ-specific expression, cytokinin levels and effects on plant development before and after the heat induction. The ipt gene transcripts were detected in leaves and stems but not roots of transgenic plants following a 2 hour, 45 degrees C treatment. Maximum mRNA levels observed occurred 2 hours after heat treatment and 46 hours later were detected only in leaves. Zeatin and zeatinriboside concentrations 2 hours after heat shock ranged from over 900 to 2000 pmol/g, representing a greater than 140- to 200-fold increase over uninduced levels. After 46 hours, approximately 50% of the cytokinins are still present in the leaves as opposed to much reduced levels in the stems. Transgenic plants were greener, shorter, had an underdeveloped root system, reduced leaf width, and increased growth of axillary buds. After a single heat treatment, plants exhibited a darker green pigment and continued growth of lateral buds. Transient accumulations of endogenous cytokinins following thermal induction did not appear to alter the plant's preprogrammed pattern of differentiation.

The effect of T-DNA copy number, position and methylation on reporter gene expression in tobacco transformants

Inter-transformant variability in the expression of introduced genes was studied in the R1 and R2 generations of 10 tobacco transformants, produced by Agrobacterium-mediated transformation. In replicated and physiologically equivalent material, tranformants showed considerable variability in the expression of the reporter gene uidA as shown by transcript levels and beta-glucuronidase (GUS) activity. However, homozygous R2 material could be investigated for seven of the transformants and among these, and in one line in which two inserts could segregate independently, this inter-transformant variability was reduced to simple bimodal expression. The two levels of expression for GUS activity in leaves were high or low (approximately 2.5 or 0.3 nmol cm-2 min-1 respectively), with no continuous variation. Transformants in the high group had single T-DNA insertions, while those in the low group had multiple T-DNA insertions, at the same or different loci. Within each group, although T-DNA was apparently integrated at different sites in the plant genome, there was no evidence of position effects. GUS activity levels of the transformants were very similar in the field and in environmentally controlled conditions under high or low light. Plants with multiple insertions and low expression also tended to have increased methylation of the integrated T-DNA.

High levels of tryptamine accumulation in transgenic tobacco expressing tryptophan decarboxylase

A full-length complementary DNA clone encoding tryptophan decarboxylase (TDC; EC 4.1.1.28) from Catharanthus roseus (De Luca V, Marineau C, Brisson N [1989] Proc Natl Acad Sci USA 86: 2582-2586) driven by the CaMV 35S promoter was introduced into tobacco (Nicotiana tabacum) to direct the synthesis of the protoalkaloid tryptamine from endogenous tryptophan. Young, fully expanded leaves of CaMV 35S-TDC transformed plants had from four to 45 times greater TDC activity than did controls. Tryptamine accumulated in transgenic plants to levels that were directly proportional to their TDC specific activity. Despite their increased tryptamine content, the growth and development of the CaMV 35S-TDC plants appeared normal with no significant differences in indole-3-acetic acid levels between high tryptamine and control plants. Plants with the highest TDC activity contained more than 1 milligram of tryptamine per gram fresh weight, a 260-fold increase over controls.