Cauliflower Mosaic Viral Promoter - A Recipe for Disaster?

An endogenous promoter LpSUT2 discovered in duckweed: a promising transgenic tool for plants

Promoters are one of the most critical elements in regulating gene expression. They are considered essential biotechnological tools for heterologous protein production. The one most widely used in plants is the 35S promoter from cauliflower mosaic virus. However, our study for the first time discovered the 35S promoter reduced the expression of exogenous proteins under increased antibiotic stress. We discovered an endogenous strong promoter from duckweed named LpSUT2 that keeps higher initiation activity under antibiotic stress. Stable transformation in duckweed showed that the gene expression of eGFP in the LpSUT2:eGFP was 1.76 times that of the 35S:eGFP at 100 mg.L-1 G418 and 6.18 times at 500 mg.L-1 G418. Notably, with the increase of G418 concentration, the gene expression and the fluorescence signal of eGFP in the 35S:eGFP were weakened, while the LpSUT2:eGFP only changed slightly. This is because, under high antibiotic stress, the 35S promoter was methylated, leading to the gene silencing of the eGFP gene. Meanwhile, the LpSUT2 promoter was not methylated and maintained high activity. This is a previously unknown mechanism that provides us with new insights into screening more stable promoters that are less affected by environmental stress. These outcomes suggest that the LpSUT2 promoter has a high capacity to initiate the expression of exogenous proteins. In conclusion, our study provides a promoter tool with potential application for plant genetic engineering and also provides new insights into screening promoters.

Genetically modified crops are superior in their nitrogen use efficiency-A meta-analysis of three major cereals

It is currently uncertain to what extent genetic transformations of strategic crops (targeting diverse traits) have improved their N use efficiency (NUE), and what the key factors affecting their NUE are. Based on data collected from 130 publications, the effect sizes of genetic transformations and the key factors influencing NUE for three major cereal crops (rice, maize, and wheat), were investigated using a meta-analysis approach. Genetic transformations increased yield, shoot biomass, N uptake efficiency (NUpE), and partial factor productivity of N (PFPN) in the crops, but decreased shoot NUE (SNUE) and grain NUE (GNUE). Transporter genes improved yield and NUE parameters more efficiently, than did the other gene types. The effect sizes for some NUE parameters varied according to crop species and experimental conditions but did not differ between the overexpression and ectopic expression methods. Most effect sizes did not correlate with gene overexpression levels. These results indicate a promising potential of genetic transformations approaches for improving certain NUE parameters.

Addressing concerns over the fate of DNA derived from genetically modified food in the human body: A review

Global commercialization of GM food and feed has stimulated much debate over the fate of GM food-derived DNA in the body of the consumer and as to whether it poses any health risks. We reviewed the fate of DNA derived from GM food in the human body. During mechanical/chemical processing, integrity of DNA is compromised. Food-DNA can survive harsh processing and digestive conditions with fragments up to a few hundred bp detectable in the gastrointestinal tract. Compelling evidence supported the presence of food (also GM food) derived DNA in the blood and tissues of human/animal. There is limited evidence of food-born DNA integrating into the genome of the consumer and of horizontal transfer of GM crop DNA into gut-bacteria. We find no evidence that transgenes in GM crop-derived foods have a greater propensity for uptake and integration than the host DNA of the plant-food. We found no evidence of plant-food DNA function/expression following transfer to either the gut-bacteria or somatic cells. Strong evidence suggested that plant-food-miRNAs can survive digestion, enter the body and affect gene expression patterns. We envisage that this multi-dimensional review will address questions regarding the fate of GM food-derived DNA and gene-regulatory-RNA in the human body.

Characterization of a strong and constitutive promoter from the Arabidopsis serine carboxypeptidase-like gene AtSCPL30 as a potential tool for crop transgenic breeding

BACKGROUND

Transgenic technology has become an important technique for crop genetic improvement. The application of well-characterized promoters is essential for developing a vector system for efficient genetic transformation. Therefore, isolation and functional validation of more alternative constitutive promoters to the CaMV35S promoter is highly desirable.

RESULTS

In this study, a 2093-bp sequence upstream of the translation initiation codon ATG of AtSCPL30 was isolated as the full-length promoter (PD1). To characterize the AtSCPL30 promoter (PD1) and eight 5' deleted fragments (PD2-PD9) of different lengths were fused with GUS to produce the promoter::GUS plasmids and were translocated into Nicotiana benthamiana. PD1-PD9 could confer strong and constitutive expression of transgenes in almost all tissues and development stages in Nicotiana benthamiana transgenic plants. Additionally, PD2-PD7 drove transgene expression consistently over twofold higher than the well-used CaMV35S promoter under normal and stress conditions. Among them, PD7 was only 456 bp in length, and its transcriptional activity was comparable to that of PD2-PD6. Moreover, GUS transient assay in the leaves of Nicotiana benthamiana revealed that the 162-bp (- 456~ - 295 bp) and 111-bp (- 294~ - 184 bp) fragments from the AtSCPL30 promoter could increase the transcriptional activity of mini35S up to 16- and 18-fold, respectively.

CONCLUSIONS

As a small constitutive strong promoter of plant origin, PD7 has the advantage of biosafety and reduces the probability of transgene silencing compared to the virus-derived CaMV35S promoter. PD7 would also be an alternative constitutive promoter to the CaMV35S promoter when multigene transformation was performed in the same vector, thereby avoiding the overuse of the CaMV35S promoter and allowing for the successful application of transgenic technology. And, the 162- and 111-bp fragments will also be very useful for synthetic promoter design based on their high enhancer activities.

Environmental impacts of genetically modified plants: A review

Powerful scientific techniques have caused dramatic expansion of genetically modified crops leading to altered agricultural practices posing direct and indirect environmental implications. Despite the enhanced yield potential, risks and biosafety concerns associated with such GM crops are the fundamental issues to be addressed. An increasing interest can be noted among the researchers and policy makers in exploring unintended effects of transgenes associated with gene flow, flow of naked DNA, weediness and chemical toxicity. The current state of knowledge reveals that GM crops impart damaging impacts on the environment such as modification in crop pervasiveness or invasiveness, the emergence of herbicide and insecticide tolerance, transgene stacking and disturbed biodiversity, but these impacts require a more in-depth view and critical research so as to unveil further facts. Most of the reviewed scientific resources provide similar conclusions and currently there is an insufficient amount of data available and up until today, the consumption of GM plant products are safe for consumption to a greater extent with few exceptions. This paper updates the undesirable impacts of GM crops and their products on target and non-target species and attempts to shed light on the emerging challenges and threats associated with it. Underpinning research also realizes the influence of GM crops on a disturbance in biodiversity, development of resistance and evolution slightly resembles with the effects of non-GM cultivation. Future prospects are also discussed.

Strength, Stability, and cis-Motifs of In silico Identified Phloem-Specific Promoters in Brassica juncea (L.)

Aphids, a hemipteran group of insects pose a serious threat to many of the major crop species including Brassica oilseeds. Transgenic strategies for developing aphid-resistant plant types necessitate phloem-bound expression of the insecticidal genes. A few known phloem-specific promoters, in spite of tissue-specific activity fail to confer high level gene-expression. Here, we identified seven orthologues of phloem-specific promoters in B. juncea (Indian mustard), and experimentally validated their strength of expression in phloem exudates. Significant cis-motifs, globally occurring in phloem-specific promoters showed variable distribution frequencies in these putative phloem-specific promoters of B. juncea. In RT-qPCR based gene-expression study promoter of Glutamine synthetase 3A (GS3A) showed multifold higher activity compared to others, across the different growth stages of B. juncea plants. A statistical method employing four softwares was devised for rapidly analysing stability of the promoter-activities across the plant developmental stages. Different statistical softwares ranked these B. juncea promoters differently in terms of their stability in promoter-activity. Nevertheless, the consensus in output empirically suggested consistency in promoter-activity of the six B. juncea phloem- specific promoters including GS3A. The study identified suitable endogenous promoters for high level and consistent gene-expression in B. juncea phloem exudate. The study also demonstrated a rapid method of assessing species-specific strength and stability in expression of the endogenous promoters.

The transformation of the photo-thermo sensitive genic male-sterile line 261S of rice via an expression vector containing the anti-Waxy gene

Transgenic photo-thermo sensitive genic male sterility Oryza sativa L. cv. "261S" plants with the anti-Waxy gene were successfully obtained using an Agrobacterium tumefaciens-mediated co-transformation method. Marker-free homozygous transgenic lines with the anti-Waxy gene were obtained. The setting seed rates of the transgenic plants via self-pollination or via crossing with the restorer line WX99075 rice and the 1000-grain weight of the transgenic plants and the F2 hybrid seeds obtained by crossing the transgenic or non-transgenic plants with the restorer line WX99075 rice, and the number of panicles of the transgenic plants and yields of the F2 hybrid rice, were analysed. Quality indexes of the transgenic plants and of the F2 hybrid seeds were analysed. Our researches results indicate that hybrid female and hybrid descendant edibility could be improved via the introduction of the anti-Waxy gene, but the grain yields of the reserve seeds via self-pollination of the transgenic photo-thermo sensitive genic sterile lines and of the hybrid rice were not affected.

Isolation and characterization of an oil palm constitutive promoter derived from a translationally control tumor protein (TCTP) gene

We have characterized an oil palm (Elaeis guineensis Jacq.) constitutive promoter that is derived from a translationally control tumor protein (TCTP) gene. The TCTP promoter was fused transcriptionally with the gusA reporter gene and transferred to monocot and dicot systems in order to study its regulatory role in a transient expression study. It was found that the 5' region of TCTP was capable of driving the gusA expression in all the oil palm tissues tested, including immature embryo, embryogenic callus, embryoid, young leaflet from mature palm, green leaf, mesocarp and stem. It could also be used in dicot systems as it was also capable of driving gusA expression in tobacco leaves. The results indicate that the TCTP promoter could be used for the production of recombinant proteins that require constitutive expression in the plant system.

Facts and fiction of genetically engineered food

The generation of genetically engineered (GE) foods has been raising several concerns and controversies that divide not only the general public but also the scientific community. The fear and importance of the new technology, as well as commercial interests, have supported many of the ongoing discussions. The recent increase in the number of GE foods approved for import into the European Union and the increasingly global commercial food trades justify revisiting the facts and fiction surrounding this technology with the aim of increasing public awareness for well-informed decisions. Techniques that have recently become available for assessing food quality and its impact on human health, as well as the wealth of scientific data previously generated, clearly support the safety of commercialized GE products.

Assessment of CaMV-mediated gene silencing and integration of CaMV into GM plants with a 35S RNA promoter

Four GM plant species (Arabidopsis thaliana, Brassica napus, Nicotiana benthamiana and N. tabacum), each expressing the gene encoding the jellyfish green fluorescent protein (GFP) regulated by the cauliflower mosaic virus (CaMV) 35S RNA promoter, were assessed for the extent of transgene silencing and viral genome integration following infection by CaMV. The first three species are systemic hosts of CaMV, while N. tabacum is only a local host for a few strains of CaMV. A generalized systemic silencing of the GFP transgene was not observed in a total of 100 plants of each species infected with CaMV, although some localized loss of GFP was observed in CaMV-infected N. benthamiana leaves, and some loss of fluorescence was observed in older leaves of uninfected as well as infected plants. Progeny seedlings obtained from the above infected plants also did not exhibit transgene silencing showing that virus infection did not affect the stability of the transgene. These progeny plants also did not show signs of virus infection, indicating that the presence of the CaMV 35S RNA promoter sequences in the plant genome did not potentiate seed transmission of the virus. Integration of infective CaMV into the CaMV 35S RNA promoter could not be detected in 944 samples taken from leaves of the above infected plant species or in 2912 samples taken from progeny seedlings. Based on a detection limit of one copy per 4000 haploid genomes, we conclude that if integration of virus does occur into the CaMV 35S RNA promoter, then it occurs at such a low frequency as to be insignificant.

The cauliflower mosaic virus (CaMV) 35S promoter sequence alters the level and patterns of activity of adjacent tissue- and organ-specific gene promoters

Here we report the effect of the 35S promoter sequence on activities of the tissue- and organ-specific gene promoters in tobacco plants. In the absence of the 35S promoter sequence the AAP2 promoter is active only in vascular tissues as indicated by expression of the AAP2:GUS gene. With the 35S promoter sequence in the same T-plasmid, transgenic plants exhibit twofold to fivefold increase in AAP2 promoter activity and the promoter becomes active in all tissue types. Transgenic plants hosting the ovary-specific AGL5:iaaM gene (iaaM coding an auxin biosynthetic gene) showed a wild-type phenotype except production of seedless fruits, whereas plants hosting the AGL5:iaaM gene along with the 35S promoter sequence showed drastic morphological alterations. RT-PCR analysis confirms that the phenotype was caused by activation of the AGL5:iaaM gene in non-ovary organs including roots, stems and flowers. When the pollen-, ovule- and early embryo-specific PAB5:barnase gene (barnase coding a RNase gene) was transformed, the presence of 35S promoter sequence drastically reduced transformation efficiencies. However, the transformation efficiencies were restored in the absence of 35S promoter, indicating that the 35S promoter might activate the expression of PAB5:barnase in non-reproductive organs such as calli and shoot primordia. Furthermore, if the 35S promoter sequence was replaced with the NOS promoter sequence, no alteration in AAP2, AGL5 or PAB5 promoter activities was observed. Our results demonstrate that the 35S promoter sequence can convert an adjacent tissue- and organ-specific gene promoter into a globally active promoter.

Transient expression in mammalian cells of transgenes transcribed from theCauliflower mosaic virus35S promoter

Gene constructs containing the Cauliflower mosaic virus (CaMV) 35S promoter and a sequence coding either for a green fluorescent protein (GFP) or for firefly luciferase were transfected into Chinese hamster ovary (CHO) cells. Both reporter genes were expressed to significant levels. The 35S promoter was 40 times less active than the human eF1 alpha promoter, which is known to be one of the most potent promoters in mammalian cells. The 35S promoter must therefore be considered to be a promoter of significant potency in mammalian cells. RT-PCR analysis suggested that transcription initiation in CHO cells occurred between the TATA box and the transcription start site of the 35S promoter that function in plant cells. Further analysis by 5'RACE confirmed that transcription was initiated in CHO cells at different sites located essentially between the TATA box and the plant transcription start site, showing that 35S promoter activity in animal cells is due to the presence of promoter elements that are functional in mammalian cells, but that are not those used in plants. The data reported here raise the possibility that genes controlled by the 35S promoter, which is commonly used in transgenic plants, have the potential for expression in animal cells.

The relevance of gene transfer to the safety of food and feed derived from genetically modified (GM) plants

In 2000, the thematic network ENTRANSFOOD was launched to assess four different topics that are all related to the testing or assessment of food containing or produced from genetically modified organisms (GMOs). Each of the topics was linked to a European Commission (EC)-funded large shared cost action (see http://www.entransfood.com). Since the exchange of genetic information through horizontal (lateral) gene transfer (HGT) might play a more important role, in quantity and quality, than hitherto imagined, a working group dealing with HGT in the context of food and feed safety was established. This working group was linked to the GMOBILITY project (GMOBILITY, 2003) and the results of the deliberations are laid down in this review paper. HGT is reviewed in relation to the potential risks of consuming food or feed derived from transgenic crops. First, the mechanisms for obtaining transgenic crops are described. Next, HGT mechanisms and its possible evolutionary role are described. The use of marker genes is presented in detail as a special case for genes that may pose a risk. Furthermore, the exposure to GMOs and in particular to genetically modified (GM) deoxyribonucleic acid (DNA) is discussed as part of the total risk assessment. The review finishes off with a number of conclusions related to GM food and feed safety. The aim of this paper is to provide a comprehensive overview to assist risk assessors as well as regulators and the general public in understanding the safety issues related to these mechanisms.

Assessing the value of transgenic crops

In the current controversy about the value of transgenic crops, matters open to empirical inquiry are centrally at issue. One such matter is a key premise in a common argument (that I summarize) that transgenic crops should be considered to have universal value. The premise is that there are no alternative forms of agriculture available to enable the production of sufficient food to feed the world. The proponents of agroecology challenge it, claiming that agroecology provides an alternative, and they deny the claim that it is well founded on empirical evidence. It is, therefore, a matter of both social and scientific importance that this premise and the criticisms of it be investigated rigorously and empirically, so that the benefits and disadvantages of transgenic-intensive agriculture and agroecology can be compared in a reliable way. Conducting adequate investigation about the potential contribution of agroecology requires that the cultural conditions of its practice (and, thus, of the practices and movements of small-scale farmers in the "third world") be strengthened--and this puts the interests of investigation into tension with the socio-economic interests driving the development of transgenics. General issues about relationship between ethical argument and empirical (scientific) investigation are raised throughout the article.

Assuring the safety of genetically modified (GM) foods: the importance of an holistic, integrative approach

Genes change continuously by natural mutation and recombination enabling man to select and breed crops having the most desirable traits such as yield or flavour. Genetic modification (GM) is a recent development which allows specific genes to be identified, isolated, copied and inserted into other plants with a high level of specificity. The food safety considerations for GM crops are basically the same as those arising from conventionally bred crops, very few of which have been subject to any testing yet are generally regarded as being safe to eat. In contrast a rigorous safety testing paradigm has been developed for GM crops, which utilises a systematic, stepwise and holistic approach. The resultant science based process, focuses on a classical evaluation of the toxic potential of the introduced novel trait and the wholesomeness of the transformed crop. In addition, detailed consideration is given to the history and safe use of the parent crop as well as that of the gene donor. The overall safety evaluation is conducted under the concept known as substantial equivalence which is enshrined in all international crop biotechnology guidelines. This provides the framework for a comparative approach to identify the similarities and differences between the GM product and its comparator which has a known history of safe use. By building a detailed profile on each step in the transformation process, from parent to new crop, and by thoroughly evaluating the significance from a safety perspective, of any differences that may be detected, a very comprehensive matrix of information is constructed which enables the conclusion as to whether the GM crop, derived food or feed is as safe as its traditional counterpart. Using this approach in the evaluation of more than 50 GM crops which have been approved worldwide, the conclusion has been that foods and feeds derived from genetically modified crops are as safe and nutritious as those derived from traditional crops. The lack of any adverse effects resulting from the production and consumption of GM crops grown on more than 300 million cumulative acres over the last 5 years supports these safety conclusions.