Neomycin Phosphotransferase II Research Articles

Safety Assessment of the CP4 EPSPS and NPTII Proteins in Eucalyptus

ABSTRACT Glyphosate herbicide treatment is essential to sustainable Eucalyptus plantation management in Brazil. Eucalyptus is highly sensitive to glyphosate, and Suzano/FuturaGene has genetically modified eucalyptus to tolerate glyphosate, with the aim of both protecting eucalyptus trees from glyphosate application damage and improving weed management. This study presents the biosafety results of the glyphosate-tolerant eucalyptus event 751K032, which expresses the selection marker neomycin phosphotransferase II (NPTII) enzyme and CP4-EPSPS, a glyphosate-tolerant variant of plant 5-enolpyruvyl-shikimate−3-phosphate synthase enzyme. The transgenic genetically modified (GM) event 751K032 behaved in the plantations like conventional non-transgenic eucalyptus clone, FGN-K, and had no effects on arthropods and soil microorganisms. The engineered NPTII and CP4 EPSPS proteins were heat-labile, readily digestible, and according to the bioinformatics analyses, unlikely to cause an allergenic or toxic reaction in humans or animals. This assessment of the biosafety of the glyphosate-tolerant eucalyptus event 751K032 concludes that it is safe to be used for wood production.

In vitro</em></strong><strong> direct regeneration and <em>Agrobacterium tumefaciens</em> mediated <em>in planta</em> transformation of <em>Ocimum sanctum L.

An in vitro regeneration system for propagation has been successfully developed for a valuable medicinal and aromatic plant ‘ Ocimum sanctum L’. In the present study, petiole explants, from in-vitro grown cultures of O. sanctum, was used for direct regeneration. The developed protocol employed 98% of regeneration frequency in addition to 9.6 shoots per explant when cultured on Murashige and Skoog (MS) medium fortified with 3 mg/L benzylamino purine (BAP) and 1 mg/L Naphthalene acetic acid (NAA). Furthermore, Agrobacterium tumefaciens Mediated genetic Transformation (ATMT) protocol (transient and stable) was also developed using LBA4404 strain harboring pBI121 with uid-A and neomycin phosphotransferase genes. The regenerated transformants were shifted on MS with kanamycin (50 mg/L) and afterwards placed on the half-strength MS medium. The validation was done through polymerase chain reaction (PCR) with neomycin phosphotransferase-II ( npt-II) & β-glucoronidase ( uid-A) gene primers. The maximum stable transformation frequency of 70% ± 0.35 was achieved. Hence, it is apparent that the established protocols i.e. in vitro direct regeneration and ATMT are appropriate for integrating novel enzymes/genes through high throughput techniques such as gene tagging, and targeted gene replacement to modulate the primary as well as secondary metabolic flux towards desired agronomic product or trait in planta.

The Specificity of Transgene Suppression in Plants by Exogenous dsRNA.

The phenomenon of RNA interference (RNAi) is widely used to develop new approaches for crop improvement and plant protection. Recent investigations show that it is possible to downregulate plant transgenes, as more prone sequences to silencing than endogenous genes, by exogenous application of double-stranded RNAs (dsRNAs) and small interfering RNAs (siRNAs). However, there are scarce data on the specificity of exogenous RNAs. In this study, we explored whether plant transgene suppression is sequence-specific to exogenous dsRNAs and whether similar effects can be caused by exogenous DNAs that are known to be perceived by plants and induce certain epigenetic and biochemical changes. We treated transgenic plants of Arabidopsis thaliana bearing the neomycin phosphotransferase II (NPTII) transgene with specific synthetic NPTII-dsRNAs and non-specific dsRNAs, encoding enhanced green fluorescent protein (EGFP), as well as with DNA molecules mimicking the applied RNAs. None of the EGFP-dsRNA doses resulted in a significant decrease in NPTII transgene expression in the NPTII-transgenic plants, while the specific NPTII-dsRNA significantly reduced NPTII expression in a dose-dependent manner. Long DNAs mimicking dsRNAs and short DNA oligonucleotides mimicking siRNAs did not exhibit a significant effect on NPTII transgene expression. Thus, exogenous NPTII-dsRNAs induced a sequence-specific and RNA-specific transgene-suppressing effect, supporting external application of dsRNAs as a promising strategy for plant gene regulation.

An efficient and rapid kanamycin screening assay for identifying true transgenics in cotton

Genetic engineering is the best suitable approach for the generation of insect resistant cotton in private and public funded laboratories. Neomycin Phosphotransferase-II is the most commonly used selectable marker gene that can catabolize to kanamycin resistant protein which helps in screening and differentiation of resistant and sensitive plants. In current paper, the optimal concentration of kanamycin was determined as 200 mg/L in control plants. Based on this standardized a procedure for screening transformed plants by spraying 200 mg/L at seedling stage. The resistant plants were reconfirmed by PCR using Npt II specific primers. About 51% and 45% of kanamycin resistant plants were showed amplification of Npt II gene at T1 and T2 generation respectively. This method is simple and fast which can be exploited for screening large number of seedlings with low cost in effective manner.

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.

Peptide-Based Polyion Complex Vesicles That Deliver Enzymes into Intact Plants To Provide Antibiotic Resistance without Genetic Modification.

Direct delivery of enzymes into intact plants using cell-penetrating peptides (CPPs) is an attractive approach for modifying plant functions without genetic modification. However, by conventional methods, it is difficult to maintain the enzyme activity for a long time because of proteolysis of the enzymes under physiological conditions. Here, we developed a novel enzyme delivery system using polyion complex vesicles (PICsomes) to protect the enzyme from proteases. We created PICsome-bearing reactive groups at the surface by mixing an anionic block copolymer, alkyne-TEG-P(Lys-COOH), and a cationic peptide, P(Lys). The PICsome encapsulated neomycin phosphotransferase II (NPTII), a kanamycin resistance enzyme, and protected NPTII from proteases in vitro. A CPP-modified PICsome delivered NPTII into the root hair cells of Arabidopsis thaliana seedlings and provided kanamycin resistance in the seedlings that lasted for 7 days. Thus, the PICsome-mediated enzyme delivery system is a promising method for imparting long-term transient traits to plants without genetic modification.

An Efficient Agrobacterium-Mediated Genetic Transformation Using Embryonic Axis in Cotton (Gossypium hirsutum L.)

Agrobacterium-mediated genetic transformation approach allows for introducing novel genes in cotton (Gossypium hirsutum L.). Development of efficient regeneration and transformation protocol is very important for recalcitrant plants like cotton. In the present study, five-day-old germinated mature embryo parts especially embryonic axis, hypocotyl and plumule of cotton ‘Lashata’ were wounded and inoculated with A. tumefaciens strain GV2260 harbouring plasmid p35S-GUS-INT. The binary plasmid p35S-GUS-INT contains neomycin phosphotransferase II (NPTII) gene driven by nopaline synthase (NOS) promoter and β-glucuronidase (GUS) gene controlled by cauliflower mosaic virus (CaMV) 35S promoter. After inoculation, explants were co-cultivated in liquid and agar-solidified MS medium for 48 h in dark condition. Agar-solidified co-cultivation medium increased transformation frequency as compared to liquid medium. The putative primary transformants were confirmed with histochemical GUS assay, PCR and RT-PCR. However, comparing the three culture explant, the embryonic axis explants had significant difference with embryonic hypocotyl and plumule explants in terms of number and percentage (%) of GUS, PCR and RT-PCR positive plant. The total transformation efficiency was recorded as 3% with varying GUS expression levels.

Estimation of neomycin phosphotransferase-II (NPT-II) protein in vegetative and reproductive tissues of transgenic chickpea (Cicer arietinum L.) and biosafety perspectives

Chickpeas are consumed in various edible forms and hence presence of NPT-II proteins encoded by kanamycin resistance gene, NPT-II, in transgenic chickpea seeds raises biosafety concerns related to human health in particular. We estimated the NPT-II protein from various tissues like leaf, pod wall, immature seeds and mature dried seeds of five different transgenic chickpea lines expressing NPT-II. Quantitative ELISA studies indicated that the amount of NPT-II proteins decrease, as chickpea plants approached physiological maturity with mature seeds having lowest NPT-II content (0.98–1.32 ng/mg Total Soluble Protein). Mature chickpea seeds are most commonly used for edible purpose and the content of NPT-II estimated possess no discernible biosafety concern. Further, bioinformatics studies also indicate that NPT-II proteins are innocuous and possibly should not be active in acidic environment in the human gut.

An optimized double T-DNA binary vector system for improved production of marker-free transgenic tobacco plants.

In the plant transformation process, marker genes play a vital role in identifying transformed cells from non-transformed cells. However, once transgenic plants have been obtained, the presence of marker genes may provoke public concern about environmental or biosafety issues. In our previous study, a double T-DNA vector system has been developed to obtain marker-free transgenic plants, but the T-DNA left border (LB) and right border (RB) of the vector showed an RB-LB-RB-LB pattern and led to high linkage integration between the selectable marker gene (SMG) and the gene of interest (GOI). To improve this double T-DNA vector system, we inverted the first T-DNA direction such that a LB-RB-RB-LB pattern resulted to avoid transcriptional read-through at the LB and the subsequent linkage transfer of the SMG and GOI. We separately inserted the green fluorescent protein (GFP) gene as the GOI and the neomycin phosphotransferase II (NPTII) gene as the SMG in both optimized and original vectors and carried out Agrobacterium-mediated tobacco transformation. Statistical analysis revealed that the linkage frequency was 25.6% in T0 plants transformed with the optimized vector, which is a 42.1% decrease compared with that of the original vector (44.2%). The frequency of obtaining marker-free transgenic plants was 66.7% in T1 plants transformed with the optimized vector, showing a 33.4% increase compared with that of the original vector (50.0%). Our results demonstrate that the optimized double T-DNA binary vector system is a more effective, economical and time-saving approach for obtaining marker-free transgenic plants.

Transgene suppression in plants by foliar application of in vitro-synthesized small interfering RNAs.

Recent research has shown that plants can uptake long dsRNAs and dsRNA-derived siRNAs that target important genes of infecting fungi or viruses when applied on the surface of plant leaves. The external RNAs were capable of local and systemic movement inducing plant resistance against the pathogens. Few studies have been made for plant gene regulation by foliar application of RNAs. In this study, several types of ssRNA and siRNA duplexes targeting the neomycin phosphotransferase II (NPTII) transgene were in vitro-synthesized and externally applied to the leaf surface of 4-week-old transgenic Arabidopsis thaliana plants. External application of the synthetic NPTII-encoding siRNAs down-regulated NPTII transcript levels in transgenic A. thaliana 1 and 7days post-treatment with a higher and more consistent effect being observed for siRNAs methylated at 3' ends. We also analyzed the effects of external NPTII-encoding dsRNA precursors and a dsRNA-derived heterogenous siRNA mix. Digestion of the NPTII-dsRNA to the heterogeneous siRNAs did not improve efficiency of the transgene suppression effect. Key Points• Foliar application of siRNAs down-regulated a commonly used transgene in Arabidopsis. • A more consistent effect was observed for methylated siRNAs. • The findings are important for development of plant gene regulation approaches.

Enhanced electrocatalytic behaviour of gold electrodes modified with ZnO nanoparticles through organophosphonate chemistry

Stable immobilization and homogenous distribution of ZnO nanostructures on solid substrates can play a fundamental role in developing nanostructured biosensing devices. In this work we studied how phosphonic acid-terminated self-assembled monolayers (SAMP of 1) can enhance the electrocatalytic behaviour of ZnO nanoparticles (NPs) immobilized on gold surface. It is well known that alkanethiols can form uniform and conformal monolayers on gold through the thiol group and it has already been shown that ZnO surface can be modified by organophosphonates. Here we focus on the application of this chemistry as a tool for the fabrication of designed architectures of ZnO nanostructures on gold electrodes. Successful surface modification was verified by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Our results indicate the formation of highly stable arrays of ZnO nanoparticles. As a proof of concept, the novel electrodes developed were tested in electrochemical assays for the detection of the transgenic protein neomycin phosphotransferase II (NPTII), showing enhanced electrocatalytic stability in immunosensor applications. The target protein could be detected down to nanomolar level by using the difference in charge transfer resistance (ΔRct) recorded in impedance spectroscopy measurements.

Induction of Transgene Suppression in Plants via External Application of Synthetic dsRNA.

Recent investigations show that exogenously applied small interfering RNAs (siRNA) and long double-stranded RNA (dsRNA) precursors can be taken up and translocated in plants to induce RNA interference (RNAi) in the plant or in its fungal pathogen. The question of whether genes in the plant genome can undergo suppression as a result of exogenous RNA application on plant surface is almost unexplored. This study analyzed whether it is possible to influence transcript levels of transgenes, as more prone sequences to silencing, in Arabidopsis genome by direct exogenous application of target long dsRNAs. The data revealed that in vitro synthesized dsRNAs designed to target the gene coding regions of enhanced green fluorescent protein (EGFP) or neomycin phosphotransferase II (NPTII) suppressed their transcript levels in Arabidopsis. The fact that, simple exogenous application of polynucleotides can affect mRNA levels of plant transgenes, opens new opportunities for the development of new scientific techniques and crop improvement strategies.

Application of CRISPR/Cas9-Mediated Gene Editing in Tomato.

CRISPR-/Cas9-mediated gene editing has been demonstrated in a number of food crops including tomato. Tomato (Solanum lycopersicum) is both an important food crop and a model plant species that has been used extensively for studying gene function, especially as it relates to fruit biology. This duality in purpose combined with readily available resources (mutant populations, genome sequences, transformation methodology) makes tomato an ideal candidate for gene editing. The CRISPR/Cas9 system routinely used in our laboratory has been applied to various tomato genotypes and the wild species, Solanum pimpinellifolium. The vector system is based on Golden Gate cloning techniques. Cassettes that contain the neomycin phosphotransferase II (NPTII) selectable marker gene that confers resistance to kanamycin, a human codon-optimized Cas9 driven by the CaMV 35S promoter, and guide RNA (gRNA) under control of the Arabidopsis U6 polymerase promoter are assembled into a T-DNA vector. Generally, we design CRISPR/Cas9 constructs that contain two gRNAs per gene target. However, we have been successful with inclusion of up to eight gRNAs to simultaneously target multiple genes and regions. Introduction of CRISPR-/Cas9-designed constructs into tomato is accomplished by transformation methodology based on Agrobacterium tumefaciens infection of young cotyledon sections and selection on kanamycin-containing medium based on the presence of the NPTII gene. The approaches for the development of CRISPR/Cas9 constructs and genotypic analyses (PCR-based amplicon sequencing and T7 endonuclease) are detailed in this chapter.

An efficient method for transgenic callus induction from Vitis amurensis petiole.

Transformation is the main platform for genetic improvement and gene function studies in plants. However, the established somatic embryo transformation system for grapevines is time-consuming and has low efficiency, which limits its utilization in functional genomics research. Vitis amurensis is a wild Vitis species with remarkable cold tolerance. The lack of an efficient genetic transformation system for it has significantly hindered the functional identification of cold stress related genes in the species. Herein, an efficient method was established to produce transformed calli of V. amurensis. Segments of petioles from micropropagated plantlets of V. amurensis exhibited better capacity to differentiate calli than leaf-discs and stem segments, and thus was chosen as target tissue for Agrobacterium-mediated transformation. Both neomycin phosphotransferase II (NPTII) and enhanced green fluorescent protein (eGFP) genes were used for simultaneous selection of transgenic calli based on kanamycin resistance and eGFP fluorescence. Several parameters affecting the transformation efficiency were optimized including the concentration of kanamycin, Agrobacterium stains, bacterial densities, infection treatments and co-cultivation time. The transgenic callus lines were verified by checking the integration of NPTII gene into calli genomes, the expression of eGFP gene and the fluorescence of eGFP. Up to 20% of the petiole segments produced transformed calli after 2 months of cultivation. This efficient transformation system will facilitate the functional analysis of agronomic characteristics and related genes not only in V. amurensis but also in other grapevine species.

Agrobacterium-Mediated Insect Resistance Gene (cry1Aa) Transfer Studies Pertaining to Antibiotic Sensitivity on Cultured Tissues of Broccoli

ABSTRACTSuccessful plant transformation requires an efficient regeneration protocol and a suitable selection method. A genetically engineered, disarmed Agrobacterium tumefaciens strain containing a binary vector pBin-1Aa with cry1Aa (insect resistance) and npt-II (neomycin phosphotransferase-II) genes was used for genetic transformation studies. Effects of antibiotics kanamycin and cefotaxime were studied to determine the aptness of kanamycin resistance as a selectable marker and for cefotaxime in controlling excessive bacterial growth during genetic transformation studies using cultured hypocotyl, cotyledon, leaf, and petiole tissues of Broccoli (Brassica oleracea L var. italica). Leaf and petiole explants exhibited decreased fresh weight as kanamycin concentration increased, resulting in full or partial inhibition of shoot regeneration. A significant or nonsignificant negative correlation occurred between kanamycin concentration and explant fresh weight over the time. Cefotaxime had little effect on regeneration potential. Growth of Agrobacterium cells was controlled at a concentration of 400 mg·L−1 cefotaxime in explants, and maximum putative transgenic shoot regeneration in explants of hypocotyls (44.88%) and cotyledons (36.29%) was obtained on MS (Murashige and Skoog)-selective shoot regeneration medium. Polymerase chain reaction analysis of genomic DNA using specifically designed primers detected the presence of the cryIAa and npt-II genes in kanamycin-resistant broccoli plantlets. Of five randomly selected putative transgenic shoots, three were positive for presence/integration of cryIAa and npt-II genes during T-DNA transfer and integration into the plant genome. Kanamycin and cefotaxime act as effective selective agents during genetic transformation pertaining to antibiotic sensitivity on cultured tissues of broccoli.

A temperature-tolerant multiplex elements and genes screening system for genetically modified organisms based on dual priming oligonucleotide primers and capillary electrophoresis.

High throughput screening systems are the preferred solution to meet the urgent requirement of increasing number of genetically modified organisms (GMOs). In this study, we have successfully developed a multiplex GMO element screening system with dual priming oligonucleotide (DPO) primers. This system can detect the cauliflower mosaic virus 35S (CaMV 35S), terminator of nopaline synthase gene (NOS), figwort mosaic virus 35S (FMV 35S) promoter, neomycin phosphotransferaseII (NPTII), Bt Cry 1Ab, phosphinothricin acetyltransferase genes (bar) and Streptomyces viridochromogenes (pat) simultaneously, which covers more than 90% of all authorized GMO species worldwide. This system exhibits a high tolerance to annealing temperatures, high specificity and a limit of detection equal to conventional PCR. A total of 214 samples from markets, national entry-exit agencies, the Institute for Reference Materials and Measurement (IRMM) and the American Oil Chemists' Society (AOCS) were also tested for applicability. This screening system is therefore suitable for GMO screening.

Direct introduction of neomycin phosphotransferase II protein into apple leaves to confer kanamycin resistance.

The recent developments of transcription activator-like effector nucleases (TALEN) and clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein-9 nuclease (Cas9) have expanded plant breeding technology. One technical issue related to the current genome editing process is residual transgenes for TALEN and CRISPR/Cas9 left in plant genomes after the editing process. Here, we aim to add transient kanamycin resistance into apple leaf cells by introducing neomycin phosphotransferase II (NPTII) into apple leaf cells using the fusion peptide system. At 75 mg/L of kanamycin for 2 days, apple JM1 leaf cells infiltrated with NPTII could be selected. Thus, we successfully demonstrated the first transient selection system of plant cells using a fusion peptide-mediated protein delivery system.

Agrobacterium-mediated genetic transformation of commercially elite rice restorer line using nptII gene as a plant selection marker.

Transformation of commercially important indica cultivars remains challenging for the scientific community even though Agrobacterium-mediated transformation protocols for a few indica rice lines have been well established. We report successful transformation of a commercially important restorer line JK1044R of indica rice hybrid JKRH 401. While following existing protocol, we optimized several parameters for callusing, regeneration and genetic transformation of JK1044R. Calli generated from the rice scutellum tissue were used for transformation by Agrobacterium harboring pCAMBIA2201. A novel two tire selection scheme comprising of Geneticin (G418) and Paramomycin were deployed for selection of transgenic calli as well as regenerated plantlets that expressed neomycin phosphotransferase-II gene encoded by the vector. One specific combination of G418 (30mgl(-1)) and Paramomycin (70 mgl(-1)) was very effective for calli selection. Transformed and selected calli were detected by monitoring the expression of the reporter gene uidA (GUS). Regenerated plantlets were confirmed through PCR analysis of nptII and gus genes specific primers as well as dot blot using gus gene specific as probe.

A Universal Positive-Negative Selection System for Gene Targeting in Plants Combining an Antibiotic Resistance Gene and Its Antisense RNA.

Gene targeting (GT) is a useful technology for accurate genome engineering in plants. A reproducible approach based on a positive-negative selection system using hygromycin resistance and the diphtheria toxin A subunit gene as positive and negative selection markers, respectively, is now available. However, to date, this selection system has been applied exclusively in rice (Oryza sativa). To establish a universally applicable positive-negative GT system in plants, we designed a selection system using a combination of neomycin phosphotransferaseII (nptII) and an antisense nptII construct. The concomitant transcription of both sense and antisense nptII suppresses significantly the level of expression of the sense nptII gene, and transgenic calli and plants become sensitive to the antibiotic geneticin. In addition, we were able to utilize the sense nptII gene as a positive selection marker and the antisense nptII construct as a negative selection marker for knockout of the endogenous rice genes Waxy and 33-kD globulin through GT, although negative selection with this system is relatively less efficient compared with diphtheria toxin A subunit. The approach developed here, with some additional improvements, could be applied as a universal selection system for the enrichment of GT cells in several plant species.