Transient Gene Expression in Intact and Organized Rice Tissues

Protoplast isolation and transient transformation system for Ginkgo biloba L

Ginkgo biloba L. has a unique evolutionary status. Owing to its high medicinal and ornamental value, ginkgo has also recently become a research hotspot. However, the large genome and long juvenile period, as well as the lack of an effective genetic transformation system, have hindered gaining a full understanding of the comprehensive functions of ginkgo genes. At present, heterologous expression of genes in model plants is the primary method used in ginkgo-related research; however, these distant plant model relatives limit reliable interpretation of the results for direct applications in ginkgo breeding. To overcome these limitations, in this study, an efficient isolation and transient expression system for ginkgo protoplasts was established. A large number of intact and homogeneous ginkgo mesophyll protoplasts were isolated using 2% cellulase and 0.25% pectinase in 0.4 M mannitol. The activity of these protoplasts remained above 90% even after 24 h. Furthermore, when the concentration of the polyethylene glycol 4000 solution was 30%-40% (w/v), the transformation efficiency of the protoplasts reached 40%. Finally, the reliability of the system was verified using subcellular localization, transient overexpression, and protein interaction experiments with ginkgo genes, thereby providing a technical platform for the identification and analysis of ginkgo gene functions. The proposed method partially compensates for the limitations associated with the lack of a genetic transformation system and provides technical support to expand research on elucidating the functions of ginkgo genes.

The Barley S-Adenosylmethionine Synthetase 3 Gene HvSAMS3 Positively Regulates the Tolerance to Combined Drought and Salinity Stress in Tibetan Wild Barley

Drought and salinity are two of the most frequently co-occurring abiotic stresses. Despite recent advances in the elucidation of the effects of these stresses individually during the vegetative stage of plants, significant gaps exist in our understanding of the combined effects of these two frequently co-occurring stresses. Here, Tibetan wild barley XZ5 (drought tolerant), XZ16 (salt tolerant), and cultivated barley cv. CM72 (salt tolerant) were subjected to drought (D), salinity (S), or a combination of both treatments (D+S). Protein synthesis is one of the primary activities of the green part of the plant. Therefore, leaf tissue is an important parameter to evaluate drought and salinity stress conditions. Sixty differentially expressed proteins were identified by mass spectrometry (MALDI-TOF/TOF) and classified into 9 biological processes based on Gene Ontology annotation. Among them, 21 proteins were found to be expressed under drought or salinity alone; however, under D+S, 7 proteins, including S-adenosylmethionine synthetase 3 (SAMS3), were exclusively upregulated in drought-tolerant XZ5 but not in CM72. HvSAMS3 carries both N-terminal and central domains compared with Arabidopsis and activates the expression of several ethylene (ET)-responsive transcription factors. HvSAMS3 is mainly expressed in the roots and stems, and HvSAMS3 is a secretory protein located in the cell membrane and cytoplasm. Barley stripe mosaic virus-based virus-induced gene silencing (BSMV-VIGS) of HvSAMS3 in XZ5 severely compromised its tolerance to D+S and significantly reduced plant growth and K+ uptake. The reduced tolerance to the combined stress was associated with the inhibition of polyamines such as spermidine and spermine, polyamine oxidase, ethylene, biotin, and antioxidant enzyme activities. Furthermore, the exogenous application of ethylene and biotin improved the tolerance to D+S in BSMV-VIGS:HvSAMS3-inoculated plants. Our findings highlight the significance of HvSAMS3 in the tolerance to D+S in XZ5.

Interspaced Repeat Sequences Confer the Regulatory Functions of AtXTH10, Important for Root Growth in Arabidopsis

An interspaced repeat sequence (IRS) is a unique sequence similar to prokaryotic CRISPR in structure. In this study, 1343 IRSs were identified in the Arabidopsis genome. Functional annotation of the IRS-related genes showed that they were associated with various growth and development processes. More than 30% of the IRSs were located in promoter regions. Deletion of some IRSs affected promoter activity, suggesting their roles in the regulation of gene expression. Next, the function of the AtXTH10 gene was further analyzed, and the expression of this gene was regulated by IRSs in its promoter region. Transgenic and mutant plants analysis indicated that the AtXTH10 gene was associated with root development by affecting cell wall structure. Moreover, the expression profiles of some key genes involved in root development signaling pathways were also affected by AtXTH10. These results suggest that IRSs could be involved in regulating the expression of genes with important roles in plant development.

Repurposing Macromolecule Delivery Tools for Plant Genetic Modification in the Era of Precision Genome Engineering

Efficient delivery of macromolecules into plant cells and tissues is important for both basic research and biotechnology product applications. In transgenic research, the goal is to deliver DNA molecules into regenerable cells and stably integrate them into the genome. Over the past 40 years, many macromolecule delivery methods have been studied. To generate transgenic plants, particle bombardment and Agrobacterium-mediated transformation are the methods of choice for DNA delivery. The rapid advance of genome editing technologies has generated new requirements on large biomolecule delivery and at the same time reinvigorated the development of new transformation technologies. Many of the gene delivery options that have been studied before are now being repurposed for delivering genome editing machinery for various applications. This article reviews the major progress in the development of tools for large biomolecule delivery into plant cells in the new era of precision genome engineering.

Omics and Edible Vaccines

Molecular farming provides an unprecedented approach for the production of metabolites or proteins of medicinal value from plants used previously only in agricultural setting. These plants act as protein factories that can synthesize a variety of proteins free from pathogens such as plasma proteins, growth factors, and vaccines. This method provides a novel, tempting, inexpensive, easy, and safe alternative to other techniques of protein or antigen production. With the advent of transgenic plants, it is possible to produce unlimited amounts of subunit vaccines (for oral use/edible and of parenteral use), protein used for pharmaceutical/medicinal purpose, recombinant proteins, antibodies, and industrial enzymes. Plants have numerous advantages over the production systems on account of scalability, safety, and are economic; for example, less cost of production is involved for Hepatitis B nucleocapsid antigen using transgenic tobacco. Biopharming or molecular farming provides an important resource for cheaper drug production used in the treatment of cancer, heart diseases, and infectious diseases. The pharmaceutical products are manufactured by genetically engineered plants that are extracted and purified, also known as pharmaceuticals produced by plants. Edible vaccines are cheaper in cost, easy to administer mostly by oral route, fail-safe, and are acceptable by society especially in developing countries. These vaccines are targeted to provide systemic as well as mucosal types of immunity. It has been predicted that in future children may get their immunization by munching on foods instead of getting enduring shots. The production of edible vaccines consists of the process of introducing the selected genes of desired quality into plant to induce these altered or transgenic plants to produce the encoded proteins in a natural way. These vaccines provide safer alternatives and help in reduction of cost of production and shipping and also decrease the potential hazards associated with conventional vaccines. However, becoming a reality and readily availability of edible vaccine is challenged by many problems of technical, regulatory, and nonscientific issues, which should be ruled out and rectified. This chapter provides insight into the current scenario and future applications of this new preventive modality.

Molecular cloning, characterization and expression analysis of the SAMS gene during adventitious root development in IBA-induced tetraploid black locust

S-Adenosylmethionine synthetase (SAMS) catalyzes the synthesis of S-adenosylmethionine (SAM), a precursor for ethylene and polyamine biosynthesis. Here, we report the isolation of the 1498 bp full-length cDNA sequence encoding tetraploid black locust (Robinia pseudoacacia L.) SAMS (TrbSAMS), which contains an open reading frame of 1179 bp encoding 392 amino acids. The amino acid sequence of TrbSAMS has more than 94% sequence identity to SAMSs from other plants, with a closer phylogenetic relationship to SAMSs from legumes than to SAMS from other plants. The TrbSAMS monomer consists of N-terminal, central, and C-terminal domains. Subcellular localization analysis revealed that the TrbSAMS protein localizes mainly to in the cell membrane and cytoplasm of onion epidermal cells and Arabidopsis mesophyll cell protoplasts. Indole-3-butyric acid (IBA)-treated cuttings showed higher levels of TrbSAMS transcript than untreated control cuttings during root primordium and adventitious root formation. TrbSAMS and its downstream genes showed differential expression in shoots, leaves, bark, and roots, with the highest expression observed in bark. IBA-treated cuttings also showed higher SAMS activity than control cuttings during root primordium and adventitious root formation. These results indicate that TrbSAMS might play an important role in the regulation of IBA-induced adventitious root development in tetraploid black locust cuttings.

Transgenic pearl millet male fertility restorer line (ICMP451) and hybrid (ICMH451) expressing Brassica juncea Nonexpressor of pathogenesis related genes 1 (BjNPR1) exhibit resistance to downy mildew disease

Brassica juncea Nonexpressor of pathogenesis-related genes 1 (BjNPR1) has been introduced into pearl millet male fertility restorer line ICMP451 by Agrobacterium tumefaciens-mediated genetic transformation. Transgenic pearl millet plants were regenerated from the phosphinothricin-resistant calli obtained after co-cultivation with A. tumefaciens strain LBA4404 harbouring Ti plasmid pSB111-bar-BjNPR1. Molecular analyses confirmed the stable integration and expression of BjNPR1 in transgenic pearl millet lines. Transgenes BjNPR1 and bar were stably inherited and disclosed co-segregation in subsequent generations in a Mendelian fashion. Transgenic pearl millet hybrid ICMH451-BjNPR1 was developed by crossing male-sterile line 81A X homozygous transgenic line ICMP451-BjNPR1. T3 and T4 homozygous lines of ICMP451-BjNPR1 and hybrid ICMH451-BjNPR1 exhibited resistance to three strains of downy mildew pathogen, while the untransformed ICMP451 and the isogenic hybrid ICMH451 plants were found susceptible. Following infection with S. graminicola, differential expression of systemic acquired resistance pathway genes, UDP-glucose salicylic acid glucosyl transferase and pathogenesis related gene 1 was observed in transgenic ICMP451-BjNPR1 and untransformed plants indicating the activation of systemic acquired resistance pathway contributing to the transgene-mediated resistance against downy mildew. The transgenic pearl millet expressing BjNPR1 showed resistance to multiple strains of S. graminicola and, as such, seems promising for the development of durable downy mildew resistant hybrids.

Molecular cloning and characterization of S-adenosylmethionine synthetase gene from Lycoris radiata

S-adenosylmethionine (SAM) synthetase catalyzes the synthesis of SAM, a molecule important for all cellular organisms. It is also considered to play an important role in salt tolerance of plants. Here, we cloned a Lycoris radiata (L. radiata) SAM synthetase gene LrSAMS to determine its biological function. The gene encodes a protein of 401 amino acids with a calculated molecular weight of 43.9 kDa. Amino acid sequence analysis of the deduced protein LrSAMS reveals high sequence identity to SAM synthetases from other organisms, such as Arabidopsis thaliana and Oryza sativa. The deduced LrSAMS protein contains conserved amino acids residues and sequences motifs that closely related to the function of SAM synthetase. Otherwise, the transcript levels of LrSAMS were significantly induced by NaCl treatment in L. radiata leaves, which implied that LrSAMS might play an important role in tolerance to salt stress in L.radiata. Complete ORF of LrSAMS was inserted into expression vector pET-29a(+) and transformed into Escherichia coli BL21 (DE3). The difference between the growth curve of the transgenic strain and control strain with blank vector showed that over-expressing LrSAMS could provide growth advantage to the engineered strain in high salt concentration.

A highly efficient rice green tissue protoplast system for transient gene expression and studying light/chloroplast-related processes

BACKGROUND

Plant protoplasts, a proven physiological and versatile cell system, are widely used in high-throughput analysis and functional characterization of genes. Green protoplasts have been successfully used in investigations of plant signal transduction pathways related to hormones, metabolites and environmental challenges. In rice, protoplasts are commonly prepared from suspension cultured cells or etiolated seedlings, but only a few studies have explored the use of protoplasts from rice green tissue.

RESULTS

Here, we report a simplified method for isolating protoplasts from normally cultivated young rice green tissue without the need for unnecessary chemicals and a vacuum device. Transfections of the generated protoplasts with plasmids of a wide range of sizes (4.5-13 kb) and co-transfections with multiple plasmids achieved impressively high efficiencies and allowed evaluations by 1) protein immunoblotting analysis, 2) subcellular localization assays, and 3) protein-protein interaction analysis by bimolecular fluorescence complementation (BiFC) and firefly luciferase complementation (FLC). Importantly, the rice green tissue protoplasts were photosynthetically active and sensitive to the retrograde plastid signaling inducer norflurazon (NF). Transient expression of the GFP-tagged light-related transcription factor OsGLK1 markedly upregulated transcript levels of the endogeneous photosynthetic genes OsLhcb1, OsLhcp, GADPH and RbcS, which were reduced to some extent by NF treatment in the rice green tissue protoplasts.

CONCLUSIONS

We show here a simplified and highly efficient transient gene expression system using photosynthetically active rice green tissue protoplasts and its broad applications in protein immunoblot, localization and protein-protein interaction assays. These rice green tissue protoplasts will be particularly useful in studies of light/chloroplast-related processes.

The myth of plant transformation

Technology development is innovative to many aspects of basic and applied plant transgenic science. Plant genetic engineering has opened new avenues to modify crops, and provided new solutions to solve specific needs. Development of procedures in cell biology to regenerate plants from single cells or organized tissue, and the discovery of novel techniques to transfer genes to plant cells provided the prerequisite for the practical use of genetic engineering in crop modification and improvement. Plant transformation technology has become an adaptable platform for cultivar improvement as well as for studying gene function in plants. This success represents the climax of years of efforts in tissue culture improvement, in transformation techniques and in genetic engineering. Plant transformation vectors and methodologies have been improved to increase the efficiency of transformation and to achieve stable expression of transgenes in plants. This review provides a comprehensive discussion of important issues related to plant transformation as well as advances made in transformation techniques during three decades.

Physical methods of nucleic acid transfer: general concepts and applications

Physical methods of gene (and/or drug) transfer need to combine two effects to deliver the therapeutic material into cells. The physical methods must induce reversible alterations in the plasma membrane to allow the direct passage of the molecules of interest into the cell cytosol. They must also bring the nucleic acids in contact with the permeabilized plasma membrane or facilitate access to the inside of the cell. These two effects can be achieved in one or more steps, depending upon the methods employed. In this review, we describe and compare several physical methods: biolistics, jet injection, hydrodynamic injection, ultrasound, magnetic field and electric pulse mediated gene transfer. We describe the physical mechanisms underlying these approaches and discuss the advantages and limitations of each approach as well as its potential application in research or in preclinical and clinical trials. We also provide conclusions, comparisons, and projections for future developments. While some of these methods are already in use in man, some are still under development or are used only within clinical trials for gene transfer. The possibilities offered by these methods are, however, not restricted to the transfer of genes and the complementary uses of these technologies are also discussed. As these methods of gene transfer may bypass some of the side effects linked to viral or biochemical approaches, they may find their place in specific clinical applications in the future.

Transient expression of GFP in immature seed tissues

Transient expression is the nonstable expression of a transgene whereby the transgene does not integrate into the host's genomic DNA. Transient expression assays have 20 years of history in plant molecular biology research, being used to answer a variety of questions. The method described here allows the ability to test promoter activity for seed-specific expression by quantifying reporter protein production in immature seed tissues. This method is especially suited to test vector activity for stable expression, test promoter activity, and discern regions of a promoter that is necessary for transcription in seed tissues. The transient expression assay is a tool that has aided a great deal of molecular biology research.

Transient transformation of plants

Transient expression in plants is a valuable tool for many aspects of functional genomics and promoter testing. It can be used both to over-express and to silence candidate genes. It is also scaleable and provides a viable alternative to microbial fermentation and animal cell culture for the production of recombinant proteins. It does not depend on chromosomal integration of heterologous DNA so is a relatively facile procedure and can lead to high levels of transgene expression. Recombinant DNA can be introduced into plant cells via physical methods, via Agrobacterium or via viral vectors.

An unusual S-adenosylmethionine synthetase gene from dinoflagellate is methylated

Background

S-Adenosylmethionine synthetase (AdoMetS) catalyzes the formation of S-Adenosylmethionine (AdoMet), the major methyl group donor in cells. AdoMet-mediated methylation of DNA is known to have regulatory effects on DNA transcription and chromosome structure. Transcription of environmental-responsive genes was demonstrated to be mediated via DNA methylation in dinoflagellates.

Results

A full-length cDNA encoding AdoMetS was cloned from the dinoflagellate Crypthecodinium cohnii. Phylogenetic analysis suggests that the CcAdoMetS gene, is associated with the clade of higher plant orthrologues, and not to the clade of the animal orthrologues. Surprisingly, three extra stretches of residues (8 to 19 amino acids) were found on CcAdoMetS, when compared to other members of this usually conserved protein family. Modeled on the bacterial AdeMetS, two of the extra loops are located close to the methionine binding site. Despite this, the CcAdoMetS was able to rescue the corresponding mutant of budding yeast. Southern analysis, coupled with methylation-sensitive and insensitive enzyme digestion of C. cohnii genomic DNA, demonstrated that the AdoMetS gene is itself methylated. The increase in digestibility of methylation-sensitive enzymes on AdoMet synthetase gene observed following the addition of DNA methylation inhibitors L-ethionine and 5-azacytidine suggests the presence of cytosine methylation sites within CcAdoMetS gene. During the cell cycle, both the transcript and protein levels of CcAdoMetS peaked at the G1 phase. L-ethionine was able to delay the cell cycle at the entry of S phase. A cell cycle delay at the exit of G2/M phase was induced by 5-azacytidine.

Conclusion

The present study demonstrates a major role of AdoMet-mediated DNA methylation in the regulation of cell proliferation and that the CcAdoMetS gene is itself methylated.

Gene transfer methods for plants and cell cultures

Agrobacterium-mediated gene transfer provides a routine and efficient gene transfer system for a variety of plant species. As this biological vector does not, however, function with important plant species, numerous alternative approaches have been studied. Of those, direct gene transfer into protoplasts, microinjection and biolistics have been demonstrated to be effective. Others, for example, viral vectors, agroinfection, liposome injection and electrophoresis may have special merits, although transgenic plants have not been produced by these techniques yet. From methods based on pollen transformation, the pollen tube pathway, pollen maturation, incubation of dry seeds, incubation of tissues, liposome fusion with tissues, macroinjection, laser treatment and electroporation of tissues no proof of integrative transformation is available, so far, and it is difficult to envisage how these approaches will ever produce transgenic cells and plants. We discuss (a) why Agrobacterium does not function with all plants, (b) what merits and disadvantages we see for the effective methods, (c) what possibilities we foresee for some of the other approaches, and (d) why we do not expect the remaining ones to be successful.

A highly efficient transient protoplast system for analyzing defence gene expression and protein-protein interactions in rice

SUMMARY The transient assay system based on mesophyll or cultured cell-derived protoplasts has been exploited in several plant species and has become a powerful tool for rapid gene functional analysis and biochemical manipulations. However, the system has not been widely used in rice owing to the difficulties in large-scale isolation of viable rice protoplasts from leaves or suspension-cultured cells. Here, we describe a significantly improved method to isolate a large number of protoplasts from stem and sheath tissues of both young and mature plants. High-level coexpression of multiple constructs and efficient suppression of exogenous and endogenous genes were observed in the stem- and sheath-derived protoplasts. A transient green fluorescent protein and luciferase-based reporter system for defence-related genes expression analysis has been established, which is useful for screening and characterizing genes involved in rice defence signalling pathways. Furthermore, a protoplast-based bimolecular fluorescence complementation (BiFC) system for the detection of protein-protein interactions in living rice cells was developed. The YFP complementation of two split-YFP halves mediated by homodimerization of the GUS and SPIN1, a cell-death related protein, was observed in transfected protoplasts. In combination with genetic, genomic and proteomic approaches, the established versatile protoplast transient assay system will facilitate large-scale functional analysis of defence-related genes in rice.

Electric pulse-mediated gene delivery to various animal tissues

Electroporation designates the use of electric pulses to transiently permeabilize the cell membrane. It has been shown that DNA can be transferred to cells through a combined effect of electric pulses causing (1) permeabilization of the cell membrane and (2) an electrophoretic effect on DNA, leading the polyanionic molecule to move toward or across the destabilized membrane. This process is now referred to as DNA electrotransfer or electro gene transfer (EGT). Several studies have shown that EGT can be highly efficient, with low variability both in vitro and in vivo. Furthermore, the area transfected is restricted by the placement of the electrodes, and is thus highly controllable. This has led to an increasing use of the technology to transfer reporter or therapeutic genes to various tissues, as evidenced from the large amount of data accumulated on this new approach for non-viral gene therapy, termed electrogenetherapy (EGT as well). By transfecting cells with a long lifetime, such as muscle fibers, a very long-term expression of genes can be obtained. A great variety of tissues have been transfected successfully, from muscle as the most extensively used, to both soft (e.g., spleen) and hard tissue (e.g., cartilage). It has been shown that therapeutic levels of systemically circulating proteins can be obtained, opening possibilities for using EGT therapeutically. This chapter describes the various aspects of in vivo gene delivery by means of electric pulses, from important issues in methodology to updated results concerning the electrotransfer of reporter and therapeutic genes to different tissues.

Evidence that direct DNA uptake through cut shoots leads to genetic transformation of Solanum aviculare Forst

The reporter genes GUS, NPTII and BAR, either separately or in combination, have been exploited to determine if DNA which can directly enter plants, circulate within the plant and enter nuclei, can also integrate into the genome in a manner which will permit gene expression. Feeding of either seed-derived or adventitious cut shoots of Solanum aviculare with the GUS gene followed by rooting of the shoots and growing on, resulted in all tissues of the plant showing GUS activity as detected cytochemically. Southern blot analysis of plants derived from the adventitious shoots confirmed the presence of the reporter gene in roots. Reporter gene expression was observed also in the F1 generation. If GUS and NPTII or GUS, NPTII and BAR were fed together, then in each case it was possible to have both expression and Southern blot confirmation of each of the genes. There was a relatively high rate of transformation of approximately 5% of the fed stems across all experiments conducted during the present study.

Two S-adenosylmethionine synthetase-encoding genes differentially expressed during adventitious root development in Pinus contorta

Two S-adenosylmethionine synthetase (SAMS) cDNAs, PcSAMS1 and PcSAMS2, have been identified in Pinus contorta. We found that the two genes are differentially expressed during root development. Thus, PcSAMS1 is preferentially expressed in roots and exhibits a specific expression pattern in the meristem at the onset of adventitious root development, whereas PcSAMS2 is expressed in roots as well as in shoots and is down-regulated during adventitious root formation. The expression of the two SAMS genes is different from the SAMS activity levels during adventitious root formation. We conclude that other SAMS genes that remain to be characterized may contribute to the observed SAMS activity, or that the activities of PcSAMS1 and PcSAMS2 are affected by post-transcriptional regulation. The deduced amino acid sequences of PcSAMS1 and PcSAMS2 are highly divergent, suggesting different functional roles. However, both carry the two perfectly conserved motifs that are common to all plant SAMS. At the protein level, PcSAMS2 shares about 90% identity to other isolated eukaryotic SAMS, while PcSAMS1 shares less than 50% identity with other plant SAMS. In a phylogenetic comparison, PcSAMS1 seems to have diverged significantly from all other SAMS genes. Nevertheless, PcSAMS1 was able to complement a Saccharomyces cerevisiae sam1 sam2 double mutant, indicating that it encodes a functional SAMS enzyme.

Transient expression of the beta-glucuronidase gene in tissues of Arabidopsis thaliana by bombardment-mediated transformation

Particle bombardment has proved to be useful for the transformation of plants. We have previously reported successful transient expression of the beta-glucuronidase (GUS) gene in cultured plant cells and tissues and the stable transformation of various plants using a pneumatic particle gun. In this chapter, we describe transient expression of the GUS gene in Arabidopsis thaliana leaves and roots using the pneumatic particle gun.

A practical assessment of transdermal drug delivery by skin electroporation

Transdermal drug delivery has many potential advantages, but the skin's poorly-permeable stratum corneum blocks delivery of most drugs at therapeutic levels. Short high-voltage pulses have been used to electroporate the skin's lipid bilayer barriers and thereby deliver compounds at rates increased by as much as four orders of magnitude. Evidence that the observed flux enhancement is due to physical alteration of the skin by electroporation, as opposed to only providing an iontophoretic driving force, is supported by a number of different transport, electrical and microscopy studies. Practical applications of electroporation's unique effects on skin are motivated by large flux increases for many different compounds, rapidly responsive delivery profiles, and efficient use of skin area and electrical charge. Greater enhancement can be achieved by combining skin electroporation with iontophoresis, ultrasound, and macromolecules. Sensation due to electroporation can be avoided by using appropriate electrical protocols and electrode design. To develop skin electroporation as a successful transdermal drug delivery technology, the strong set of existing in vitro mechanistic studies must be supplemented with studies addressing in vivo/clinical issues and device design.

Differential expression of the S-adenosyl-L-methionine synthase genes during pea development

Two genes coding for S-adenosyl-l-methionine synthase (SAMS, EC 2.5. 1.6) were previously isolated from pea (Pisum sativum) ovaries. Both SAMS genes were highly homologous throughout their coding regions but showed a certain degree of sequence divergence within the 5' and the 3' untranslated regions. These regions have been used as gene-specific probes to analyze the differential expression of SAMS1 and SAMS2 genes in pea plants. The ribonuclease protection assay revealed different expression patterns for each individual gene. SAMS1 was strongly expressed in nearly all tissues, especially in roots. SAMS2 expression was weaker, reaching its highest level at the apex. Following pollination, SAMS1 was specifically up-regulated, whereas SAMS2 was expressed constitutively. The up-regulation of SAMS1 during ovary development was also observed in unpollinated ovaries treated with auxins. In unpollinated ovaries an increase in SAMS1 expression was observed as a consequence of ethylene production associated with the emasculation process. In senescing ovaries both SAMS1 and SAMS2 genes showed increased expression. Ethylene treatment of unpollinated ovaries led to an increase in the SAMS1 mRNA level. However, SAMS2 expression remained unchangeable after ethylene treatment, indicating that SAMS2 induction during ovary senescence was not ethylene dependent. SAMS mRNAs were localized by in situ hybridization at the endocarp of developing fruits and in the ovules of senescing ovaries. Our results indicate that the transcriptional regulation of SAMS genes is developmentally controlled in a specific way for each gene.

Gene transfer by electroporation

Electroporation of cells in the presence of DNA is widely used for the introduction of transgenes either stably or transiently into bacterial, fungal, animal, and plant cells. A review of the literature shows that electroporation parameters are often reported in an incomplete or incorrect manner, forcing researchers to rely too much on a purely empirical trial and error approach. The goal of this article is to provide the reader with an understanding of electrical circuits used in electroporation experiments as well as physical and biological aspects of the electroporation process itself. Further, a simple paradigm is provided which unites all electroporation parameters. This article should be particularly useful to those new to the technique.

Transient and stable electrotransformations of intact black Mexican sweet maize cells are obtained after preplasmolysis

When interested in plant cell transformation, the cell wall is often considered as a barrier to DNA transfer, which is only overcome by wounding or wall degrading enzymes. In this work, we demonstrate that cell plasmolysis before electropulsation is an efficient approach to DNA delivery into intact plant cells. Using such a method, transient expression (β-glucuronidase and chloramphenicol acetyltransferase) and stable expression (phosphinotricin acetyltransferase) of exogenous genes are obtained in intact black Mexican sweet maize cells.

Electropermeabilization of intact maize cells induces an oxidative stress

By applying electric field pulses through cell suspensions, cell membranes can be permeabilized transiently, giving free access to the cytosol. Electropulsation is now routinely used in cell biology when introducing various molecules such as proteins and nucleic acids into the cell. But the molecular and cellular bases of cell electropermeabilization are still unclear. In the present study, we observed that electropermeabilization of intact black Mexican sweet (BMS) maize cells induces a generation of oxygen species (oxidative jump). Using the chemiluminescent probe lucigenin, we have shown that the electro-induced chemiluminescent response depends on the level of the stress factor as shown by its dependence on the electric parameters (electric field intensity, duration, and number of pulses). While the electroinduced cell permeabilization has a short life, the oxidative jump that is triggered by this electropermeabilization is a much longer-lived response. The electroinduced loss in viability is linearly correlated to permeabilization. However, there is no correlation between the oxidative jump and the loss in viability. The modulation of oxygen species electroinduction by antioxidant products (dimethylsulfoxide, sodium L-ascorbate, and glutathione) does not lead to an increase in cell viability. Such results are different to those observed with mammalian cells and indicate that even if the same phenomenon is observed with mammalian cells and indicate that even if the same phenomenon is observed when pulsing mammalian or intact plant cells, the associated metabolic response is not the same.

Transgenic grain legumes obtained by in planta electroporation-mediated gene transfer

Electroporation-mediated gene transfer into intact plant tissues was demonstrated in pea, cowpea, lentil, and soybean plants. Transient expression of a chimeric gus reporter gene was used to monitor the uptake and expression of the introduced DNA in electroporated nodal axillary buds in vivo. The branches that grew out of the nodal meristems were chimeric and expressed the introduced gene up to 20 d after electroporation. Transgenic R1 pea, lentil, and cowpea plants were recovered from seeds originating on these chimeric branches as shown by Southern blot hybridization and GUS expression. Transgenic R2 soybean and lentil plants were also obtained. Segregation ratios in these populations showed a strong bias against transgene presence or expression.

Stable transformation via electroporation into maize Type II callus and regeneration of fertile transgenic plants

Maize Type II callus tissue was used as the plant material for genetic transformation via electroporation. Plasmid DNA containing a selectable marker gene (either neomycin phosphotransferase (npt-II) or phosphinothricin acetyl transferase (bar)), and a screenable marker gene (gus A) was incubated with the tissue prior to electroporation. Electroporated callus tissue was placed on selection medium containing kanamycin sulfate or Bast(™). No kanamycin resistant colonies were recovered whereas four independent Basta(™) resistant callus isolates were recovered from a total of 544 cuvettes electroporated. After 8 to 16 weeks on the Basta(™) containing medium, selected calli were isolated and maintained in individual selection plates for 4 to 6 weeks until sufficient tissue accumulated. Enzyme assays and DNA analyses were performed to verify the transformation events. Several plants were regenerated from individual callus isolates. The plants derived from one callus isolate were male sterile while those derived from the other isolates were both male and female fertile. Most plants showed Basta(™) resistance. DNA analyses confirmed the presence of the introduced bar gene(s) in the primary regenerants and their progeny. The integration patterns of the inserted DNA appeared to be complex.

Rapid optimization of electroporation conditions for plant cells, protoplasts, and pollen

The optimization of electroporation conditions for maximal uptake of DNA during direct gene transfer experiments is critical to achieve high levels of gene expression in transformed plant cells. Two stains, trypan blue and fluorescein diacetate, have been applied to optimize electroporation conditions for three plant cell types, using different square wave and exponential wave electroporation devices. The different cell types included protoplasts from tobacco, a stable mixotrophic suspension cell culture from soybean with intact cell walls, and germinating pollen from alfalfa and tobacco. Successful electroporation of each of these cell types was obtained, even in the presence of an intact cell wall when conditions were optimized for the electroporation pulse. The optimal field strength for each of these cells differs, protoplasts having the lowest optimal pulse field strength, followed by suspension cells and finally germinating pollen requiring the strongest electroporation pulse. A rapid procedure is described for optimizing electroporation parameters using different types of cells from different plant sources.

Oat leaf base: tissue with an efficient regeneration capacity

An efficient short term regeneration system using seedling derived oat (Avena sativa) leaf tissue has been developed. Callus derived from the leaf base showed a higher response of plant regeneration than callus initiated from mesocotyls and more mature parts of the leaves. A correlation between the nuclear DNA content of the donor material, as analysed with flow cytometry, and its ability to form callus was observed. Somatic embryogenesis was histologically recognised from callus derived from tissue close to the apical meristem. Plant regeneration media with various concentrations of auxin were tested. Callus from three different cultivars had a similar regeneration potential with an optimal regeneration frequency of 60%. About 2 months after inoculation regenerated plantlets could be moved to a greenhouse for cultivation.

Production of transgenic sugarcane (Saccharum officinarum L.) plants by intact cell electroporation

We describe an efficient procedure for genetic transformation of commercial sugarcane varieties POJ 2878 and Ja 60-5. The transformation protocol is based on electroporation of a plasmid conferring GUS activity into cell clusters isolated from embryogenic calli. Six to eight weeks after electroporation, Ja 60-5 plants regenerated from electroporated tissues were tested and confirmed to be transgenic using histochemical glucuronidase and Southern hybridization analysis. Electroporation of intact cells is an efficient and reproducible method for sugarcane transformation and may also be useful for transformation of other plants.

Electroporation-mediated gene transfer into intact nodal meristems in planta. Generating transgenic plants without in vitro tissue culture

Transient expression and stable integration and expression of transgenes were observed in the tissues and offspring of certain leguminous plants after electroporation of DNA into intact nodal meristems in planta. The method described in this article thus allows the study of transgene expression in tissues differentiating from meristematic cells present in the treated buds. In addition, transgenic plants can be recovered in the offspring of electroporated individuals. Therefore, this technique allows the production of transgenic leguminous plants without the need for in vitro tissue culture, often a major hurdle with this family.

Transient expression of gus gene in intact seed embryos of Indica rice after electroporation-mediated gene delivery

Two-day-old germinating intact seed embryos of Oryza sativa variety Basmati 370 were electroporated with a view to examine suitability of this system for gene delivery. The experiments were done with a plasmid having gus gene under the control of CaMV 35S promoter. Spectrofluorophotometric GUS assay revealed high activity of the introduced gene when embryos were given three electrical pulses at 1600 V cm(-1) and 100 μF capacitance with a pulse length of 75 ms. Additionally, histochemical localization of GUS activity in seedlings and various organs such as leaves, coleoptiles and roots was also done. Expression of GUS activity was studied up to 15 days and found to be organ-specific, thereby showing that embryos can indeed serve as efficient recipient system. Use of cycloheximide revealed that GUS activity appears as a result of early protein synthesis after electroporation and is substantially stable in vivo.

Electroporation-mediated DNA delivery to seedling tissues ofPhaseolus vulgaris L. (common bean)

DNA was delivered to intact embryonic axes of the legumePhaseolus vulgaris L. through electroporation. Expression of the ß-glucuronidase reporter gene was observed in hypocotyl and epicotyl tissue in a spot-like manner. Transgene expression was high when a single pulse of 260 ms at a field strength of 225 V·cm(-1) was applied but could be achieved within a wide range of electrical conditions. Linearization of plasmid DNA greatly enhanced transient expression levels. The procedure was successful for embryonic axes of all testedP. vulgaris cultivars, for similar explants of several large-seeded leguminous species, as well as for some other tissues ofP. vulgaris.

Genetic transformation of plants by protoplast electroporation

This article describes an optimized protocol for the electroporation of tobacco mesophyll protoplasts together with notes and data on the effects of various parameters and suggestions for work with protoplasts of other species. In this protocol, electroporation is achieved by means of electrical pulses from a high-voltage, capacitive-discharge unit. Procedures are described for measurement of protoplast viability with Evan's blue, the detection of transient expression of CAT and GUS gene plasmid constructs, and for the recovery of stable transformants based on selection for kanamycin resistance.

Quantitative study of molecular transport due to electroporation: uptake of bovine serum albumin by erythrocyte ghosts

Electroporation is believed to involve the creation of aqueous pathways in lipid bilayer membranes by transient elevation of the transmembrane voltage to approximately 1 V. Here, results are presented for a quantitative study of the number of bovine serum albumin (BSA) molecules transported into erythrocyte ghosts caused by electroportion. 1) Uptake of BSA was found to plateau at high field strength. However, this was not necessarily an absolute maximum in transport. Instead, it represented the maximum effect of increasing field strength for a particular pulse protocol. 2) Maximum uptake under any conditions used in this study corresponded to approximately one-fourth of apparent equilibrium with the external solution. 3) Multiple and longer pulses each increased uptake of BSA, where the total time integral of field strength correlated with uptake, independent of inter-pulse spacing. 4) Pre-pulse adsorption of BSA to ghost membranes appears to have increased transport. 5) Most transport of BSA probably occurred by electrically driven transport during pulses; post-pulse uptake occurred, but to a much lesser extent. Finally, approaches to increasing transport are discussed.

Electropermeabilization of cells in tissues assessed by the qualitative and quantitative electroloading of bleomycin

Using cells in suspension, electropermeabilization is a technique extensively used to transfect living cells or to introduce a variety of compounds inside the cells. Here we demonstrate the reality of the tissue electropermeabilization using qualitative and quantitative determinations of the electroloading of bleomycin considered as an nonpermeant molecule that serves as an indicator of the permeabilization. In tissues, cell electropermeabilization is achieved for electric field intensities lower than those necessary to permeabilize the same cells in suspension. We also emphasize the importance of the geometry of the electric field lines defined by the electrodes for permeabilizing a whole tissue, for example a tumor.

Production of fertile transgenic maize by electroporation of suspension culture cells

Fertile, transgenic maize plants were generated by electroporation of suspension culture cells that were treated with a pectin-degrading enzyme. Electroporation of cells from two different suspension cultures, one derived from A188 X B73 and one derived from a B73-related inbred, with a plasmid containing the bar gene, resulted in high-frequency recovery of stably transformed callus lines. Plants were regenerated from thirteen transformed callus lines and transmission of bar to progeny was demonstrated.

Fertile transgenic Indica rice plants obtained by electroporation of the seed embryo cells

We have obtained fertile transgenic plants of Indica rice variety IR36, by using electroporation to transfer the neomycin phosphotransferase II (nptII) gene into cells of mature embryos. Resistant calli were selected in the presence of 30 μg/ml G418. Nearly thirty transgenic plants were regenerated within three months after transformation. Many of them yielded seeds following self-pollination. Data from molecular analysis and enzyme assay proved that the foreign gene was stably integrated into the genome of resistant calli, R0 and R1 plants, and also expressed. Mendelian segregation of the nptII gene was observed in R1 progeny plants.

Effects of tissue type and promoter strength on transient GUS expression in sugarcane following particle bombardment

Effects of tissue type and promoter strength on transient GUS expression in the sugarcane (Saccharum spp. hybrids) cultivar NCo 310 were evaluated following microprojectile bombardment of leaf explants. GUS expression was histochemically or fluorometrically measured 48 h after delivery of the uidA gene. High levels of GUS expression were obtained in leaf segments isolated from young, expanding sugarcane leaves cultured for 1, 3, or 6 d prior to bombardment. The promoter derived from the maize ubiquitin 1 gene (Ubi-1) produced significantly more GUS foci and higher GUS activity levels compared to the recombinant Emu, rice actin 1 (Act1), and CaMV 35S promoters. Our transient expression system should facilitate efforts to identify promoters and elements which will regulate desired gene expression patterns in sugarcane and aid in development of an efficient stable transformation system.

Gene transfer by electroporation into intact scutellum cells of wheat embryos

Gene transfer into intact cells was achieved by electroporating zygotic wheat embryos without any special pretreatment. Electroporation was tissue specific in so far as scutellum cells were found to be much more susceptible to gene transfer than other cell types of the embryo. The orientation of the embryos in the electroporation chamber also influenced the number of transformed scutellum cells; during electroporation, as in electrophoresis, the negatively charged plasmid DNA molecules seemed to move towards the positive electrode. Therefore, the embryos were arranged so that the scutella faced the negative electrode. The use of plasmids carrying either two chimeric anthocyanin regulatory genes or a chimeric gusA gene allowed clear identification of transformed cells in the scutellum. On some of the embryos, more than 100 transformed scutellum cells were found after electroporation with single electric pulses of 275 V/cm discharged from a 960-μF capacitor and with 100 μg DNA/ml electroporation buffer. Using the anthocyanin marker system, visibly transformed cells grew to produce red sectors.