Detection of vector- and selectable marker-free transgenic maize with a linear GFP cassette transformation via the pollen-tube pathway

Tissue culture-independent approaches to revolutionizing plant transformation and gene editing

Despite the transformative power of gene editing for crop improvement, its widespread application across species and varieties is limited by the transformation bottleneck that exists for many crops. The genetic transformation of plants is hindered by a general reliance on in vitro regeneration through plant tissue culture. Tissue culture requires empirically determined conditions and aseptic techniques, and cannot easily be translated to recalcitrant species and genotypes. Both Agrobacterium-mediated and alternative transformation protocols are limited by a dependency on in vitro regeneration, which also limits their use by non-experts and hinders research into non-model species such as those of possible novel biopharmaceutical or nutraceutical use, as well as novel ornamental varieties. Hence, there is significant interest in developing tissue culture-independent plant transformation and gene editing approaches that can circumvent the bottlenecks associated with in vitro plant regeneration recalcitrance. Compared to tissue culture-based transformations, tissue culture-independent approaches offer advantages such as avoidance of somaclonal variation effects, with more streamlined and expeditious methodological processes. The ease of use, dependability, and accessibility of tissue culture-independent procedures can make them attractive to non-experts, outperforming classic tissue culture-dependent systems. This review explores the diversity of tissue culture-independent transformation approaches and compares them to traditional tissue culture-dependent transformation strategies. We highlight their simplicity and provide examples of recent successful transformations accomplished using these systems. Our review also addresses current limitations and explores future perspectives, highlighting the significance of these techniques for advancing plant research and crop improvement.

A comprehensive review of in planta stable transformation strategies

Plant transformation remains a major bottleneck to the improvement of plant science, both on fundamental and practical levels. The recalcitrant nature of most commercial and minor crops to genetic transformation slows scientific progress for a large range of crops that are essential for food security on a global scale. Over the years, novel stable transformation strategies loosely grouped under the term "in planta" have been proposed and validated in a large number of model (e.g. Arabidopsis and rice), major (e.g. wheat and soybean) and minor (e.g. chickpea and lablab bean) species. The in planta approach is revolutionary as it is considered genotype-independent, technically simple (i.e. devoid of or with minimal tissue culture steps), affordable, and easy to implement in a broad range of experimental settings. In this article, we reviewed and categorized over 300 research articles, patents, theses, and videos demonstrating the applicability of different in planta transformation strategies in 105 different genera across 139 plant species. To support this review process, we propose a classification system for the in planta techniques based on five categories and a new nomenclature for more than 30 different in planta techniques. In complement to this, we clarified some grey areas regarding the in planta conceptual framework and provided insights regarding the past, current, and future scientific impacts of these techniques. To support the diffusion of this concept across the community, this review article will serve as an introductory point for an online compendium about in planta transformation strategies that will be available to all scientists. By expanding our knowledge about in planta transformation, we can find innovative approaches to unlock the full potential of plants, support the growth of scientific knowledge, and stimulate an equitable development of plant research in all countries and institutions.

A Prospective Review on Selectable Marker-Free Genome Engineered Rice: Past, Present and Future Scientific Realm

As a staple food crop, rice has gained mainstream attention in genome engineering for its genetic improvement. Genome engineering technologies such as transgenic and genome editing have enabled the significant improvement of target traits in relation to various biotic and abiotic aspects as well as nutrition, for which genetic diversity is lacking. In comparison to conventional breeding, genome engineering techniques are more precise and less time-consuming. However, one of the major issues with biotech rice commercialization is the utilization of selectable marker genes (SMGs) in the vector construct, which when incorporated into the genome are considered to pose risks to human health, the environment, and biodiversity, and thus become a matter of regulation. Various conventional strategies (co-transformation, transposon, recombinase systems, and MAT-vector) have been used in rice to avoid or remove the SMG from the developed events. However, the major limitations of these methods are; time-consuming, leftover cryptic sequences in the genome, and there is variable frequency. In contrast to these methods, CRISPR/Cas9-based marker excision, marker-free targeted gene insertion, programmed self-elimination, and RNP-based delivery enable us to generate marker-free engineered rice plants precisely and in less time. Although the CRISPR/Cas9-based SMG-free approaches are in their early stages, further research and their utilization in rice could help to break the regulatory barrier in its commercialization. In the current review, we have discussed the limitations of traditional methods followed by advanced techniques. We have also proposed a hypothesis, “DNA-free marker-less transformation” to overcome the regulatory barriers posed by SMGs.

A stress-responsive transcription factor PeNAC1 regulating beta-D-glucan biosynthetic genes enhances salt tolerance in oat

A Populus euphratica NAC gene regulates (1,3; 1,4)-β-D-glucan content in oat developing seed and improves the spikelet number and grain number per spike in transgenic oat under salinity conditions Salinity is the major factor affecting the production and quality of oat, and improving oat salt tolerance to increase yield and quality is vital. (1,3;1,4)-β-D-glucan in Gramineae is the key component in response to various environmental signals, and it is the most important functional ingredient in oat grain. The NAC transcription factors are important candidate genes used in genetic engineering to improve plant abiotic stress tolerance. In this study, we introduced Populus euphratica PeNAC1, controlled by its own promoter, into hexaploid cultivated oat and produced six transgenic lines. Compared to the non-transgenic control, the expression of PeNAC1 significantly improved the seed germination rate, seedling survival rate, and leaf chlorophyll content in the transgenic plants under salt stress. These physiological changes increased the spikelet number and grain number per spike in the transgenic oat under salinity conditions and reduced the yield loss per plant. The results indicated that the heterologous expression of PeNAC1 plays an effective role in improving the salt tolerance in transgenic oat. In addition, overexpressing PeNAC1 significantly increased the (1,3;1,4)-β-D-glucan content as well as the expression level of the (1,3;1,4)-β-D-glucan biosynthetic genes AsCslF3, AsCslF6, and AsCslF9 in the transgenic lines under salt stress, which suggested that PeNAC1 regulates the synthesis of (1,3;1,4)-β-D-glucan. Our research should assist in the discovery of the diverse action modes of NAC proteins, while PeNAC1 will be useful for improving the salt tolerance and quality of oat through molecular breeding.

ptxD/Phi as alternative selectable marker system for genetic transformation for bio-safety concerns: a review

Antibiotic and herbicide resistance genes are the most common marker genes for plant transformation to improve crop yield and food quality. However, there is public concern about the use of resistance marker genes in food crops due to the risk of potential gene flow from transgenic plants to compatible weedy relatives, leading to the possible development of “superweeds” and antibiotic resistance. Several selectable marker genes such as aph, nptII, aaC3, aadA, pat, bar, epsp and gat, which have been synthesized to generate transgenic plants by genetic transformation, have shown some limitations. These marker genes, which confer antibiotic or herbicide resistance and are introduced into crops along with economically valuable genes, have three main problems: selective agents have negative effects on plant cell proliferation and differentiation, uncertainty about the environmental effects of many selectable marker genes, and difficulty in performing recurrent transformations with the same selectable marker to pyramid desired genes. Recently, a simple, novel, and affordable method was presented for plant cells to convert non-metabolizable phosphite (Phi) to an important phosphate (Pi) for developing cells by gene expression encoding a phosphite oxidoreductase (PTXD) enzyme. The ptxD gene, in combination with a selection medium containing Phi as the sole phosphorus (P) source, can serve as an effective and efficient system for selecting transformed cells. The selection system adds nutrients to transgenic plants without potential risks to the environment. The ptxD/Phi system has been shown to be a promising transgenic selection system with several advantages in cost and safety compared to other antibiotic-based selection systems. In this review, we have summarized the development of selection markers for genetic transformation and the potential use of the ptxD/Phi scheme as an alternative selection marker system to minimize the future use of antibiotic and herbicide marker genes.

Current progress and challenges in crop genetic transformation

Plant transformation remains the most sought-after technology for functional genomics and crop genetic improvement, especially for introducing specific new traits and to modify or recombine already existing traits. Along with many other agricultural technologies, the global production of genetically engineered crops has steadily grown since they were first introduced 25 years ago. Since the first transfer of DNA into plant cells using Agrobacterium tumefaciens, different transformation methods have enabled rapid advances in molecular breeding approaches to bring crop varieties with novel traits to the market that would be difficult or not possible to achieve with conventional breeding methods. Today, transformation to produce genetically engineered crops is the fastest and most widely adopted technology in agriculture. The rapidly increasing number of sequenced plant genomes and information from functional genomics data to understand gene function, together with novel gene cloning and tissue culture methods, is further accelerating crop improvement and trait development. These advances are welcome and needed to make crops more resilient to climate change and to secure their yield for feeding the increasing human population. Despite the success, transformation remains a bottleneck because many plant species and crop genotypes are recalcitrant to established tissue culture and regeneration conditions, or they show poor transformability. Improvements are possible using morphogenetic transcriptional regulators, but their broader applicability remains to be tested. Advances in genome editing techniques and direct, non-tissue culture-based transformation methods offer alternative approaches to enhance varietal development in other recalcitrant crops. Here, we review recent developments in plant transformation and regeneration, and discuss opportunities for new breeding technologies in agriculture.

Pollen Tube Pathway-Mediated Cotton Transformation

Although many gene transfer methods have been employed for successfully obtaining transgenic cotton, the major constraint in cotton improvement is the limitation of genotype because the majority of transgenic methods require plant regeneration from a single transformed cell which is limited by cotton tissue culture. Comparing with other plant species, it is difficult to induce plant regeneration from cotton; currently, only a limited number of cotton cultivars can be cultured for obtaining regenerated plants. Thus, developing a simple and genotype-independent genetic transformation method is particularly interested for cotton. In this chapter, we present a simple, cost-efficient, and genotype-independent cotton transformation method - pollen tube pathway-mediated transformation. This method uses pollen tube pathway to deliver transgene into cotton embryo sacs and then insert foreign genes into cotton genome. There are three major steps for pollen tube pathway-mediated genetic transformation, which include injection of foreign genes into pollen tube, integration of foreign genes into plant genome, and selection of transgenic plants.

Novel Pollen Magnetofection System for Transformation of Cotton Plant with Magnetic Nanoparticles as Gene Carriers

Plant genetic transformation systems have facilitated insights into molecular plant biology and revolutionized commercial agriculture. Unfortunately, agrobacterium-mediated transformation was still the main method although its subsequent regeneration process from tissue culture in cotton remained arduous even after 30 years of technological advances. At the same time, a number of transformation methods based on pollen grains have been developed, such as electroporation, biolistic bombardment, ultra-sonication, and Agrobacterium incubation in plant pollens. But these pollen-based techniques have not been widely adopted. In this chapter, we have presented a protocol of pollen-based transformation technology in cotton, "pollen magnetofection," to directly produce transgenic seeds without tissue culturing. In this system, magnetic nanoparticles loaded with pure plasmid DNA carrying functional genes were delivered into pollens via pollen apertures in the presence of a magnetic field. Afterward, these magnetofected pollens were used for pollination, to produce transformed seeds. Pollen magnetofection is a genotype-independent transformation system; in addition, exogenous DNA was successfully integrated into the genome and stably expressed in the successive generations. We emphasize that pollen magnetofection is a most efficient platform for genetic transformation of cotton and other crops with high-throughput and efficient potential infield operation.

Transgenic Cotton: From Biotransformation Methods to Agricultural Application

Transgenic cotton is among the first transgenic plants commercially adopted around the world. Since it was first introduced into the field in the middle of the 1990s, transgenic cotton has been quickly adopted by cotton farmers in many developed and developing countries. Transgenic cotton has offered many important environmental, social, and economic benefits, including reduced usage of pesticides, indirect increase of yield, minimizing environmental pollution, and reducing labor and cost. Agrobacterium-mediated genetic transformation method is the major method for obtaining transgenic cotton. However, pollen tube pathway-mediated method is also used, particularly by scientists in China, to breed commercial transgenic cotton. Although transgenic cotton plants with disease resistance, abiotic stress tolerance, and improved fiber quality have been developed in the past decades, insect-resistant and herbicide-tolerant cottons are the two dominant cottons in transgenic cotton market.

Research Progress on Tissue Culture and Genetic Transformation of Kenaf (Hibiscus cannabinus)

Recent research progresses on tissue culture (e.g. fast reproduction, another culture, protoplast culture and organogenesis) and genetic transformation of kenaf were reviewed and summarized in this paper. Existing problems were discussed, aiming to provide scientific references for promoting tissue culture and genetic transformation of kenaf.

Oil palm drought inducible DREB1 induced expression of DRE/CRT- and non-DRE/CRT-containing genes in lowland transgenic tomato under cold and PEG treatments

Dehydration-responsive element binding (DREB) transcription factor plays an important role in controlling the expression of abiotic stress responsive genes. An intronless oil palm EgDREB1 was isolated and confirmed to be a nuclear localized protein. Electrophoretic mobility shift and yeast one-hybrid assays validated its ability to interact with DRE/CRT motif. Its close evolutionary relation to the dicot NtDREB2 suggests a universal regulatory role. In order to determine its involvement in abiotic stress response, functional characterization was performed in oil palm seedlings subjected to different levels of drought severity and in EgDREB1 transgenic tomato seedlings treated by abiotic stresses. Its expression in roots and leaves was compared with several antioxidant genes using quantitative real-time PCR. Early accumulation of EgDREB1 in oil palm roots under mild drought suggests possible involvement in the initiation of signaling communication from root to shoot. Ectopic expression of EgDREB1 in T1 transgenic tomato seedlings enhanced expression of DRE/CRT and non-DRE/CRT containing genes, including tomato peroxidase (LePOD), ascorbate peroxidase (LeAPX), catalase (LeCAT), superoxide dismutase (LeSOD), glutathione reductase (LeGR), glutathione peroxidase (LeGP), heat shock protein 70 (LeHSP70), late embryogenesis abundant (LeLEA), metallothionine type 2 (LeMET2), delta 1-pyrroline-5- carboxylate synthetase (LePCS), ABA-aldehyde oxidase (LeAAO) and 9-cis- Epoxycarotenoid dioxygenase (LeECD) under PEG treatment and cold stress (4 °C). Altogether, these findings suggest that EgDREB1 is a functional regulator in enhancing tolerance to drought and cold stress.

Advances in Maize Transformation Technologies and Development of Transgenic Maize

Maize is the principal grain crop of the world. It is also the crop where genetic engineering has been employed to a great extent to improve its various traits. The ability to transform maize is a crucial step for application of gene technology in maize improvement. There have been constant improvements in the maize transformation technologies over past several years. The choice of genotype and the explant material to initiate transformation and the different types of media to be used in various stages of tissue culture can have significant impact on the outcomes of the transformation efforts. Various methods of gene transfer, like the particle bombardment, protoplast transformation, Agrobacterium-mediated, in planta transformation, etc., have been tried and improved over years. Similarly, various selection systems for retrieval of the transformants have been attempted. The commercial success of maize transformation and transgenic development is unmatched by any other crop so far. Maize transformation with newer gene editing technologies is opening up a fresh dimension in transformation protocols and work-flows. This review captures the various past and recent facets in improvement in maize transformation technologies and attempts to present a comprehensive updated picture of the current state of the art in this area.

Overexpression of CtCHS1 Increases Accumulation of Quinochalcone in Safflower

Carthami flos, the dried petal of safflower (Carthamus tinctorius L.) has been widely used in traditional Chinese medicine to treat cardiovascular and cerebrovascular diseases, in which quinochalcone glucosides such as hydrosafflower yellow A (HSYA), carthamin are uniquely present and have been identified as active compounds. In the present study, through sequencing of a safflower floret cDNA library and subsequent microarray analysis, we found 23 unigenes (5 PALs, 1 C4Hs, 5 4CLs, 6 CHSs, 2 CHIs, 2 DFRs, 2 FLSs) involved in flavonoid pathway, of which 4 were up-regulated differentially during quinochalcone glucosides accumulation with the floret developing stage. The up-regulated genes were verified by PCR methods. Considering chalcone synthase are entry enzyme in flavonoid biosynthesis, CHS1 was focused on target gene to verify its function furtherly. Bioinformation analysis showed that CHS1 shared 86.94% conserved residues with CHS from other plants. Subcellular localization showed that CtCHS1 was localized in cytoplasm in onion epidermal cells. The transgenic safflower plant with overexpression CtCHS1 by Agrobacterium-mediated pollen-tube pathway method was firstly generated. The results present that expression of PAL2, PAL3, CHS1, CHS4, CHS6 increased and expression of CHI1 and CHI2 decreased in the transgenic plant floret. Meanwhile, the accumulation of quinochalcone glucosides increased by ∼20-30% and accumulation of quercetin-3-β-D-glucoside and quercetin decreased by 48 and 63% in the transgenic plant floret. These results suggested that CtCHS1 played an important role in quinochalcone glucosides biosynthesis rather than flavonol biosynthesis. These results also demonstrated that the pollen-tube pathway method was an efficient method for gene transformation in safflower. Our study will provide a deep understanding of potential synthetic genes involved in quinochalcone biosynthetic pathway.

Methods for genetic transformation in Dendrobium

The genetic transformation of Dendrobium orchids will allow for the introduction of novel colours, altered architecture and valuable traits such as abiotic and biotic stress tolerance. The orchid genus Dendrobium contains species that have both ornamental value and medicinal importance. There is thus interest in producing cultivars that have increased resistance to pests, novel horticultural characteristics such as novel flower colours, improved productivity, longer flower spikes, or longer post-harvest shelf-life. Tissue culture is used to establish clonal plants while in vitro flowering allows for the production of flowers or floral parts within a sterile environment, expanding the selection of explants that can be used for tissue culture or genetic transformation. The latter is potentially the most effective, rapid and practical way to introduce new agronomic traits into Dendrobium. Most (69.4 %) Dendrobium genetic transformation studies have used particle bombardment (biolistics) while 64 % have employed some form of Agrobacterium-mediated transformation. A singe study has explored ovary injection, but no studies exist on floral dip transformation. While most of these studies have involved the use of selector or reporter genes, there are now a handful of studies that have introduced genes for horticulturally important traits.

Transgenic Cotton Plants Expressing Cry1Ia12 Toxin Confer Resistance to Fall Armyworm (Spodoptera frugiperda) and Cotton Boll Weevil (Anthonomus grandis)

Gossypium hirsutum (commercial cooton) is one of the most economically important fibers sources and a commodity crop highly affected by insect pests and pathogens. Several transgenic approaches have been developed to improve cotton resistance to insect pests, through the transgenic expression of different factors, including Cry toxins, proteinase inhibitors, and toxic peptides, among others. In the present study, we developed transgenic cotton plants by fertilized floral buds injection (through the pollen-tube pathway technique) using an DNA expression cassette harboring the cry1Ia12 gene, driven by CaMV35S promoter. The T0 transgenic cotton plants were initially selected with kanamycin and posteriorly characterized by PCR and Southern blot experiments to confirm the genetic transformation. Western blot and ELISA assays indicated the transgenic cotton plants with higher Cry1Ia12 protein expression levels to be further tested in the control of two major G. hirsutum insect pests. Bioassays with T1 plants revealed the Cry1Ia12 protein toxicity on Spodoptera frugiperda larvae, as evidenced by mortality up to 40% and a significant delay in the development of the target insects compared to untransformed controls (up to 30-fold). Also, an important reduction of Anthonomus grandis emerging adults (up to 60%) was observed when the insect larvae were fed on T1 floral buds. All the larvae and adult insect survivors on the transgenic lines were weaker and significantly smaller compared to the non-transformed plants. Therefore, this study provides GM cotton plant with simultaneous resistance against the Lepidopteran (S. frugiperda), and the Coleopteran (A. grandis) insect orders, and all data suggested that the Cry1Ia12 toxin could effectively enhance the cotton transgenic plants resistance to both insect pests.

A magnetic nanoparticle-based multiple-gene delivery system for transfection of porcine kidney cells

Superparamagnetic nanoparticles are promising candidates for gene delivery into mammalian somatic cells and may be useful for reproductive cloning using the somatic cell nuclear transfer technique. However, limited investigations of their potential applications in animal genetics and breeding, particularly multiple-gene delivery by magnetofection, have been performed. Here, we developed a stable, targetable and convenient system for delivering multiple genes into the nuclei of porcine somatic cells using magnetic Fe₃O₄ nanoparticles as gene carriers. After surface modification by polyethylenimine, the spherical magnetic Fe₃O₄ nanoparticles showed strong binding affinity for DNA plasmids expressing the genes encoding a green (DNA_GFP) or red (DNA_DsRed) fluorescent protein. At weight ratios of DNA_GFP or DNA_DsRed to magnetic nanoparticles lower than or equal to 10∶1 or 5∶1, respectively, the DNA molecules were completely bound by the magnetic nanoparticles. Atomic force microscopy analyses confirmed binding of the spherical magnetic nanoparticles to stretched DNA strands up to several hundred nanometers in length. As a result, stable and efficient co-expression of GFP and DsRed in porcine kidney PK-15 cells was achieved by magnetofection. The results presented here demonstrate the potential application of magnetic nanoparticles as an attractive delivery system for animal genetics and breeding studies.

Cotton transformation via pollen tube pathway

Although many gene transfer methods have been employed for successfully obtaining transgenic cotton, the major constraint in cotton improvement is the limitation of genotype because the majority of transgenic methods require plant regeneration from a single transformed cell which is limited by cotton tissue culture. Comparing with other plant species, it is difficult to induce plant regeneration from cotton; currently, only a limited number of cotton cultivars can be cultured for obtaining regenerated plants. Thus, development of a simple and genotype-independent genetic transformation method is particularly important for cotton community. In this chapter, we present a simple, cost-efficient, and genotype-independent cotton transformation method-pollen tube pathway-mediated transformation. This method uses pollen tube pathway to deliver transgene into cotton embryo sacs and then insert foreign genes into cotton genome. There are three major steps for pollen tube pathway-mediated genetic transformation, which include injection of -foreign genes into pollen tube, integration of foreign genes into plant genome, and selection of transgenic plants.

Transgenic cotton: from biotransformation methods to agricultural application

Transgenic cotton is among the first transgenic plants commercially adopted around the world. Since it was first introduced into the field in the middle of 1990s, transgenic cotton has been quickly adopted by cotton farmers in many developed and developing countries. Transgenic cotton has offered many important environmental, social, and economic benefits, including reduced usage of pesticides, indirect increase of yield, minimizing environmental pollution, and reducing labor and cost. Agrobacterium-mediated genetic transformation method is the major method for obtaining transgenic cotton. However, pollen tube pathway-mediated method is also used, particularly by scientists in China, to breed commercial transgenic cotton. Although transgenic cotton plants with disease-resistance, abiotic stress tolerance, and improved fiber quality have been developed in the past decades, insect-resistant and herbicide-tolerant cotton are the two dominant transgenic cottons in the transgenic cotton market.

Histological study of organogenesis in Cucumis melo L. after genetic transformation: why is it difficult to obtain transgenic plants?

Melon (Cucumis melo L.) is widely considered as a recalcitrant species for genetic transformation. In this study, we developed different regeneration and transformation protocols and we examined the regeneration process at different steps by histological studies. The highest regeneration rate (1.13 ± 0.02 plants per explant) was obtained using cotyledon explants of the 'Védrantais' genotype on Murashige and Skoog (MS) medium supplemented with 0.2 mg/l 6-benzylaminopurine (BAP) and 0.2 mg/l dimethylallylaminopurine (2-iP). Agrobacterium tumefaciens-mediated transformations with the uidA reporter gene were realized on cotyledon explants cultivated in these conditions: 70-90% of explants expressed a transient GUS activity during the early stages of regeneration, however, only few transgenic plants were obtained (1.8-4.5% of stable transformation with the GV2260pBI101 strain). These results revealed a low capacity of melon GUS-positive cells to regenerate transgenic plants. To evaluate the influence of the Agrobacterium infection on plant regeneration, histological analyses were conducted on explants 2, 7, 15, and 28 days after co-culture with the GV2260pBI101 strain. Genetic transformation occurred in epidermal and sub-epidermal cells and reached the meristematic structures expressing a high level of GUS activity during 14 days of culture; but after this period, most of the meristematic structures showed premature cell vacuolization and disorganization. This disruption of the GUS-positive meristematic areas could be responsible of the difficulties encountered to regenerate melon plants after genetic transformation.

Recent advances in plant transformation

Plant genetic engineering has become one of the most important molecular tools in the modern molecular breeding of crops. Over the last decade, significant progress has been made in the development of new and efficient transformation methods in plants. Despite a variety of available DNA delivery methods, Agrobacterium- and biolistic-mediated transformation remain the two predominantly employed approaches. In particular, progress in Agrobacterium-mediated transformation of cereals and other recalcitrant dicot species has been quite remarkable. In the meantime, other transgenic-enabling technologies have emerged, including generation of marker-free transgenics, gene targeting, and chromosomal engineering. Although transformation of some plant species or elite germplasm remains a challenge, further advancement in transformation technology is expected because the mechanisms of governing the regeneration and transformation processes are now better understood and are being creatively applied to designing improved transformation methods or to developing new enabling technologies.

Optimization of soybean (Glycine max (L.) Merrill) in planta ovary transformation using a linear minimal gus gene cassette

Soybean transformation by ovary-drip was improved by optimizing the length of the transformation pathway by cutting the styles. These modifications facilitated soybean transformation manipulation and improved transformation reproducibility and efficiency. Using a linear minimal gus gene cassette as the foreign DNA, a maximum transformation frequency of 11% was obtained in flowers of the soybean cultivar 'Liaodou 14' with their styles mostly removed, whereas removal of only the stigma, partial style cutting and partial ovary cutting gave transformation frequencies of 0%, 1%, and 2%, respectively. An average transformation frequency of 8.2% was obtained when 619 flowers from three soybean cultivars ('Liaodou 14', 'Liaodou 13', and 'Tiefeng 29') were transformed by this optimized method. Southern blotting analysis showed that the gus reporter gene (encoding beta-glucuronidase) was stably inherited with a simple pattern. Reverse transcription-polymerase chain reaction (RT-PCR) and GUS staining confirmed the expression of the gus gene in transgenic plants.