Soybean genetic transformation: A valuable tool for the functional study of genes and the production of agronomically improved plants

An ex vitro hairy root system from petioles of detached soybean leaves for in planta screening of target genes and CRISPR strategies associated with nematode bioassays

MAIN CONCLUSION

The ex vitro hairy root system from petioles of detached soybean leaves allows the functional validation of genes using classical transgenesis and CRISPR strategies (e.g., sgRNA validation, gene activation) associated with nematode bioassays. Agrobacterium rhizogenes-mediated root transformation has been widely used in soybean for the functional validation of target genes in classical transgenesis and single-guide RNA (sgRNA) in CRISPR-based technologies. Initial data showed that in vitro hairy root induction from soybean cotyledons and hypocotyls were not the most suitable strategies for simultaneous performing genetic studies and nematode bioassays. Therefore, an ex vitro hairy root system was developed for in planta screening of target molecules during soybean parasitism by root-knot nematodes (RKNs). Applying this method, hairy roots were successfully induced by A. rhizogenes from petioles of detached soybean leaves. The soybean GmPR10 and GmGST genes were then constitutively overexpressed in both soybean hairy roots and tobacco plants, showing a reduction in the number of Meloidogyne incognita-induced galls of up to 41% and 39%, respectively. In addition, this system was evaluated for upregulation of the endogenous GmExpA and GmExpLB genes by CRISPR/dCas9, showing high levels of gene activation and reductions in gall number of up to 58.7% and 67.4%, respectively. Furthermore, morphological and histological analyses of the galls were successfully performed. These collective data validate the ex vitro hairy root system for screening target genes, using classical overexpression and CRISPR approaches, directly in soybean in a simple manner and associated with nematode bioassays. This system can also be used in other root pathosystems for analyses of gene function and studies of parasite interactions with plants, as well as for other purposes such as studies of root biology and promoter characterization.

CRISPR/LbCas12a-Mediated Genome Editing in Soybean

Currently methods for generating soybean edited lines are time-consuming, inefficient, and limited to certain genotypes. Here we describe a fast and highly efficient genome editing method based on CRISPR-Cas12a nuclease system in soybean. The method uses Agrobacterium-mediated transformation to deliver editing constructs and uses aadA or ALS genes as selectable marker. It only takes about 45 days to obtain greenhouse-ready edited plants at higher than 30% transformation efficiency and 50% editing rate. The method is applicable to other selectable markers including EPSPS and has low transgene chimera rate. The method is also genotype-flexible and has been applied to genome editing of several elite soybean varieties.

Establishing a reproducible approach to study cellular functions of plant cells with 3D bioprinting

Capturing cell-to-cell signals in a three-dimensional (3D) environment is key to studying cellular functions. A major challenge in the current culturing methods is the lack of accurately capturing multicellular 3D environments. In this study, we established a framework for 3D bioprinting plant cells to study cell viability, cell division, and cell identity. We established long-term cell viability for bioprinted Arabidopsis and soybean cells. To analyze the generated large image datasets, we developed a high-throughput image analysis pipeline. Furthermore, we showed the cell cycle reentry of bioprinted cells for which the timing coincides with the induction of core cell cycle genes and regeneration-related genes, ultimately leading to microcallus formation. Last, the identity of bioprinted Arabidopsis root cells expressing endodermal markers was maintained for longer periods. The framework established here paves the way for a general use of 3D bioprinting for studying cellular reprogramming and cell cycle reentry toward tissue regeneration.

Isolation and characterization of drought and ABA responsive promoter of a transcription factor encoding gene from rice

Water deficit is a significant impediment to enhancing rice yield. Genetic engineering tools have enabled agriculture researchers to develop drought-tolerant cultivars of rice. A common strategy to achieve this involves expressing drought-tolerant genes driven by constitutive promoters such as CaMV35S. However, the use of constitutive promoters is often limited by the adverse effects it has on the growth and development of the plant. Additionally, it has been observed that monocot-derived promoters are more successful in driving gene expression in monocots than in dicots. Substitution of constitutive promoters with stress-inducible promoters is the currently used strategy to overcome this limitation. In the present study, a 1514 bp AP2/ERF promoter that drives the expression of a transcription factor was cloned and characterized from drought-tolerant Indian rice genotype N22. The AP2/ERF promoter was fused to the GUS gene (uidA) and transformed in Arabidopsis and rice plants. Histochemical GUS staining of transgenic Arabidopsis plants showed AP2/ERF promoter activity in roots, stems, and leaves. Water deficit stress and ABA upregulate promoter activity in transformed Arabidopsis and rice. Quantitative PCR for uidA expression confirmed induced GUS activity in Arabidopsis and rice. This study showed that water deficit inducible Os-AP2/ERF-N22 promoter can be used to overcome the limitations of constitutive promoters. Transformants overexpressing Os-AP2/ERF-N22 showed higher relative water content, membrane stability index, total chlorophyll content, chlorophyll stability index, wax content, osmotic potential, stomatal conductance, transpiration rate, photosynthetic rate and radical scavenging activity. Drought tolerant (N22) showed higher expression of Os-AP2/ERF-N22 than the susceptible (MTU1010) cultivar.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-022-01246-9.

Progress in Soybean Genetic Transformation Over the Last Decade

Soybean is one of the important food, feed, and biofuel crops in the world. Soybean genome modification by genetic transformation has been carried out for trait improvement for more than 4 decades. However, compared to other major crops such as rice, soybean is still recalcitrant to genetic transformation, and transgenic soybean production has been hampered by limitations such as low transformation efficiency and genotype specificity, and prolonged and tedious protocols. The primary goal in soybean transformation over the last decade is to achieve high efficiency and genotype flexibility. Soybean transformation has been improved by modifying tissue culture conditions such as selection of explant types, adjustment of culture medium components and choice of selection reagents, as well as better understanding the transformation mechanisms of specific approaches such as Agrobacterium infection. Transgenesis-based breeding of soybean varieties with new traits is now possible by development of improved protocols. In this review, we summarize the developments in soybean genetic transformation to date, especially focusing on the progress made using Agrobacterium-mediated methods and biolistic methods over the past decade. We also discuss current challenges and future directions.

Convergence of Bar and Cry1Ac Mutant Genes in Soybean Confers Synergistic Resistance to Herbicide and Lepidopteran Insects

Soybean is a globally important crop species, which is subject to pressure by insects and weeds causing severe substantially reduce yield and quality. Despite the success of transgenic soybean in terms of Bacillus thuringiensis (Bt) and herbicide tolerance, unforeseen mitigated performances have still been inspected due to climate changes that favor the emergence of insect resistance. Therefore, there is a need to develop a biotech soybean with elaborated gene stacking to improve insect and herbicide tolerance in the field. In this study, new gene stacking soybean events, such as bialaphos resistance (bar) and pesticidal crystal protein (cry)1Ac mutant 2 (M#2), are being developed in Vietnamese soybean under field condition. Five transgenic plants were extensively studied in the herbicide effects, gene expression patterns, and insect mortality across generations. The increase in the expression of the bar gene by 100% in the leaves of putative transgenic plants was a determinant of herbicide tolerance. In an insect bioassay, the cry1Ac-M#2 protein tested yielded higher than expected larval mortality (86%), reflecting larval weight gain and weight of leaf consumed were less in the T1 generation. Similarly, in the field tests, the expression of cry1Ac-M#2 in the transgenic soybean lines was relatively stable from T0 to T3 generations that corresponded to a large reduction in the rate of leaves and pods damage caused by Lamprosema indicata and Helicoverpa armigera. The transgenic lines converged two genes, producing a soybean phenotype that was resistant to herbicide and lepidopteran insects. Furthermore, the expression of cry1Ac-M#2 was dominant in the T1 generation leading to the exhibit of better phenotypic traits. These results underscored the great potential of combining bar and cry1Ac mutation genes in transgenic soybean as pursuant of ensuring resistance to herbicide and lepidopteran insects.

Molecular interaction of charcoal rot pathogenesis in soybean: a complex interaction

Charcoal rot (CR) is a major disease of soybean, which is caused by Macrophomina phaseolina (Mp). Increasing temperatures and low rainfall in recent years have immensely benefitted the pathogen. Hence, the search for genetically acquired resistance to this pathogen is essential. The pathogen is a hemibiotroph, which germinates on the root surface and colonizes epidermal tissue. Several surface receptors initiate pathogenesis, followed by the secretion of various enzymes that provide entry to host tissue. Several enzymes and other converging cascades in the pathogen participate against host defensive responses. β-glucan of the fungal cell wall is recognized as MAMPs (microbe-associated molecular patterns) in plants, which trigger host immune responses. Kinase receptors, resistance, and pathogenesis-related genes correspond to host defense response. They work in conjunction with hormone-mediated defense pathway especially, the systemic acquired resistance, calcium-signaling, and production of phytoalexins. Due to its quantitative nature, limited QTLs have been identified in soybean for CR resistance. The present review attempts to provide a functional link between M. phaseolina pathogenicity and soybean responses. Elucidation of CR resistance responses would facilitate improved designing of breeding programs, and may help in the selection of corresponding genes to introgress CR resistant traits.

Expression of a maize SOC1 gene enhances soybean yield potential through modulating plant growth and flowering

Yield enhancement is a top priority for soybean (Glycine max Merr.) breeding. SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) is a major integrator in flowering pathway, and it is anticipated to be capable of regulating soybean reproductive stages through its interactions with other MADS-box genes. Thus, we produced transgenic soybean for a constitutive expression of a maize SOC1 (ZmSOC1). T1 transgenic plants, in comparison with the nontransgenic plants, showed early flowering, reduced height of mature plants, and no significant impact on grain quality. The transgenic plants also had a 13.5-23.2% of higher grain weight per plant than the nontransgenic plants in two experiments. Transcriptome analysis in the leaves of 34-day old plants revealed 58 differentially expressed genes (DEGs) responding to the expression of the ZmSOC1, of which the upregulated FRUITFULL MADS-box gene, as well as the transcription factor VASCULAR PLANT ONE-ZINC FINGER1, contributed to the promoted flowering. The downregulated gibberellin receptor GID1B could play a major role in reducing the plant height. The remaining DEGs suggested broader effects on the other unmeasured traits (e.g., photosynthesis efficiency and abiotic tolerance), which could contribute to yield increase. Overall, modulating expression of SOC1 in soybean provides a novel and promising approach to regulate plant growth and reproductive development and thus has a potential either to enhance grain yield or to change plant adaptability.

Circadian Rhythms in Legumes: What Do We Know and What Else Should We Explore?

The natural timing devices of organisms, commonly known as biological clocks, are composed of specific complex folding molecules that interact to regulate the circadian rhythms. Circadian rhythms, the changes or processes that follow a 24-h light–dark cycle, while endogenously programmed, are also influenced by environmental factors, especially in sessile organisms such as plants, which can impact ecosystems and crop productivity. Current knowledge of plant clocks emanates primarily from research on Arabidopsis, which identified the main components of the circadian gene regulation network. Nonetheless, there remain critical knowledge gaps related to the molecular components of circadian rhythms in important crop groups, including the nitrogen-fixing legumes. Additionally, little is known about the synergies and trade-offs between environmental factors and circadian rhythm regulation, especially how these interactions fine-tune the physiological adaptations of the current and future crops in a rapidly changing world. This review highlights what is known so far about the circadian rhythms in legumes, which include major as well as potential future pulse crops that are packed with nutrients, particularly protein. Based on existing literature, this review also identifies the knowledge gaps that should be addressed to build a sustainable food future with the reputed “poor man’s meat”.

Comparison of the seed nutritional composition between conventional varieties and transgenic soybean overexpressing Physaria FAD3-1

BACKGROUND

PfFAD3 transgenic soybean expressing omega-3 fatty acid desaturase 3 of Physaria produces increased level of α-linolenic acid in seed. Composition data of non-transgenic conventional varieties is important in the safety assessment of the genetically-modified (GM) crops in the context of the natural variation.

RESULTS

The natural variation was characterized in seed composition of 13 Korean soybean varieties grown in three locations in South Korea for 2 years. Univariate analysis of combined data showed significant differences by variety and cultivation environment for proximates, minerals, anti-nutrients, and fatty acids. Percent variability analysis demonstrated that genotype, environment and the interaction of environment with genotype contributed to soybean seed compositions. Principal component analysis and orthogonal projections to latent structure discriminant analysis indicated that significant variance in compositions was attributable to location and cultivation year. The composition of three PfFAD3 soybean lines for proximates, minerals, anti-nutrients, and fatty acids was compared to a non-transgenic commercial comparator (Kwangankong, KA), and three non-transgenic commercial varieties grown at two sites in South Korea. Only linoleic and linolenic acids significantly differed in PfFAD3-1 lines compared to KA, which were expected changes by the introduction of the PfFAD3-1 trait in KA.

CONCLUSION

Genotype, environment, and the interaction of environment with genotype contributed to compositional variability in soybean. PfFAD3-1 soybean is equivalent to the conventional varieties with respect to these components. © 2020 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Progresses, Challenges, and Prospects of Genome Editing in Soybean (Glycine max)

Soybean is grown worldwide for oil and protein source as food, feed and industrial raw material for biofuel. Steady increase in soybean production in the past century mainly attributes to genetic mediation including hybridization, mutagenesis and transgenesis. However, genetic resource limitation and intricate social issues in use of transgenic technology impede soybean improvement to meet rapid increases in global demand for soybean products. New approaches in genomics and development of site-specific nucleases (SSNs) based genome editing technologies have expanded soybean genetic variations in its germplasm and have potential to make precise modification of genes controlling the important agronomic traits in an elite background. ZFNs, TALENS and CRISPR/Cas9 have been adapted in soybean improvement for targeted deletions, additions, replacements and corrections in the genome. The availability of reference genome assembly and genomic resources increases feasibility in using current genome editing technologies and their new development. This review summarizes the status of genome editing in soybean improvement and future directions in this field.

Functional characterization of wheat myo-inositol oxygenase promoter under different abiotic stress conditions in Arabidopsis thaliana

The production of wheat is severely affected by abiotic stresses such as cold, drought, salinity, and high temperature. Although constitutive promoters are frequently used to regulate the expression of alien genes, these may lead to undesirable side-effects in transgenic plants. Therefore, identification and characterization of an inducible promoter that can express transgene only when exposed to stresses are of great importance in the genetic engineering of crop plants. Previous studies have indicated the abiotic stress-responsive behavior of myo-inositol oxygenase (MIOX) gene in different plants. Here, we isolated the MIOX gene promoter from wheat (TaMIOX). The in-silico analysis revealed the presence of various abiotic stress-responsive cis-elements in the promoter region. The TaMIOX promoter was fused with the UidA reporter gene and transformed into Arabidopsis thaliana. The T₃ single-copy homozygous lines were analyzed for GUS activity using histochemical and fluorometric assays. Transcript expression of TaMIOX::UidA was significantly up-regulated by heat (five fold), cold (seven fold), and drought (five fold) stresses as compared to transgenic plants grown without stress-induced conditions. The CaMV35S::UidA plants showed very high GUS activity even in normal conditions. In contrast, the TaMIOX::UidA plants showed prominent GUS activity only in stress treatments (cold, heat, and drought), which suggests the inducible behavior of the TaMIOX promoter. The substrate myo-inositol feeding assay of TaMIOX::UidA plants showed lesser GUS activity as compared to plants treated in abiotic stress conditions. Results support that the TaMIOX promoter could be used as a potential candidate for conditional expression of the transgene in abiotic stress conditions.

GmNAC8 acts as a positive regulator in soybean drought stress

NAC proteins represent one of the largest transcription factor (TF) families involved in the regulation of plant development and the response to abiotic stress. In the present study, we elucidated the detailed role of GmNAC8 in the regulation of drought stress tolerance in soybean. The GmNAC8 protein was localized in the nucleus, and expression of the GmNAC8 gene was significantly induced in response to drought, abscisic acid (ABA), ethylene (ETH) and salicylic acid (SA) treatments. Thus, we generated GmNAC8 overexpression (OE1 and OE2) and GmNAC8 knockout (KO1 and KO2) lines to determine the role of GmNAC8 in drought stress tolerance. Our results revealed that, compared with the wild type (WT) plant, GmNAC8 overexpression and GmNAC8 knockout lines exhibited significantly higher and lower drought tolerance, respectively. Furthermore, the SOD activity and proline content were significantly higher in the GmNAC8 overexpression lines and significantly lower in the GmNAC8 knockout lines than in the WT plants under drought stress. In addition, GmNAC8 protein was found to physically interact with the drought-induced protein GmDi19-3 in the nucleus. Moreover, the GmDi19-3 expression pattern showed the same trend as the GmNAC8 gene did under drought and hormone (ABA, ETH and SA) treatments, and GmDi19-3 overexpression lines (GmDi19-3-OE9, GmDi19-3-OE10 and GmDi19-3-OE31) showed enhanced drought tolerance compared to that of the WT plants. Hence, the above results indicated that GmNAC8 acts as a positive regulator of drought tolerance in soybean and inferred that GmNAC8 probably functions by interacting with another positive regulatory protein, GmDi19-3.

Overexpression of the bioactive lunasin peptide in soybean and evaluation of its anti-inflammatory and anti-cancer activities in vitro

Lunasin, a bioactive peptide with a variety of physiological functions, was overexpressed in soybean to generate a transgenic soybean. Polymerase chain reaction (PCR) analysis suggested that lunasin was successfully inserted into the soybean genome, and three transgenic lines, L12, L43, and L45, were selected for further study. Lunasin expression was characterized in the lines by Western blot and ultra-performance liquid chromatography with tandem mass spectrometry. Enzyme-linked immunosorbent assay showed that lunasin content in L12, L43, and L45 lines was 1.47 mg g-1, 1.32 mg g-1 and 1.98 mg g-1, respectively; these values were significantly higher than that in wild-type soybean (0.94 mg g-1). Lunasin enrichments from transgenic soybean (LET) exhibited stronger DPPH, ABTS+, and oxygen radical scavenging activity than lunasin enrichments from wild-type soybean (LEW). Further, LET presented superior anti-inflammatory activity on lipopolysaccharide-induced macrophage cells compared to LEW, and it significantly suppressed the release of nitric oxide (NO) and pro-inflammatory cytokines including interleukin-1 and -6. Moreover, LET showed higher anti-proliferation activity on MDA-MB-231 cells than LEW. Immunofluorescence staining showed that LET could internalize into NIH-3T3 cells, and localize in the nucleus. In conclusion, it is feasible and efficient to produce lunasin through a transgenic soybean expression system. Lunasin overexpressing soybean could be consumed as a functional food in the diets of patients with cancer and obesity in the future.

CRISPR/Cas9-Based Gene Editing in Soybean

CRISPR/Cas9 (clustered regularly interspaced short palindromic repeat/CRISPR associated Cas9)-based gene editing is a robust tool for functional genomics research and breeding programs in various crops. In soybean, a number of laboratories have obtained mutants by CRISPR/Cas9 system; however, there has been not yet a detailed method for the CRISPR/Cas9-based gene editing in soybean. Here, we describe the procedures for constructing the CRISPR/Cas9 plasmid suitable for soybean gene editing and the modified protocols for Agrobacterium-mediated soybean transformation and regeneration from cotyledonary node explants containing the Cas9/sgRNA (single guide RNA) transgenes.

Raman Spectroscopic and Chemometric Investigation of Lipid-Protein Ratio Contents of Soybean Mutants

Seeds belonging to fourth generation mutants (M4) of Ataem-7 cultivar (A7) variety and S04-05 (S) breeding line salt-tolerant soybeans were investigated by Raman spectroscopy, complemented by chemometrics methods, in order to evaluate changes induced by mutations in the relative lipid-protein contents, and to find fast, efficient strategies for discrimination of the mutants and the control groups based on their Raman spectra. It was concluded that gamma irradiation caused an increase in the lipid to protein ratio of the studied Ataem-7 variety mutants, while it led to a decrease of this ratio in the investigated S04-05 breeding line mutants. These results were found to be in agreement with data obtained by reflectance spectrum analysis of the seeds in the full ultraviolet to near-infrared spectral region and suggest the possibility of developing strategies where gamma irradiation can be used as a tool to improve mutant soybean plants targeted to different applications, either enriched in proteins or in lipids. Ward's clustering and principal component analysis showed a clear discrimination between mutants and controls and, in the case of the studied S-type species, discrimination between the different mutants. The grouping scheme is also found to be in agreement with the compositional information extracted from the analysis of the lipid-protein contents of the different samples.

Genome Editing in Agriculture: Technical and Practical Considerations

The advent of precise genome-editing tools has revolutionized the way we create new plant varieties. Three groups of tools are now available, classified according to their mechanism of action: Programmable sequence-specific nucleases, base-editing enzymes, and oligonucleotides. The corresponding techniques not only lead to different outcomes, but also have implications for the public acceptance and regulatory approval of genome-edited plants. Despite the high efficiency and precision of the tools, there are still major bottlenecks in the generation of new and improved varieties, including the efficient delivery of the genome-editing reagents, the selection of desired events, and the regeneration of intact plants. In this review, we evaluate current delivery and regeneration methods, discuss their suitability for important crop species, and consider the practical aspects of applying the different genome-editing techniques in agriculture.

GmBZL3 acts as a major BR signaling regulator through crosstalk with multiple pathways in Glycine max

BACKGROUND

Brassinosteroids (BRs) play a crucial role in plant vegetative growth and reproductive development. The transcription factors BZR1 and BES1/BZR2 are well characterized as downstream regulators of the BR signaling pathway in Arabidopsis and rice. Soybean contains four BZR1-like proteins (GmBZLs), and it was reported that GmBZL2 plays a conserved role in BR signaling regulation. However, the roles of other GmBZLs have not been thoroughly studied, and the targets of GmBZLs in soybean remain unclear.

RESULTS

In this study, we first characterized GmBZL3 in soybean from gene expression patterns, conserved domains in coding sequences, and genomic replication times of four GmBZL orthologous. The results indicated that GmBZL3 might play conserved roles during soybean development. The overexpression of GmBZL3P219L in the Arabidopsis BR-insensitive mutant bri1-5 partially rescued the phenotypic defects including BR-insensitivity, which provides further evidence that GmBZL3 functions are conserved between soybean and the homologous Arabidopsis genes. In addition, the identification of the GmBZL3 target genes through ChIP-seq technology revealed that BR has broad roles in soybean and regulates multiple pathways, including other hormone signaling, disease-related, and immunity response pathways. Moreover, the BR-regulated GmBZL3 target genes were further identified, and the results demonstrate that GmBZL3 is a major transcription factor responsible for BR-regulated gene expression and soybean growth. A comparison of GmBZL3 and AtBZR1/BES1 targets demonstrated that GmBZL3 might play conserved as well as specific roles in the soybean BR signaling network. Finally, the identification of two natural soybean varieties of the GmBZL3 mutantion by SNP analysis could facilitate the understanding of gene function during soybean development in the future.

CONCLUSIONS

We illustrate here that GmBZL3 orchestrates a genome-wide transcriptional response that underlies BR-mediated soybean early vegetative growth, and our results support that BRs play crucial regulatory roles in soybean morphology and gene expression levels.

Increased Production of α-Linolenic Acid in Soybean Seeds by Overexpression of Lesquerella FAD3-1

Soybean is a major crop that is used as a source of vegetable oil for human use. To develop transgenic soybean with high α-linolenic acid (ALA; 18:3) content, the FAD3-1 gene isolated from lesquerella (Physaria fendleri) was used to construct vectors with two different seed-specific promoters, soybean β-conglycinin (Pβ-con) and kidney bean phaseolin (Pphas), and one constitutive cauliflower mosaic virus 35S promoter (P35S). The corresponding vectors were used for Agrobacterium-mediated transformation of imbibed mature half seeds. The transformation efficiency was approximately 2%, 1%, and 3% and 21, 7, and 17 transgenic plants were produced, respectively. T-DNA insertion and expression of the transgene were confirmed from most of the transgenic plants by polymerase chain reaction (PCR), quantitative real-time PCR (qPCR), reverse transcription PCR (RT-PCR), and Southern blot analysis. The fatty acid composition of soybean seeds was analyzed by gas chromatography. The 18:3 content in the transgenic generation T₁ seeds was increased 7-fold in Pβ-con:PfFAD3-1, 4-fold in Pphas : PfFAD3-1, and 1.6-fold in P35S:PfFAD3-1 compared to the 18:3 content in soybean "Kwangankong". The increased content of 18:3 in the Pβ-con:PfFAD3-1 soybean (T₁) resulted in a 52.6% increase in total fatty acids, with a larger decrease in 18:1 content than 18:2 content. The increase in 18:3 content was also maintained and reached 42% in the Pphas : PfFAD3-1 transgenic generation T₂. Investigations of the agronomic traits of 12 Pβ-con:PfFAD3-1 transgenic lines (T₁) revealed that plant height, number of branches, nodes, pods, total seeds, and total seed weight were significantly higher in several transgenic lines than those in non-transgenic soybean. Especially, an increase in seed size was observed upon expression of the PfFAD3-1 gene with the β-conglycinin promoter, and 6%-14% higher seed lengths were measured from the transgenic lines.

Increase in isoflavonoid content in Glycine max cells transformed by the constitutively active Ca2+ independent form of the AtCPK1 gene

Calcium-dependent protein kinases (CDPKs) represent a class within a multigene family that plays an important role in biotic and abiotic plant stress responses and is involved in the regulation of secondary metabolite biosynthesis. Our previous study showed that overexpression of the mutant constitutively active Ca2+ independent form of the AtCPK1 gene (AtCPK1-Ca) significantly increased the biosynthesis of anthraquinones and stilbenes in Rubia cordifolia L. and Vitis amurensis Rupr. transgenic cell cultures, respectively. Here, we have established transgenic calli of soybean plants Glycine max (L.) Merr. that express the AtCPK1-Ca gene. Heterologous expression of the AtCPK1-Ca gene provoked a 5.2-fold increase in total isoflavone production up to 208.09 mg/L, along with an increase in isoflavone aglycones production up to 6.60 mg/L, which is 3-fold greater than that of the control culture. The production of prenylated isoflavones significantly increased, reaching 3.78 mg/L, 13-fold higher than in the control culture. The expression levels of 4-coumarate:CoA ligases, isoflavone synthases, 2-hydroxyisoflavanone dehydratase, isoflavone dimethylallyltransferase, and coumestrol 4-dimethylallyltransferase genes in transgenic cell cultures significantly increased. Thus, heterologous expression of the AtCPK1-Ca gene can be used to bioengineer plant cell cultures that produce isoflavonoids.

Improvement of Soybean Agrobacterium-Mediated Transformation Efficiency by Adding Glutamine and Asparagine into the Culture Media

As a genetically modified crop, transgenic soybean occupies the largest global scale with its food, nutritional, industrial, and pharmaceutical uses.Efficient transformation is a key factor for the improvement of genetically modified soybean. At present, the Agrobacterium-mediated method is primarily used for soybean transformation, but the efficiency of this method is still relatively low (below 5%) compared with rice (above 90%). In this study, we examined the influence of l-glutamine and/or l-asparagine on Agrobacterium-mediated transformation in soybean and explored the probable role in the process of Agrobacterium-mediated transformation. The results showed that when the amino acids l-glutamine and l-asparagine were added separately or together to the culture medium, the shoot induction frequency, elongation rate, and transformation frequency were improved. The combined effects of l-glutamine and l-asparagine were better than those of l-glutamine and l-asparagine alone. The 50 mg/L l-glutamine and 50 mg/L l-asparagine together can enhance the transformation frequency of soybean by attenuating the expression level of GmPRs (GmPR1, GmPR4, GmPR5, and GmPR10) and suppression of the plant defense response. The transgene was successfully transmitted to the T1 generation. This study will be useful in genetic engineering of soybean.

Isolation and characterization of a promoter responsive to salt, osmotic and dehydration stresses in soybean

Drought stress is the main limiting factor of soybean yield. Currently, genetic engineering has been one important tool in the development of drought-tolerant cultivars. A widely used strategy is the fusion of genes that confer tolerance under the control of the CaMV35S constitutive promoter; however, stress-responsive promoters would constitute the best alternative to the generation of drought-tolerant crops. We characterized the promoter of α-galactosidase soybean (GlymaGAL) gene that was previously identified as highly up-regulated by drought stress. The β-glucuronidase (GUS) activity of Arabidopsis transgenic plants bearing 1000- and 2000-bp fragments of the GlymaGAL promoter fused to the uidA gene was evaluated under air-dried, polyethylene glycol (PEG) and salt stress treatments. After 24 h of air-dried and PEG treatments, the pGAL-2kb led to an increase in GUS expression in leaf and root samples when compared to the control samples. These results were corroborated by qPCR expression analysis of the uidA gene. The pGAL-1kb showed no difference in GUS activity between control and treated samples. The pGAL-2kb promoter was evaluated in transgenic soybean roots, leading to an increase in EGFP expression under air-dried treatment. Our data indicates that pGAL-2kb could be a useful tool in developing drought-tolerant cultivars by driving gene expression.

Soybean [Glycine max (L.) Merr]

In this chapter we describe an Agrobacterium tumefaciens transformation method of soybean that utilizes mature half seeds and regeneration from the cotyledonary node region. This method results in fertile transformed soybean plants and transgenic seed in approximately 9 months. Using mature half seeds as starting material has proven to be a reliable method that does not require additional wounding for infection to occur. We have continued to make improvements in the protocol, resulting in an efficient plant regeneration system.