Efficiency Of Agrobacterium-mediated Transformation Research Articles

Enhancing Agrobacterium-mediated plant transformation efficiency through improved ternary vector systems and auxotrophic strains.

Agrobacterium-mediated transformation is an essential tool for functional genomics studies and crop improvements. Recently developed ternary vector systems, which consist of a T-DNA vector and a compatible virulence (vir) gene helper plasmid (ternary helper), demonstrated that including an additional vir gene helper plasmid into disarmed Agrobacterium strains significantly improves T-DNA delivery efficiency, enhancing plant transformation. Here, we report the development of a new ternary helper and thymidine auxotrophic Agrobacterium strains to boost Agrobacterium-mediated plant transformation efficiency. Auxotrophic Agrobacterium strains are useful in reducing Agrobacterium overgrowth after the co-cultivation period because they can be easily removed from the explants due to their dependence on essential nutrient supplementation. We generated thymidine auxotrophic strains from public Agrobacterium strains EHA101, EHA105, EHA105D, and LBA4404. These strains exhibited thymidine-dependent growth in the bacterial medium, and transient GUS expression assay using Arabidopsis seedlings showed that they retain similar T-DNA transfer capability as their original strains. Auxotrophic strains EHA105Thy- and LBA4404T1 were tested for maize B104 immature embryo transformation using our rapid transformation method, and both strains demonstrated comparable transformation frequencies to the control strain LBA4404Thy-. In addition, our new ternary helper pKL2299A, which carries the virA gene from pTiBo542 in addition to other vir gene operons (virG, virB, virC, virD, virE, and virJ), demonstrated consistently improved maize B104 immature embryo transformation frequencies compared to the original version of pKL2299 (33.3% vs 25.6%, respectively). Therefore, our improved Agrobacterium system, including auxotrophic disarmed Agrobacterium strains and a new ternary helper plasmid, can be useful for enhancing plant transformation and genome editing applications.

Development of super-infective ternary vector systems for enhancing the Agrobacterium-mediated plant transformation and genome editing efficiency.

Agrobacterium-mediated transformation remains a cornerstone of plant biology, fueling advancements in molecular genetics, new genomic techniques (NGTs), and the biotech industry. However, recalcitrant crops and technical hurdles persist as bottlenecks. The goal was to develop super-infective ternary vector systems that integrate a novel salicylic acid-degrading enzyme, GABA, and ethylene-degrading enzymes, targeting the transformation of crops by neutralizing plant defense system on Agrobacterium. Firstly, both the effect and activity of introducing enzymes were validated in EHA105, an important Agrobacterium strain. Our study demonstrates that all ternary vector (Tv) system variants significantly enhance reporter expression in transient assays with Nicotiana benthamiana and Cannabis sativa. Specifically, incorporating a constitutive virG mutation with novel enzyme combinations increased GFP and RUBY expression in C. sativa by >5-fold and 13-fold, respectively. The Tv system, combined with a geminivirus replicon, markedly boosted GUS gene expression in tomato, enhancing genome editing efficiency. Notably, compared to controls, Tv-VS demonstrated up to 18-fold and 4.5-fold increases in genome editing efficiency in C. sativa and tomato, respectively. Additionally, stable transformation rates in tomato and Arabidopsis improved significantly, with Tv-VS showing a remarkable 2.5-fold increase in transformation efficiency compared to control strains. The research marks notable progress in Agrobacterium-mediated plant transformation. The innovative ternary vectors overcome plant defense mechanisms, enabling genetic manipulation in previously challenging plant species. This development is anticipated to broaden the applications of plant genetic engineering, contributing to advancements in crop genome editing.

Factors influencing Agrobacterium-mediated genetic transformation efficiency in bread wheat (Triticum aestivum L.)

Assessment of the efficiency of Agrobacterium tumefaciens mediated transformation in four bread wheat varieties was focused and upon optimization of experiments done to obtain tangible results. The four varieties, Fielder, Navojoa, Baj and Kachu/saul, were transformed with optimized protocols and randomly selected from a selection medium amalgamated with phosphinothricin (Glufosinate). Initially, the variety Fielder has proceeded with 36 different concentrations of synthetic auxins 2,4-D and picloram as 36 treatments. The treatment 30 (48 μg of 2,4-D and 64 μg of picloram) has shown higher efficiency and is comparable in terms of the three traits studied. Additionally, antioxidants and growth regulators were adjusted to obtain better results towards reasonable transformation frequency. Additional varieties were also tested and selected against the selectable marker PPT based on the optimization for the variety Fielder. Selected genotypes were subjected for gusA or Bar gene PCR amplification. The result revealed the frequency of transgenesis in the range of 60 to 70% with the varieties studied. However, the whole experiment needs further repetitions for confirmatory results. Transgenic genotypes of the Fielder variety showed moderate to strong GUS expression in leaves, anthers, seeds, seed coats, and roots compared to non-transgenic control plant tissues. PPT leaf painting assay showed the lack of necrosis on the painted area of leaves in transgenic genotypes compared to the non-transgenic ones.

Optimization of Factors Affecting the Efficiency of Agrobacterium-Mediated Transformation of Wolffia arrhiza

Optimization of Factors Affecting the Efficiency of Agrobacterium-Mediated Transformation of Wolffia arrhiza

Oxicam-type nonsteroidal anti-inflammatory drugs enhance Agrobacterium-mediated transient transformation in plants.

Agrobacterium-mediated transformation is a key innovation for plant breeding, and routinely used in basic researches and applied biology. However, the transformation efficiency is often the limiting factor of this technique. In this study, we discovered that oxicam-type nonsteroidal anti-inflammatory drugs, including tenoxicam (TNX), increase the efficiency of Agrobacterium-mediated transient transformation. TNX treatment increased the transformation efficiency of Agrobacterium-mediated transformation of Arabidopsis thaliana mature leaves by agroinfiltration. The increase of efficiency by TNX treatment was not observed in dde2/ein2/pad4/sid2 quadruple mutant, indicating that TNX inhibits the immune system mediated by jasmonic acid, ethylene, and salicylic acid against to Agrobacterium. We also found that TNX-treatment is applicable for the transient expression and subcellular localization analysis of fluorescent-tagged proteins in Arabidopsis leaf cells. In addition, we found that TNX increases the efficiency of Agrobacterium-mediated transient transformation of Jatropha. Given that treatment with oxicam compounds is a simple and cost effective method, our findings will provide a new option to overcome limitations associated with Agrobacterium-mediated transformation of various plant species.

Development of a miniaturized Ti-plasmid and helper plasmid system for Agrobacterium-mediated plant transformation

Tumor-inducing (Ti) plasmid is the requisite for Agrobacterium-mediated plant transformation. Over decades, continuous efforts have been made to improve the efficiency of Agrobacterium-mediated plant transformation and most of them focused on the binary vector system. A binary vector system comprises of a binary vector of which transferred DNA (T-DNA) resided on and a Ti plasmid to carry those essential virulence genes. In this study, we constructed a miniaturized helper Ti plasmid, designated as pYL102, with the aim to enhance the overall Agrobacterium-mediated transformation rate. The size of pYL102 was reduced to ~60% of the original plasmid pCAMBIA5105. Subsequently, pYL102 was coupled with the broad host range (BHR) bacterial expression vector, pYL101C, of which the key regulatory virulence gene, virG-N54D, was cloned in and expressed under the control of a strong constitutive PINTc promoter. To test the functionality of the constructed vector system, A. tumefaciens C58C1 carrying pYL102, pYL101C::virG-N54D and the transformation vector pGWB2::e35S-sfGFP was used to transform Nicotiana benthamiana leaves by agroinfiltration. Green fluorescence was observed in spots infiltrated with Agrobacterium carrying the test plasmids. The fluorescence intensity from the test agroinfiltrated leaves was significantly higher than those of the mock-infiltrated leaves (p<0.01), indicating the vector system can be used for plant transformation.

Optimisation of plant tissue culture conditions in a popular semi-dwarf indica rice cultivar ADT 39 for effective Agrobacterium-mediated transformation

The in vitro culture conditions plays a critical role in promoting callus and shoot induction in rice during Agrobacterium-mediated transformation. In this research, an attempt was made to optimize the key factors affecting the efficiency of Agrobacterium-mediated transformation in ADT 39 rice cultivar. Among the different combinations of the NB-Asmedia tried with varying concentrations of casein hydrolysate from 0.25 g l-1 to 1.25 g l-1, the media containing 0.5 g l-1 casein hydrolysate supplemented with 2 mg l-1 2,4-Dichlorophenoxyacetic acid (2,4-D), 1 mg l-16-Benzylaminopurie (6-BAP) and 1mg l-1 Naphthalene Acetic Acid (NAA) was found to be the best with callus induction frequency of 94.44 per cent. Incubation in NB-As media after infection for 20 min. considerably reduced the Agrobacterium overgrowth after co-cultivation. For shoot induction, regeneration media RNMH30 containing varied concentrations of 6-BAP from 2 mg l-1 to 4 mg l-1 was tried, the media containing 3.0 mg l-1 6-BAP added with 1 mg l-1 NAA recorded the highest shoot induction frequency of 71.11 per cent. The overall transformation efficiency in ADT 39 with the optimized culture conditions was found to be 7.96 per cent. Key words: ADT 39, Agrobacterium-mediated transformation, Callus induction frequency, Shoot induction frequency, Transformation efficiency.

Effect of ‘Chloroxynil’ on Agrobacterium-mediated transformation efficiency of Lilium cv ‘Manissa’

As a powerful technique, gene transformation can produce new lily cultivars with specific characteristics such as new flower colors and resistance to pathogens. However, it is difficult to use this technique in monocot plants like lilies. A new phenolic compound called ‘chloroxynil’ has been introduced to replace ‘acetosyringone’ and is considered to improve transformation efficiency of Lilium. Our results showed that the addition of chloroxynil into the inoculation and co-cultivation media significantly improved the transformation efficiency. At 4 μM, chloroxynil-mediated callus regeneration increased 7 days after it was transferred to the regeneration medium. Transformation efficiency was 6.6 % at 100 μM acetosyringone, while 11.1 % at 4 μM CX. Finally, 11 kanamycin-resistant plants were successfully produced at 4 μM CX, and gene transformation in the plantlets was validated by PCR and RT-PCR techniques.

TRA1: A Locus Responsible for Controlling Agrobacterium-Mediated Transformability in Barley.

In barley (Hordeum vulgare L.), Agrobacterium-mediated transformation efficiency is highly dependent on genotype with very few cultivars being amenable to transformation. Golden Promise is the cultivar most widely used for barley transformation and developing embryos are the most common donor tissue. We tested whether barley mutants with abnormally large embryos were more or less amenable to transformation and discovered that mutant M1460 had a transformation efficiency similar to that of Golden Promise. The large-embryo phenotype of M1460 is due to mutation at the LYS3 locus. There are three other barley lines with independent mutations at the same LYS3 locus, and one of these, Risø1508 has an identical missense mutation to that in M1460. However, none of the lys3 mutants except M1460 were transformable showing that the locus responsible for transformation efficiency, TRA1, was not LYS3 but another locus unique to M1460. To identify TRA1, we generated a segregating population by crossing M1460 to the cultivar Optic, which is recalcitrant to transformation. After four rounds of backcrossing to Optic, plants were genotyped and their progeny were tested for transformability. Some of the progeny lines were transformable at high efficiencies similar to those seen for the parent M1460 and some were not transformable, like Optic. A region on chromosome 2H inherited from M1460 is present in transformable lines only. We propose that one of the 225 genes in this region is TRA1.

Nitric oxide donor regulates Agrobacterium-mediated genetic transformation efficiency in soybean [Glycine max (L.) Merrill

The present study investigates the potentiality of Sodium nitroprusside (SNP) to enhance the efficiency of genetic transformation in soybean. Half-seeds cultured on co-cultivation [4.44 μM N6-benzyl adenine (BA) and 30 μM SNP]; shoot induction (4.44 μM BA and 30 μM SNP) and rooting medium [4.93 μM indole 3-butyric acid (IBA) and 30 μM SNP] exhibited improved transformation efficiency (34.6%) in contrast to the regeneration system devoid of SNP (23%). The putatively transformed plants were evaluated by GUS assay and molecular analysis like PCR and Southern hybridization. Furthermore, the transformation system developed herein entails a shorter period (75-days) for developing plantlets from half-seeds of soybean. The outcome of this study revealed that the addition of SNP increased regeneration efficiency of plants, which translated to improved transformation efficiency in soybean. This study is the first report employing sodium nitroprusside to enhance transformation efficiency in soybean.

Utilization of sucrose during cocultivation positively affects Agrobacterium-mediated transformation efficiency in sugar beet (Beta vulgaris L.)

Sugar beet (Beta vulgaris L.) is one of the most important industrial crops throughout world. With the availability of suitable genetic transformation technologies, the yield, quality, and stress tolerance of sugar beet could be improved significantly. However, low transformation efficiencies seriously limit the application of molecular technologies to the genetic improvement of sugar beet. With the aim of improving gene transfer techniques for sugar beet, the effect of different sucrose concentrations during cocultivation on the initial Agrobacterium-mediated transformation efficiencies in sugar beet was tested. To develop an efficient experimental system through which the effect of sucrose could be tested, first, a prolific regeneration system was optimized by testing the effect of different plant growth regulators on in vitro regeneration and rooting efficiencies from sugar beet cotyledonary node explants. The highest mean number of regenerated shoots per explant was obtained when the cotyledonary node explants excised from young seedlings were grown on MS medium supplemented with 1.0 mg/L 6-benzylaminopurine. Using this regeneration system, the effect of different concentrations of sucrose included in the cocultivation medium on the initial genetic transformation efficiencies observed in T0 plants was tested using an Agrobacterium tumefaciens strain carrying the pBin19/35S:GUS-INT construct. The inclusion of 4.5% sucrose in the cocultivation medium resulted in significantly higher transformation (34.09%) and expression efficiencies (22.72%), confirmed by polymerase chain reaction and β-glucuronidase assays, respectively, in regenerated T0 seedlings. If translated into stably inherited transformation efficiencies, these findings could contribute to the success of genetic transformation studies in sugar beet and other crops recalcitrant to Agrobacterium-mediated transformation.

The infiltration efficiency of Agrobacterium-mediated transient transformation in four apple cultivars

Studies of gene function in apple fruits (Malus domestica) have been hindered by the long juvenile period of apple fruit trees. Transient gene expression is a relatively simple method for gene functional analyses, and has been broadly applied to several plant species; however, few studies have reported a method for systematic transient expression in apple fruits. Here, we developed a highly efficient and robust Agrobacterium-mediated transient expression system for apple fruit, which allows rapid analysis of diverse gene functions. Using a β-glucuronidase gene (GUS) as a reporter for Agrobacterium-mediated transformation, we found that the most suitable infiltration pressure for gene function assays in ‘Red Fuji’, ‘Granny Smith’ and ‘Royal Gala’ fruits was −90 kPa, but −70 kPa in ‘Golden Delicious’. The infiltration efficiency of ‘Golden Delicious’ was higher than that of the other apple cultivars. Transient silencing of MdMYB10, an anthocyanin biosynthesis regulator, altered anthocyanin content in ‘Red Fuji’, demonstrating that vacuum infiltration with Agrobacterium can be used for gene functional analysis. Also a significant positive correlation was found between microcrack density and infiltration efficiency. We conclude that this method represents a general tool for efficient and targeted transient regulation of gene expression in apple fruits.

Effects of Medium Composition and Genetic Background on Agrobacterium-Mediated Transformation Efficiency of Lentinula edodes.

The establishment of genetic transformation method is crucial for the functional genomics research in filamentous fungi. Although the transformation method has been developed in several types of fungi, a highly efficient and convenient transformation system is desperately needed in Lentinula edodes. Present work established the Agrobacterium-mediated transformation (ATMT) of basidiomycete L. edodes in both monokaryon and dikaryon mycelia by using constructed binary plasmid pCAMBIA-1300-GFP. Then, the transformation efficiency of ATMT was evaluated by using different mediums for recipient incubation and different varieties of L. edodes. The results showed that in dikaryon strain W1, the positive hygromycin-resistant transformants was observed in all medium with the positive frequency of selected transformants that ranged from 0 to 30%. While in the monokaryon strain W1-26, only the millet medium group obtained positive transformants with a positive frequency of 75.48%. Moreover, three dikaryotic wild strains (YS55, YS3334, and YS3357) and two dikaryotic cultivated strains (W1 and S606) showed the highest transformation efficiency, with 32.96% of the germination frequency, and 85.12% of positive frequency for hygromycin-resistant transformants. This work demonstrated that Agrobacterium-mediated transformation was successfully performed in L. edodes, and the genotype of recipients as well as the medium for mycelial incubation were suggested to play key roles in determining the transformation efficiency. These findings may provide new avenues for the genetic modification of edible mushroom and may extend the cognition of DNA-mediated transformation in filamentous fungi.

Comparison of regeneration capacity and Agrobacterium-mediated cell transformation efficiency of different cultivars and rootstocks of Vitis spp. via organogenesis

The success of in vitro plant regeneration and the competence of genetic transformation greatly depends on the genotype of the species of interest. In previous work, we developed a method for the efficient Agrobacterium-mediated genetic transformation via organogenesis of V. vinifera cultivar Thompson Seedless, by using meristematic bulk (MB) as starting tissue. In this study, we applied this method for the regeneration and transformation of MBs obtained from the Italian cultivar Ciliegiolo and two of the commonly used Vitis rootstocks, 110 Richter and Kober 5BB, in comparison with Thompson Seedless. The A. tumefaciens strain EHA105, harbouring pK7WG2 binary vector, was used for the transformation trials, which allowed selection through the enhanced-green fluorescent protein (eGFP) and the neomycin phosphotransferase (nptII) gene. Putative transformed tissues and/or shoots were identified by either a screening based on the eGFP expression alone or its use in combination with kanamycin in the medium. MBs obtained from Thompson Seedless showed the highest regeneration and transformation cell competence, which subsequently allowed the recovery of stably transformed plants. Ciliegiolo, 110 Richter, and Kober 5BB, produced actively growing transgenic calli showing eGFP fluorescence, more consistently on selective media, but had no regenerative competence.

Enhanced Agrobacterium-mediated transformation efficiency of banana cultivar Grand Naine by reducing oxidative stress

Efficient protocols were developed for somatic embryogenesis (SE) and recovery of genetic transformants of banana cultivar Grand Naine. The efficiency of embryogenic callus formation was enhanced up to 14% by spraying 2, 4-dichlorophenoxyacetic acid (20 mg/l) on immature male flower buds (IMFBs) before inoculation of explants (immature male flowers) on the callus induction medium (CIM). Embryogenic cell suspension (ECS) derived from callus was used for Agrobacterium tumefaciens-mediated transformation harboring β-glucuronidase (GUS) as a reporter and hygromycin phosphotransferase (hpt II) as the selection marker genes. Four antioxidants (melatonin, quercetin, gallic acid, and α-tocopherol) were tested during and after Agrobacterium infection of ECS to reduce the oxidative stress. Melatonin boosted up nearly 1.5-fold [72.3 ± 7.5 plantlets/ml settled cell volume (SCV)] higher transformation efficiency as compared to without antioxidant treated (46.7 ± 2.5 plantlets/ml SCV) culture. Scanning electron microscopy (SEM) revealed that melatonin reinforced the bacterial attachment to the plant cell and also maintained surface morphology of the cells. The expression of the reporter gene in putatively transformed ECS and different tissues has been demonstrated by histochemical GUS assay. The transgenic plants were confirmed by PCR for the presence of hpt II and GUS amplicon. The optimized efficient protocols pave the way to generate the high number of transgenic lines with desirable traits in important commercial banana cultivar Grand Naine.

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.

Elimination of macro elements from inoculation and co-cultivation media enhances the efficiency of Agrobacterium-mediated transformation in Petunia.

In order to evaluate the effect of inoculation and co-cultivation media elements on transformation frequency in Petunia hybrida, modified MS media with different elements were tested on Alvan and Large Flower Alvan (LF Alvan), two local cultivars. Leaf explants of both cultivars were inoculated with Agrobacterium tumefaciens strain LBA4404 (pBI121) containing neomycin phosphotransferase (nptII) and an intron-containing β-glucuronidase (gus) genes. When medium lacking KH2PO4, NH4NO3, KNO3, and CaCl2 was used as inoculation and co-cultivation medium, a higher frequency of transformation for Alvan (22%) and LF Alvan (16%) was obtained. Kanamycin resistant plantlets were stained blue by GUS assay. Furthermore, polymerase chain reaction (PCR) analysis revealed the presence of both gus and nptII genes in all putative transformants. Finally, southern blot hybridization confirmed insertion of 1-4 copies of gus gene in transgenic plants.

Research and Application of Lipoic Acid in Plants

Lipoic acid is a kind of small molecular compound with strong oxidizing properties. It has been widely used in medicine and has achieved good results since its discovery. However, it is less used in plants, and the biosynthetic pathway is not clear. The content in the plant is mainly measured by high-performance liquid chromatography(HPLC). At present, it is mainly used as an additive to the culture medium for plant tissue culture and Agrobacterium-mediated plant genetic transformation, in order to reduce the browning rate of explants, improve Agrobacterium-mediated genetic transformation efficiency.

Small-Molecule Screening to Increase Agrobacterium-Mediated Transformation Efficiency in Legumes.

Agrobacterium-mediated transformation is a powerful strategy for plant genetic engineering. However, the transformation efficiency of some grain legume crops is generally low. In this chapter, we describe a chemical screening procedure for improving the efficiency of Agrobacterium-mediated transformation of a model legume, Lotus japonicus. Moreover, we explain the transformation protocol using chloroxynil, a phenolic compound that improves the efficiency.

Transcriptome Analysis of Maize Immature Embryos Reveals the Roles of Cysteine in Improving Agrobacterium Infection Efficiency.

Maize Agrobacterium-mediated transformation efficiency has been greatly improved in recent years. Antioxidants, such as, cysteine, can significantly improve maize transformation frequency through improving the Agrobacterium infection efficiency. However, the mechanism underlying the transformation improvement after cysteine exposure has not been elucidated. In this study, we showed that the addition of cysteine to the co-cultivation medium significantly increased the Agrobacterium infection efficiency of hybrid HiII and inbred line Z31 maize embryos. Reactive oxygen species contents were higher in embryos treated with cysteine than that without cysteine. We further investigated the mechanism behind cysteine-related infection efficiency increase using transcriptome analysis. The results showed that the cysteine treatment up-regulated 939 genes and down-regulated 549 genes in both Z31 and HiII. Additionally, more differentially expressed genes were found in HiII embryos than those in Z31 embryos, suggesting that HiII was more sensitive to the cysteine treatment than Z31. GO analysis showed that the up-regulated genes were mainly involved in the oxidation reduction process. The up-regulation of these genes could help maize embryos to cope with the oxidative stress stimulated by Agrobacterium infection. The down-regulated genes were mainly involved in the cell wall and membrane metabolism, such as, aquaporin and expansin genes. Decreased expression of these cell wall integrity genes could loosen the cell wall, thereby improving the entry of Agrobacterium into plant cells. This study offers insight into the role of cysteine in improving Agrobacterium-mediated transformation of maize immature embryos.