Agrobacterium-mediated Transformation Protocol Research Articles

Effect of Explant, Genotype and Plant Growth Regulators on Regeneration and Agrobacterium-Mediated Transformation of Potato

A B S T R A C T The objective of the present study is to develop an efficient protocol for plant regeneration and Agrobacterium-mediated transformation of potato cultivars Desiree, Agria and Marfona grown under Iranian agricultural conditions. The regeneration efficiency from internode, leaf and petiole explants was examined. The results from all Shoot Induction Medium (SIM) combinations and all cultivars together indicate highly efficient shoot regeneration from internode (4.56 shoots per explant). The response of petiole and leaf explants was lower, 3.83 and 2.55 shoots per explant, respectively. The highest efficiency of shoot regeneration was achieved with internode explants of cultivar Desiree (6.64 shoots per explant) on Murashige and Skoog (MS) medium supplemented with thidiazuron (TDZ) 1 mg LG 1 + 6-benzyladenine (BAP) 1 mg LG 1 . For plant transformation, internode explants were inoculated and co-cultivated with Agrobacterium tumefaciens strain LBA4404 harboring a binary vector pBI-121 containing β-glucuronidase (GUS) and nptII genes. Reverse transcriptase-polymerase chain reaction analysis and histochemical assay for β-glucuronidase indicated that the gene coding for this enzyme was integrated in the potato genome and could be expressed in potato tissues. The presence of nptII gene in the kanamycin resistant plants was verified by polymerase chain reaction analysis. The transformation frequency ranged from 22-42%.

Genotype independent and efficient Agrobacterium-mediated genetic transformation of the medicinal plant Withania somnifera Dunal

Withania somnifera one of the most reputed Indian medicinal plant has been extensively used in traditional and modern medicines as active constituents. A high frequency genotype and chemotype independent Agrobacterium-mediated transformation protocol has been developed for W. somnifera by optimizing several factors which influence T-DNA delivery. Leaf and node explants of Withania chemotype was transformed with A. tumefaciens strain GV3101 harboring pIG121Hm plasmid containing the gusA gene encoding β-glucuronidase (GUS) as a reporter gene and the hptII and the nptII gene as selection markers. Various factors affecting transformation efficiency were optimized; as 2 days preconditioning of explants on MS basal supplemented with TDZ 1 μM, Agrobacterium density at OD600 0.4 with inclusion of 100 μM acetosyringone (As) for 20 min co-inoculation duration with 48 h of co-cultivation period at 22 °C using node explants was found optimal to improved the number of GUS foci per responding explant from 36 ± 13.2 to 277.6 ± 22.0, as determined by histochemical GUS assay. The PCR and Southern blot results showed the genomic integration of transgene in Withania genome. On average basis 11 T0 transgenic plants were generated from 100 co-cultivated node explants, representing 10.6 % transformation frequency. Our results demonstrate high frequency, efficient and rapid transformation system for further genetic manipulation in Withania for producing engineered transgenic Withania shoots within very short duration of 3 months.

Agrobacterium-mediated in planta genetic transformation of sugarcane setts.

An efficient, reproducible, and genotype-independent in planta transformation has been developed for sugarcane using setts as explant. Traditional Agrobacterium-mediated genetic transformation and in vitro regeneration of sugarcane is a complex and time-consuming process. Development of an efficient Agrobacterium-mediated transformation protocol, which can produce a large number of transgenic plants in short duration is advantageous. Hence, in the present investigation, we developed a tissue culture-independent in planta genetic transformation system for sugarcane using setts collected from 6-month-old sugarcane plants. The sugarcane setts (nodal cuttings) were infected with three Agrobacterium tumefaciens strains harbouring pCAMBIA 1301-bar plasmid, and the transformants were selected against BASTA(®). Several parameters influencing the in planta transformation such as A. tumefaciens strains, acetosyringone, sonication and exposure to vacuum pressure, have been evaluated. The putatively transformed sugarcane plants were screened by GUS histochemical assay. Sugarcane setts were pricked and sonicated for 6min and vacuum infiltered for 2min at 500mmHg in A. tumefaciens C58C1 suspension containing 100µM acetosyringone, 0.1% Silwett L-77 showed the highest transformation efficiency of 29.6% (with var. Co 62175). The three-stage selection process completely eliminated the chimeric transgenic sugarcane plants. Among the five sugarcane varieties evaluated using the standardized protocol, var. Co 6907 showed the maximum transformation efficiency (32.6%). The in planta transformation protocol described here is applicable to transfer the economically important genes into different varieties of sugarcane in relatively short time.

Stable integration of mgfp5 transgenes following Agrobacterium-mediated transformation in Boesenbergia rotunda cell suspension culture

Boesenbergia rotunda, a herb in the ginger family, contains numerous beneficial compounds, such as flavonoids, flavones and cyclohexenyl chalcone derivatives, that have great potential for pharmaceutical applications. However, the low concentration of the bioactive compounds limits their commercial application. In this study, a simple and reliable Agrobacterium-mediated transformation protocol for B. rotunda cell suspension culture was successfully developed. The minimal inhibitory concentration and natural tolerance of the selective agent, hygromycin, against the cells were 20 mg l−l and 30 mg l−l in liquid media and solid media, respectively. The highest number of transformed regenerants (18 ± 0.00 per ml settled cell volume) was recorded when cells were infected with Agrobacterium tumefaciens harbouring pCAMBIA1304 for 10 min and co-cultivated for 2 days. Prolonged infection time (> 10 min) and co-cultivation period (> 2 days), however, did not increase the transformation efficiencies. The results clearly show that infection and co-cultivation periods strongly influenced the transformation efficiency in ginger. The transformed cells were recovered and showed green fluorescent signals under ultraviolet excitation. An intense blue colour was observed in the transformed cells after β-glucuronidase (GUS) histochemical staining, further confirming the functionality of the GUS enzymes in the regenerants. Polymerase chain reaction analysis of 3-, 6-, 9- and 12-month-old transformed cells confirmed that the protocol enabled stable integration of the mgfp5 gene. Moreover, the comparatively high number of transformed regenerants in this study made it possible to generate a large number of transgenic cells in a short period, which would be useful for high-throughput functional screening of enzymes involved in the biosynthetic pathways of bioactive compounds.

Agrobacterium-mediated transformation of tomato (Lycopersicon esculentum L. cv. Hezuo 908) with improved efficiency

We developed an efficient and rapid Agrobacterium-mediated tomato transformation protocol by using cotyledon and hypocotyl as explants. The transgenic nature of the regenerants was confirmed through β-glucuronidase activity staining, polymerase chain reaction (PCR), quantitative real-time PCR (qPCR) analysis and northern blot analysis. In the used protocol, the optimized experimental conditions of the tomato genetic transformation were Agrobacterium liquid concentration, equivalent to optical density (OD600) of 1.0, 20 min (cotyledon) or 30 min (hypocotyl) infection time and 2 d of co-culturing period. The optimized medium for shoot induction was Murashige & Skoog (MS) medium + 0.5 mg/L indole-3-acetic acid (IAA) + 0.5 mg/L 6-benzylaminopurine (BAP) for cotyledon and MS + 0.5 mg/L IAA + 2.0 mg/L BAP for hypocotyl. The root induction rate was the highest on the MS medium, supplemented with 0.1 mg/L IAA. The transformation frequency reached 40% per explant. The received results are a base for a larger scale development of transformation procedure.

Obtaining of transgenic alfalfa for improved phytoremediation the petroleum contaminated soils

Background. The possibility of using transgenic plants and their complexes with microorganisms to clean up soil from oil pollution is a topical area of researches. In our work the transgenic alfalfa plants with a gene rhlA, responsible for the biosynthesis of biosurfactant - ramnolipid, were obtained. Rhamnolipids help to reduce the surface tension of the hydrocarbon oil and its desorbtion from soil particles, thereby facilitating its recycling by microorganism. Material and methods. The protocol for agrobacterium-mediated transformation was optimized, transgenic alfalfa plants with a gene rhlA were obtained and their status was confirmed by molecular analysis. Results. Cultivation of the control and the transgenic alfalfa plants in soil polluted with 4 % oil showed the advantage of plants emitting ramnolipids: recycle oil was 71 % for 56 days and it was 20 % higher compared with the control plants. When used together, the transgenic plants and microorganism Candida maltosa increased the degree of degradation of the oil to 86 %. Conclusion. The results suggest promising application of transgenic plants and the complex “transgenic plants - microorganisms” to increase the efficiency of bioremediation.

Agrobacterium tumefaciens-mediated transformation of big bluestem (Andropogon gerardii Vitman)

Big bluestem (Andropogon gerardii Vitman) is native to the Great Plains of North America and is an important warm-season forage and ornamental grass. Recently it has been proposed as one of the more ideal biomass producers for cellulosic ethanol production due to its high biomass yield and low input needs. A robust genetic transformation protocol is needed for germplasm improvement or functional genomics studies in big bluestem. In the present study we report, for the first time the establishment of a reproducible Agrobacterium-mediated transformation protocol for big bluestem. Mature seeds of a big bluestem cultivar Bison were cultured for producing embryogenic calli, which were then used for infection by the Agrobacterium tumefaciens strain AGL1 harboring either the binary vector pTF101.1, which carries the glufosinate resistance (bar) gene or a modified binary vector pMDC32 which carries the hygromycin resistance gene (hpt). Glufosinate ammonium at 6 mg L−1 or hygromycin B at 250 mg L−1 was used effectively to select for resistant callus followed by lowered concentrations of both during regeneration and rooting. Based on PCR test alone or in combination with herbicide leaf painting, the overall transformation frequency was 2.8–3.6 % by using the pTF101.1 vector and 2.4–3.3 % by using the modified pMDC32 vector, both of which are comparable to transformation frequencies reported for other grasses. PCR test showed that all Basta®-resistant plants following the leaf painting contain the bar gene and subsequent Southern blot analysis confirmed that the all tested transgenic plants resulted from independent transgenic events.

A simple and highly efficient Agrobacterium-mediated transformation protocol for Setaria viridis

The production and use of sugarcane in Brazil is very important for bioenergy production and is recognized as one of the most efficient in the world. In our laboratory, Setaria viridis is being tested as a model plant for sugarcane. S. viridis has biological attributes (rapid life cycle, small genome, diploid, short stature and simple growth requirements) that make it suitable for use as a model system. We report a highly efficient protocol for Agrobacterium-mediated genetic transformation of S. viridis. The optimization of several steps in tissue culture allowed the rapid regeneration of plants and increased the rate of transformation up to 29%. This protocol could become a powerful tool for functional genomics in sugarcane.

Improvement of Agrobacterium-mediated transformation frequency in multiple modern elite commercial maize (Zea mays L.) inbreds by media modifications

The current study describes a robust, high-frequency Agrobacterium-mediated transformation protocol suitable for multiple recalcitrant modern elite commercial maize inbreds employing media modifications with glucose, cupric sulfate and a cytokinin, 6-benzylaminopurine (BAP). An optimal combination of these three key elements in the co-cultivation, resting, and selection media resulted in 4- to 14-fold improvements in transformation frequencies at the T0 plant level of 9.7, 31.9, 9.6 and 10.0 % for PH4CN, PH12BN, PHW0V and PH17R8, respectively. Transformation frequency in PH1CP1 was also improved at the T0 tissue level from 2.5 to 8.3 %. The addition of cupric sulfate and BAP in the co-cultivation medium improved transformation frequency in all inbreds except PH4CN. The use of cupric sulfate and BAP in combination with additional glucose in the selection medium was especially important, significantly improving the transformation frequency in 3 (PH4CN, PHW0V and PH1CP1) out of 5 inbreds by increasing the proliferation of high quality regenerable tissue. It was observed that the amount/ratio of these three components needed to be optimized for each inbred. The results in this study can be applied to optimize the tissue culture response and improve transformation frequency in other recalcitrant elite commercial maize inbreds.

<i>Agrobacterium</i>-Mediated Transformation of Mexican Lime (<i>Citrus aurantifolia</i> Swingle) Using Optimized Systems for Epicotyls and Cotyledons

Transgenic Mexican lime (Citrus aurantifolia Swingle) was produced through two explant sources, each using systems previously optimized for each source. One used epicotyls segments, which was the predominant explant for transgenic Citrus production following co-cultivation with Agrobacterium, and has a well-established protocol. The other procedure used embryo cotyledons from mature seeds, which was developed in our lab as an alternative for stable Citrus transformation. Cotyledon transformation and regeneration protocols were optimized by comparing variables in culture medium composition on shoot regeneration and four parameters in transient transformation. The optimized protocols were compared, and frequency of regeneration, frequency of transgenic plant-recovery and stable transformation efficiency indicated the superiority of the cotyledon protocol for Agrobacterium-mediated genetic transformation in Mexican lime. The tissue choice resulted in marked improvement in shoot regeneration (14.1% of explants producing shoots in epicotyls; 55.8% in cotyledons), stable transformation frequency (11.4% of epicotyls explants; 40.2% in cotyledons), and frequency of transgenic plant-recovery (37.9% in epicotyl explants; 92.6% in cotyledons). Thus, easy availability of explants using embryo cotyledons from mature seeds, technical simplicity, shortening of transformation time-course, and higher transformation and regeneration frequencies makes this new system an attractive alternative over the previously published Citrus transformation protocols. In the course of this project, we generated Mexican lime with a Recombinase Mediated Exchange Cassette landing pad, which was designed for stacking transgenes.

Application of sonication in combination with vacuum infiltration enhances the Agrobacterium-mediated genetic transformation in Indian soybean cultivars.

Soybean is a recalcitrant crop to Agrobacterium-mediated genetic transformation. Development of highly efficient, reproducible, and genotype-independent transformation protocol is highly desirable for soybean genetic improvement. Hence, an improved Agrobacterium-mediated genetic transformation protocol has been developed for cultivar PK 416 by evaluating various parameters including Agrobacterium tumefaciens strains (LBA4404, EHA101, and EHA105 harboring pCAMBIA1304 plasmid), sonication duration, vacuum infiltration pressure, and vacuum duration using cotyledonary node explants of soybean prepared from 7-day-old seedlings. The transformed plants were successfully developed through direct organogenesis system. Transgene expression was assessed by GUS histochemical and gfp visual assays, and integration was analyzed by PCR and Southern blot hybridization. Among the different combinations and durations evaluated, a maximum transformation efficiency of 18.6 % was achieved when the cotyledonary node explants of cv. PK 416 were sonicated for 20 s and vacuum infiltered for 2 min at 250 mmHg in A. tumefaciens EHA105 suspension. The amenability of the standardized protocol was tested on four more soybean cultivars JS 90-41, Hara Soy, Co 1, and Co 2 in which all the cultivars responded favorably with transformation efficiency ranging from 13.3 to 16.6 %. The transformation protocol developed in the present study would be useful to transform diverse soybean cultivars with desirable traits.

Apricot (Prunus armeniaca L.).

A protocol for Agrobacterium-mediated stable transformation of whole leaf explants of the apricot (Prunus armeniaca) cultivars 'Helena' and 'Canino' is described. Regenerated buds were selected using a two-step selection strategy with paromomycin sulfate and transferred to bud multiplication medium 1 week after they were detected for optimal survival. After buds were transferred to bud multiplication medium, antibiotic was changed to kanamycin and concentration increased gradually at each transfer to fresh medium in order to eliminate possible escapes and chimeras. Transformation efficiency, based on PCR analysis of individual putative transformed shoots from independent lines, was 5.6%. Green and healthy buds, surviving high kanamycin concentration, were transferred to shoot multiplication medium where they elongated in shoots and proliferated. Elongated transgenic shoots were rooted in a medium containing 70 μM kanamycin. Rooted plants were acclimatized following standard procedures. This constitutes the only transformation protocol described for apricot clonal tissues and one of the few of Prunus.

Populus trichocarpa.

Populus trichocarpa Nisqually-1 is a clone of black cottonwood that is widely used as a model woody plant. It was the first woody plant to have a full genome sequence and remains today as the model for growth, metabolism, development, and adaptation for all woody dicotyledonous plants. It is one of the best-annotated plant genomes available. It is also currently studied to improve bioenergy feedstocks and to learn about responses to environmental variation that may result from climate change. It is the best characterized woody plant for lignin biosynthesis. In spite of its role as a model woody plant, many important genetic applications have been limited because it was particularly difficult for DNA transformation. The ability to transform P. trichocarpa is a central component of a systems biology approach to the study of metabolic and developmental processes, where in combination with genome and transcriptome sequencing, all the expressed genes for specific pathways can be defined, cloned, and characterized for biological function. We previously reported on a method for Agrobacterium-mediated genetic transformation in P. trichocarpa(Song et al. Plant Cell Physiol 47: 1582-1589, 2006). Since then, we have optimized the protocol based on many experiments that varied in tissue manipulation, media, DNA constructs and Agrobacterium strains. A modified step-by-step protocol for Agrobacterium-mediated transformation of stem explants is described here. The health of the tissue explants and the time of cocultivation are among the critical steps in the protocol for successful transformation. This updated protocol should be helpful to many laboratories that are currently carrying out P. trichocarpa transformation. It should also encourage many labs that have not yet had success with P. trichocarpa to try again.

Agrobacterium-mediated genetic transformation of yam (Dioscorea rotundata): an important tool for functional study of genes and crop improvement.

Although genetic transformation of clonally propagated crops has been widely studied as a tool for crop improvement and as a vital part of the development of functional genomics resources, there has been no report of any existing Agrobacterium-mediated transformation of yam (Dioscorea spp.) with evidence of stable integration of T-DNA. Yam is an important crop in the tropics and subtropics providing food security and income to over 300 million people. However, yam production remains constrained by increasing levels of field and storage pests and diseases. A major constraint to the development of biotechnological approaches for yam improvement has been the lack of an efficient and robust transformation and regeneration system. In this study, we developed an Agrobacterium-mediated transformation of Dioscorea rotundata using axillary buds as explants. Two cultivars of D. rotundata were transformed using Agrobacterium tumefaciens harboring the binary vectors containing selectable marker and reporter genes. After selection with appropriate concentrations of antibiotic, shoots were developed on shoot induction and elongation medium. The elongated antibiotic-resistant shoots were subsequently rooted on medium supplemented with selection agent. Successful transformation was confirmed by polymerase chain reaction, Southern blot analysis, and reporter genes assay. Expression of gusA gene in transgenic plants was also verified by reverse transcription polymerase chain reaction analysis. Transformation efficiency varied from 9.4 to 18.2% depending on the cultivars, selectable marker genes, and the Agrobacterium strain used for transformation. It took 3–4 months from Agro-infection to regeneration of complete transgenic plant. Here we report an efficient, fast and reproducible protocol for Agrobacterium-mediated transformation of D. rotundata using axillary buds as explants, which provides a useful platform for future genetic engineering studies in this economically important crop.

Cowpea [Vigna unguiculata (L.) Walp

Agrobacterium tumefaciens-mediated transformation is an efficient method for incorporating genes and recovering stable transgenic plants in cowpea because this method offers several advantages such as the defined integration of transgenes, potentially low copy number, and preferential integration into transcriptional active regions of the chromosome. Cotyledonary node explants of cowpea present an attractive target for T-DNA delivery followed by regeneration of shoots via axillary proliferation without involvement of a de novo regeneration pathway. In this chapter, we describe a detailed protocol for Agrobacterium-mediated transformation of the cowpea variety Pusa Komal. The seedling cotyledonary node explants are used for cocultivation with an Agrobacterium strain EHA105 harboring standard binary vector, pCAMBIA2301 or pNOV2819, and putative transformed plants are selected using aminoglycoside antibiotic or mannose as sole carbon source, respectively. The entire process includes explant infection to transgenic seed generation in greenhouse.

Clovers (Trifolium spp.).

Clovers (Trifolium spp.) constitute one of the major forage legumes widely grown for its rich protein content and its major role in maintaining environmental sustainability by improving the soil fertility. Gene technology can assist plant improvement efforts in clovers (Trifolium spp.), aiming to improve forage quality, yield, and adaptation to biotic and abiotic stresses. An efficient and reproducible protocol for Agrobacterium-mediated transformation of a range of Trifolium species, using cotyledonary explants and different selectable marker genes, is described. The protocol is robust and allows for genotype and Agrobacterium strain-independent transformation of clovers. Stable meiotic transmission of transgenes has been demonstrated for selected transgenic clovers carrying single T-DNA inserts recovered from Agrobacterium-mediated transformation. This methodology can also be successfully used for "isogenic transformation" in clovers: the generation of otherwise identical plants with and without the transgene from the two cotyledons of a single seed. Stable transgenes may be used in further functional genomics, develop new traits and profile gene expression using reporters, and facilitate purification of tissue or single cells.

Medicago truncatula transformation using leaf explants.

Legumes have been for a long time recalcitrant to efficient Agrobacterium transformation. The choice and use of model legume plants (Medicago truncatula and Lotus japonicus) for molecular studies has triggered extensive studies devoted to the development of efficient Agrobacterium-mediated transformation protocols for these two plants. In M. truncatula, transformation protocols rely on the use of highly regenerable lines obtained by recurrent in vitro culture selection. These protocols are based on Agrobacterium-mediated transformation of M. truncatula followed by somatic embryogenesis-mediated plant regeneration. We describe here the protocol developed for M. truncatula R108-1 (c3).

Agrobacterium tumefaciens-mediated genetic transformation of Digitalis purpurea L.

Genetic transformation is a tool of special interest for developing new biotechnological strategies for the production of bio-active compounds such as cardenolides, which are exclusively obtained from plants. To date, Digitalis plants are the main economically viable source of cardenolides for the pharmaceutical industry. This study describes the development of efficient plant regeneration and Agrobacterium-mediated genetic transformation protocols for Digitalis purpurea L. First, a plant regeneration procedure starting from leaf segments of in vitro-cultivated plants was established and the minimal inhibitory concentration of G-418 (geneticin) for callus induction was determined. Both leaf segments and callus tissue were sensitive to G-418 70 mg l−1. Afterwards, two Agrobacterium strains were used to test their T-DNA transfer ability on D. purpurea leaf tissues, EHA105 and C58C1RifR (pMP90), both harboring the binary vector pTJK136. Strain C58C1RifR (pMP90) yielded a higher number of transformed plants than EHA105. Successful transformation was confirmed by histochemical β-glucuronidase (GUS) assays of the putative transgenic tissues and PCR analyses using β-glucuronidase (uidA)- and neomycin phosphotransferase II (nptII)-specific primers. Southern blot hybridization confirmed the stable integration of the nptII gene in the transgenic plants. In total, 518 independent transgenic lines were regenerated with an average of 6.91 transgenic lines per initial leaf segment infected with A. tumefaciens strain C58C1RifR (pMP90). To date, only a few studies have been published on the genetic transformation of Digitalis species. The protocols for plant regeneration and genetic transformation described in this paper will contribute to functional studies for a better understanding of cardenolide biosynthetic pathways and the metabolic engineering of cardenolides to develop high-yielding improved genotypes.

Establishment of an Agrobacterium-mediated genetic transformation procedure for the experimental model orchid Erycina pusilla

The establishment of a genetic transformation system for Erycina pusilla (E. pusilla) would be a major step for orchid research and help establish the species as a potential experimental model. Here we describe the development of an efficient selection and plant regeneration protocol for Agrobacterium-mediated transformation of E. pusilla protocorms. Plants were transformed with a binary plasmid containing the Arabidopsis thaliana gene Methionine sulfoxide reductase B7 (MSRB7) using the A. tumefaciens strain EHA105. Explants were selected on hygromycin-containing New Dogashima medium (Tokuhara and Mii in Plant Cell Rep 13(1):7–11, 1993) with 6-benzylaminopurine and α-naphthaleneacetic acid for 5 months to diminish the ratio of false positive explants, and it was determined that 3 month-old E. pusilla protocorms represented the optimal stage for transformation. Positive transformants were confirmed by Southern blot and PCR analyses, and by methyl viologen tolerance assays. Since E. pusilla has a shorter life cycle than most other orchids, self-pollinated T1 progeny was obtained within only 18 months. In addition, the results indicated that overexpression of MSRB genes can be used to avoid the effects of abiotic stress in economically important plants such as orchids.

Agrobacterium-mediated high-frequency transformation of an elite commercial maize (Zea mays L.) inbred line.

An improved Agrobacterium -mediated transformation protocol is described for a recalcitrant commercial maize elite inbred with optimized media modifications and AGL1. These improvements can be applied to other commercial inbreds. This study describes a significantly improved Agrobacterium-mediated transformation protocol in a recalcitrant commercial maize elite inbred, PHR03, using optimal co-cultivation, resting and selection media. The use of green regenerative tissue medium components, high copper and 6-benzylaminopurine, in resting and selection media dramatically increased the transformation frequency. The use of glucose in resting medium further increased transformation frequency by improving the tissue induction rate, tissue survival and tissue proliferation from immature embryos. Consequently, an optimal combination of glucose, copper and cytokinin in the co-cultivation, resting and selection media resulted in significant improvement from 2.6 % up to tenfold at the T0 plant level using Agrobacterium strain LBA4404 in transformation of PHR03. Furthermore, we evaluated four different Agrobacterium strains, LBA4404, AGL1, EHA105, and GV3101 for transformation frequency and event quality. AGL1 had the highest transformation frequency with up to 57.1 % at the T0 plant level. However, AGL1 resulted in lower quality events (defined as single copy for transgenes without Agrobacterium T-DNA backbone) when compared to LBA4404 (30.1 vs 25.6 %). We propose that these improvements can be applied to other recalcitrant commercial maize inbreds.