Agrobacterium Tumefaciens-mediated Genetic Transformation Research Articles

Construction of ATMT system of Fusarium oxysporum and evaluation of its promoting effect on Glycyrrhiza uralensis

This study aims to evaluate the in vivo function of Fusarium oxysporum in Glycyrrhiza uralensis by salt tolerance,indoleacetic acid(IAA) production capacity, phosphate-dissolving capacity, and iron carrier production capacity. The stable genetic transformation system of the F. oxysporum was established by Agrobacterium tumefaciens-mediated genetic transformation( ATMT)technology, and the stability and staining efficiency of transformants were detected by the cloning of the marker gene green fluorescent protein(GFP) and the efficiency of β-glucuronidase staining(GUS). Efficient and stable transformants were selected for restaining G. uralensis and evaluating its influence on the growth of the G. uralensis seedlings. The results show that F. oxysporum has good salt tolerance and could still grow on potato glucose agar(PDA) medium containing 7% sodium chloride, but the growth rate slows down with the increase in sodium chloride content in PDA medium. F. oxysporum has the function of producing indoleacetic acid, and the concentration of IAA in its fermentation broth is about 3. 32 mg · m L~(-1). In this study, the genetic transformation system of F. oxysporum is successfully constructed, and the ATMT system is efficient and stable. One transformant with both high staining efficiency and genetic stability is selected, and the restaining rate of the transformant in G. uralensis is 76. 92%, which could significantly improve the main root length of one-month-old G. uralensis seedlings and promote the growth and development of G. uralensis seedlings. The results of this study can lay the foundation for the development of biological bacterial fertilizer and the growth regulation of high-quality G. uralensis.

Tissue culture and Agrobacterium-mediated genetic transformation of the oil crop sunflower

Sunflower is one of the four major oil crops in the world. ‘Zaoaidatou’ (ZADT), the main variety of oil sunflower in the northwest of China, has a short growth cycle, high yield, and high resistance to abiotic stress. However, the ability to tolerate adervesity is limited. Therefore, in this study, we used the retention line of backbone parent ZADT as material to establish its tissue culture and genetic transformation system for new variety cultivating to enhance resistance and yields by molecular breeding. The combination of 0.05 mg/L IAA and 2 mg/L KT in MS was more suitable for direct induction of adventitious buds with cotyledon nodes and the addition of 0.9 mg/L IBA to MS was for adventitious rooting. On this basis, an efficient Agrobacterium tumefaciens-mediated genetic transformation system for ZADT was developed by the screening of kanamycin and optimization of transformation conditions. The rate of positive seedlings reached 8.0%, as determined by polymerase chain reaction (PCR), under the condition of 45 mg/L kanamycin, bacterial density of OD600 0.8, infection time of 30 min, and co-cultivation of three days. These efficient regeneration and genetic transformation platforms are very useful for accelerating the molecular breeding process on sunflower.

Establishment of genome-editing system and assembly of a near-complete genome in broomcorn millet.

The ancient crop broomcorn millet (Panicum miliaceum L.) is an indispensable orphan crop in semi-arid regions due to its short life cycle and excellent abiotic stress tolerance. These advantages make it an important alternative crop to increase food security and achieve the goal of zero hunger, particularly in light of the uncertainty of global climate change. However, functional genomic and biotechnological research in broomcorn millet has been hampered due to a lack of genetic tools such as transformation and genome-editing techniques. Here, we successfully performed genome editing of broomcorn millet. We identified an elite variety, Hongmi, that produces embryogenic callus and has high shoot regeneration ability in in vitro culture. We established an Agrobacterium tumefaciens-mediated genetic transformation protocol and a clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9-mediated genome-editing system for Hongmi. Using these techniques, we produced herbicide-resistant transgenic plants and edited phytoene desaturase (PmPDS), which is involved in chlorophyll biosynthesis. To facilitate the rapid adoption of Hongmi as a model line for broomcorn millet research, we assembled a near-complete genome sequence of Hongmi and comprehensively annotated its genome. Together, our results open the door to improving broomcorn millet using biotechnology.

Characterization of regulatory genes Plhffp and Plpif1 involved in conidiation regulation in Purpureocillium lavendulum.

Purpureocillium lavendulum is an important biocontrol agent against plant-parasitic nematodes, primarily infecting them with conidia. However, research on the regulatory genes and pathways involved in its conidiation is still limited. In this study, we employed Agrobacterium tumefaciens-mediated genetic transformation to generate 4,870 random T-DNA insertion mutants of P. lavendulum. Among these mutants, 131 strains exhibited abnormal conidiation, and further in-depth investigations were conducted on two strains (designated as #5-197 and #5-119) that showed significantly reduced conidiation. Through whole-genome re-sequencing and genome walking, we identified the T-DNA insertion sites in these strains and determined the corresponding genes affected by the insertions, namely Plhffp and Plpif1. Both genes were knocked out through homologous recombination, and phenotypic analysis revealed a significant difference in conidiation between the knockout strains and the wild-type strain (ku80). Upon complementation of the ΔPlpif1 strain with the corresponding wildtype allele, conidiation was restored to a level comparable to ku80, providing further evidence of the involvement of this gene in conidiation regulation in P. lavendulum. The knockout of Plhffp or Plpif1 reduced the antioxidant capacity of P. lavendulum, and the absence of Plhffp also resulted in decreased resistance to SDS, suggesting that this gene may be involved in the integrity of the cell wall. RT-qPCR showed that knockout of Plhffp or Plpif1 altered expression levels of several known genes associated with conidiation. Additionally, the analysis of nematode infection assays with Caenorhabditis elegans indicated that the knockout of Plhffp and Plpif1 indirectly reduced the pathogenicity of P. lavendulum towards the nematodes. The results demonstrate that Agrobacterium tumefaciens - mediated T-DNA insertion mutagenesis, gene knockout, and complementation can be highly effective for identifying functionally important genes in P. lavendulum.

Transient Expression Assay and Microscopic Observation in Kumquat Fruit.

Citrus fruits encompass a diverse family, including oranges, mandarins, grapefruits, limes, kumquats, lemons, and others. In citrus, Agrobacterium tumefaciens-mediated genetic transformation of Hongkong kumquat (Fortunella hindsii Swingle) has been widely employed for gene function analysis. However, the perennial nature of woody plants results in the generation of transgenic fruits taking several years. Here, we show the procedures of Agrobacterium-mediated transient transformation and live-cell imaging in kumquat (F. crassifolia Swingle) fruit, using the actin filament marker GFP-Lifeact as an example. Fluorescence detection, western blot analysis, and live-cell imaging with confocal microscopy demonstrate the high transformation efficiency and an extended expression window of this system. Overall, Agrobacterium-mediated transient transformation of kumquat fruits provides a rapid and effective method for studying gene function in fruit, enabling the effective observation of diverse cellular processes in fruit biology.

Highly efficient Agrobacterium rhizogenes-mediated hairy root transformation in citrus seeds and its application in gene functional analysis.

Highly efficient genetic transformation technology is beneficial for plant gene functional research and molecular improvement breeding. However, the most commonly used Agrobacterium tumefaciens-mediated genetic transformation technology is time-consuming and recalcitrant for some woody plants such as citrus, hampering the high-throughput functional analysis of citrus genes. Thus, we dedicated to develop a rapid, simple, and highly efficient hairy root transformation system induced by Agrobacterium rhizogenes to analyze citrus gene function. In this report, a rapid, universal, and highly efficient hairy root transformation system in citrus seeds was described. Only 15 days were required for the entire workflow and the system was applicable for various citrus genotypes, with a maximum transformation frequency of 96.1%. After optimization, the transformation frequency of Citrus sinensis, which shows the lowest transformation frequency of 52.3% among four citrus genotypes initially, was increased to 71.4% successfully. To test the applicability of the hairy roots transformation system for gene functional analysis of citrus genes, we evaluated the subcellular localization, gene overexpression and gene editing in transformed hairy roots. Compared with the traditional transient transformation system performed in tobacco leaves, the transgenic citrus hairy roots displayed a more clear and specific subcellular fluorescence localization. Transcript levels of genes were significantly increased in overexpressing transgenic citrus hairy roots as compared with wild-type (WT). Additionally, hairy root transformation system in citrus seeds was successful in obtaining transformants with knocked out targets, indicating that the Agrobacterium rhizogenes-mediated transformation enables the CRISPR/Cas9-mediated gene editing. In summary, we established a highly efficient genetic transformation technology with non-tissue-culture in citrus that can be used for functional analysis such as protein subcellular localization, gene overexpression and gene editing. Since the material used for genetic transformation are roots protruding out of citrus seeds, the process of planting seedlings prior to transformation of conventional tissue culture or non-tissue-culture was eliminated, and the experimental time was greatly reduced. We anticipate that this genetic transformation technology will be a valuable tool for routine research of citrus genes in the future.

Agrobacterium tumefaciens-mediated transformation of embryogenic callus and CRISPR/Cas9-mediated genome editing in ‘Feizixiao’ litchi

Litchi (Litchi chinensis Sonn.) is a type of commercially prevalent subtropical and tropical fruit. Since litchi has a highly heterozygous genetic background and a long reproductive cycle, conventional breeding methods (such as hybridization) have limited ability to nurture new litchi cultivars. Here, an efficient and stable Agrobacterium tumefaciens-mediated genetic transformation of embryogenic callus was established in ‘Feizixiao’ litchi. Transgenic materials were verified using polymerase chain reaction (PCR) analysis, β-glucuronidase (GUS) assay, and green fluorescent protein (GFP) assay. To implement the technology of the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/associated protein 9 (CRISPR/Cas9) technology in ‘Feizixiao’ litchi and verify the validity of these transformation systems, the litchi polyphenol oxidase gene (LcPPO, JF926153) was knocked out. Various categories of mutations, covering base insertions, deletions, and substitutions, were found in transgenic materials via sequence analysis. The transformation system achieved high feasibility and efficiency, and the system of CRISPR/Cas9 was successfully employed to edit genes in ‘Feizixiao’ litchi. This work provides an essential foundation for investigating the functions of genes and accelerating litchi genetic improvement.

Salicylic acid promotes terpenoid synthesis in the fungi Sanghuangporus baumii

Sanghuangporus baumii is a medicinal fungi with anti-inflammatory, liver protection and antitumour effects. Terpenoids are one of the main medicinal ingredients of S. baumii. However, terpenoid production by wild-type S. baumii cannot meet the market demand, which affects its application in medical care. Therefore, exploring how to increase terpenoid content in S. baumii is a promising path in this research field. Salicylic acid (SA) is a secondary metabolite. In this study, a concentration of 350 μmol/L SA was added into fungal cultivations for 2 and 4 days, and then the transcriptome and metabolome of untreated mycelia and treated with SA were analysed. The expression of some genes in the terpenoids biosynthesis pathway increased in SA-induced cultivations, and the content of isopentenyl pyrophosphate (IPP) and geranylgeranyl-PP (GGPP) increased significantly as well as the contents of triterpenoids, diterpenoids, sesquiterpenoids and carotenoids. The gene FPS was considered to be a key gene regulating terpenoid biosynthesis. Therefore, FPS was overexpressed in S. baumii by Agrobacterium tumefaciens-mediated genetic transformation. The gene FPS and its downstream gene (LS) expression levels were confirmed to be increased in the FPS overexpressing transformant, and terpenoid content was 36.98% higher than that of the wild-type strain in the evaluated cultivation conditions.

CRISPR/Cas9 and Agrobacterium tumefaciens virulence proteins synergistically increase efficiency of precise genome editing via homology directed repair in plants.

CRISPR/Cas9 genome editing and Agrobacterium tumefaciens-mediated genetic transformation are widely-used plant biotechnology tools derived from bacterial immunity-related systems, each involving DNA modification. The Cas9 endonuclease introduces DNA double-strand breaks (DSBs), and the A. tumefaciens T-DNA is released by the VirD2 endonuclease assisted by VirDl and attached by VirE2, transferred to the plant nucleus and integrated into the genome. Here, we explored the potential for synergy between the two systems and found that Cas9 and three virulence (Vir) proteins achieve precise genome editing via the homology directed repair (HDR) pathway in tobacco and rice plants. Compared with Cas9T (Cas9, VirD1, VirE2) and CvD (Cas9-VirD2) systems, the HDR frequencies of a foreign GFPm gene in the CvDT system (Cas9-VirD2, VirD1, VirE2) increased 52-fold and 22-fold, respectively. Further optimization of the CvDT process with a donor linker (CvDTL) achieved a remarkable increase in the efficiency of HDR-mediated genome editing. Additionally, the HDR efficiency of the three rice endogenous genes ACETOLACTATE SYNTHASE (ALS), PHYTOENE DESATURASE (PDS), and NITROGEN TRANSPORTER 1.1 B (NRT1.1B) increased 24-, 32- and 16-fold, respectively, in the CvDTL system, compared with corresponding Cas9TL (Cas9T process with a donor linker). Our results suggest that collaboration between CRISPR/Cas9 and Agrobacterium-mediated genetic transformation can make great progress towards highly efficient and precise genome editing via the HDR pathway.

Establishment of an efficient regeneration and Agrobacterium transformation system in mature embryos of calla lily (Zantedeschia spp.).

Calla lily (Zantedeschia spp.) have great aesthetic value due to their spathe-like appearance and richness of coloration. However, embryonic callus regeneration is absent from its current regeneration mechanism. As a result, constructing an adequate and stable genetic transformation system is hampered, severely hindering breeding efforts. In this research, the callus induction effectiveness of calla lily seed embryos of various maturities was evaluated. The findings indicated that mature seed embryos were more suitable for in vitro regeneration. Using orthogonal design experiments, the primary elements influencing in vitro regeneration, such as plant growth regulators, genotypes, and nanoscale materials, which was emergent uses for in vitro regeneration, were investigated. The findings indicated that MS supplemented with 6-BA 2mg/L and NAA 0.1mg/L was the optimal medium for callus induction (CIM); the germination medium (GM) was MS supplemented with 6-BA 2mg/L NAA 0.2mg/L and 1mg/L CNTs, and the rooting medium (RM) was MS supplemented with 6-BA 2mg/L NAA 0.7mg/L and 2mg/L CNTs. This allowed us to verify, in principle, that the Agrobacterium tumefaciens-mediated genetic transformation system operates under optimal circumstances using the GUS reporter gene. Here, we developed a seed embryo-based genetic transformation regeneration system, which set the stage for future attempts to create new calla lily varieties.

Multiplex CRISPR/Cas9-mediated knockout of the phytoene desaturase gene in Coffea canephora

Coffea canephora (2n = 2x = 22 chromosomes) is a species with extensive genetic diversity and desirable agronomic traits for coffee breeding programs. However, obtaining a new coffee cultivar through conventional breeding techniques may require more than 30 years of crossing cycles and selection, which hampers the effort of keeping up with market demands and rapidly proposing more resilient to climate change varieties. Although, the application of modern biotechnology tools such as precision genetic engineering technologies may enable a faster cultivar development process. Therefore, we aimed to validate the CRISPR/Cas9 system to generate mutations on a selected genotype of C. canephora, the clone 14. Embryogenic calli and a multiplex binary vector containing two sgRNAs targeting different exons of the CcPDS gene were used. The sgRNAs were under the C. canephora U6 promoter regulation. The target gene encodes phytoene desaturase, an enzyme essential for photosynthesis involved in β-carotene biosynthesis. Somatic seedlings and embryos with albino, variegated and green phenotypes regenerated after Agrobacterium tumefaciens-mediated genetic transformation were analyzed by verifying the insertion of the Cas9 gene and later by sequencing the sgRNAs target regions in the genome of Robusta modified seedlings. Among them, 77% had the expected mutations, and of which, 50% of them had at least one target with a homozygous mutation. The genotype, temperature of co-cultivation with the bacteria, and light intensity used for subsequent embryo regeneration appeared to strongly influence the successful regeneration of plants with a mutated CcPDS gene in the Coffea genus.

In vitro</em></strong><strong> direct regeneration and <em>Agrobacterium tumefaciens</em> mediated <em>in planta</em> transformation of <em>Ocimum sanctum L.

An in vitro regeneration system for propagation has been successfully developed for a valuable medicinal and aromatic plant ‘ Ocimum sanctum L’. In the present study, petiole explants, from in-vitro grown cultures of O. sanctum, was used for direct regeneration. The developed protocol employed 98% of regeneration frequency in addition to 9.6 shoots per explant when cultured on Murashige and Skoog (MS) medium fortified with 3 mg/L benzylamino purine (BAP) and 1 mg/L Naphthalene acetic acid (NAA). Furthermore, Agrobacterium tumefaciens Mediated genetic Transformation (ATMT) protocol (transient and stable) was also developed using LBA4404 strain harboring pBI121 with uid-A and neomycin phosphotransferase genes. The regenerated transformants were shifted on MS with kanamycin (50 mg/L) and afterwards placed on the half-strength MS medium. The validation was done through polymerase chain reaction (PCR) with neomycin phosphotransferase-II ( npt-II) & β-glucoronidase ( uid-A) gene primers. The maximum stable transformation frequency of 70% ± 0.35 was achieved. Hence, it is apparent that the established protocols i.e. in vitro direct regeneration and ATMT are appropriate for integrating novel enzymes/genes through high throughput techniques such as gene tagging, and targeted gene replacement to modulate the primary as well as secondary metabolic flux towards desired agronomic product or trait in planta.

Optimization of Agrobacterium tumefaciens-Mediated Genetic Transformation of Maize

Immature embryos of inbred maize (Zea mays) lines (H8183, H8184, and H8185) were used for Agrobacterium infection. We used the β-glucuronidase gene (GUS) as the target gene and the glufosinate resistance gene (bar) as the selection marker. We conducted research on several aspects, such as different genotypes, coculture conditions, screening agent concentrations, and concentrations of indole-3-butytric acid (IBA), 6-benzylaminopurine (6-BA), and ascorbic acid (Vc) in the differentiation medium. We optimized the genetic transformation system, and the obtained results indicated that among the three lines studied, the induction rate of H8185 was the highest at 93.2%, followed by H8184, with H8183 having the lowest induction rate (80.1%). The best coculture method was that using the N6 coculture medium layered with a sterile filter paper. Using orthogonal analysis, we found that the optimal combination of the three factors in the differentiation medium was A3 (1 mg mL−1 IBA), B3C1 (1.6 mg mL−1 6-BA), and D3 (1.5 mg mL−1 Vc). Through GUS staining analysis, Bar test-strip analysis, and polymerase chain reaction, five transgenic plants were finally obtained. This study established the optimal conditions for genetic transformation in maize.

Agrobacterium tumefaciens–mediated genetic transformation and overexpression of the flavonoid 3′5′-hydroxylase gene increases the flavonoid content of the transgenic Aconitum carmichaelii Debx. plant

Agrobacterium tumefaciens–mediated genetic transformation and overexpression of the flavonoid 3′5′-hydroxylase gene increases the flavonoid content of the transgenic Aconitum carmichaelii Debx. plant

Optimization of Micropropagation and Genetic Transformation Protocols for Paulownia elongata : A Short Rotation Fast Growing Bioenergy Tree.

Various steps of micropropagation include selection of suitable explant, establishment of adventitious shoot induction cultures, proliferation, rooting, and acclimatization of the resulting plantlets. A systematic protocol is provided for the micropropagation and Agrobacterium tumefaciens-mediated genetic transformation of a fast growing, multipurpose tree, Paulownia elongata. Our studies show that optimum shoot induction is on half leaf with petiole explant on MS medium supplemented with 25μM thidiazuron and 10μM indole-3 acetic acid. Micropropagation protocols provided here are applicable to explants collected from the primed in vitro raised seedlings on MS medium containing 2.5μM 6-benzylaminopurine (BAP) or actively growing shoots collected from greenhouse or field growing plants. We also discuss a possible role of "Python" script guided protocol optimization for higher and consistent multiplication of shoots that can be very helpful for scaled up production in commercial settings. To facilitate future plant improvement and gene editing possibilities, an A. tumefaciens based genetic transformation protocol and molecular identification of transgenic plants using Polymerase Chain Reaction (PCR) and Reverse Transcriptase-PCR (RT-PCR) techniques have also been optimized.

Agrobacterium tumefaciens-Mediated Genetic Transformation of the Ect-endomycorrhizal Fungus Terfezia boudieri.

Mycorrhizal desert truffles such as Terfezia boudieri, Tirmania nivea, and Terfezia claveryi, form mycorrhizal associations with plants of the Cistaceae family. These valued truffles are still collected from the wild and not cultivated under intensive farming due to the lack of basic knowledge about their biology at all levels. Recently, several genomes of desert truffles have been decoded, enabling researchers to attempt genetic manipulations to enable cultivation. To execute such manipulations, the development of molecular tools for genes transformation into truffles is needed. We developed an Agrobacterium tumefaciens-mediated genetic transformation system in T. boudieri. This system was optimized for the developmental stage of the mycelia explants, bacterial optical density, infection and co-cultivation durations, and concentrations of the selection antibiotics. The pFPL-Rh plasmid harboring hph gene conferring hygromycin resistance as a selection marker and the red fluorescent protein gene were used as visual reporters. The optimal conditions were incubation with 200 μM of acetosyringone, attaining a bacterial optical density of 0.3 OD600; transfer time of 45 min; and co-cultivation for 3 days. This is the first report on a transformation system for T. boudieri, and the proposed protocol can be adapted for the transformation of other important desert truffles as well as ectomycorrhizal species.

Soybean Embryonic Axis Transformation: Combining Biolistic and Agrobacterium-Mediated Protocols to Overcome Typical Complications of In Vitro Plant Regeneration.

The first successful attempt to generate genetically modified plants expressing a transgene was preformed via T-DNA-based gene transfer employing Agrobacterium tumefaciens-mediated genetic transformation. Limitations over infectivity and in vitro tissue culture led to the development of other DNA delivery systems, such as the biolistic method. Herein, we developed a new one-step protocol for transgenic soybean recovery by combining the two different transformation methods. This protocol comprises the following steps: agrobacterial preparation, seed sterilization, soybean embryo excision, shoot-cell injury by tungsten-microparticle bombardment, A. tumefaciens-mediated transformation, embryo co-cultivation in vitro, and selection of transgenic plants. This protocol can be completed in approximately 30–40 weeks. The average efficiency of producing transgenic soybean germlines using this protocol was 9.84%, similar to other previously described protocols. However, we introduced a more cost-effective, more straightforward and shorter methodology for transgenic plant recovery, which allows co-cultivation and plant regeneration in a single step, decreasing the chances of contamination and making the manipulation easier. Finally, as a hallmark, our protocol does not generate plant chimeras, in contrast to traditional plant regeneration protocols applied in other Agrobacterium-mediated transformation methods. Therefore, this new approach of plant transformation is applicable for studies of gene function and the production of transgenic cultivars carrying different traits for precision-breeding programs.

Identification of the genes involved in growth characters of medicinal fungus Ophiocordyceps sinensis based on Agrobacterium tumefaciens-mediated transformation.

Ophiocordyceps sinensis, one of the well-known and precious fungal species in the world, parasitizes soil-dwelling larvae of ghost moths on the Tibetan Plateau. The genetic intractability of this extremely psychrophilic and slow-growing O. sinensis fungus is a major limitation on the molecular study. In this study, an Agrobacterium tumefaciens-mediated genetic transformation (ATMT) system for this fungus was established. ATMT procedure was optimized based on the fungal recipient, Agrobacterium strains, and different co-cultivation conditions. Blastospores were ideal recipients for this system. Acetosyringone (AS) was not essential for the transformation of O. sinensis. Sixty to 100 hygromycin B-resistant transformants per 1 × 106 blastospores were obtained. Southern blot analysis indicated the presence of a random single-copy integration of T-DNA into the O. sinensis genome. The insertional transformants with altered growth characters such as colony, blastospore, and fruiting body production were selected to identify the T-DNA flanking sequences by modified hiTAIL-PCR and FPNI-PCR techniques. Eight genes, including genes for an MFS transporter, a 2-oxoglutarate dehydrogenase, a DNA-directed RNA polymerase III complex subunit Rpc37, a cytochrome oxidase subunit I, a mitochondrial import inner membrane translocase subunit tim54, a cytidine deaminase, a phosphoribosylaminoimidazole carboxylase, and a histone H3-like centromeric protein cse-4 were identified. This ATMT system provides a useful tool for gene discovery and characterization of O. sinensis and contributes to the better understanding of the mysterious life cycle of O. sinensis and the molecular interaction between this fungus and its host insects.

A Procedure for Agrobacterium tumefaciens Mediated Genetic Transformation of Sweet Potato

Many sweet potato plants have been successfully transformed but the transgenic plants regenerated, however, have been limited to a few genotypes. Reported in this paper is a procedure in which several explants of three sweet potato genotypes from Papua New Guinea (PNG) were used to transform and regenerate transgenic plants. To achieve stable transformation, an efficient shoot regeneration system for different explants was developed. The shoot regeneration protocol developed enabled for a reproducible stable transformation mediated by Agrobacterium tumefaciens strain 1065. The plasmid pVDH65 contains the npt II gene for kanamycin (km) resistance, hpt gene for hygromycin resistance and Gus-intron reporter gene (GUS) for β-glucuronidase. Explants inoculated with the bacterial strain were co-cultured for 3, 5 and 7 days (d) in the dark on Murashige and Skoog (MS) medium without growth hormones. After co-cultivation, the explants were washed in liquid MS medium containing 500 mg L-1 cefotaxime, rinsed in sterile, deionised water for 10 mins and cultured on km selection medium containing 100 mg L-1 km followed by transfer of explants to 125 mg L-1 km after 14 d of culture. The km-resistant shoots selected on the former km concentration were transferred to the latter for double selection. Km-resistant shoots obtained at 125 mg L-1 were rooted on MS based medium also containing 0.008 mg L-1 IAA, 0.03 mg L-1 kinetin and 0.001 mg L-1 folic acid. This double selection method led to effective elimination of escapes (up to 75%) and successful recovery of transgenic plants from stem explants at more than 25%, leaf discs 10% and petioles 13.3% of each sweet potato cultivar. Polymerase chain reaction (PCR) analysis of the three km-resistant and GUS-positive plants revealed the presence of the expected fragment for npt II. This is the first report of successfully transforming sweet potato plants with bacterial strain 1065 and selection of transgenic plants at km concentrations higher than 100 mg L-1.

Development of a rapid and highly efficient Agrobacterium-mediated transformation system for pigeon pea [Cajanus cajan (L.) Millsp

ABSTRACTAn efficient genetic transformation system is a prerequisite for studying gene functions, molecular breeding program, and introducing new traits. Agrobacterium tumefaciens-mediated genetic transformation is a widely preferred and accepted method for many plants, including pigeon pea. However, the efficiency of transformation of pigeon pea using the existing protocols is low and time-consuming. In the present study, we developed a rapid and highly efficient transformation system of pigeon pea, using embryonic axis-attached cotyledons as explants. We systematically investigated the influence of varying optical densities of Agrobacterium suspension, duration of incubation, and co-cultivation on the transformation efficiency. In our system, a transformation efficiency of approximately 83% was achieved using Agrobacterium cells at an optical density (OD600) of 0.25, infection time of 15 min, and co-culturing with explants for 72 h in the light with 100µM acetosyringone. The entire procedure, starting from seed to establishment of transformed plants in soil, was achieved in 35–40 days. This is a rapid and highly efficient protocol for Agrobacterium-mediated transformation of pigeon pea, which could potentially be a useful reference, not only for the genetic improvement of pigeon pea but also for other recalcitrant leguminous plants.