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

Agrobacterium tumefaciens-Mediated Plant Transformation: A Review

Agrobacterium tumefaciens-mediated plant transformation is the most dominant technique for the transformation of plants. It is used to transform monocotyledonous and dicotyledonous plants. A. tumefaciens apply for stable and transient transformation, random and targeted integration of foreign genes, as well as genome editing of plants. The Advantages of this method include cheapness, uncomplicated operation, high reproducibility, a low copy number of integrated transgenes, and the possibility of transferring larger DNA fragments. Engineered endonucleases such as CRISPR/Cas9 systems, TALENs, and ZFNs can be delivered with this method. Nowadays, Agrobacterium-mediated transformation is used for the Knock in, Knock down, and Knock out of genes. The transformation effectiveness of this method is not always desirable. Researchers applied various strategies to improve the effectiveness of this method. Here, a general overview of the characteristics and mechanism of gene transfer with Agrobacterium is presented. Advantages, updated data on the factors involved in optimizing this method, and other useful materials that lead to maximum exploitation as well as overcoming obstacles of this method are discussed. Moreover, the application of this method in the generation of genetically edited plants is stated. This review can help researchers to establish a rapid and highly effective Agrobacterium-mediated transformation protocol for any plant species.

Overexpression of AtMYB12 transcription factor simultaneously enhances quercetin-dependent metabolites in radish callus

The study aimed to enhance quercetin production in radish by optimizing Agrobacterium tumefaciens-mediated in-planta transformation. This protocol involved infecting radish seed embryo axis with A. tumefaciens EHA105 strain carrying the 35S::AtMYB12. Radish seeds were infected with the Agrobacterium suspension (0.8 OD600) for 30 min, followed by sonication for 60 s and vacuum infiltration for 90 s at 100 mm Hg. A 3-day co-cultivation in Murashige and Skoog medium with 150 μM acetosyringone yielded a transformation efficiency of 59.6% and a transgenic callus induction rate of 32.3%. Transgenic plant and callus lines were confirmed by GUS histochemical assay, PCR, and qRT-PCR. The transgenic lines showed an increased expression of flavonoid pathway genes (AtMYB12, CHS, F3H, and FLS) and antioxidant genes (GPX, APX, CAT, and SOD) compared to WT plants. Overexpression of AtMYB12 in transgenic callus increased enzyme activity of phenylalanine ammonia lyase, catalase, and ascorbate peroxidase. In half-strength MS medium with 116.8 mM sucrose, the highest growth index (7.63) was achieved after 20 days. In AtMYB12 overexpressed callus lines, phenolic content (357.31 mg g-1 dry weight), flavonoid content (463 mg g-1 dry weight), and quercetin content (48.24 mg g-1 dry weight) increased significantly by 9.41-fold. Micro-wounding, sonication, and vacuum infiltration improved in-planta transformation in radishes. These high-quercetin-content transgenic callus lines hold promise as valuable sources of flavonoids.

A simple and efficient genetic transformation system for soybean (Glycine max (L.) Merrill) targeting apical meristem of modified half-seed explant

The present study is an attempt to establish a fast, highly reproducible transformation with a simplified regeneration system in soybean targeting the apical meristem. The modified half-seed explants from soybean cultivar (cv.) JS335 were subjected to different time intervals of sonication (0, 1, 10, 20, and 30 min) and vacuum infiltration (0, 1, 10, 20, and 30 min) in the presence of Agrobacterium tumefaciens strain EHA105 harbouring pCAMBIA1301. The explants were then co-cultivated and subjected to a modified plant regeneration process that involves only two steps (1) primary shoot regeneration, and (2) in vitro rooting of primary shoot. The rooted plantlets were hardened and maintained in the greenhouse until maturity. Sonication treatment of 10 min, followed by plant regeneration using a modified method, recorded the highest transformation efficiency of 26.3% compared to other time duration tested. Furthermore, 10 min of vacuum infiltration alone resulted in even higher transformation efficiency after regeneration, reaching 28.0%. Interestingly, coupling sonication and vacuum infiltration for 10 min respectively produced the highest transformation efficiency after regeneration of 38.0%. The putative transformants showed gus expression in mature leaves, trifoliate leaves, flowers, and pods. The presence of hpt II was also confirmed in putative transformants, with an amplicon size of 500 bp. Quantitative real-time PCR confirmed the existence of hpt II as one to two copies in the soybean genome of T0 plants. Furthermore, the segregation pattern was observed in the T1 generation soybean plants which were confirmed using PCR for hpt II. The optimized protocol when tested with other Indian soybean cultivars showed an enhanced transformation efficiency ranging from 19.3% (cv. MAUS47) to 36.5% (cv. CO1). This optimized protocol could provide a reliable platform to overcome the challenges that are associated with the genetic engineering of soybean.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03715-8.

Development of two protocols for Agrobacterium-mediated transformation of white clover (Trifolium repens) via the callus system

White clover (Trifolium repens) is one of the most widely cultivated livestock forage plants whose persistence is severely affected by abiotic stresses. For the white clover, efficient regeneration systems is still a great necessity. In this study, inoculating 4-day-old cotyledons into MS media fortified with 0.4 mg·L-1 6-BA and 2 mg·L-1 2,4-D significantly increased the callus induction rate. Roots and cotyledons proved to be better explants, followed by hypocotyls, leaves, and petioles for callus induction. The development of differentiated structures occurred effectively on MS supplemented with 1 mg·L-1 6-BA and 0.1 mg·L-1 NAA. To increase transformation, we investigated various factors affecting the Agrobacterium tumefaciens transformation in white clover. The optimal conditions for root-derived callus and 4-day-old cotyledons were as follows: Agrobacterium suspension density with OD600 of 0.5, 20 mg·L-1 AS, and 4 days of co-cultivation duration. Subsequently, we developed two transformation protocols: transformation after callus induction from 4-day-old roots (Protocol A) and transformation before initiation of callus from cotyledons (Protocol B). The transformation frequencies varied from 1.92 to 3.17% in Protocol A and from 2.76 to 3.47% in Protocol B. We report the possibility to regenerate multiple transgenic white clover plants from a single genetic background. Our research may also contribute to successful genetic manipulation and genome editing in white clover.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03591-2.

Establishment of Agrobacterium-mediated transformation system to Juglans sigillata Dode 'Qianhe-7'

An efficient genetic transformation system is of great significance for verifying gene function and improving plant breeding efficiency by gene engineering. In this study, a stable Agrobacterium mediated genetic transformation system of Juglans sigillata Dode 'Qianhe-7' was investigated using callus and negative pressure-assisted and ultrasonic-assisted transformation selection. The results showed that the axillary shoot leaves were suitable to induce callus and the callus proliferation rate could reach 516.27% when induction calli were cultured on DKW medium containing 0.5 mg L^-1 indole-3-butyric acid, 1.2 mg L^-1 2,4-dichlorophenoxyacetic acid and 0.5 mg L^-1 kinetin for 18 d. In addition, negative pressure infection was the optimal infection method with the lowest browning rate (0.00%), high GFP conversion rate (16.67%), and better growth status. To further prove the feasibility of this genetic transformation system, the flavonol synthetase (JsFLS₅) gene was successfully transformed into the into leaf-derived callus of 'Qianhe-7'. JsFLS₅ expression and the content of total flavonoids in transformed callus were improved significantly compared with the untransformed callus, which proved that we had an efficient and reliable genetic transformation system using leaf-derived callus of Juglans sigillata.

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.

A simple and efficient Agrobacterium-mediated in planta transformation protocol for horse gram (Macrotyloma uniflorum Lam. Verdc.)

BACKGROUND

Recalcitrant nature is a major constraint for the in vitro regeneration and genetic transformation of leguminous species members. Therefore, an improved genetic transformation in horse gram has been developed via in planta method, in which Agrobacterium strain harboring binary vector pCAMBIA2301 was used for the transformation. Several factors affecting in planta transformations were put forth viz. Agrobacterium cell density, co-cultivation, and sonication combined with vacuum infiltration duration which were optimized.

RESULTS

Germinated seeds were sonicated and vacuum infiltrated with different densities of Agrobacterium culture and co-cultivated in half-strength MS medium with 100 μM of acetosyringone for 48 h. Seedlings were washed with cefotaxime and sowed in vermiculite soil for maturation. T1 plants were subjected to histochemical and molecular analysis to ensure transformation efficiency. Among various combinations analyzed, maximum transformation efficiency (20.8%) was attained with seeds of 5 min sonication combined with vacuum infiltration with 0.6 optical density of Agrobacterium culture.

CONCLUSIONS

It concludes that a different Agrobacterium cell density with sonication combined with vacuum infiltration has improved transgenic efficiency in horse gram plants. This simple and efficient method is feasible for the stable expression of foreign genes that could be beneficial for future food security.

Isopentenyl Transferase (IPT) Gene Transfer to Perennial Ryegrass Through Sonication-Assisted Agrobacterium-Mediated Transformation (SAAT), Vacuum and Heat Treatment

The successful introduction of isopentenyl transferase (IPT) gene into perennial ryegrass, cultivars Numan and Grassland using Agrobacterium tumefaciens via three explants (callus, seed and meristem tip) under three individual experiment was evaluated. In the first experiment, the calli were inoculated with LBA4404 Agrobacterium strain under vacuum, heat and in combination of both at 42 °C for 5 min followed by vacuum treatment (390 mm Hg pressure) for 15 min. Sonication-assisted Agrobacterium-mediated transformation (SAAT) was applied for seed and meristem tip transformation of perennial ryegrass for the first time. Results showed positive effects of heat treatment on transformation efficiency during Agro-infection in both cultivars. However, heat shock treatment was more effective in 'Grassland' than 'Numan' (14.2% vs 9.2%). In addition, high transformation efficiency of about 46.65% and 29.15% was observed using meristem tip explants of 'Grassland' and 'Numan' based on IPT and RD29A positive PCR results, respectively. Seed transformation efficiency in 'Grassland' and 'Numan' under SAAT method reached to 37.5% and 16.65%, respectively. Results of these experiments revealed that LBA4404 strain was more efficient than GV3101 in transformation of both perennial ryegrass cultivars. The DNA-blot analysis confirmed that a single T-DNA copy of the IPT gene was integrated into the genomic DNA of the positive transgenic T0 plants which obtained from callus and meristem tip explants of 'Grassland' after heat and SAAT treatment, respectively. Because monocots are not the host of Agrobacterium tumefaciens, this novel protocol can be used in further experiments on genetic transformation of perennial ryegrass cultivars.

Comparison of efficiency and time to regeneration of Agrobacterium-mediated transformation methods in Medicago truncatula

BACKGROUND

Tissue culture transformation of plants has an element of art to it, with protocols passed on between labs but often not directly compared. As Medicago truncatula has become popular as a model system for legumes, rapid transformation is critical, and many protocols exist, with varying results.

RESULTS

The M. truncatula ecotypes, R108 and A17, were utilized to compare the effect of a modification to a previously used protocol based on shoot explants on the percentage of transformed plants produced from calli. This percentage was then compared to that of two additional transformation protocols based on root explants in the R108 ecotype. Variations in embryonic tissue sources, media components, time for transformation, and vectors were analyzed.

CONCLUSIONS

While no A17 transgenic plants were obtained, transgenic plantlets from the R108 ecotype were produced in as little as 4 months with a comparison of the two widely studied ecotypes under a single set of conditions. While the protocols tested gave similar results in percentage of transformed plants produced, considerations of labor and time to transgenics that vary between the root explant protocols tested were discovered. These considerations may influence which protocol to choose for introducing a single transgene versus creating lines with multiple mutations utilizing a CRISPR/Cas9 construct.

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.

Genotype-independent and enhanced in planta Agrobacterium tumefaciens-mediated genetic transformation of peanut [Arachis hypogaea (L.)]

Agrobacterium infection and regeneration of the putatively transformed plant from the explant remains arduous for some crop species like peanut. Henceforth, a competent and reproducible in planta genetic transformation protocol is established for peanut cv. CO7 by standardizing various factors such as pre-culture duration, acetosyringone concentration, duration of co-cultivation, sonication and vacuum infiltration. In the present investigation, Agrobacterium tumefaciens strain EHA105 harboring the binary vector pCAMBIA1301-bar was used for transformation. The two-stage selection was carried out using 4 and 250 mg l^-1 BASTA^® to completely eliminate the chimeric and non-transformed plants. The transgene integration into plant genome was evaluated by GUS histochemical assay, polymerase chain reaction (PCR), and Southern blot hybridization. Among the various combinations and concentrations analyzed, highest transformation efficiency was obtained when the 2-day pre-cultured explants were subjected to sonication for 6 min and vacuum infiltrated for 3 min in Agrobacterium suspension, and co-cultivated on MS medium supplemented with 150 µM acetosyringone for 3 days. The fidelity of the standardized in planta transformation method was assessed in five peanut cultivars and all the cultivars responded positively with a transformation efficiency ranging from minimum 31.3% (with cv. CO6) to maximum 38.6% (with cv. TMV7). The in planta transformation method optimized in this study could be beneficial to develop superior peanut cultivars with desirable genetic traits.

Involvement of exogenous polyamines enhances regeneration and Agrobacterium-mediated genetic transformation in half-seeds of soybean

The present work demonstrates the participation of polyamines (PAs) to improve direct regeneration and Agrobacterium-mediated transformation in soybean half-seeds. The inclusion of PAs to culture medium along with optimal plant growth regulators (PGRs) enhanced shoot induction [98.3 %; 4.44 µM N6-benzyladenine (BA) and 103.27 µM spermidine] and elongation [90.0 %; 1.45 µM gibberellic acid (GA3) and 49.42 µM spermine]. The polyamine putrescine (62.08 µM) alone greatly enriched root induction (96.3 %). The influence of PAs on transformed plant production was assessed by comparing optimized protocol (comprising PAs and PGRs) with a regeneration system involving only PGRs. Plant transformation was performed in half-seeds of cultivar DS 97-12 using strain EHA105 harboring pCAMBIA1301. Transgene expression and integration was confirmed by GUS staining, PCR, and Southern hybridization. The transformed explants/materials successively cultured on co-cultivation (BA and spermidine), shoot induction (BA and spermidine), shoot elongation (GA3 and spermine), and rooting medium (putrescine) showed enhanced transformation efficiency (29.3 %) compared with its counterparts (14.6 %) with respective PGR alone [BA, GA3, or indole-3-butyric acid (IBA)]. Overall findings of the study suggest that involvement of PAs improved T-DNA transfer during co-cultivation, and delivered most suitable condition for efficient regeneration/survival, which led to enhanced transformation efficiency in soybean.