Multiplex PCR assay for identification of commonly used disarmed Agrobacterium tumefaciens strains

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.

The Three-Cornered Alfalfa Hopper, Spissistilus festinus, Is a Vector of Grapevine Red Blotch Virus in Vineyards

Spissistilus festinus (Hemiptera: Membracidae) transmit grapevine red blotch virus (GRBV, Grablovirus, Geminiviridae) in greenhouse settings; however, their role as a vector of GRBV in vineyards is unknown. Following controlled exposures of aviruliferous S. festinus for two weeks on infected, asymptomatic vines in a California vineyard in June and a 48 h gut clearing on alfalfa, a nonhost of GRBV, approximately half of the released insects tested positive for GRBV (45%, 46 of 102), including in the salivary glands of dissected individuals (11%, 3 of 27), indicating acquisition. Following controlled exposures of viruliferous S. festinus for two to six weeks on GRBV-negative vines in vineyards in California and New York in June, transmission of GRBV was detected when two S. festinus were restricted to a single leaf (3%, 2 of 62 in California; 10%, 5 of 50 in New York) but not with cohorts of 10-20 specimens on entire or half shoots. This work was consistent with greenhouse assays in which transmission was most successful with S. festinus exposed to a single leaf (42%, 5 of 12), but rarely occurred on half shoots (8%, 1 of 13), and never on entire shoots (0%, 0 of 18), documenting that the transmission of GRBV is facilitated through the feeding of fewer S. festinus on a restricted area of grapevine tissue. This work demonstrates S. festinus is a GRBV vector of epidemiological importance in vineyards.

Genetic Transformation of Recalcitrant Upland Switchgrass Using Morphogenic Genes

Switchgrass (Panicum virgatum) is an excellent feedstock for biofuel production. While genetic transformation is routinely done in lowland switchgrass, upland cultivars remain recalcitrant to genetic transformation. Here we report the establishment of an efficient and reproducible transformation protocol for two upland cultivars, 'Summer' and 'Blackwell', by ectopic overexpression of morphogenic genes, Baby boom (Bbm) and Wuschel2 (Wus2). Two auxotrophic Agrobacterium strains, LBA4404Thy- and EHA105Thy-, each harboring the same construct containing ZmBbm, ZmWus2, and a green fluorescence protein (GFP) gene, ZsGreen1, were used to infect immature leaf segments derived from in vitro grown seedlings. The Agrobacterium strains also contain a transformation helper plasmid that carry additional copies of Agrobacterium virulence genes. GFP-expressing calli were identified and selected for regeneration. The highest transformation efficiency of 6% was obtained for the tetraploid cultivar Summer when LBA4404Thy- was used for infection, which is twice of that for the octoploid cultivar Blackwell. LBA4404Thy- consistently outperformed EHA105Thy- on transformation frequency across the two cultivars. Fifteen randomly selected putative transgenic plants of Summer and Blackwell, representing independent callus events, were confirmed as transgenic by the presence of the transgene, ZmAls, and the absence of AtuFtsZ, a chromosomal gene specific to the Agrobacterium strain LBA4404 using polymerase chain reaction. Transgene integration and expression was further confirmed by the detection of GFP in roots, and the resistance to herbicide injury to leaves of selected putative transgenic plants. The ZmBbm and ZmWus2 genes were successfully removed from 40 to 33.3% of the transgenic plants of Summer and Blackwell, respectively, via the Cre-Lox recombination system upon heat treatment of GFP-expressing embryogenic calli. Our successful transformation of recalcitrant upland switchgrass provides a method for gene function analysis and germplasm enhancement via biotechnology.

A New Plant Expression System for Producing Pharmaceutical Proteins

In the past decade, interest in the production of recombinant pharmaceutical proteins in plants has tremendously progressed because plants do not harbor mammalian viruses, are economically competitive, easily scalable, and capable of carrying out complex post-translational modifications required for recombinant pharmaceutical proteins. Mucuna bracteata is an essential perennial cover crop species widely planted as an underground cover in oil palm and rubber plantations. As a legume, they have high biomass, thrive in its habitat, and can fix nitrogen. Thus, M. bracteata is a cost-efficient crop that shows ideal characteristics as a platform for mass production of recombinant protein. In this study, we established a new platform for the transient production of a recombinant protein in M. bracteata via vacuum-assisted agro-infiltration. Five-week-old M. bracteata plants were vacuum infiltrated with Agrobacterium tumefaciens harboring a plasmid that encodes for an anti-toxoplasma immunoglobulin (IgG) under different parameters, including trifoliate leaf positional effects, days to harvest post-infiltration, and the Agrobacterium strain used. Our results showed that vacuum infiltration of M. bracteata plant with A. tumefaciens strain GV3101 produced the highest concentration of heterologous protein in its bottom trifoliate leaf at 2 days post-infiltration. The purified anti-toxoplasma IgG was then analyzed using Western blot and ELISA. It was demonstrated that, while structural heterogeneity existed in the purified anti-toxoplasma IgG from M. bracteata, its transient expression level was two-fold higher than the model platform, Nicotiana benthamiana. This study has laid the foundation towards establishing M. bracteata as a potential platform for the production of recombinant pharmaceutical protein.

Agrobacterium-mediated vacuum infiltration and floral dip transformation of rapid-cycling Brassica rapa

BACKGROUND

Rapid-cycling Brassica rapa (RCBr), also known as Wisconsin Fast Plants, are small robust plants with a short lifecycle that are widely used in biology teaching. RCBr have been used for decades but there are no published reports of RCBr genetic transformation. Agrobacterium-mediated vacuum infiltration has been used to transform pakchoi (Brassica rapa ssp. chinensis) and may be suitable for RCBr transformation. The floral dip transformation method, an improved version of vacuum infiltration, could make the procedure easier.

RESULTS

Based on previous findings from Arabidopsis and pakchoi, plants of three different ages were inoculated with Agrobacterium. Kanamycin selection was suboptimal with RCBr; a GFP screen was used to identify candidate transformants. RCBr floral bud dissection showed that only buds with a diameter less than 1 mm carried unsealed carpels, a key point of successful floral dip transformation. Plants across a wide range of inflorescence maturities but containing these immature buds were successfully transformed, at an overall rate of 0.1% (one per 1000 T₁ seeds). Transformation was successful using either vacuum infiltration or the floral dip method, as confirmed by PCR and Southern blot.

CONCLUSION

A genetic transformation system for RCBr was established in this study. This will promote development of new biology teaching tools as well as basic biology research on Brassica rapa.

Comparison and evaluation of two diagnostic methods for detection of npt II and GUS genes in Nicotiana tabacum

To diminish the time required for some diagnostic assays including polymerase chain reaction (PCR), loop-mediated isothermal amplification (LAMP) and also a visual detection protocol on the basis of npt II and GUS genes in transgenic tobacco plants were used. Agrobacterium tumefaciens-mediated transformation of Nicotiana tabacum leaf discs was performed with plant transformation vector of pBI 121. From kanamycin-resistant plants selected by their antibiotic resistance, four plants were selected for DNA isolation. Presence of the transgene was confirmed in the transformants by PCR and LAMP. In this regard, all LAMP and PCR primers were designed on the basis of the gene sequences of npt II and GUS. The LAMP assay was applied for direct detection of gene marker from plant samples without DNA extraction steps (direct LAMP assay). Also, a novel colorimetric LAMP assay for rapid and easy detection of npt II and GUS genes was developed here, its potential compared with PCR assay. The LAMP method, on the whole, had the following advantages over the PCR method: easy detection, high sensitivity, high efficiency, simple manipulation, safety, low cost, and user friendly.