Agrobacterium-mediated gene transfer: recent advancements and layered immunity in plants

Tobacco Plant: A Novel and Promising Heterologous Bioreactor for the Production of Recombinant Bovine Chymosin

The natural source of chymosin, a key enzyme in the dairy industry, is insufficient for rapidly growing cheese industries. Large-scale production of recombinant proteins in heterologous hosts provides an efficient alternative solution. Here, the codon-optimized synthetic prochymosin gene, which has a CAI index of 0.926, was subcloned from a cloning vector (pUC57-bCYM) into the pBI121 vector, resulting in the construct named pBI121-bCYM. CAI ranges from 0 to 1 and higher CAI improves gene expression in heterologous hosts. The overexpression of the prochymosin gene was under the control of constitutive CaMV 35S promoter and NOS terminator and was transferred into the tobacco via A. tumefaciens strain LBA4404. Explant type, regeneration method, inoculation temperature, cell density (OD600) of Agrobacterium for inoculation, and acetosyringone concentration were leaf explants, direct somatic embryogenesis, 19 °C, 0.1, and 100 µM, respectively. The successful integration and expression of the prochymosin gene, along with the bioactivity of recombinant chymosin, were confirmed by PCR, RT-PCR, and milk coagulation assay, respectively. Overall, this study reports the first successful overexpression of the codon-optimized prochymosin form of the bovine chymosin enzyme in the tobacco via indirect transformation. Production of recombinant bovine chymosin in plants can be an easy-to-scale-up, safe, and inexpensive platform.

Mechanisms of Virulence Reprogramming in Bacterial Pathogens

Bacteria are single-celled organisms that carry a comparatively small set of genetic information, typically consisting of a few thousand genes that can be selectively activated or repressed in an energy-efficient manner and transcribed to encode various biological functions in accordance with environmental changes. Research over the last few decades has uncovered various ingenious molecular mechanisms that allow bacterial pathogens to sense and respond to different environmental cues or signals to activate or suppress the expression of specific genes in order to suppress host defenses and establish infections. In the setting of infection, pathogenic bacteria have evolved various intelligent mechanisms to reprogram their virulence to adapt to environmental changes and maintain a dominant advantage over host and microbial competitors in new niches. This review summarizes the bacterial virulence programming mechanisms that enable pathogens to switch from acute to chronic infection, from local to systemic infection, and from infection to colonization. It also discusses the implications of these findings for the development of new strategies to combat bacterial infections.

Melatonin strongly enhances the Agrobacterium- mediated transformation of carnation in nitrogen-depleted media

With the rising demand for new cultivars of carnation, efficient transformation protocols are needed to enable the bioengineering of new traits. Here, we established a novel and efficient Agrobacterium-mediated transformation system using callus as the target explant for four commercial carnation cultivars. Leaf-derived calli of all cultivars were inoculated with Agrobacterium tumefaciens strain LBA4404 containing the plasmid pCAMBIA 2301 harboring genes for β-glucuronidase (uidA) and neomycin phosphotransferase (nptII). Polymerase chain reaction (PCR) and histochemical assays confirmed the presence of uidA and β-glucuronidase (GUS), respectively in transgenic shoots. The effect on transformation efficiency of medium composition and the presence of antioxidants during inoculation and co-cultivation was investigated. The transformation efficiency was increased in Murashige and Skoog (MS) medium lacking KNO₃ and NH₄NO_3, and also in MS medium lacking macro and micro elements and Fe to 5% and 3.1% respectively, compared to 0.6% in full-strength medium. Transformation efficiency was increased dramatically to 24.4% across all carnation cultivars by the addition of 2 mg/l melatonin to nitrogen-depleted MS medium. Shoot regeneration was also doubled in this treatment. The establishment of this efficient and reliable transformation protocol can advance the development of novel carnation cultivars through molecular breeding approaches.

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.