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Production of VNPs, VLPs, and Chimeras
Published in Nicole F Steinmetz, Marianne Manchester, Viral Nanoparticles, 2019
Nicole F Steinmetz, Marianne Manchester
This method exploits the plant bacterium Agrobacterium tumefaciens, which causes crown-gall disease in plants. Agrobacterium tumefaciens can invade wounded plant cells and transform the cells resulting in tumor growth. The bacteria contain a tumor-inducing plasmid, the Ti-plasmid. During infection, a segment of the Ti-plasmid is transferred into the plant cell; this segment is referred to as transfer or T-DNA. The T-DNA is incorporated into the plant genome by recombination, resulting in transient expression of the T-DNA genes. The T-DNA is flanked by 25-bp direct repeats, termed the left and right borders, that mediate the recombination event. Transfer of the T-DNA is induced by activation of the so-called virulence (vir) genes on the Ti-plasmid. Phenolic compounds, mainly acetosyringone, that are produced and released from wounded plant cells initiate expression of the vir genes. The T-DNA encodes for growth hormones, which stimulate tumor formation, as well as for unnatural amino acids such as nopaline, mannopine, and octopine, which serve as an energy source for the bacterium. The reader is referred to the following textbooks for more information on the biology of Agrobacterium and its use as an expression system: Molecular Biology of the Cell (Alberts et al., 2008) and Agrobacterium: From Biology to Biotechnology (Tzvi & Vitaly, 2008).
Agricultural biotechnology
Published in Firdos Alam Khan, Biotechnology Fundamentals, 2018
The most commonly used vectors for gene transfer in higher plants are based on tumor-inducing mechanism of the soil bacterium A. tumefaciens, which is the causal organism for crown gall disease. On the other hand, a closely related species A. rhizogenes causes hairy root disease. An understanding of the molecular basis of these diseases led to the utilization of these bacteria for developing gene transfer systems. It has been shown that the disease is caused by the transfer of a DNA segment from the bacterium to the plant nuclear genome. The DNA segment, which is transferred, is called T-DNA and is part of a large Ti (tumor-inducing) plasmid found in virulent strains of A. tumefaciens. Similarly, Ri (root-inducing) megaplasmids are found in the virulent strains of A. rhizogenes. The Ti and Ri plasmids, inducing crown gall disease and hairy root disease, respectively, have been studied in great detail during the last decade. However, we will discuss only those aspects of these plasmids that are relevant to the design of vectors for gene transfer in higher plants. Most Ti plasmids have four regions in common: Region A, comprising T-DNA, is responsible for tumor induction so that mutations in this region lead to the production of tumors with altered morphology. Sequences homologous to this region are always transferred to plant nuclear genome so that the region is described as T-DNA (transferred DNA).Region B is responsible for replication.Region C is responsible for conjugation.Region D is responsible for virulence so that mutations in this region abolish virulence and plays a crucial role in the transfer of T-DNA into the plant nuclear genome. The components of this Ti plasmid have been used for developing efficient plant transformation vectors.
Establishment and elicitation of transgenic root culture of Plantago lanceolata and evaluation of its anti-bacterial and cytotoxicity activity
Published in Preparative Biochemistry & Biotechnology, 2021
Samaneh Rahamouz-Haghighi, Khadijeh Bagheri, Ali Sharafi, Hossein Danafar
One of the plant diseases is hairy root (HR) which is caused by Agrobacterium rhizogenes.[1] HR occurs when root loci (rol) genes harbored by the root inducing plasmid (Ri) of A. rhizogenes integrate into the nuclear genome of the infected plant cells. It is believed that numerous factors impact the frequency of A. rhizogenes mediated transformation in host plants like bacterial strains, Acetosyringone as well as salt concentration in co-cultivation media.[2] The high growth rate of transformed root cultures is very attractive for the industrial production of secondary metabolites.[3] In a study, Sudha et al. mentioned that the effects of endogenous hormones and bacterial strains reacted to the rol gene products might lead to tumors.[4] The T-DNA regions, chromosomal virulence (chv) and virulence (vir) genes, are essential for DNA transference from bacteria to the host plant cells. The rol A, B, C and D genes are supported by TL-DNA that separates the Ri-plasmid of A. rhizogenes from the Ti-plasmid in A. tumefaciens.[5,6] The rolB induced HR and plays a key role in the secretion of active auxin performed by indoxyl-β-oxidase activity.[7] On the other hand, rolA, rolC, rolD, and other open reading frames act together in order to promote root induction.[8]