Types and Characteristics of Plant Genetic Transformation Vectors

The purpose of plant genetic transformation is to introduce foreign genes into recipient cells so that they can stably express the corresponding protein products. Since the success of the first transgenic tobacco in 1983, a variety of plant genetic transformation systems have been established. A large number of valuable engineered strains are widely used in plant transformation systems. In view of this, it is necessary to select corresponding types of transformation methods and transformation vectors according to different recipient plants or different transformation purposes. This article focuses on the development of plant transformation vectors, the selection of vectors and the application of vector design.

The establishment of genetic transformation methods is the primary problem to be solved in plant genetic engineering. In recent years, there have been many methods for genetic transformation of higher plants, which can be roughly divided into the following categories: based on the genetic characteristics of transformation, they can be divided into two categories: transient expression transformation and stable genetic transformation; taking vector characteristics as the object of investigation, It can be divided into non-vector-mediated genetic transformation and biological vector-mediated genetic transformation. Biological vector-mediated genetic transformation can be subdivided into two categories: viral vector and plasmid vector-mediated genetic transformation.

Viral vector-mediated genetic transformation belongs to transient expression transformation. Simply put, it is the use of viral vectors to infect plants to efficiently express the target gene and produce a large amount of protein. This transient expression transformation system has the following advantages: The foreign gene is directly introduced into the plant cell by the plant virus vector, and the system is distributed throughout the plant, without the need for a long transformation process from explants to regenerated plants. It helps to quickly predict whether the foreign gene can be successfully expressed in the plant; The virus can produce a large amount of foreign protein due to the efficient self-replication and expression ability of the virus; The DNA of the virus vector is generally not integrated into the nuclear genome of the plant. It will not affect the expression of other functional genes in the recipient plant itself. Of course, viral vectors also have obvious defects: Viral vectors cannot integrate foreign genes into chromosomes, so they cannot be passed on to the offspring according to Mendelian laws, and they have no advantage in long-term expression of foreign proteins; Due to the high frequency of mutations in the virus's own genome, it has the possibility of causing disease and may induce disease; The instability of the virus vector itself can easily cause the loss of foreign genes. In view of this, viral vector-mediated genetic transformation is mainly used in two fields: one field is the application of virus-induced gene silencing (VIGS) and other methods to the function research of genes; the other field is in high efficiency expression of foreign protein.

In contrast to the above-mentioned viral vector-mediated transient expression transformation, stable genetic transformation refers to the introduction of one or more DNA copies into plant cells and integration into plant chromosomes: stably inherited by screening transformed cells and regenerating plants. The advantages of stable genetic transformation are obvious. Using the stable genetic transformation system, it is possible to study the function of specific genes in plant cells, physiological and ecological functions; to analyze the functions of specific sequences in genes or specific amino acid sequences of proteins; The important thing is to be able to continuously express new proteins in plants, or continue to specifically remove the expression of a certain protein. In the transformation system mediated by biological vectors, researchers mostly use Agrobacterium (such as Agrobacterium tumefaciens and Agrobacterium rhizogenes) vectors as vectors for stable genetic transformation. Studies have shown that these two Agrobacterium have Ti plasmid or Ri plasmid and have the ability to transfer DNA in a specific region into plant chromosomes. Researchers can construct foreign DNA into the T-DNA region of the plasmid, transfer it to plant host cells, and obtain transgenic plants capable of expressing foreign genes. It is precisely the in-depth research and application of them that have created a new situation in plant genetic engineering today.

Regardless of whether it is a viral vector or a plasmid vector, the following conditions must be met as a plant transformation vector: It can successfully introduce the target gene into the recipient plant cell; It has effective DNA that can be recognized by the replication and transcription system of the recipient plant cell sequence (including replicon start site, promoter and enhancer and other cis-acting elements) to ensure that the imported foreign gene can replicate and express normally in the recipient plant cell.