This means the gene product of the selectable marker becomes the selecting factor for the survival. The three groups of selectable markers are antibiotic resistance genes, antimetabolite marker genes, and herbicide resistance genes.
Most widely used selectable markers are the antibiotic resistance genes. Hence, only the transformants can grow in the medium, which contains the corresponding antibiotic. However, all transformants may not contain the gene of interest. Some transformants may only have the vector with the selectable marker. Sequencing or gene expression analysis only permits the detection of recombinants that have the gene of interest.
Reporter gene is a type of marker genes used to quantify the gene expression. They are fused to the regulatory sequence of the gene of interest. Apart from the analysis of the expression of the gene of interest, reporter genes allow studying the function of the gene regulatory elements and the effect of transcription factors on the gene expression.
Also, reporter genes are vital in the identification of the tissue-specific or pathway-specific gene expression. Therefore, differentiation of the transformed and non-transformed cells is important to continue with further experimentation.
Hence, researchers incorporate a selectable marker gene to vector for easy selection of the transformed cells from non-transformed cells. A selectable marker is a DNA sequence , especially a gene useful in identification of the transformed cells.
This marker gene exhibits a trait which suits an artificial selection of transformed cells from non-transformed cells on a media. Most common selectable markers used in molecular biology are antibiotic resistant genes. An antibiotic resistance gene is inserted into the vector and transformed into host cells especially to the host bacterium.
That particular antibiotic is incorporated into the growing medium of the bacterium. Due to the presence of the selective marker, under the selective conditions, only cells that contain the appropriate selectable marker can survive. Non-transformed cells are unable to grow in the antibiotic-containing medium.
Therefore, due to the selectable marker which is antibiotic resistant, transformed cells are easily identified. Genes that confer traits for antimetabolites, herbicides are used as selective markers in cloning vectors in plant genetic engineering.
However, this cotransformation of selective markers into genetically modified organisms has negative effects on the environment and human. The release of antibiotic resistant bacteria can increase the antibiotic resistivity of human pathogens.
It can contaminate the product or biomass by antibiotics and can lose the selective pressure as a result of antibiotics degradation and inactivation.
Figure Plasmid vector for gene transfer with selectable marker. Reporter genes are genes that enable the detection or measurement of the inserted gene expression. These reporter genes can be attached to regulatory sequences of the gene of interest to signal the expression location or levels.
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Acta Physiol Plant 23, — Download citation. Received : 05 January
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