Selectable marker genes

Biopharmaceuticals in Plants Toward the Next Century of Medicine 

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DNA construct will often contain an effect gene and a selectable marker gene (such as antibiotic or herbicide resistance), both of which are bracketed by promoter and terminator sequences. A plasmid vector carries this cassette of genetic information into the plant genome by one of the above methods. 

Figure 19 Sample gel of the results of a PCR. Lane 1 is a 100-bp molecular marker lanes 2-6 are samples. The presence of the top bands (the species-specific endogenous gene) demonstrates that the PCR amplification was successfiil. Lack of the middle band (the introduced effect gene) and the bottom band (the selectable marker gene) in lane 3 indicates that sample is negative for the effect gene. Presence of all three bands in the remaining lanes indicates the samples are positive for the effect gene...

The plant sample in lane 6 is also positive for the transgene of interest. Because the band for the effect gene (middle band) is typically fainter than the band for the selectable marker gene (bottom band), it appears that for lane 6, the PCR product amplitication for the effect gene is below the assay detection threshold. Because the selectable marker is clearly present and the PCR amplitication worked, lane 6 can be interpreted as a positive result for the transgene of interest. 

Ap(R) This selectable marker gene is for the resistance of ampicUlin (beta-lactamase), which degrades penicillins to enable selection of the desired DHFR vector. 

Miki, B. and McHugh, S. (2004). Selectable marker genes in transgenic plants applications, alternatives and biosafety. J. Biotechnol. 107(3) 193-232. 

Corneille, S. et al. (2001). Efficient elimination of selectable marker genes from the plastid genome by the CRE-lox site-specific recombination system. Plant. . 27 171-178. 

Over several decades, multiple vector systems for recombinant gene expression in E. coli have been developed. Modem vectors suitable for recombinant protein production vary in the used promoter system in the presence or absence of coding sequences for affinity tags upstream or downstream of the multiple cloning site (MCS) and of sequences coding for leader peptides for the protein export. Moreover, different origins of replication (ori), antibiotic selection marker genes and MCS are used. 

Buchananwollaston, V., Snape, A., and Cannon, F. 1992. A plant selectable marker gene based on the detoxification of the herbicide dalapon. Plant Cell Rep., 11, 627-631. 

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