Marker-Free Plant Transformation

Selection marker genes perform a critical function of identifying transformed cells or tissues in the plant transformation processes. The commonly used marker genes confer resistance to antibiotics or herbicides that suppress the growth of untransformed cells and allow the transformed cells to grow. Therefore, most transformation processes involve introduction of a marker gene along with the gene-of-interest. However, this marker gene serves no purpose once the transgenic clone has been isolated, and many regulatory agencies worldwide recommend removal of the marker genes from commercially applicable transgenic plants. To address this issue, plant biotechnologists have developed a number of approaches for removing marker genes from transgenic clones. This chapter provides a review of these methods and technical details of the two most commonly used approaches. Site-specific recombination systems such as E. coli phage P1 derived Cre-lox system have been widely used as a molecular scissor to precisely excise marker genes from the transgene locus. Similarly, dual T-DNA vector system, consisting of separate vectors for marker genes and the gene-of-interest to develop genetically segregated loci for each gene, has been widely practiced.