Figure 1.

Approaches for co-transformation to produce selectable marker gene (SMG)-free transgenic plants. After the GOI and SMG are integrated on unlinked loci, marker-free transgenic plants can be obtained in the sequential generation after genetic segregation. (A) Mixture method of Agrobacterium co-transformation. Two Agrobacterium strains each contain a transformation vector. One vector has the GOI and the other has the SMG, which are used together to co-transform plants. (B) One-strain method of Agrobacterium co-transformation. One Agrobacterium contains two transformation vectors: one with the GOI and the other one with the SMG. (C) Super binary vector for co-transformation. The super binary vector contains separated T-DNA constructs: one with the GOI and the other with the SMG. (D) Two pairs of right borders and left borders used for co-transformation. A small right border-left border fragment is inserted into the polylinker of a standard binary vector in between a GOI and an SMG, which are already present in another set of left border and right border. (E) Double ‘RB’ T-DNA approach for co-transformation. The vector is designed in such a way that two right borders (RB1 and RB2) and one left border (LB) are presented as depicted in the figure. Two T-DNA fragments (RB1-SMG-RB2-GOI-LB and RB2-GOI-LB) may be transferred and be integrated on unlinked loci. (F) ‘Read-through’ method for co-transformation. The SMG is placed outside the left border. T-DNA fragment transfers to plant genome could be RB-GOI-LB or RB-GOI-LB-SMG (a ‘read through’ product). If RB-GOI-LB or RB-GOI-LB-SMG is integrated on unlinked loci, marker-free transgenic plants can be obtained through genetic segregation. Abbreviations. RB: T-DNA right border, LB: T-DNA left border, GOI: gene of interest, SMG: selectable marker gene.