Figure 1.

Transposon-based transformation. A, Model of Ds transposition from an extrachromosomal T-DNA into the genome of a plant cell. The T-DNA contains a Tpa gene expression cassette (blue), a Ds element carrying an expression cassette for the nptII gene inserted between the ends of the maize element Ac (orange), and a codA gene inserted between regulatory sequences (red). Plant transformation is initiated by the transfer of single-stranded (ss) and virE2-coated (gray circles) T-DNA from Agrobacterium (A. tum) to the plant cell nucleus (step 1). After obtaining its double-stranded (ds) form, expression of the Tpa and codA genes will result in the production of Tpa (blue circles) and the conversion of 5FC to toxic 5-fluorouracil, respectively (step 2). Tpa will bind to the Ac-derived sequences and catalyze excision of Ds (steps 3 and 4). The excised element, possibly together with broken T-DNA fragments, may integrate into the plant cell genome (step 5). Application of a sequential selection on kanamycin and 5FC was predicted to yield transformants that contained a Ds element and lacked T-DNA. B, Diagram of the T-DNA of pSIM269 and pSIM401. Black triangles represent the left and right border of the T-DNA.