Received April 28, 2003
Returned for revision June 6, 2003
Accepted June 13, 2003
Targeted Integration of T-DNA into the Tobacco Genome at Double-Stranded Breaks: New Insights on the Mechanism of T-DNA Integration
Mary-Dell M. Chilton and Qiudeng Que *
Syngenta Biotechnology, Inc., 3054 Cornwallis Road, P.O. Box 12257, Research Triangle Park, North Carolina 27709-2257
* Corresponding author; email: qiudeng.que{at}syngenta.com.
Agrobacterium tumefaciens T-DNA normally integrates into random sites in the plant genome. We have investigated targeting of T-DNA by nonhomologous end joining process to a specific double-stranded break created in the plant genome by I-CeuI endonuclease. Sequencing of genomic DNA/T-DNA junctions in targeted events revealed that genomic DNA at the cleavage sites was usually intact or nearly so, whereas donor T-DNA ends were often resected, sometimes extensively, as is found in random T-DNA inserts. Short filler DNAs were also present in several junctions. When an I-CeuI site was placed in the donor T-DNA, it was often cleaved by I-CeuI endonuclease, leading to precisely truncated targeted T-DNA inserts. Their structure requires that T-DNA cutting occurred before or during integration, indicating that T-DNA is at least partially double stranded before integration is complete. This method of targeting full-length T-DNA with considerable fidelity to a chosen break point in the plant genome may have experimental and practical applications. Our findings suggest that insertion at break points by nonhomologous end joining is one normal mode of entry for T-DNA into the plant genome.
