Plant Biotechnology Reports, vol. 9, no. 6, pp. 431-442
Plastid transformation is conducted by homologous recombination. Plastid transformation using a vector-containing promoter and/or terminator sequences homologous to the plastid DNA for transgene expression often results in the generation of unintended extrachromosomal DNA molecules derived from the initial plastid DNA molecule via intramolecular recombination. All the extrachromosomal DNA molecules, including those lacking the ori sequence, found in the T0 plastid-transformed tobacco plants were still detected in the T3 plants. These results suggest that the extrachromosomal DNA molecules are newly generated from the initially transformed plastid DNA that is transmitted to the progeny during each generation. In addition, inward, outward, and overlap extension PCR of the extrachromosomal DNA molecules confirmed that these molecules were circular.