Analysis of the T-DNA structure in a large number of transgenic petunias generated by Agrobacterium-mediated transformation.

Southern hybridisation was performed on ninety-six transgenic petunias that had been selected for resistance to kanamycin. Just over half of the plants contained intact copies of the T-DNA. The most common rearrangements (at least 24 plants out of 96) were simple deleted derivatives that had lost one or both ends of the T-DNA. T-DNAs lacking the left border occurred at a frequency of 20%, and estimates of the frequency of T-DNAs lacking the right border were at least this high. Three plants contained grossly rearranged T-DNAs, of which all expressed the kanamycin resistance gene but only one transmitted the gene to progeny. Two plants lacked T-DNA homology altogether and did not express kanamycin resistance in their leaves or their progeny. Circumstantial evidence suggests that plants containing a chimaeric kanamycin resistance gene driven by the ocs promoter do not root efficiently in the presence of kanamycin. There was no correlation between intactness of the T-DNA and Mendelian inheritance of the kanamycin-resistance phenotype. However, a disproportionate number of plants showing non-Mendelian inheritance had a high copy number of their T-DNA.