Analysis of T-DNA Flanking Sequences and Event-Specific Detection of Transgenic Alfalfa with Gene Encoding Betaine Aldehyde Dehydrogenase

The gene encoding betaine aldehyde dehydrogenase (BADH) has been transformed into alfalfa (Medicago sativa L.) and resulted in 42 transgenic plants with improved salt tolerance. However, these transgenic lines were derived from the same transformant vector, which were unable to distinguish them from each other using common methods. For differentiating these transformants at molecular level, thermal asymmetric interlaced polymerase chain reaction (TAIL-PCR) was performed to separate the T-DNA flanking sequences for identifying transgenic plants in event-specific detection. A total of 6 sequences flanking either the left or the right borders of the T-DNA were obtained. The left border sequence of T-DNA was completely deleted from the vector and not integrated into the genome of alfalfa in the transgenic plant B196. Although the left border flanking sequence in the transgenic plant B127 was reserved, it was filled with a DNA sequence of unknown origin. The forward and backward primers for PCR were designed based on the characteristics of the flanking sequences originating from the vector sequence and the alfalfa genomic sequence adjacent to the integrated vector sequence, respectively. According to the result of PCR amplification in the 42 BADH-transgenic lines, plants B106, B125, B127, B138, B157, B158, B289, B295, and B305 presented the same amplification banding pattern. Plants B196, B203, B220, and B223 exhibited the same banding pattern, which was different from that amplified from other plants. These results indicated that the plants with identical amplification banding patterns may come from the same transformation event.