Evaluation of a Transgenic Lettuce with Big-Vein Disease Resistance for Biosafety Assessment

Lettuce big-vein disease is a soil-borne viral disease found in major lettuce production areas worldwide. We have developed a transgenic lettuce line with resistance to the disease by introducing the inverted repeats of the coat protein gene of Mirafiori lettuce virus (MiLV). In this study, the transgenic lettuce was evaluated for biosafety assessment by comparing its characteristics with those of a parental non-transformed cultivar ‘Kaiser’. There was no significant difference between the transgenic and the non-transgenic lettuce in pollen fertility, pollen dispersal, seed productivity, seed dispersal, dormancy, germination, growth of seedlings under low or high temperature, chromatographic patterns of leaf extracts, or effects of lettuce plants on growth of broccoli or on soil microflora. There was a significant difference in pollen size, but the difference was small. The length of cotyledon of the transgenic lettuce was a little shorter than that of ‘Kaiser,’ while there was no difference in other morphological characteristics examined. Next we detected the CP gene and the npt II gene (kanamycin resistance gene) by PCR in the transgenic lettuce of T₁, T₂ and T₃ generations. The CP gene was detected in the transgenic lettuce of all generations. On the other hand, the npt II gene was detected in T₁ plants, but not in the transgenic lettuce of T₂ or T₃ generation. DNA sequences flanking T-DNA insertions in the transgenic lettuce of T₂ generation were determined using inverse PCR, and the result indicated that the right side of the T-DNA including the npt II gene has been truncated in the transgenic lettuce.