GERMINAL TRANSPOSITIONS OF THE MAIZE ELEMENT DISSOCIATION FROM T-DNA LOCI IN TOMATO

We have analyzed the pattern of germinal transpositions of artificial Dissociation (Ds) transposons in tomato. T-DNA constructs carrying Ds were transformed into tomato, and the elements were transactivated by crossing to lines transformed dth a stabilized Activator (sAc) that ex pressed the transposase gene. The sAc T-DMA carried a GUS gene to moni tor its segregation. The Ds elements were inserted in a marker gene so that excision from the T-DNA could be monitored. The Ds elements also carried a genetic marker that was intended to be used for reinsertion selection of the elements after excision. Unfortunately, this gene wa s irreversibly inactivated on crossing to sAc. Germinal excision frequ encies of Ds averaged 15-40%, but there nas large variation between an d within plants. Southern hybridization analysis of stable transposed Ds elements indicated that although unique transpositions predominate, early transposition events can lead to large clonal sectors in the ge rmline of developing plants and to sibling offspring carrying the same transposition event. Multiple germinal transpositions from three diff erent loci were examined for uniqueness, and 15 different transpositio ns were identified from each of three T-DNA loci that carried a single independent Ds. These were mapped relative to the donor T-DNA loci, a nd for each locus 70-80% of the transposed elements were closely linke d to the donor site.