Characterization of theAc/Ds behaviour in transgenic tomato plants using plasmid rescue

We describe the use of plasmid rescue to facilitate studies on the behaviour ofDs andAc elements in transgenic tomato plants. The rescue ofDs elements relies on the presence of a plasmid origin of replication and a marker gene selective inEscherichia coli within the element. The position within the genome of modifiedDs elements, rescued both before and after transposition, is assigned to the RFLP map of tomato. Alternatively to the rescue ofDs elements equipped with plasmid sequences,Ac elements are rescued by virtue of plasmid sequences flanking the element. In this way, the consequences of the presence of an (active)Ac element on the DNA structure at the original site can be studied in detail. Analysis of a library ofAc elements, rescued from the genome of a primary transformant, shows thatAc elements are, infrequently, involved in the formation of deletions. In one case the deletion refers to a 174 bp genomic DNA sequence immediately flankingAc. In another case, a 1878 bp internalAc sequence is deleted.