LINKED AND UNLINKED TRANSPOSITION OF A GENETICALLY MARKED DISSOCIATION ELEMENT IN TRANSGENIC TOMATO

We have introduced a genetically marked Dissociation transposable elem ent (Ds(neo)) into tomato. In the presence of Ac transposase, Ds(neo) excised from an integrated T-DNA and reinserted at numerous new sites in the tomato genome. The marker genes of Ds(neo) (NPTII) and the T-DN A (HPT) facilitated identification of plants bearing transposon excisi ons and insertions. To explore the feasibility of gene tagging strateg ies in tomato using Ds(neo), we examined the genomic distribution of D s(neo) receptor sites, relative to the location of the donor T-DNA loc us. Restriction fragment length polymorphism mapping of transposed Ds( neo) elements was conducted in two tomato families, derived from indep endent primary transformants each bearing Ds(neo) within a T-DNA at a unique position in the genome. Transposition of Ds(neo) generated clus ters of insertions that were positioned on several different tomato ch romosomes. Ds(neo) insertions were often located on the same chromosom e as the T-DNA donor site. However, no insertion showed tight linkage to the T-DNA. We consider the frequency and distance of Ds(neo) transp osition observed in tomato to be well suited for transposon mutagenesi s. Our study made use of a novel, stable allele of Ac (Ac3) that we di scovered in transgenic tomato. We determined that the Ac3 element bear s a deletion of the outermost 5 base pairs of the 5'-terminal inverted repeat. Though incapable of transposition itself, Ac3 retained the ab ility to mobilize Ds(neo). We conclude that a dual element system, com posed of the stable Ac3 trans-activator in combination with Ds(neo), i s an effective tool for transposon tagging experiments in tomato.