Genetic transactivation of Dissociation elements in transgenic tomato plants

Abstract

We have previously reported on the behaviour of the maize transposable elements Activator (Ac) and Dissociation (Ds) in transgenic tomato plants. To continue our study of the Ac-Ds family in tomato, we have constructed two Ds elements and a stable Ac derivative designated Transposase (Ts101). The two constructed Ds elements each contain a bacterial β-galactosidase gene to facilitate cloning the elements from the tomato genome by marker rescue. In Ds202, the central 1.6 kb HindIII fragment of Ac was replaced by a chimaeric bacterial β-galactosidase gene. Ds204 contains the β-galactosidase fragment from pUC19 flanked by 185 bp and 131 pb of the 5′ and 3′ termini (relative to the direction of transcription) of Ac. The Ts101 element was constructed by deleting about 50 nucleotides, including the inverted repeat, from the 3′ end of Ac. Ts101 and the two Ds elements were stable in transformed tomato plants. Transgenic plants containing either one of the two constructed Ds elements of Ds1, an element previously cloned from the maize Adh1 locus, were crossed to transgenic plants containing either Ts101 or an intact Ac element. Southern hybridization analysis showed that Ds1 and Ds202 excised from their resident T-DNA locations in all progeny which contained either Ts101 or Ac, but were stable in siblings which had not inherited a transposase. While Southern analysis did not identify transposed Ds elements in the F1 progeny, analysis of an F2 population indicated that the Ds elements had reintegrated in the tomato genome. In contrast to these results, no Ac-catalyzed excision of Ds204 was detected, even though the element contained the terminal regions of Ac capable of forming secondary structure. We have shown that Ds elements can be transactivated in transgenic tomato plants by crossing to plants containing an Ac or Ts element.