Properties of the maize transposable element Activator in transgenic tobacco plants: a versatile inter-species genetic tool.

The maize controlling element Activator (Ac) transposes autonomously from an integrated T-DNA vector to new sites in the genomes of tobacco and other heterologous plant species. Here we demonstrate that critical functions required for transposition of Ac in maize are conserved in tobacco and that Ac transposes at high frequency for at least five generations. Ac structure and terminal sequences are conserved upon transposition and a characteristic 8-bp duplication of target sequences is generated upon integration. Ac remains unmethylated, transcriptionally active, and capable to trans-activate transposition of the nonautonomous Dissociation (Ds) element throughout several generations. In tobacco, as in maize, Ac transposes adjacent to low copy or unique DNA, and transcriptional analysis of unique target DNA provides evidence that an Ac element transposed into a gene. In maize, increasing copies of Ac delay the timing and reduce the frequency of early transposition of Ac and Ds. In tobacco, increasing copies of Ac correlate with an increased frequency of Ds trans-activation. These data firmly establish that the Ac and Ds transposable elements are versatile genetic tools well suited for use as insertional mutagens and demonstrate that thorough investigation of mechanism and regulation of transposition is facilitated in heterologous settings.