Independent transposition of multiple Ac elements in the same transgenic tomato cell.

To effectively use transposable elements for the genetic manipulation of plant species lacking well characterized endogenous elements, it is important to evaluate the behavior of known transposable elements following their introduction into heterologous host species. One critical parameter concerns the timing of transposition in relation to the development of the transgenic host since this will affect the frequency with which transposition events are captured in the gametes. In order to examine whether different elements in the same cell are differentially active during development, we used Southern hybridizations to assess the activity of Activator (Ac) elements in progeny plants derived from a tomato transformant carrying five Ac's at two loci. All of the elements at one locus transposed in the primary transformant at a developmental stage resulting in the transmission of newly transposed elements to the next generation. In contrast, one or more of the Ac's at the second locus were not active at this stage and were transmitted to the next generation at the original donor T-DNA insertion site. These elements were, however, transpositionally active in somatic tissue. These results demonstrated that individual transposable elements in the same transformed cell can be differentially activated during development.