THE TRANSPOSITION FREQUENCY OF TAG1 ELEMENTS IS INCREASED IN TRANSGENIC ARABIDOPSIS LINES

Tag1 was identified as a highly active endogenous transposable element in transgenic Arabidopsis thaliana Landsberg erecta plants carrying t he maize transposable element Activator (Ac). Here, we describe experi ments designed to determine the basis for the high activity of Tag1. T he frequency of transposition of Tag1 elements was compared in lines c ontaining or lacking Ac transposase to assess the effect of Ac transpo sase on Tag1 activity. Three populations of nontransgenic plants, incl uding nontransformed regenerants, were also analyzed. The high level o f activity of Tag1 did not correlate with the presence or absence of A c transposase but was significantly higher in transgenic lines. This r esult was maintained through at least six generations after transforma tion. These data suggest that Tag1 transposition is stimulated by proc esses that occur during the Agrobacterium transformation and that ther eafter remain active. Two Tag1 elements are tightly linked in the Land sberg erecta genome and map to the lower arm of chromosome 1. Tag1 ele ments were found in only a few A. thaliana ecotypes but were present i n four other Arabidopsis species.