The low level of activity of Arabidopsis thaliana Tag1 transposon correlates with the absence of two minor transcripts in Medicago truncatula

Tag1 is an element from the hAT (hobo, Ac, Tam) family of DNA transposable elements present in Arabidopsis thaliana ecotype Landsberg. We have compared its behavior in the A. thaliana ecotype Columbia and in the legume model plant Medicago truncatula. As previously described Tag1 transposed efficiently in A. thaliana ecotype Columbia. In contrast, only somatic excision, but no germinal excision or transposition events could be detected in M. truncatula, indicating that Tag1 is poorly active in this plant. These differences in activity correlated with the absence of two minor Tag1 transcripts in M. truncatula transgenic lines but not with the structure of the T-DNA loci or the methylation of the element. These results indicate that Tag1 is not suitable for insertion mutagenesis in M. truncatula.