Tnt1 transposition events are induced by in vitro transformation of Arabidopsis thaliana, and transposed copies integrate into genes

Tissue culture has been shown to induce the transposition of plant transpos able elements; their insertion at novel sites results in somaclonal variati on. Introduction of the tobacco retrotransposon Tnt1 into Arabidopsis thali ana by co-cultivation of root explants with Agrobacterium tumefaciens induc es its transposition at a high frequency, but no transposed copies are foun d in plants transformed by the in planta procedure. Transposition occurs in the transformed root cells or in the calli derived from them, allowing the regeneration of transformed plants with up to 26 transposed copies of Tnt1 . Analysis of Tnt1 integration sites in Arabidopsis shows that the Tnt1 end onuclease does not show any cleavage-site specificity at the sequence level . The insertion sites are unlinked and distributed on all five Arabidopsis chromosomes. The fact that the majority of the integration sites are locate d in coding regions. and none in repeated sequences. demonstrates the poten tial of Tnt1 as a tool for gene tagging.