Transient occurrence of extrachromosomal DNA of an Arabidopsis thaliana transposon-like element, Tat1.

Analysis of 11 genomic clones containing the S-adenosylmethionine synthetase 1 gene (sam1) of Arabidopsis thaliana revealed the presence of a 431-base-pair (bp) insertion in the 3' end of sam1 in one of these clones. The inserted sequence, called Tat1, shows structural features of a transposon. It is flanked by a 5-bp duplication of the target site DNA and has 13-bp inverted repeats at its termini. Two highly homologous elements situated in a different genomic context were isolated from a genomic library. Genomic Southern analysis indicates that there are at least four copies of Tat1 present in the A. thaliana ecotype Columbia genome. Different hybridization patterns are observed with DNAs derived from different ecotypes of Arabidopsis thaliana, indicating that the element has moved since the divergence of these ecotypes. In two populations of A. thaliana, linear extrachromosomal Tat1-homologous DNA has been observed. The presented data are consistent with the hypothesis that Tat1 is an active transposable element.