Transient occurrence ofextrachromosomal DNA ofanArabidopsis thaliana transposon-like element, Tatl

Analysis of11genomic clones containing the S-adenosylmethionine synthetase 1gene(sam)) ofArabidopsis thaiana revealed thepresence ofa431-base-pair (bp) insertion inthe3'endofsamlinoneofthese clones. Theinserted sequence, called Tat), shows structural features ofatranspo- son. Itisflanked bya5-bpduplication ofthetarget site DNA andhas13-bp inverted repeats atitstermini. Twohighly homologous elements situated inadifferent genomic context wereisolated froma genomic library. Genomic Southern analysis indicates thatthere areatleast fourcopies ofTat) present intheA.thalina ecotype Columbia genome. Different hybridization patterns areobserved withDNAsderived from different ecotypes ofArabidopsis thaliana, indicating that the element hasmovedsince thedivergence ofthese ecotypes. In twopopulations ofA.thaliana, linear extrachromosomal Tat)- homologous DNAhasbeenobserved. Thepresented dataare consistent withthehypothesis that Tatlisanactive transpos- able element. Transposable elements andtransposon-like elements have beenisolated fromanincreasing number ofplant species over thelast decade. Theseelements arecharacterized bythe presence ofterminally inverted repeats andtheapparent ability togenerate duplications ofthetarget site uponinte- gration (for reviews, seerefs. 1and2).Manyelements isolated fromseveral plant species contain homologous in- verted repeats. Onthis basis theelements Tam)andTam2 fromAntirrhinum majus(3), Tgm)fromsoybean (4), SpmJ8 frommaize (5), andPis) frompea(6)belong tooneclass of transposons starting withthesequence 5'CACTA--3', whereas AciDsfrommaize(7), Tam3fromAntirrhinum majus(8), Tpc)fromPetroselium crispum (9), Ips-r from Pisumsativum (10), andTat)fromArabidopsis thaliana (described inthis paper) constitute asecond class oftrans- posons showing mutual homology intheir inverted repeats. This paper describes three copies ofanArabidopsis trans- poson-like element, designated Tat). tEvidence ispresented that Tat)isanactive (nonautonomous) transposon.