Transposition of the maize controlling element "Activator" in tobacco

Transposition of the maize autonomous controlling element Activator (Ac) and a nonautonomous derivative, Dissociation (Ds), was investigated in tobacco cells. Tobacco protoplasts were transformed with Ti-plasmid vectors that contained Ac or Ds flanked by short maize wx gene sequences. The structures of the elements and surrounding wx and T-DNA sequences were investigated in nine Ac and five Ds tobacco transformants by digestion with restriction enzymes, Southern blotting, and hybridization using specific probes. In four of the nine Ac transformed lines, Ac had excised from its original position in the T-DNA and inserted at new sites in the tobacco genome. Ds did not excise from its original T-DNA position in any of the transformants examined. Two Ac fragments and cellular flanking sequences were cloned from a line of tobacco in which Ac had transposed. Fragments, comprised of sequences flanking the newly integrated Ac elements, were used as hybridization probes to normal tobacco DNA and to the tobacco DNA from which they were isolated. The Ac copies were integrated into repetitive tobacco DNA sequences. Two tobacco fragments containing empty Wx donor sites were cloned from the DNA of the same Ac transformant and sequenced. Both sequences are among the types of excision products observed to result from Ac-catalyzed excision events in maize. Our results indicate that the maize controlling element Ac is capable of self-catalyzed transposition in tobacco.