The activity of a maize autonomous controlling element, Activator (Ac), and a non-autonomous derivative, Dissociation (Ds) were investigated in tobacco cells transformed with Ti plasmid vectors that contained Ac9 or Ds9 flanked by short maize wx gene sequences within their T-DNA (Fedoroff, N., Wessler, S., and Shure, M., Cell 35:235-242, 1983; Schell, J., Kaulen, H., Kreuzaler, E., Eckes, P., Rosahl, S., Willmitzer, L., Spena, A., Baker, B. and Fedoroff, N. in Molecular Biology of Development, C. S. H. Symp. Quant. Biol., 50, 1985 in press). The structures of the elements and surrounding wx and T-DNA sequences were determined in nine Ac and five Ds tobacco transformants by digestion with restriction enzymes, Southern blotting and hybridization using specific probes. The results of our analysis indicated that in four out of nine Ac-transformed lines Ac had excised from its original position within the T-DNA and was inserted at several new sites within the tobacco genome. Ds did not excise from its original T-DNA position in any of the transformants examined. Two newly located Ac fragments along with 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 two newly located Ac copies were integrated into repetitive tobacco DNA sequences. Two tobacco Wx revertant fragments situated within different T-DNA copies from which Ac had excised were cloned and sequenced. Excision of Ac from the one T-DNA examined was accompanied by loss of two base pairs of the original 8 bp repeated Wx target sequence. Our results indicate that the maize controlling element, Ac, is capable of transposition in a heterologous plant cell.
B. J. Baker, J. Schell, H. Lorz and N. Fedoroff1
of Washington, Baltimore, Maryland
Return to the MNL 60 On-Line Index
Return to the Maize Newsletter Index
Return to the Maize Genome Database Page