USE OF THE MAIZE TRANSPOSONS ACTIVATOR AND DISSOCIATION TO SHOW THAT PHOSPHINOTHRICIN AND SPECTINOMYCIN RESISTANCE GENES ACT NON-CELL-AUTONOMOUSLY IN TOBACCO AND TOMATO SEEDLINGS

Cell-autonomous genes have been used to monitor the excision of both endogenous transposons in maize and Antirrhinum, and transposons introduced into transgenic plants. In tobacco and Arabidopsis, the streptomycin phosphotransferase (SPT) gene reveals somatic excision of the maize transposon Activator (Ac) as green sectors on a white background in cotyledons of seedlings germinated in the presence of streptomycin. Cotyledons of tomato seedlings germinated on streptomycin-containing medium do not bleach, suggesting that a different assay for transposon excision in tomato is desirable. We have tested the use of the spectinomycin resistance (SPEC) gene (aadA) and a Basta resistance (BAR) gene (phosphinothricin acetyltransferase, or PAT) for monitoring somatic excision of A c in tobacco and tomato. Both genetic and molecular studies demonstrate that genotypically variegated individuals that carry clones of cells from which A c or Ds have excised from either SPEC or BAR genes, can be phenotypically completely resistant to the corresponding antibiotic. This demonstrates that these genes act non-cell-autonomously, in contrast to the SPT gene in tobacco. Possible reasons for this difference are discussed.