Sulfonamide resistance gene for plant transformation.

The sulfonamide resistance gene from plasmid R46 encodes for a mutated dihydropteroate synthase insensitive to inhibition by sulfonamides. Its coding sequence was fused to the pea ribulose bisphosphate carboxylase/oxygenase transit peptide sequence. Incubation of isolated chloroplasts with the fusion protein synthesised in vitro, showed that the bacterial enzyme was transported to the chloroplast stroma and processed into a mature form. Expression of the gene fusion in transgenic plants resulted in a high level of resistance to sulfonamides. Direct selection of transformed shoots on leaf explants was efficient using sulfonamides as sole selective agents. Transformed shoots rooted normally on sulfonamides at concentrations toxic for untransformed ones. Sulfonamide resistance was transmitted to the progeny of transformed plants as a single Mendelian dominant character. These results demonstrate that this chimeric gene can be used as an efficient and versatile selectable marker for plant transformation.