Conventional Agrobacterium-mediated transformation methods rely on complex and genotype-specific tissue culture media for
selection, proliferation, and regeneration of genetically modified cells. Resulting transgenic plants may not only contain
selectable marker genes but also carry fragments of the vector backbone. Here, we describe a new method for the production
of transgenic plants that lack such foreign DNA. This method employs vectors containing the bacterial isopentenyltransferase
(
ipt) gene as backbone integration marker. Agrobacterium strains carrying the resulting
ipt gene-containing “cytokinin” vectors were used to infect explants of various Solanaceous plant species as well as canola (
Brassica napus). Upon transfer to hormone-free media, 1.8% to 9.9% of the infected explants produced shoots that contained a marker-free
T-DNA while lacking the backbone integration marker. These frequencies often equal or exceed those for backbone-free conventional
transformation.
Keywords Marker-free transformation - Isopentenyltransferase - Vector backbone DNA