Some questions about marker genes, there are pictures.

The recombinant plasmid contains the kanamycin resistance gene (the first step), which generally encodes an acetylase. The recombinant plasmid transfected with Agrobacterium can survive in the medium containing kanamycin. But those without transfection cannot.

This method is used to screen successfully transfected Agrobacterium, that is, Agrobacterium carrying the target gene.