Only those parts of the T i -plasmid that are absolutely essential for transfer into the plant and integration into the plant s genome are used. It is important that the tumor regenerates into a complete plant containing the foreign gene and that the latter is not lost during differentiation. The next challenge is meiosis, but it was principally solved. Many working groups use genes whose products cause resistances against antibiotics like the gene causing resistance against kanamycin. It retains its ability to be fully active within the plant cell, i.e. the plant cells are now resistant against kanamycin.
Untreated cells are sensitive towards kanamycin.
It turned out that one of the genes could be transferred to tobacco and that its expression is induced by light. The search for suitable promoters lead, among others, to the cauliflower-mosaic virus . It was considered as an alternative to the T i -plasmid. The genome of this virus integrates into the host cell s genome, but integration seems to be too unstable for reproducible results. Transfer and expression of many genes tried so far remained without success.