Organisation of T-DNA - T-DNA (transferred DNA) is that Ca. 23 kb segment of Ti/Ri plasmids, which is transferred into the plant genome during Agrobacterium infection. T-DNA is defined on both its sides by a 24 bp direct repeat border sequence, and contains the genes for tumour/hairy root induction and those for opine biosynthesis. pTi has three genes, which are involved in crowngall formation.

Two of these genes encode enzymes, which together convert trypophan into IAA (indole, 3­- acetic acid). A deletion of these two genes produces shooty crowngalls; therefore, the locus was earlier called shooty locus.

The third gene, ipt, encodes an enzyme which produces the zeatin type cytokinin isopentenyl adenine. A deletion or abolition of ipt results in rooty crowngalls; as a result, it was earlier designated as rooty locus. In addition, genes involved in opine biosynthesis are located near the right border of T-DNA.