Figure 1. Basic steps in transformation of plant cells by Agrobacterium tumefaciens. The T-DNA transfer is represented according to updated knowledge on this process, although many of involved mechanisms have not been elucidated yet and the experimental results only allow hypothesize about it. Entering of T-DNA complex into the plant cell is almost completely uncharacterized and experimentally only the VirB7-VirB9 disulfide bound heterodimers have been evidenced. The most important events are briefly mentioned in chronological order (boxes 1 through 13). Each step is described in the text.