permanently joint to the plant genome. The T-DNA region is flanked at both ends by 24bp sequences. Within the host plant cell's genome, the T-DNA of Agrobacterium is expressed to produced two main groups of proteins. One group is responsible for the production of plant growth hormones. As these hormones are produced, there will be an increase in the rate of cell division and therefore the formation of crown gall tumors. The second group of proteins are responsible for driving the synthesis of opines in the host plant cells. The specific opines produced depends on the type of the Ti plasmid but not on the plant host. These opines cannot be utilized by the plant host, and will instead be exported out of the plant cell where it can be taken up by the Agrobacterium cells. The bacteria possess genes in other regions of the Ti plasmid that allows the catabolism of opines. Transfer apparatus Transfer apparatuses encoded within the Ti plasmid have to achieve two objectives: allow the conjugative transfer of the Ti plasmid between bacteria and allow the delivery of the T-DNA and certain effector proteins into host plant cells. These are achieved by the Tra/Trb system and the VirB/VirD4 system respectively, which are members of the type IV secretion system (T4SS). For the Ti plasmid and T-DNA to be transferred via conjugation, they must first be processed by different proteins, such as the relaxase enzyme (TraA/VirD2) and the DNA transfer and replication (Dtr) proteins. Together, these proteins will recognize and bind to a region known as the origin of transfer (oriT) in the Ti plasmid to form the relaxosome complex. For the T-DNA, a nick will be created at the T-DNA's border sequence, and the nicked T-strand will be transported to the cell membrane, where the rest of the transfer machinery is present. Within the VirB/VirD4 system, the VirD2 relaxase is aided by the accessory factors VirD1, VirC1 and VirC2 while it processes the DNA substrate. Furthermore, the VirD2 relaxase and the VirC proteins will contribute to the delivery of the DNA strand to the VirD4 receptor at the cell membrane. This receptor is an essential component of T4SSs, and is thought to energize and mediate the transfer of the DNA into the translocation channel between two cells. The table below summarizes the proteins encoded in the virB operon that makes up the translocation channel of the