Progress on molecular mechanism of T-DNA transport and integration.

Agrobacterium-mediated transformation is probably the most widely used method to introduce genes into plants. Great progress has been made in recent years in studies on the mechanism of Agrobacterium-mediated transformation. Agrobacterium genetically transforms plants by transferring a portion of the resident Ti-plasmid, the T-DNA, to the plant. VirD2 and VirE2 accompany the T-DNA into the plant cell. Both proteins may aid in T-DNA transfer, nuclear targeting and integration into the plant genome. In recent years, some Arabidopsis rat (resistant to transformation) mutants are deficient in T-DNA integration according to some studies. These results showed that plant genes participate in the T-DNA transport and integration process. This paper discusses our current knowledge about the functions of virulence protein, namely VirD2 and VirE2, and plant genes in several aspect of Agrobacterium transformation. The paper discusses two different classes of integration patterns in detail: one is T-DNA right border being linked to genomic sequences by the VirD2 protein, the other is T-DNA integration via SDSA (synthesis-dependent strand-annealing). According to the latest studies we elaborated the T-DNA integration model based on genomic DSB (double-strand breaks) and proposed a new opinion about the mechanism of T-DNA integration.