Agrobacterium aiming for the host chromatin: Host and bacterial proteins involved in interactions between T-DNA and plant nucleosomes

Agrobacterium genetically transforms its hosts by transferring a segment of DNA (T-DNA) into the host cell and integrating it into the host genome. Integration requires a close interaction between T-DNA, which is packaged into a nucleoprotein complex (T-complex) by bacterial virulence (Vir) proteins, and the host chromatin. This interaction is facilitated by the host protein VIP 1, which binds both to the major protein component of the T-complex, VirE2, and to the core histones. Recently, VIP1 has been demonstrated to mediate the interaction between plant nucleosomes and VirE2-DNA complexes (i.e., synthetic T-complexlike structures) in vitro. Here, we discuss major implications of these observations-such as the possible role of core histone modifications, proteasomal uncoating of the T-complex mediated by the bacterial F-box protein VirF, and the need for changes in chromatin structure to render it accessible to the T-DNA integration-for the process of chromatin targeting of foreign DNA and its integration into the eukaryotic genome.