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Using transmission electron immunomicroscopy, VirB2 protein has been revealed at the surface of acetosyringon-treated A. tumefaciens cells. VirB2 was seen within long flexible and short structures localized at the opposite poles of the cells. These structures were not observed in cells not treated with acetosyringon and in agrobacterial cells treated with this reagent but carrying no Ti-plasmid. Labeled complexes [antibodies to virB2 protein + (A protein + colloidal gold)] bound to pili at a certain periodicity.

The review deals with the supramembrane and membrane structures involved in the initial contact (attachment) of an agrobacterial cell with a bacterial or plant cell during the transfer of the agrobacterial genetic information. The relationships between the donor cell attachment to the recipient cell surface and the infection and conjugation processes are discussed. Experimental data on the recently found agrobacterial pili and surface protein rhicadhesin, which are involved in the conjugative transfer of the plasmid between agrobacteria, are considered. The role of adhesive and conjugative pili of E. coli in the initial and tight contacts is analyzed in the context of the recently proved similarity between the mechanisms of agrobacterial transformation in plants and conjugative transfer in bacteria. Possible involvement of the pilus in the conjugative transfer of agrobacterial DNA across the membranes of donor and recipient (bacterial and plant) cells is discussed.

Using colloidal gold-labelled VirB1-specific antibodies, it was found that VirB1 proteins are included into the composition of short pilus-like structures, which emerge at the poles of acetosyringone (AS)-induced agrobacterial cells.