Nuclear localization of Agrobacterium VirE2 protein in plant cells.

The Agrobacterium single-stranded DNA (ssDNA) intermediate T-strand is likely transferred to the plant cell nucleus as a complex with a single VirD2 molecule at its 5' end and multiple VirE2 molecules along its length. VirD2 contains a nuclear localization signal (NLS); however, because the T-strand is principally coated with VirE2 molecules, VirE2 also might assist in nuclear uptake. Indeed, VirE2 fused to a reporter protein localizes to plant cell nuclei, a process mediated by two amino acid sequences with homology to the bipartite NLS of Xenopus nucleoplasmin. Moreover, tumorigenicity of an avirulent virE2 mutant is restored when inoculated on transgenic plants expressing VirE2, supporting in planta function of VirE2.