During the
infection of plants, Agrobacterium tumefaciens introduces several Virulence
proteins including VirE2,
VirF, VirD5 and VirE3 into plant cells in addition to the
T-DNA. Here, we report that double mutation of
virF and virE3 leads to strongly diminished
tumor formation on tobacco, tomato and sunflower. The VirE3
protein is translated from a polycistronic
mRNA containing the virE1, virE2 and virE3 genes, in Agrobacterium. The VirE3
protein has nuclear localization sequences, which suggests that it is transported into the plant cell nucleus upon translocation. Indeed we show here that VirE3 interacts in vitro with
importin-alpha and that a VirE3-GFP fusion
protein is localized in the nucleus. VirE3 also interacts with two other
proteins, viz. pCsn5, a component of the COP9 signalosome and pBrp, a plant specific general
transcription factor belonging to the
TFIIB family. We found that VirE3 is able to induce transcription in yeast when bound to
DNA through the GAL4-BD. Our data indicate that the translocated effector
protein VirE3 is transported into the nucleus and there it may interact with the
transcription factor pBrp to induce the expression of genes needed for
tumor development.