Mechanism of T-DNA Transfer

Abstract

Upon cutting at the T-DNA borders the VirD2 protein of Agrobacterium tumefaciens is tightly (most probably covalently) attached to the 5’ end of the processed T-DNA. Therefore, it was proposed to be transferred into the plant cell together with the T-DNA, and to perform several functions within the plant cell: it may protect the T-DNA against nucleases, it may target it into the plant nucleus and it (or a protein attached to it) may integrate it into the plant chromosome. Here we analyze the property of the VirD2 protein in nuclear targeting. We demonstrate that VirD2 protein contains two nuclear localization signals (NLS) which are functional in yeast as well as in plant cells. One of these signals is located in the N-terminal part of the protein and its sequence resembles that of a single-cluster type NLS, whereas the other is located in the C-terminal part and belongs to the bipartite type NLS. The involvement of these sequences in the entry of the T-DNA into the nucleus is discussed.