Agrobacterium tumefaciens-mediated transformation of plants by the pTF-FC2 plasmid is efficient and strictly dependent on the MobA protein.

In the transformation of plants by Agrobacterium tumefaciens the VirD2 protein has been shown to pilot T-DNA during its transfer to the plant cell nucleus. Other studies have shown that the MobA protein of plasmid RSF1010 is capable of mediating its transfer from Agrobacterium cells to plant cells by a similar process. We have demonstrated previously that plasmid pTF-FC2, which has some similarity to RSF1010, is also able to transfer DNA efficiently. In this study, we performed a mutational analysis of the roles played by A . tumefaciens VirD2 and pTF-FC2 MobA in DNA transfer-mediated by A. tumefaciens carrying pTF-FC2. We show that MobA+/VirD2+ and MobA+/VirD2- strains were equally proficient in their ability to transfer a pTF-FC2-derived plasmid DNA to plants and to transform them. However, the MobA-/VirD2+ strain showed a DNA transfer efficiency of 0.03% compared with that of the other two strains. This sharply contrasts with our results that VirD2 can rather efficiently cleave the oriT sequence of pFT-FC2 in vitro . We therefore conclude that MobA plays a major VirD2-independent role in plant transformation by pTF-FC2.