Research Interests   Plant-Microbe Interactions; Gene Transfer from Bacteria to Plants

The goal of our research is to define the mechanism of horizontal DNA transfer between two kingdoms. The neoplastic plant disease, crown gall tumor, is used as a model system for this study. Crown gall tumor results from the infection by a pathogenic bacterium, Agrobacterium tumefaciens. During infection the bacterium donates a piece of plasmid DNA that is stably integrated into the plant nuclear genome. Expression of genes encoded within the transferred DNA leads to uncontrolled growth of a transformed cell.

The DNA transfer process requires the participation of the virulence (vir) genes of the plasmid. Proteins of the virB region and VirD4 are essential for DNA transfer. It is postulated that the DNA travels to the plant cell through a transport pore generated by the VirB proteins. A focus of our current research is to elucidate the structure of the transport pore and to define the role an individual VirB protein plays in the assembly and function of the pore. Molecular, biochemical and genetic approaches are used in these studies. A similar transport pore is used for the transfer of plasmid DNA and large protein complexes in other systems.

The synthesis of the virulence proteins requires interactions between the bacterium and the plant cell. Two Vir proteins, VirA and VirG, and a signal molecule from plant cells activate transcription of the vir genes. How the signal from the plant cell is transmitted to the bacterium is another focus of our research. Using mutants of virA and virG we are investigating the mechanism of activation of the vir gene transcription. These studies include the structure-function analysis of the Vir proteins.

Judd, P., Mahli, D. and Das, A. (2005) Molecular characterization of the Agrobacterium tumefaciens DNA transfer protein VirB6. Microbiol.151:3483-3492. (pdf)

Judd, P.K., Kumar, R.B. & Das, A. (2005) Spatial location and requirements for the assembly of the Agrobacterium tumefaciens type IV secretion apparatus. Proc. Natl. Acad. Sci. USA 102:11498-11503. (pdf)

Judd, P.K., Kumar, R.B. & Das, A. (2005) The type IV secretion apparatus protein VirB6 of Agrobacterium tumefaciens localizes to a cell pole. Mol. Microbiol. 55:115-124. (pdf)

Kumar, R. and Das, A. (2002) Polar location and functional domains of the Agrobacterium tumefaciens DNA transfer protein VirD4. Mol. Microbiol. 43:1523-1532. (pdf)

Kumar, R. and Das, A. (2001) Polar location and functional domains of the Agrobacterium tumefaciens DNA transfer protein VirD4. Mol. Microbiol. 43:1523-32. (Medline citation).

Kumar, R. and Das, A. (2001) Functional analysis of the Agrobacterium tumefaciens T-DNA transport pore protein VirB8. J. Bacteriol. 183:3636-3641. (Medline citation).

Ke, J., Khan, R., Johnson, T., Somers, D. and Das, A.(2000) High efficiency gene transfer to recalcitrant plants by Agrobacterium tumefaciens. Plant Cell Reports .

Kumar, R.B., Xie, Y.H., Das, A. (2000) Subcellular localization of the Agrobacterium tumefaciens T-DNA transport pore proteins: VirB8 is essential for the assembly of the transport pore. Mol. Microbiol. 36(3):608-17. (Medline citation)

Abuodeh, R.O., Orbach, M.J., Mandel, M.A., Das, A., Galgiani, J.N. (2000) Genetic Transformation of Coccidioides immitis Facilitated by Agrobacterium tumefaciens. J. Infect. Dis. 181(6):2106-2110. (Medline citation)

Das, A., Xie, Y.H. (2000) The Agrobacterium T-DNA transport pore proteins VirB8, VirB9, and VirB10 interact with one another. J. Bacteriol. 182(3):758-63. (Medline citation)