Journal Article

Transferred DNA (T-DNA)-Associated Proteins of Agrobacterium tumefaciens Are Exported Independently of VirB

Chen, Lishan, Li, Catherine M., Nester, Eugene W.

2000

Overview

The transfer of T-DNA from Agrobacterium to plant cells is mediated by a system which involves the virB operon of the Ti plasmid. We report that VirE2 and VirD2, two T-DNA-associated proteins, as well as VirF, a protein known to be secreted into plant cells, are present in the periplasm and supernatant fractions of growing cells of Agrobacterium as are VirJ and ChvE, two known periplasmic proteins. Two cytoplasmic proteins, Ros and chloramphenicol acetyl transferase, and a VirE2 :: green fluorescent protein construct were not detected in the above fraction. Export of VirE2 into the culture supernatant did not require any Ti plasmid genes, except for VirE1, a specific chaperone for VirE2. The levels of the VirE2 and VirD2 proteins in the supernatant increased significantly when cells were grown at 19 degrees C as compared with 28 degrees C. When Agrobacterium expressed the oncogenic suppressive activity protein (Osa), VirE2 and VirF proteins could not be detected in the supernatant or the periplasm and the level of VirD2 was greatly reduced. However, oncogenic suppressive activity protein did not block the accumulation of VirJ and ChvE in the periplasm. Our data suggest that VirD2, VirE2, and VirF are transported across the cytoplasmic membrane by a specific pathway, independent of virB. Thus, transfer of the T-complex of Agrobacterium may take place in two steps, the first mediated by an unidentified pathway and the second by the virB system.

• Publisher: National Academy of Sciences of the United States of America,National Acad Sciences,National Academy of Sciences,The National Academy of Sciences
• Subject: Agrobacterium / Agrobacterium radiobacter / Agrobacterium tumefaciens / Agrobacterium tumefaciens - physiology / Antibodies / Bacteria / bacterial proteins / Bacterial Proteins - genetics / Bacterial Proteins - metabolism / Biological Sciences / Cell growth / cell membranes / ChvE protein / Deoxyribonucleic acid / DNA / DNA, Bacterial / DNA, Bacterial - genetics / DNA, Bacterial - metabolism / DNA-binding proteins / genetic complementation / genetics / Kalanchoe / Membrane Proteins / Membrane Proteins - genetics / Membrane Proteins - metabolism / metabolism / microbiology / mutants / Osa protein / Periplasm / physiology / Plant cells / Plants / Plants - microbiology / plasmids / protein secretion / Proteins / Ros protein / Secretion / temperature / Toxins / Transcription Factors / Transcription Factors - genetics / Transcription Factors - metabolism / transfer DNA / virB gene / VirD2 protein / VirE2 protein / VirF protein / VirJ protein / Virulence / Virulence Factors / Viruses