Scott E. Stachel1,2, Eugene W. Nester3,4, Patricia Zambryski2
1Department of Microbiology and Immunology, SC-42, University of Washington, Seattle, WA 98195.
2Laboratorium voor Genetica, Rijksuniversiteit Gent, B-9000 Gent, Belgium
3Department of Microbiology and Immunology, SC-42, University of Washington, Seattle, WA 98195; and tLaboratorium voor Genetica,
4Rijksuniversiteit Gent, B-9000 Gent, Belgium
Tóm tắt
The virulence genes of
Agrobacterium
are required for this organism to genetically transform plant cells. We show that
vir
gene expression is specifically induced by a small (<1000 Da) diffusible plant cell metabolite present in limiting quantities in the exudates of a variety of plant cell cultures. Active plant cell metabolism is required for the synthesis of the
vir
-inducing factor, and the presence of bacteria does not stimulate this production.
vir
-inducing factor is (
i
) heat and cold stable; (
ii
) pH stable, although
vir
induction with the factor is sensitive above pH 6.0; and (
iii
) partially hydrophobic. Induction of
vir
gene expression was assayed by monitoring β-galactosidase activity in
Agrobacterium
strains that carry gene fusions between each of the
vir
loci and the
lac
Z gene of
Escherichia coli. vir
-inducing factor (partially purified on a C-18 column) induces both the expression in
Agrobacterium
of six distinct loci and the production of T-DNA circular molecules, which are thought to be involved in the transformation process.
vir
-inducing factor potentially represents the signal that
Agrobacterium
recognizes in nature as a plant cell susceptible to transformation.
