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FIG. 2.
Two-way exchange of chemical signals between A. tumefaciens and host plants. Wound-released chemical stimuli are
perceived by the VirA to VirG proteins, which leads to transcription of
vir promoters. T-DNA is processed by the VirD2 protein, and
single-stranded linear T strands are formed by strand displacement. T
strands and VirE2 are translocated from the bacteria via a pore encoded
by the virB operon and form a T complex within the plant
cytoplasm. T complexes are transported into the nucleoplasm via the
host protein karyopherin alpha, and the T-DNA is integrated into
genomic DNA. Transferred genes encode phytohormone synthases that lead
to plant cell proliferation and opine synthases that provide nutrients
to the colonizing bacteria. Opines are released from the plant cell,
enter the bacteria via dedicated opine permeases, and are catabolized
via opine-specific catabolic proteins. Opine permeases and catabolic
enzymes are encoded by the Ti plasmid. For the sake of clarity, the
relative orientations of vir genes and T-DNA have been
inverted.
