The wounded plant cell release certain chemicals phenolic compounds and sugars which are recognized as signals by agrobacterium.
The signal induced result in a sequence of biochemical events in Agrobacterium that helps in the transfer of T-DNA of T- Plasmid.
Attachment of Agrobacterium to plant cell
The Agrobacterium attached to plant cells through polysaccharides, particularly cellulose fibers produced by he bacterium.
Several chromosomal virulence (chv) genes responsible for the attachment of bacterial cells to the plant cells have been identified.
Production of virulence protein
As the signal induction occurs in the Agrobacterium cells attached to the plant cells a series of events take place that result in the production of virulence protein
To start with signal induction by phenolics stimulate vir A which in turn activates (by phosphorylation) vir G.
This induces expression of virulence genes of Ti plasmid to produce the corresponding virulence protein (D1, D2, E2, B etc.)
Certain sugars (glucose galactose, xylose) that induce virulence genes have been identified.
Production of T- DNA strand
The right and left borders of T-DNA are recognized by vir D1/vir D2 proteins.
These proteins are involved in the production single stranded T-DNA its protection and export to plant cells.
The ss T-DNA gets attached to vir D2
Transfer of T-DNA out of Agrobacterium
The ss T-DNA –Vir D2 Complex in association with vir G is exported from the bacterial cell. Vir B products from the transport apparatus.
Transfer of T-DNA into plant cells and integration
The T-DNA vir D2 complex crosses the plant plasma membrane.
In the plant cells TDNA gets covered with vir E2.
This covering protects the T-DNA from degradation by nucleases.
Vir D2 and Vir E2 interact with a variety of plant protein complex enters the nucleus through nuclear pore complex within the nucleus the T-DNA gets integrated into the plant chromosome through a process referred to illegitimate recombination.
This difference from the homologous recombination as it does not depend on the sequence similarity