Molecular Genetics

Other Pages

Agrobacteria are biological vectors for introduction of genes into plants.

• Agrobacteria attach to plant cell surfaces at wound sites.
• The plant releases wound signal compounds, such as acetosyringone.
• The signal binds to virA on the Agrobacterium membrane.
• VirA with signal bound activates virG.
• Activated virG turns on other vir genes, including vir D and E.
• vir D cuts at a specific site in the Ti plasmid (tumor-inducing), the left border. The left border and a similar sequence, the right border, delineate the T-DNA, the DNA that will be transferred from the bacterium to the plant cell
• Single stranded T-DNA is bound by vir E product as the DNA unwinds from the vir D cut site. Binding and unwinding stop at the right border.
• The T-DNA is transferred to the plant cell, where it integrates in nuclear DNA.
• T-DNA codes for proteins that produce hormones and opines. Hormones encourage growth of the transformed plant tissue. Opines feed bacteria a carbon and nitrogen source.

Implications and Further Information:

• A symbiotic relationship is set up in which the plant tissue supplies a carbon and nitrogen source to the bacterium and the bacterium has encouraged the growth of the plant tissue.
• Agrobacterium is a natural trans-kingdom genetic engineer.
• The transferred genes are not required for the transfer process. There is thus wide latitude in engineering the T-DNA region.