Agrobacterium is a soil bacterium that causes crown gall disease in plants like tomato and sunflower by transferring tumor-inducing plasmid (Ti plasmid) DNA into the plant cell. The Ti plasmid contains a segment called T-DNA that gets integrated into the plant genome. For gene transfer to occur, the plant cells must produce phenolic compounds to activate virulence genes in Agrobacterium, allowing the T-DNA to be transferred and integrated. The transformed plant cells can then be regenerated into whole plants.