Final answer:
The Ti plasmid of Agrobacterium tumefaciens causes tumor formation in infected plant tissues, which researchers have utilized to genetically modify plants by inserting desired DNA fragments.
Step-by-step explanation:
The Ti plasmid of Agrobacterium tumefaciens contains genes that cause the formation of a plant tumor, or a gall, in infected tissues. This plasmid, known specifically as the tumor-inducing (Ti) plasmid, is part of the bacterium's genetic equipment to transfer its DNA to dicotyledonous plants, leading to tumor formation. This process is a result of the integration of DNA from the Ti plasmid into the plant cell's genome. Researchers have learned to manipulate the Ti plasmids to remove the tumor-causing genes, allowing them to utilize these plasmids to introduce desired DNA fragments into the plant genome, hence facilitating the creation of genetically modified plants. This is done to enhance certain traits in plants, such as resistance to diseases or pests, and can have a significant impact on agricultural practices.