Which part of Agrobacterium is used to transfer genes to plants?

The Ti plasmid, or tumor-inducing plasmid, is a crucial part of Agrobacterium that is utilized for transferring genes into plant cells. This plasmid carries genes that can induce crown gall tumors in plants; however, scientists have cleverly modified it to deliver desirable genes into plant genomes without causing disease. When Agrobacterium infects a plant, the Ti plasmid can be incorporated into the plant's DNA, resulting in stable transformation.

In genetic engineering, researchers exploit the naturally occurring mechanism of Agrobacterium tumefaciens as a tool to introduce genes of interest into plants. By replacing the tumor-inducing genes on the Ti plasmid with genes that provide beneficial traits—such as herbicide resistance, pest resistance, or improved nutritional content—scientists can create genetically modified plants.

The other options listed do not serve this specific function: RNA plasmids and vector plasmids are not associated with the natural gene transfer mechanisms of Agrobacterium, and chloroplast DNA refers to the genetic material found in plant chloroplasts, which is distinct from the role of the Ti plasmid in transferring genes.