These methods will be described briefly below. A bacteria with the name Agrobacterium Tumefasciens has the ability to induce a kind of benign tumor growth in the plant it infects. This it achieves by inserting some genes into the DNA of the plant. Then the recipient cells are exposed to the bacterium, so that they become infected by it. The bacterial DNA with the engineered gene is then inserted into the DNA of the recipient.
Viruses are pieces of DNA encapsulated within a protein shell.
Their DNA enters the cell at infection and goes to the cell nucleus. There the virus DNA forces the cell to make many thousands of copies of the virus. The viruses used for gene transfer are modified so that they will not induce virus copying in the cell. They will introduce the desired DNA into the DNA of the recipient in similar manner as the Bacterium tumefasciens. Along with it some virus genes also are inserted.