Question: Passage $\mathrm{V}$
For many years, researchers have been interested in developing edible vaccines that would provide protection against various bacterial and viral diseases. An edible vaccine is a genetically modified organism (GMO) that is created when genes from the bacteria or virus being vaccinated against are inserted into plant cells. As the plants grow, they produce proteins from the bacteria or virus that the researchers are attempting to vaccinate against. When a person eats the plant, the viral or bacteria proteins serve as antigens, which initiates a primary immune response.
Some of the plants that are of interest in edible vaccine development are bananas, potatoes, tomatoes, corn, rice, tobacco, and soybeans. While early research focused on growing crops that produced edible products such as bananas, the most recent research is focused on extracting material from the leaves and seeds of the plants, dehydrating it, and putting it into capsules that can be swallowed. This allows for a more predictable dosage of the vaccine and eliminates concerns that the crops containing the vaccine would be accidentally eaten by individuals who are not in need of the vaccine. The term edible vaccine has now been replaced with the term plantderived oral vaccine.
The development of plant-derived oral vaccines solves many problems associated with injectable vaccines. Because plant-derived oral vaccines are grown in crops, there is no problem with storage or refrigeration that is required of most traditional vaccines. These plant-derived vaccines also require no special training to administer. Additionally, when a vaccine is taken orally, it provides mucosal immunity due to the production of IgA antibodies by the immune system-in addition to systemic immunity. Since 90 percent of diseases enter the body through a mucus membrane, a vaccine that coerces mucosal immunity is of great benefit in the prevention of many diseases.
In order to engineer a plant-derived oral vaccine, genes from the microbe to be vaccinated against must be placed into the plant genome. Which of the following choices would be the most reasonable way to achieve this goal?

Options:
A. Perform polymerase chain reaction (PCR) to amplify copies of the bacterial or viral genes and then insert the copies into the plant cells by transduction.
B. Insert the bacterial or viral genes of interest into a plasmid, which can serve as a vector to transfer the gene to the plant cell.
C. Clone the genes into a bacterial cell and allow it to conjugate with a plant cell.
D. Use DNA hybridization to allow the genes of interest from the bacterial or viral genome to hybridize with the plant DNA.
Answer: While polymerase chain reaction (PCR) is used to amplify copies of target DNA, it would not help to get the viral or bacterial genes of interest into plant cells. This eliminates choice A. Choice $C$ suggests that the genes could be cloned into a bacterial cell and transferred to a plant cell by conjugation. Conjugation is unique to certain species of bacteria and occasionally is seen in fungi, but it does not happen in plants. So choice $C$ is eliminated. Choice D suggests that the genes of interest should be hybridized to the DNA of the plant. Since hybridization occurs between complementary base pairs, this would suggest that the DNA sequence of the gene of interest and the plant would have to be the same, which is not the case. This leaves choice B as the best option. Bacterial or viral genes can be spliced into plasmids. The plasmids serve as vectors to deliver the gene of interest to a variety of cell types, including plants. The correct answer is B.