Biology Now, 2e

176 ■ CHAPTER 10 How Genes Work

GENETICS

contrast, Medicago produced its vaccine, ready

for testing, in just 19 days.

To make a flu vaccine in plants, Vézina and his

team use genetic engineering in much the same

way that it was used to create a gene therapy

for Wiskott-Aldrich syndrome, as described in

Chapter 8. They identify and synthesize a single

viral gene that codes for hemagglutinin, a protein

found on the surface of flu viruses. To make

large quantities of that viral protein, the scien-

tists at Medicago first insert the hemagglutinin

gene into small, rod-shaped bacteria called

“agrobacteria,” which infect plants. Loaded with

the hemagglutinin gene, these agrobacteria

are then exposed to the tobacco plants: a

robotic arm lifts a tray containing 5-week-old

tobacco plants secured to the surface, flips

the tray upside down, and dips the plants into

a liquid solution swimming with the bacteria.

Once the plants are immersed in the liquid, the

technicians turn on a vacuum, sucking air out of

the leaves and pulling bacteria into them—like

dipping a sponge into water, squeezing it, and

then releasing it to soak up the liquid.

When the plants are returned to the green-

house, their leaves are floppy and almost trans-

lucent, like wet tissue paper. Now things are

cooking. Once the bacteria are inside the leaves,

the bacterial cells release the viral hemag-

glutinin gene into the plant cells, where it is

transported into plant cell nuclei to begin the

process of gene expression: making a protein

from DNA via the two steps of transcription

and translation.

“When you get the Agrobacterium solution

into the leaf, it will invade the cells and there

will be a burst of viral gene expression in the

plant cell,” said Vézina. “The plant takes over

and uses its machinery to produce the protein”

(Figure 10.5).

Two-Step Dance, Transcription: DNA to RNA

The first step in gene expression—in this case,

for a flu gene in a plant cell—is transcrip-

tion, the synthesis of RNA based on a DNA

template. In the nucleus, an enzyme called

By 2005, Medicago had begun to receive

calls asking about its product and when

it would begin clinical trials, the first step toward

getting a drug approved by the U.S. Food and

Drug Administration (FDA). “I was surprised.

Even the FDA was asking, ‘When are we going

to see your vaccine?’” recalls Vézina. “They were

keen on technologies like this because they know

how much vaccines cost, and they’re interested

in anything that can decrease that cost.”

One of the first vaccines that Medicago

produced was a vaccine for influenza virus H1N1,

or swine flu, the most common cause of the flu

in 2009 (Figure 10.4). In the previous H1N1

pandemic, it had taken months for vaccines

grown in chicken eggs to reach the market. By

Figure 10.4

Swine flu

In 2009, people around the world donned masks as a precaution against

influenza virus H1N1, nicknamed “swine flu” because it contained DNA from

bird, swine, and human flu viruses. The virus caused a pandemic, killing an

estimated 284,500 people.

Plant researcher Louis-Philippe Vézina cofounded

Medicago in 1997 and served as the company’s

chief scientific officer until 2014, overseeing all

scientific research and development.

LOUIS-PHILIPPE VÉZINA