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tist Paul Berg carried out the first successful gene splicing
experiment. Shortly after, researchers Herbert W. Boyer and
Stanley N. Cohen transferred genetic material into a bacterium and demonstrated that the new genes were reproduced along with the organism’s native DNA. Since then,
scientists have used GE to render crops resistant to pests,
herbicides, and drought conditions, and to improve their
nutrient profiles. In addition, GE has led to innovations in
medicine, biofuels, and bioremediation.
Ho W genetIc engIneerIng Works
The two most common approaches to creating GE plants
involve the use of recombinant DnA technology and can
be broken down into two basic steps. First, researchers
identify and isolate a gene of interest, then they introduce
that gene into plant cells to create a transgenic, or GE plant.
In one method, researchers recruit the natural soil bacterium Agrobacterium tumefaciens and replace some of its
genes with those encoding the desired trait. The bacterium
is then allowed to infect a plant, during which it transfers its
DNA into the plant’s genome in a process biologists refer
to as transformation. The result is a new, genetically modified plant, also known as a transgenic crop.
Another approach involves attaching the DNA of interest
to the surfaces of gold or tungsten microparticles. Researchers then use an instrument known as a biolistic gene gun
to blast the particles into a plant’s cells. This method is
also known as microprojectile bombardment. Some of the
DNA will get inserted into the genome through a process
known as homologous recombination (Biocat. Agric. Biotech., 3:31-37, 2014).
These transformation methods have been described
as “brute force” methods owing to their high failure rates,
which require numerous attempts before a candidate for
a commercial product is identified. According to a recent
survey of agricultural biotechnology developers, more than
10,000 genes are evaluated on average for each commercial product ( http://tinyurl.com/PhillipsMcDougallStudy).
The evaluation includes bioinformatics assessments, which
involve the use of computers to compare genetic sequences,
and helps ensure the safety of GE crops by eliminating
sequences that are genetically similar, or homologous,
with known allergens and toxins. Bioinformatics can also
help predict whether the gene will have the desired function, according to a review article in the Journal of Agricultural and Food Chemistry by Laura S. Privalle and coworkers
Out of those 10,000 genes, roughly 500 are selected
for proof-of-concept experiments. Then, more than 1,000
transgenic organisms are further evaluated, as described
below. Finally, one or two of these organisms are chosen for
commercialization. Not surprisingly, the process of developing a single commercialized GE product comes with significant costs of both time and money, averaging about 13
years and $150 million. (See sidebar: “Interesting stats about
genetically engineered crops” on page 75.)
evAlUAtIng A ge croP cAnDIDAte
In order to select the most promising GE crop candidates from the hundreds of transgenic organisms created,
researchers perform numerous tests. Before a candidate can
proceed, it must demonstrate that the gene was inserted at
a location that does not disrupt essential cellular functions,
that the inserted gene is expressed at desirable levels, and
that the desired trait is present and passed on to progeny.
The GE plant must also be evaluated for how well it performs as a crop: Is the yield adequate, and is the desired
phenotype—the characteristic the plant was engineered
to have—observed? Simply having the correct genotype—
or genetic composition—does not guarantee the intended
characteristic will show up in the organism, since environmental and developmental conditions can play a role in
gene expression (J. Ag. Food Chem., 61:8260-8266, 2013).