(right) next to King Edward which has not been genetically modified (left). Research field belonging to the
Swedish University of Agricultural Sciences in 2019. GM crops grown today, or under development, have been modified with various
traits. These traits include improved
shelf life,
disease resistance, stress resistance,
herbicide resistance,
pest resistance, production of useful goods such as biofuel or drugs, and ability to absorb toxins and for use in
bioremediation of pollution. Recently,
research and development has been targeted to
enhancement of crops that are locally important in
developing countries, such as insect-resistant
cowpea for Africa and insect-resistant
brinjal (eggplant).
Extended shelf life The first genetically modified crop approved for sale in the U.S. was the
FlavrSavr tomato, which had a longer shelf life. First sold in 1994, FlavrSavr tomato production ceased in 1997. It is no longer on the market. In November 2014, the USDA approved a
GM potato that prevents bruising. In February 2015,
Arctic Apples were approved by the USDA, becoming the first genetically modified apple approved for US sale.
Gene silencing was used to reduce the expression of
polyphenol oxidase (PPO), thus preventing enzymatic browning of the fruit after it has been sliced open. The trait was added to
Granny Smith and
Golden Delicious varieties. The FDA approved the apples in March 2015.
Improved photosynthesis Plants use
non-photochemical quenching to protect them from excessive amounts of sunlight. Plants can switch on the quenching mechanism almost instantaneously, but it takes much longer for it to switch off again. During the time that it is switched on, the amount of energy that is wasted increases. A genetic modification in three genes allows to correct this (in a trial with tobacco plants). As a result, yields were 14-20% higher, in terms of the weight of the dry leaves harvested. The plants had larger leaves, were taller and had more vigorous roots. Another improvement that can be made on the photosynthesis process (with
C3 pathway plants) is on
photorespiration. By inserting the C4 pathway into C3 plants, productivity may increase by as much as 50% for
cereal crops, such as rice.
Improved biosequestration capability The
Harnessing Plants Initiative focuses on creating GM plants that have increased root mass, root depth and suberin content.
Nitrogen fixation Plants such as
legumes obtain nitrogen through a
symbiotic relationship with
diazotrophic bacteria that
fix nitrogen from the air and transfer it to the soil in the form of
ammonia, where it is absorbed by the roots. Other crops, including
cereals important for human consumption such as
corn/maize,
wheat, and
rice, generally depend on
nitrogen fertilizers. The use of these fertilizers contributes to the
eutrophication of water bodies and to
climate change due to
nitrous oxide emissions. Without fertilizers, these plants grow less and produce fewer grains. Recent research has developed innovative strategies to supply nitrogen more sustainably, reducing dependence on synthetic fertilizers. Approaches include
genetically engineering non-legume crops to serve as more effective hosts for nitrogen-fixing microbes, transferring nitrogen-fixing genes (
nif genes) to soil bacteria to establish a symbiotic relationship with cereals similar to that of legumes, or, more challenging, directly introducing these genes into plants to enable them to fix their own nitrogen. Other strategies focus on enhancing crops’ nitrogen-use efficiency, allowing them to achieve optimal growth with reduced nitrogen inputs.
Improved nutritional value Edible oils Some GM soybeans offer improved oil profiles for processing. Soybeans have been genetically modified to improve the quality of
soybean oil. Soy oil has a
fatty acid profile that makes it susceptible to
oxidation, which makes it
rancid, which limits its usefulness in the food industry. Genetic modifications increased the amount of
oleic acid and
stearic acid and decreased the amount of
linolenic acid.
DuPont Pioneer has developed a soybean with a high content of
monounsaturated fatty acids (oleic acid) and a lower content of
polyunsaturated fatty acids (
linoleic and linolenic acids), with oleic acid levels above 80%, and began marketing it in 2010. In comparison,
Monsanto’s
MON 87705 soybean also exhibits elevated oleic acid levels and reduced polyunsaturated fatty acids, MON 87705 also has a reduction in
saturated fatty acids, including
palmitic and
stearic acids, compared with conventional soybean oil.
Vitamin enrichment Golden Rice, developed by the
International Rice Research Institute (IRRI), provides increased amounts of
vitamin A. It was engineered with three genes capable of biosynthesizing
beta-carotene, a precursor of vitamin A, in the edible parts of the rice. The goal is to produce a
biofortified food for cultivation and consumption in regions with
vitamin A deficiency.
Toxin reduction A genetically modified
cassava under development offers lower
cyanogen glucosides and enhanced protein and other nutrients (called BioCassava). In November 2014, the USDA approved a potato that prevents bruising and produces less
acrylamide when fried.
Stress resistance Plants have been engineered to tolerate non-biological
stressors, such as
drought,
frost, and high
soil salinity. Drought tolerance in
genetically modified plants is achieved by inserting genes that regulate physiological and biochemical responses to water stress. A common example is the introduction of
transcription factors from the HD-Zip I family, originally isolated from drought-resistant plants such as
sunflowers. These regulatory genes act by increasing the expression of proteins involved in
antioxidant defense, maintaining cell integrity, and improving water use efficiency, allowing the plant to survive periods of water scarcity with less impact on growth and productivity. Another possible mechanism for drought resistance occurs through the modification of plant genes responsible for the mechanism known as
crassulacean acid metabolism (CAM), which allows plants to survive despite low water levels. This is promising for crops that require a lot of water, such as rice, wheat, soybeans, and poplar, to accelerate their adaptation to water-limited environments. Several salinity tolerance mechanisms have been identified in salt-tolerant crops. For example, rice, canola and tomato crops have been genetically modified to increase their tolerance to salt stress.
Herbicides Glyphosate The most prevalent GM trait is herbicide tolerance, where
glyphosate-tolerance is the most common.
Glyphosate (the active ingredient in Roundup and other herbicide products) kills plants by interfering with the
shikimate pathway in plants, which is essential for the synthesis of the
aromatic amino acids phenylalanine,
tyrosine, and
tryptophan. The shikimate pathway is not present in animals, which instead obtain aromatic amino acids from their diet. More specifically, glyphosate inhibits the enzyme
5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). This trait was developed because the herbicides used on grain and grass crops at the time were highly toxic and not effective against narrow-leaved weeds. Thus, developing crops that could withstand spraying with glyphosate would both reduce environmental and health risks, and give an agricultural edge to the farmer. Some micro-organisms have a version of EPSPS that is resistant to glyphosate inhibition. One of these was isolated from an
Agrobacterium strain CP4 (CP4 EPSPS) that was resistant to glyphosate. The CP4 EPSPS gene was engineered for plant
expression by
fusing the 5' end of the gene to a
chloroplast transit peptide derived from the
petunia EPSPS. This transit peptide was used because it had shown previously an ability to deliver bacterial EPSPS to the chloroplasts of other plants. This CP4 EPSPS gene was
cloned and
transfected into
soybeans. The
plasmid used to move the gene into soybeans was PV-GMGTO4. It contained three bacterial genes, two CP4 EPSPS genes, and a gene
encoding beta-glucuronidase (GUS) from
Escherichia coli as a marker. The DNA was injected into the soybeans using the
particle acceleration method. Soybean cultivar A54O3 was used for the
transformation.
Bromoxynil Tobacco plants have been engineered to be resistant to the herbicide
bromoxynil.
Glufosinate Crops have been commercialized that are resistant to the herbicide
glufosinate, as well. Crops engineered for resistance to multiple herbicides to allow farmers to use a mixed group of two, three, or four different chemicals are under development to combat growing herbicide resistance. The modification is achieved by inserting the
pat or
bar gene, responsible for the synthesis of the enzyme
phosphinothricin acetyltransferase (PAT), which converts
L-phosphinothricin (glufosinate) to non-toxic products by
acetylation of the
amino group, inactivating the active ingredient and thus conferring herbicide tolerance on the plant. The
bar and
pat genes were isolated from
Streptomyces hygroscopicus and
Streptomyces viridochromogenes in 1987 and 1988, respectively. Other methods for conferring resistance to glufosinate have been reported, but to date only the
pat or
bar genes have been used commercially in the development of crops resistant to this herbicide. Inserting a bacterial aryloxyalkanoate dioxygenase gene,
aad1 makes the corn resistant to 2,4-D. The USDA had approved maize and soybeans with the mutation in September 2014.
Dicamba Monsanto has requested approval for a stacked strain that is tolerant of both glyphosate and
dicamba. The request includes plans for avoiding
herbicide drift to other crops. Significant damage to other non-resistant crops occurred from dicamba formulations intended to reduce
volatilization drifting when sprayed on resistant soybeans in 2017. The newer dicamba formulation labels specify to not spray when average wind speeds are above to avoid particle drift, average wind speeds below to avoid
temperature inversions, and rain or high temperatures are in the next day forecast. However, these conditions typically only occur during June and July for a few hours at a time.
Pest resistance Insects Tobacco, corn, rice and some other crops have been engineered to express genes encoding for insecticidal proteins from
Bacillus thuringiensis (Bt). The introduction of Bt crops during the period between 1996 and 2005 has been estimated to have reduced the total volume of insecticide active ingredient use in the United States by over 100 thousand tons. This represents a 19.4% reduction in insecticide use. In the late 1990s, a
genetically modified potato that was resistant to the
Colorado potato beetle was withdrawn because major buyers rejected it, fearing consumer opposition. Papaya, potatoes, and squash have been engineered to resist viral pathogens such as
cucumber mosaic virus which, despite its name, infects a wide variety of plants. By 2010, 80% of Hawaiian papaya plants were genetically modified. Potatoes were engineered for resistance to
potato leaf roll virus and
Potato virus Y in 1998. Poor sales led to their market withdrawal after three years. Yellow squash that were resistant to at first two, then three viruses were developed, beginning in the 1990s. The viruses are watermelon, cucumber and zucchini/courgette yellow mosaic. Squash was the second GM crop to be approved by US regulators. The trait was later added to zucchini. Many strains of corn have been developed in recent years to combat the spread of
Maize dwarf mosaic virus, a costly virus that causes stunted growth which is carried in
Johnson grass and spread by aphid insect vectors. These strands are commercially available although the resistance is not standard among GM corn variants.
By-products Drugs In 2012, the FDA approved the first
plant-produced pharmaceutical, a treatment for
Gaucher's Disease. Tobacco plants have been modified to produce therapeutic antibodies.
Biofuel Algae is under development for use in
biofuels. The focus of Microalgae for mass production for biofuels modifying the algae to produce more lipid has become a focus yet will take years to see results due to the cost of this process to extract lipids. Researchers in Singapore were working on GM
jatropha for biofuel production.
Syngenta has USDA approval to market a maize trademarked Enogen that has been genetically modified to convert its starch to sugar for
ethanol. Some trees have been
genetically modified to either have less
lignin, or to express lignin with chemically labile bonds. Lignin is the critical limiting factor when using wood to make
bio-ethanol because lignin limits the accessibility of
cellulose microfibrils to
depolymerization by
enzymes. Besides with trees, the chemically labile lignin bonds are also very useful for cereal crops such as maize,
Materials Companies and labs are working on plants that can be used to make
bioplastics. Potatoes that produce industrially useful starches have been developed as well.
Oilseed can be modified to produce fatty acids for
detergents, substitute
fuels and
petrochemicals.
Non-pesticide pest management products Besides the modified oilcrop above,
Camelina sativa has also been modified to produce
Helicoverpa armigera pheromones and is in progress with a
Spodoptera frugiperda version. The
H. armigera pheromones have been tested and are effective.
Bioremediation Scientists at the University of York developed a weed (
Arabidopsis thaliana) that contains genes from bacteria that could clean
TNT and
RDX-explosive soil contaminants in 2011. 16 million hectares in the US (1.5% of the total surface) are estimated to be contaminated with TNT and RDX. However
A. thaliana was not tough enough for use on military test grounds. Modifications in 2016 included
switchgrass and
bentgrass. Genetically modified plants have been used for
bioremediation of contaminated soils.
Mercury,
selenium and organic pollutants such as
polychlorinated biphenyls (PCBs). Marine environments are especially vulnerable since pollution such as
oil spills are not containable. In addition to anthropogenic pollution, millions of tons of
petroleum annually enter the marine environment from natural seepages. Despite its toxicity, a considerable fraction of petroleum oil entering marine systems is eliminated by the hydrocarbon-degrading activities of microbial communities. Particularly successful is a recently discovered group of specialists, the so-called
hydrocarbonoclastic bacteria (HCCB) that may offer useful genes.
Asexual reproduction Crops such as
maize reproduce sexually each year. This randomizes which genes get propagated to the next generation, meaning that desirable traits can be lost. To maintain a high-quality crop, some farmers purchase seeds every year. Typically, the seed company maintains two
inbred varieties and crosses them into a
hybrid strain that is then sold. Related plants like
sorghum and gamma grass are able to perform
apomixis, a form of asexual reproduction that keeps the plant's DNA intact. This trait is apparently controlled by a single dominant gene, but traditional breeding has been unsuccessful in creating asexually-reproducing maize. Genetic engineering offers another route to this goal. Successful modification would allow farmers to replant harvested seeds that retain desirable traits, rather than relying on purchased seed.
Other Genetic modifications to some crops also exist, which make it easier to process the crop, i.e. by growing it in a more compact form. Crops such as tomatoes have been modified to be seedless. Tobacco has been modified to produce
chlorophyll c in addition to
a and
b, increasing growth rates. The transgene was discovered in
marine algae, which uses it to gain energy from the blue light that is able to penetrate seawater more effectively than longer wavelengths. ==Crops==