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Genetically Modified World: Part I

Performance-Enhanced Plants

Corn is one of many crops that has been genetically modified to be pest-resistant or herbicide-resistant. It has become so successful that in the U.S. about 60% of corn grown is GM corn.

Advancing technologies are constantly changing every aspect of modern life, from how we treat our colds to helping us feel more energetic. Over the past two decades, this has extended to giving us the option of growing and purchasing foods that have been genetically modified (GM). As with all major advancements, GM crops have been met with resistance, although they offer a more efficient means of generating nutrient-rich produce and saving thousands of lives.

While many opponents of GM crops argue that they are “unnatural,” this certainly isn’t a new or unnatural human approach; we’ve been molding the plants around us to make them more useful for our nutritional needs since prehistoric times, or for around 10,000 years. During this time, people have been selecting for certain desirable traits in plants, such as bigger fruits or pest tolerance, controlling what the generations of crops to come would look like.

In the early 1900s, the agriculture business completely changed with the advent of mass-produced farming machinery, pesticides, herbicides (to kill weeds), fertilizers, and the creation of more vigorous, higher-yielding “hybrid” plants. While this so-called “Green Revolution” created crops with unprecedented yields, it was met with trepidation by the public, just as the GM agricultural revolution that began in the 1990s is being met today.

The number of GM crops around the world has skyrocketed since the first creations in the early 1990s; in 1996, they took up about 6,500 square miles, but by 2009 they covered nearly 520,000 square miles, spread across 25 countries, 16 of which are developing. While the industry had a very successful start in the U.S., it slowed down globally as it encountered several hurdles, from showing that the industry is safe for people and the environment, to settling intellectual property disputes raised by the companies that made GM crops, to gaining public acceptance. Fear of “Franken-foods” has driven many policies in the world concerning GM crops, and is why they must be labeled on shelves in countries in the European Union and elsewhere. But are these fears justified?

Genetically modified plants (also generically called genetically modified organisms, or GMOs) are plants that have had genes from other plants or organisms inserted into them. These “foreign” genes can make their new plant hosts have a range of desirable traits that make farming much more efficient, such as requiring less water, using less fertilizer, and/or making do with poorer soil. Two of the most widely used traits in GM crops are toxicity to insects, and resistance to herbicides. So it’s no surprise that GM crops have been repeatedly shown to outperform “normal” crops. But the researchers haven’t stopped there; other GM crops have been designed to produce high amounts of vitamins and potentially virus vaccines!

The FLAVR SAVR Tomato Sets the Stage: The first GM crop found its way to grocery store shelves in 1994. It was a tomato genetically modified to stay hard even when ripe. Why would this be useful? For a long time, commercially sold tomatoes have been harvested when still firm and green, and then treated with ethylene gas to ripen them. This is so they’re not transported soft and damaged. So much for being “natural.”

How did the GM tomato “FLAVR SAVR,” as it was called, keep its youthful firmness while still becoming red and ripe? It comes down to an enzyme called polygalacturonase (“PG” for short). Made by ripening tomatoes, PG breaks down the structural supports in plant cell walls (specifically pectin, a substance whose structural stability is what makes jellies and jams firm). Researchers thought that if they could just stop the unripe, green tomatoes from producing PG, they could prevent them from becoming soft. And they were right. To achieve this feat, scientists used antisense RNA technology; they knew the RNA sequence that the tomato used to create PG, and so they introduced an interfering RNA sequence (an antisense one) that bonded to the native sequence, preventing it from functioning.

But how did this antisense RNA find its way into the tomato plant? With a little help from nature. The researchers used a species of bacteria that normally attacks a variety of plants (specifically the bacteria Agrobacterium tumefaciens) but replaced part of the bacteria’s infectious genome with the desired antisense sequence. When the tomatoes were exposed to this modified bacteria, the sequence found its way to the plant’s genome. While “FLAVR SAVR” only lasted a few years on the market due to its not being profitable, this same strategy (and same bacteria) has been used again and again to create GM crops.

Soybeans: Herbicide Resistors: The second GM crops to arrive in supermarkets were GM soybeans. They were much more successful than the tomatoes, and today, GM soybeans are the most commonly used GM crop in the world. In 2005 in the U.S., nearly 90 percent of the soybeans grown were GM soybeans.

And how exactly have these crops been modified? Many have been made resistant to an herbicide called glyphosate (for you chemists out there, it’s [N-(phosphonomethyl)glycine]), which is more commonly known as Monsanto’s weed-killer “Roundup.” Most commercially sold herbicides are nonselective plant-killers, functioning by disrupting the plant’s ability to carry out photosynthesis (vital to its survival). Some herbicides, like glyphosate, go so far as to destroy the plant’s ability to make amino acids. So you can imagine how making a crop resistant to a toxic herbicide like glyphosate can make things more convenient; spray the entire field with herbicides and the only thing left standing are the soybeans, or “Roundup Ready Soybeans.”

But how do you make a plant resistant to glyphosate? Bacteria again come to the rescue. A mutant bacteria strain (Salmonella typhimurium) was found to resist the killing power of glyphosate, and researchers were able to isolate the gene responsible for this resistance and put it into the genome of soybeans, as well as several other crops. (Specifically, the gene encodes for a mutant version of the protein normally targeted by glyphosate; this mutant functions, but isn’t recognized by the glyphosate.)

So what are the problems with spraying a field with general plant-killing herbicides? Possible herbicide-resistant weeds, for one. Just as bacteria can become resistant to antibiotics over time, plants can also have mutations which may cause a few herbicide-resistant weeds to become a “super-weed” epidemic. There is also some evidence that the glyphosate-resistant genes may jump from GM crops to weeds and other plants, but weeds don’t need GM crops to become herbicide-resistant. While there’s some question over whether using GM soybeans is actually more profitable, it’s thought that the general simplicity of using Roundup Ready Soybeans has made many farming converts.

Bt Corn: Next to soybeans, corn is the most commonly used GM crop worldwide. In 2005 in the U.S., about 60 percent of corn grown was GM. While some GM corn has been made to be herbicide-resistant, like GM soybeans, many have also been made to be pest-resistant or more nutritional. The manner in which GM corn has become pest-resistant is by borrowing a gene from, you guessed it, bacteria, specifically Bacillus thuringiensis, commonly known as “Bt.” In the wild, the bacteria creates a small toxic protein, which is released when Bt is eaten by an insect.

In the digestive track of the insect, the digested protein binds to the cells lining the gut and ruptures them, killing the insect. The toxin works well against many different kinds of insects, including the orders Lepidoptera (which includes the European corn borer, the cotton bollworm, the tomato fruitworm, and other moths and butterflies), Diptera (flies and mosquitos), and Coleoptera (beetles, including corn rootworms).

Researchers isolated the gene from Bt that creates this toxic protein and put it into the genomes of many GM crops, including corn, tobacco, cotton, and tomatoes. While this successfully kills many very harmful crop pests, it has been criticized for also killing nontargeted insects and beneficial insects. However, proponents of Bt GM crops argue that using these crops is more environmentally sound than spraying massive amounts of pesticides.

Cotton: A Success in Developing Countries: Cotton is the next most widely used GM crop globally after Bt corn. After being approved early on in the U.S., in 1995, it quickly made its way around the world. As of last year, it covered nearly 62,000 square miles of fields (comprising 45 percent of all cotton acreage). It is mostly grown in India, China, and the U.S., and has been touted by some as a standard-bearer for the success of GM crops in reducing poverty in developing countries. Like Bt corn, the Bt cotton also has the Bt insecticide gene, allowing farmers to spend much less money on large amounts of expensive pesticides. Bt cotton also has significantly higher yields (about 30 to 40 percent) than normal cotton, resulting in higher incomes than with normal cotton, which has helped to reduce poverty levels in developing countries that grow it, with particular success in India.

“Golden Rice”: While the much-publicized “Golden Rice” is not available on grocery shelves yet, it is quite justified in receiving the attention it has. About 140 million people suffer from vitamin A deficiency, a serious malnutrition problem in poverty conditions, where diets consist of low-nutritional staple foods. Every year, nearly 3 million children die from vitamin A deficiency. This is why researchers created Golden Rice. Golden Rice is a GM rice that contains beta-carotene, the same chemical that gives carrots their orange color and which is a precursor our bodies can turn into vitamin A. (And it gives Golden Rice its distinctive yellow hue.) To create Golden Rice, researchers basically borrowed multiple enzymes necessary to make beta-carotene, from daffodils and a soil bacterium. Although Golden Rice is not sold commercially yet (but may be as early as 2012), it is estimated that it could save the lives of 40,000 children in India alone, every year.

What Does the GM Future Hold?: The future of GM crops is exciting, if tumultuous. As just one example, already some GM bananas are being developed that may vaccinate against cholera or hepatitis B. However, GM crops still have many hurdles in front of them, which they must overcome to be widely grown and accepted. These range from biotechnology companies with intellectual property rights, to concerns about herbicide-resistant plants’ possible effects on the environment, and consumers’ health. To date, there are many conflicting results on whether GM crops cause health problems; it is still unresolved. The reality is that GM crops are here and it is our responsibility to make sure they are being carefully evaluated and used, while also ensuring that such hurdles do not unnecessarily stall them from saving thousands of lives.

Check “Biology Bytes” next week for Part II of this series on the “Genetically Modified World,” where we will explore organisms that have been genetically engineered to be quite different from their normal brethren.

For more on genetically modified crops see Dominic W. S. Wong’s The ABCs of Gene Cloning, Felicia Wu and William P. Butz’s The Future of Genetically Modified Crops, the National Research Council’s workshop summary on “Genetically Engineered Organisms, Wildlife, and Habitat,” C. Neal Stewart, Jr.’s Genetically Modified Planet, Wikipedia’s article on “Genetically Modified Crops,” or Matin Qaim’s Benefits of genetically modified crops for the poor: household income, nutrition, and health

Biology Bytes author Teisha Rowland is a science writer, blogger at All Things Stem Cell, and graduate student in molecular, cellular, and developmental biology at UCSB, where she studies stem cells. Send any ideas for future columns to her at science@independent.com.


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