Engineering a Better Soybean
by Randy Weckman
Gene splicing.
 Does that phrase conjure up an image requiring the scientist's steady hand, a tiny knife, and a microscope? If so, you're mistaken about biotechnology. But if instead you think of Shakespeare's scene in MacBeth set on the heath, with three “ladies” stirring a bubbling cauldron, you're probably on the right track.
Although biotechnology employs cutting-edge science – in fact it is science evolving at breakneck speed – there are striking similarities to the pot of “bubble, bubble, toil and trouble.” Instead of a concoction of eye of newt and toe of frog, biotechnologists use gall of plant, sugars, gelatin, amino acids, and genes from whatever. And while the scientists are not exactly chanting over their cauldron, they do use loud sounds – not really Hip Hop, but close – to wound plant tissue enough so that gall of plant can work its magic with the genes from wherever, maybe even a frog.
As Good As It Is Just Isn't Good Enough
Mother Nature did a pretty good job with soybeans, but a team of researchers at the University of Kentucky College of Agriculture is making them even better— resistant to pests, more healthful, tastier, and more versatile.
The soybean plant, first cultivated by the Chinese in ancient times and introduced into the U.S. in the 1940s, has been a major human and livestock feedstuff, carrying in its beans a very high level of protein as well as oil that has a wide variety of uses.
But even as good as the soybean is the team believes it can be even better both for farmers and consumers. For farmers, the team is working to make a more productive, disease- and insect-resistant plant. For consumers, the team is working toward making a soybean whose oil is more flavorful and healthful.
The team's work has been by necessity both basic and applied in nature. Because of the nascent quality of biotechnology and because of the mysteries of the soybean plant itself and of the diseases and insects that can cause serious losses to soybeans, the team has had to investigate the basic biology of the plant as well as the life cycles of diseases and insects at their minimalist levels.
Glenn Collins
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The team – made up of Glenn Collins, an agronomist who specializes in cellular biology, Said Ghabrial, plant virologist, David Hildebrand, plant biochemist, and Todd Pfeiffer, a plant breeder – works to improve the soybean as a joint enterprise. They collaborate at strategic times to brainstorm on an attack plan. They also work independently on various facets of the project: Collins in putting selected genes into the plant tissue; Ghabrial in identifying and characterizing the economically important viruses infecting soybeans; Hildebrand on the biochemical aspects; and Pfeiffer on evaluating and developing the genetically engineered varieties into seed stock for producers to use. |
Hit 'Em With All You've Got
The bridge to the team members' independent work is Glenn Collins' laboratory.
“We use tissue culture and transformation systems to introduce genes into the soybean plant,” Collins said.
Tissue culture refers to the growth or maintenance of plant cells, organs, or tissues in a culture dish or flask. The goal is to genetically engineer the plant cell's genetic material and then grow the cells into plants that are able to reproduce seed that carries the new genes.
Collins uses a variety of techniques to insert foreign genetic material into the soybean cells, including gene guns and a bacterium called the crown gall bacterium. Gene guns bombard plant cells with such force that micro-projectiles carrying the genes penetrate the cell wall and membranes. Alternatively, sound waves – sonication – cause microscopic wounds in the plant tissue. The wounded regions in plant tissue become portals for entry of soil bacteria (Agrobacterium) that in the non-engineered form cause crown gall in plants. The Agrobacterium transports new genetic material, as well as its own, into the soybean tissue.
“What makes Agrobacterium unique and useful to researchers is its ability to transfer a tiny bit of its own genetic material – its DNA – into other plants. Because of this property, we are able to snip out the part of its genetic material that causes tumors (galls) in plants, and replace it with useful genes of choice,” he said.
In addition to the gene of choice, Collins also adds what are called selectable marker genes and reporter genes into the crown gall DNA. Selectable marker genes allow the cells that have the new genetic material inserted into them to tolerate an otherwise lethal exposure to an antibiotic or herbicide that is used to kill non-transformed cells. The reporter genes “glow” |
Said Ghabrial
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under black lights when the new genetic material is incorporated into the plant cells, reporting to the scientists that the first phase has been accomplished with the new, useful gene in the cells. At that point, if everything goes as planned (and it often doesn't), only cells with the new genetic material are left and Collins' attention turns to growing them into plants.
“Engineering new genes from diverse sources into the soybean plant's chromosomes is somewhat of a hit-or-miss, random process. Therefore, we have to generate many separate insertion events in order to identify those which give the desired new trait.” The next step, equally fraught with the potential for failure, is to grow the cells into plants capable of reproducing themselves through seed.
Master Chef
David Hildebrand |
To grow the cells into soybean plants requires Collins to become a cook of sorts. He must modify the soup the cells live in so that they will replicate into callus, an undifferentiated mass of cells, and then proceed through organogenesis, the process of forming the roots and shoots and other plant organs necessary for the plant cells to become a functioning plant.
“It's something like making bread. We have to add sugars, amino acids, minerals, and vitamins to nourish the plant cells. And we have to keep temperature, light, and pH at the just right levels to keep the plant cells growing,” he said. |
At a critical point, Collins adds plant hormones to coax the cells to change from calli into embryos, shoots, and roots on their way to becoming plants.
And even if the transfer goes well enough and the researchers are able to grow plants with the new genetic material inside each cell, there's no guarantee that the new genetic material will express itself as planned.
“It's still pretty much a hit-or-miss proposition. But the payoff is huge when the hit comes through,” Collins said.
Eureka ! Success!
Nonetheless, the team has been successful in getting three transgenic lines of soybeans with some limited resistance to bean pod mottle virus.
Said Ghabrial, the plant pathologist of the team, isolated several viral genes believed to confer resistance to bean pod mottle virus and soybean mosaic virus. Molecular clones of these genes were made available to Collins' lab to insert into soybean cells.
“We inserted the coat protein gene of bean pod mottle virus into the soybean genome so that the soybean cells would make the viral coat protein. When the virus infects the plant, the resident coat protein interferes with virus infection and replication,” Ghabrial said.
Todd Pfeiffer, another research team member, is producing offspring and evaluating them for resistance to the virus. In the meantime, the team continues to work toward new lines with resistance.
“We hope the engineered plants will have enough resistance in field tests. If not, we'll try again,” Pfeiffer said.
In another project, David Hildebrand, the plant biochemist on the team, is studying the metabolic pathways of fatty acids to discover the link between saturated and polyunsaturated to monounsaturated fats.
“We're putting genes into soybean that will convert saturated to monounsaturated fatty acids in developing soybean seeds,” Hildebrand said. |
Todd Pfeiffer
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"We want to make an oil that's the most healthful plant oil known. To do that, we're getting from any source we can genes that encode for enzymes that desaturate fat to make it more healthful for consumers,” he said.
The team also is taking genetic material from flax and putting it in soybeans, with the goal of increasing the levels of omega-3 fatty acid, a polyunsaturated fatty acid which research shows to be important in helping consumers decrease coronary heart disease, and perhaps the occurrence of some types of cancer.
“It may take us four or five years, but I'm confident we'll develop a soybean that's as high in omega-3 fatty acid as linseed oil from flax,” Hildebrand said.
Not only would achieving a high level of omega-3 fatty acid level in soybeans benefit the consumers of soybean oil, Hildebrand believes that feeding it to laying hens would help poultry producers increase the levels of omega-3 fatty acids in eggs, making them also more healthful for consumers.
In collaboration with researchers at Ohio State University and University of Georgia , the UK team has an impressive list of successes that includes: developing five efficient tissue culture systems; introducing five genes in soybeans; and developing two methods, for which patents have been applied, to introduce genes into soybeans.
Hildebrand summed up the team's enthusiasm: “More and more in genetic engineering we'll be doing what chemists do in factories – getting the plant to do the work for us. It's exciting to consider what we can do for nutrition with genetic engineering; but do it better and more exactly with no unhealthy by-products.”
Soybeans are Important to a Healthful Diet
by Ellen Brightwell
“People eating soybeans or soy foods receive high-quality protein. Soybeans contain high levels of important nutrients such as calcium, iron and several B-vitamins as well as fiber,” said Sandra Bastin, Extension food and nutrition specialist.
Scientists have also identified compounds in soybeans that apparently reduce the risk of some chronic diseases and help control some potentially serious health problems.
“People who eat soy foods regularly have lower rates of several types of cancer,” Bastin said, “Eating soy foods regularly helps lower cholesterol levels, reduces the risk for heart disease, helps control diabetes and kidney disease, and possibly decreases the threat of osteoporosis.”
In addition to dried or fresh green soybeans, consumers can choose from a variety of soy foods. These include:
- Soy milk , a rich, creamy milk made by pressing the liquid from ground soybeans. It is lactose- and casein-free and available in many flavors.
- Tofu , a cheese-like food made by curdling fresh soy milk. Tofu often is called “bean curd.”
- Soy flour , made from roasted soybeans ground into a flour.
- Textured soy protein , made from soy flour with the fat removed. TSP has a texture similar to ground beef when moisture is added back into it.
- Soy grits , made from toasted, cracked soybeans.
- Tempeh , made by controlled fermentation of whole soybeans. It has a mushroom-like flavor.
- Miso , a salty, fermented condiment made of ground soybeans.
- Soy meat analogs mimic the taste, texture and appearance of meat.
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