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New Mexico State University

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NMSU Genetic Research Could Mean More Nutritious Beans and Alfalfa

LAS CRUCES - In inch-long test tubes, scientists at New Mexico State University cut and splice strands of genetic material that contain an unusual message for plants like alfalfa, beans and peanuts. This message reads: Make and store corn protein.

If received and understood by these legume plants, the messace could have far-reaching implications for making them more nutritionally balanced. Improved legumes could contain all of the protein necessary to keep humans, as well as agricultural livestock, healthy.

Scientists Suman Bagga and Champa Sengupta-Gopalan with NMSU's Plant Genetic Engineering Laboratory for Desert Adaptation recently reported a significant advance on this research front in the January issue of Plant Physiology. They found that adding a corn protein storage gene (called the 15kD zein gene) produced high levels of corn protein in tobacco. Tobacco is used as a model plant for research because it is hearty and grows fast.

PGEL researchers also found that the zein protein is stored in novel molecular bodies in leaf cells of the genetically modified plants. An electron microscope picture of these bodies taken by Hank Adams, a biologist with NMSU's Electron Microscopy Laboratory, was featured on the cover of Plant Physiology.

If this discovery holds up in other legumes, more nutritionally complete plants for animal and human consumption may someday make their way to the world's marketplace.

"Scientists have long talked theoretically about the concept of making crop plants more nutritious," said Gary Cunningham, associate dean and director of NMSU's Agricultural Experiment Station (AES). "This research is important because it is the first time we've shown that we can actually modify plants so they are more nutritionally complete."

If this genetic work could be used to boost the protein quality of other food staples, the implications for enhancing human nutrition increase.

"If we can use a similar technique to improve rice or any other staple food like wheat, barley or potatoes, it would have worldwide importance," Cunningham said. Two-thirds of the world's population relies on rice as a staple food source, according to the U.S. Rice Council.

When plant geneticists talk about improving plants, nutritional quality, the most important aspect they're after is protein, said John Kemp, PGEL director.

"Protein is one of the most important nutrients for growth and maintenance," said Ann Bock, an AES human nutrition scientist. "That's growth and maintenance in children and maintenance in adults." Proteins regulate and sustain key body functions like blood clotting, fluid balance, hormone and enzyme production, vision and cell repair.

To be nutritionally balanced, plants need to produce a full complement of proteins that contain amino acids, which are necessary for human and animal survival.

"No plant protein found in nature has the right balance of amino acids for high nutritional value," Kemp said. "What we're really after are the nine essential amino acids that we can't make ourselves. The other 11 our bodies can make."

Legumes like alfalfa and beans are high in the essential amino acid lysine and deficient in two important amino acids --methionine and cysteine. Methionine is one of the nine essential amino acids, while cysteine is considered semiessential because it can be derived from methionine when cysteine is in short supply.

Corn, however, is low in lysine and rich in both methionine and cysteine. By inserting the zein gene from corn into legumes, PGEL scientists are creating more nutritionally balanced plants containing all of the essential amino acids.

Nutritionists teach people to eat vegetables and grains that complement each other in proteins to make a balanced diet, Bock said.

For years, people in Hispanic and Native American cultures have put together vegetable combinations that work fairly well. The typical Mexican meal that includes rice, beans and a corn tortilla includes all the required amino acids.

"But if this research could someday lead to a pinto bean product that would be accepted by people, it could have a significant impact on those who have incomes truly at the poverty level" Bock said. "A bean with high-quality protein might be able to keep things going in the body until families could afford to buy other food items." Beans also are good sources of nutrients like soluble fiber and B vitamins, she added.

If the zein gene can be used to beef up protein in forage crops like alfalfa, the PGEL research would also have implications for animal nutrition.

New Mexico's largest cash crop is alfalfa, which supports the state's dairy industry that brings in cash receipts from milk and milk products exceeding $220 million annually.

"If we can improve the nutritional quality of alfalfa for cattle, it could take milk production less expensive in New Mexico," Cunningham said. "In other countries, this also could be very important, particularly where animal products are in short supply. This research could lead to decreased costs of animal products worldwide, because it would be cheaper and easier to feed animals with nutritionally-balanced forages."

Having enough methionine is especially important for cows, which are ruminant animals with four stomachs, said Mark Petersen, an AES animal nutritionist.

In the first stomach known as the rumen, microorganisms break down the fiber or cellulose from forage like alfalfa, releasing energy for the plants. The microbes need methionine to live and work efficiently.

"This research has potential since we already use alfalfa as part of our normal feeding management. Producers would just have to switch over to the genetically improved variety, if it was economical," Petersen said.

While commercial production of nutritionally-improved plants may still be years away, PGEL research has brought science one step closer. When the scientists realized they had found a body in the tobacco cells that had never been seen before, they were excited. "I was amazed. Seeing the electron microscope picture was a beautiful experience," Bagga said. "I knew it was something important."

Although it might sound like the scientists have cooked up a quick batch of high-tech vegetable soup, there's no easy recipe for the job of inserting genes from one plant into another.

Sengupta-Gopalan said. Less fertilizer means less cost and less chance of contaminating ground water supplies. "My research goal is to improve the nitrogen use in legumes and to someday transfer those characteristics into non-legume plants."