Professor Rick Helm (right)
and technician Gael Cockrell
(center), both with the
University of Arkansas, perform
an allergy test on the skin
of an anesthetized, soybean-
sensitive pig. ARS plant
molecular biologist Eliot
Herman observes. The allergy
test is similar to that used
The team resorted to biotechnology after analysis of the soybean genome
revealed the P34 gene in domestic cultivars and in their wild cousins.
"The simplest approach would be to find a soybean without the protein,
but we found that all the domestic varieties and wild soybeans had it,"
says Herman, who recently transferred from Beltsville to the Donald
Danforth Plant Science Center in St. Louis, Missouri, but is assigned
to ARS' Plant Genetics Research Unit, Columbia, Missouri.
More Than Just a Sneeze
Soybeans are considered one of the "big eight" food allergen
sources. The others are eggs, milk, peanuts, wheat, fish, shellfish,
and tree nuts. And while P34's exact function still isn't known, the
researchers do know it belongs to a class of proteins called cysteine
proteases. It causes 65 percent or more of allergic reactions in soy-sensitive
individuals and does so by binding with IgE antibodies circulating in
A severe but rare reaction to soybeans is anaphylactic shock, in which
a sensitized person's airways rapidly constrict. Usually, though, the
legume causes nonfatal reactions, including hives, itching, and diarrhea.
"The only cure is avoidance of the food product. The difficulty
with this is the number of products derived from peanuts, soybeans,
and other legumes," notes Helm, an immunologist specializing in
food allergens at the Arkansas Children's Hospital Research Institute.
Follow the Biotech Road
Although scientists appear to have shut off the gene for making P34,
farmers aren't likely to see the knockout soybeans commercialized just
yet. More tests are needed to prove they're indeed hypoallergenic, or
less allergy causing. So far, though, the researchers are encouraged
by early results from human blood serum tests in which antibodies that
normally bind to P34 couldn't detect the allergen in knockout beans.
The hypoallergenic beans will also have to pass muster on an agronomic
checklist that includes seed production, yield, pest resistance, oil
and protein composition, and other criteria important to soy farmers
To expedite research that could eventually yield a new commercial cultivar,
Pioneer Hi-Bred International is propagating the researchers' most promising
knockout strain on field plots in Hawaii. The tropical climate there
allows for two crops per season versus one on the U.S. mainland.
The knockout strain, derived from the soybean cultivar Jack, got its
start from a clump of embryonic plant cells called a callus. The scientists
cultured the material in the lab specifically for the purpose of knocking
out the P34 gene. To do this, they used a biotech method called gene-silencing.
Once they knew for sure they had silenced P34 in the callus, they regenerated
the cells into whole plants and propagated them further for their seed.
After obtaining a uniform plant population by selecting for three generations,
they checked the knockout beans' growth, development, and P34 activity
against those of an unaltered control group.
"The yield looks perfectly normal. The plants develop and grow
at a normal rate. The seeds set at a normal rate, and they all seem
to have the same kinds of protein, oil, and other good stuff in them,"
Herman reports. "It looks like silencing P34 doesn't hurt the plant's
Additionally, no new proteins emerged to take P34's place as a human
allergen. "We assayed the transgenic plants with antisera from
people who were allergic to soybeans. We wanted to see whether taking
one allergen out caused any new proteins to become allergenic. The answer
is no," Herman says.
Besides making agronomic assessments, the researchers will use seed
harvested from the Hawaiian bean plots to begin trials with piglets,
which require lots of feed as they grow and develop. Helm will lead
the studies at Little Rock using part of a $784,000 grant that he, Herman,
Glenn Furuta, and Susan Hefle were awarded by USDA's Initiative for
Future Agriculture and Food Systems. They were recognized for their
development of an animal model to predict the allergenicity of genetically
modified food. Furuta is at Children's Hospital/Harvard Medical School.
Hefle is with the University of Nebraska.
Their study will include skin-prick allergenicity tests and feeding
trials using newborn piglets. "We'll use unaltered soybeans versus
the knockout soybeans to see what allergic reactions occur in the animals,"
Helm says. Like human babies, he notes, piglets eventually outgrow their
sensitivity to soybean allergens. But until that time, an affected piglet
can experience vomiting, diarrhea, dehydration, and skin rashes. "Because
this seems to be a food allergy problem, it should be manageable by
getting rid of whatever the pigs are allergic to," adds Herman.
Information from the pig studies and others could serve as the springboard
for clinical trials with humans.
"We're doing human testing only in the in vitro sense," says
Herman. "We use human blood serum to test for P34 in the laboratory."
But doing clinical tests with human subjects is a responsibility that
will ultimately rest on the shoulders of whoever decides to commercialize
the knockout beans as a hypoallergenic variety, he adds.
Miracle Crop Market
The potential effect such beans could have on the industry and on consumers
may be far reaching, not so much because of the number of soy-sensitive
people there are, but because of the multitude of products derived from
the crop, which generated $12 billion in 2000 U.S. farm sales. Some
products that could potentially benefit from hypoallergenic soybeans
include baby formulas, soy milk, flour, cereals, grits, and pet food.
"You're never going to make a completely allergy-free soybean
plant because you're not going to be able to eliminate all the proteins
in it," says Helm. Rather, "we're looking to make a safer
product." Many soy-sensitive consumers are also allergic to other
foods, particularly those among the big eight. Singling out soy's major
allergen could shorten the list of products they need to avoid.By
Agricultural Research Service Information Staff.
This research is part of Plant Biological and Molecular Processes,
an ARS National Program (#302) described on the World Wide Web at http://www.nps.ars.usda.gov.
To reach scientists mentioned in this article, contact Jan
Suszkiw, USDA-ARS Information
Staff, 5601 Sunnyside Ave., Beltsville, MD 20705; phone (301) 504-1630,
fax (301) 504-1641.