"In the transgenic approach,
we find a particular gene that controls the trait we're interested in, like
early ripening or prolonged shelf life," he says. "Then, using
molecular tools, we reengineer the gene, confirm it's what we want, and
introduce it into a plant so it becomes part of that plant's genome. The plant
then possesses the new trait."
Traditional breeding allows transferring hundreds of genes in a relatively
random manner. Good or bad traits are sometimes haphazardly passed along to the
new plant. With genetically engineered plants, however, scientists know exactly
what's going into the plant and what traits will be expressed by the
Tomatoes With Staying Power
If the season is right, you may find a brilliant red tomato sitting on a
table in Mattoo's office. The tomato might look like it was just picked, but
chances are it's one of his transgenic tomatoes that has been sitting there for
In collaboration with a Purdue University scientist in West Lafayette,
Indiana, Mattoo has developed a novel means for slowing ripening by introducing
a gene that controls only this function. He has been perfecting his technique
for creating transgenic vegetables for the last 8 yearsin Beltsville and
Mattoo's new transgenic tomatoes have 2.5 times more lycopene than
nontransgenic tomatoes. Lycopene is a carotenoid that has strong antioxidant
properties. Antioxidants prevent oxygen radicals from causing damage in cells.
Carotenoids aid in preventing early blindness in children, preventing cancer,
enhancing cardiovascular health, and slowing aging. Not only are the transgenic
tomatoes richer in lycopene, they're also more robust and more solid compared
to traditional tomatoes.
Another tomato genetically engineered by Mattoo has a longer shelf life. Its
cell membranes deteriorate more slowly during and after ripening. "The
plants bearing these tomatoes bloom three or four times over the season,"
he says, "whereas regular tomatoes normally produce just two
In a plant, thousands of genes control many functions. "Some genes are
'turned on' only at a certain developmental stage or in response to an
environmental cue. Other times they're simply turned off," says Mattoo.
"Using genetic manipulation, we can turn these genes on or off at any
particular time during growth and development. The genes we introduce into
tomatoes are not always switched on. They come on only when engineered to do
so, for instance, only when the fruit starts ripening."
Mailing Genes to the Correct Address
Mattoo has a passion and a gift for discovering how plant cells work and for
creating easy-to-use methods for improving vegetable production. His latest
endeavor is to "mail" the protein product of a beneficial gene to a
specific location within a plant cell so that the protein will be more useful
for the crop.
In this "ZIP Code" system, as Mattoo refers to it, the gene is
constructed so that it carries with it a defined DNA sequence that, when
translated by the cell, produces a protein with an added signal defining the
protein's destination. This signal guides the new protein to its proper spot in
the plant cell.
This ZIP Code system has been shown by other scientists to work like the
Post Office ZIP Codes, in that the destination signal is set in place before
gene transfer. This method ensures that the product of the new gene will not
end up at a place in the cell where it could be damaged. The system can work
with many fruits and vegetables.
With the new transgenic foods, Mattoo says the genetic material can be
engineered so that it is expressed only under controlled conditions. Each gene
is carefully reconstructed to check that all the elements are in place and in
sync. No single block is left unchecked.
"Imagine construction of a bridge," says Mattoo. "The
engineer has to ensure that all parts are properly placed and aligned. Any
single misstep can undo the bridge. Similarly, genes used to produce transgenic
crops are vigorously tested and all elements checked."
Strict Safety Precautions Followed
Mattoo's newly modified tomato has some advantages, such as reduced spoilage
and increased nutritional and health benefits. But before it can be made
available as a food, it will undergo rigorous testing for health and
"The public's confidence in food safety is too important to
compromise," says John W. Radin, ARS national program leader in
Beltsville, Maryland. "This type of product, however, represents the next
generation of genetically engineered foods. It will bring to the consumer's
table important benefits that could not have been achieved using traditional
breeding programs."By Tara
Weaver-Missick, Agricultural Research Service Information Staff.
This research is part of Plant Biological and Molecular Processes, an
ARS National Program (#301) described on the World Wide Web at
Autar K. Mattoo is located
at the USDA-ARS Vegetable
Laboratory, 10300 Baltimore Ave., Bldg. 10-A, Beltsville, MD 20705; phone
(301) 504-7380, fax (301) 504-5555.