By GINA KOLATA
The New York Times
Published: June 28, 2012
Original link: http://www.nytimes.com/2012/06/29/science/flavor-is-the-price-of-tomatoes-scarlet-hue-geneticists-say.html
A gene mutation that makes a tomato uniformly red also stifles genes that contribute to its
taste, researchers say.
Plant geneticists say they have discovered an answer to a near-universal question: Why are
tomatoes usually so tasteless?
Yes, they are often picked green and shipped long distances. Often they are refrigerated,
which destroys their flavor and texture. But now researchers have discovered a genetic
reason that diminishes a tomato’s flavor even if the fruit is picked ripe and coddled.
The unexpected culprit is a gene mutation that occurred by chance and that was discovered
by tomato breeders. It was deliberately bred into almost all tomatoes because it conferred
an advantage: It made them a uniform luscious scarlet when ripe.
Now, in a paper published in the journal Science, researchers report that the very gene that
was inactivated by that mutation plays an important role in producing the sugar and aromas
that are the essence of a fragrant, flavorful tomato. And these findings provide a road map
for plant breeders to make better-tasting, evenly red tomatoes.
The discovery “is one piece of the puzzle about why the modern tomato stinks,” said Harry
Klee, a tomato researcher at the University of Florida in Gainesville who was not involved in
the research. “That mutation has been introduced into almost all modern tomatoes. Now we
can say that in trying to make the fruit prettier, they reduced some of the important
compounds that are linked to flavor.”
The mutation’s effect was a real surprise, said James J. Giovannoni of the United States
Department of Agriculture Research Service, an author of the paper. He called the wide
adoption of tomatoes that ripen uniformly “a story of unintended consequences.”
Breeders stumbled upon the variety about 70 years ago and saw commercial potential.
Consumers like tomatoes that are red all over, but ripe tomatoes normally had a ring of
green, yellow or white at the stem end. Producers of tomatoes used in tomato sauce or
ketchup also benefited. Growers harvest this crop all at once, Dr. Giovannoni said, and
“with the uniform ripening gene, it is easier to determine when the tomatoes are ripe.”
Then, about 10 years ago, Ann Powell, a plant biochemist at the University of California,
Davis, happened on a puzzle that led to the new discovery.
Dr. Powell, a lead author of the Science paper, was studying weed genes. Her colleagues
had put those genes into tomato plants, which are, she said, the lab rats of the plant world.
To Dr. Powell’s surprise, tomatoes with the genes turned the dark green of a sweet pepper
before they ripened, rather than the insipid pale green of most tomatoes today.
“That got me thinking,” Dr. Powell said. “Why do fruits bother being green in the first
place?” The green is from chloroplasts, self-contained energy factories in plant cells, where
photosynthesis takes place. The end result is sugar, which plants use for food. And, Dr.
Powell said, the prevailing wisdom said sugar travels from a plant’s leaves to its fruit. So
chloroplasts in tomato fruit seemed inconsequential.
Still, she said, the thought of dark green tomatoes “kind of bugged me.” Why weren’t the
leaves dark green, too?
About a year ago, she and her colleagues, including Dr. Giovannoni, decided to investigate.
The weed genes, they found, replaced a disabled gene in a tomato’s fruit but not in its
leaves. With the weed genes, the tomatoes turned dark green.
The reason the tomatoes had been light green was that they had the uniform ripening
mutation, which set up a sort of chain reaction. The mutation not only made tomatoes turn
uniformly green and then red, but also disabled genes involved in ripening. Among them are
genes that allow the fruit to make some of its own sugar instead of getting it only from
leaves. Others increase the amount of carotenoids, which give tomatoes a full red color and,
it is thought, are involved in flavor.
To test their discovery, the researchers used genetic engineering to turn on the disabled
genes while leaving the uniform ripening trait alone. The fruit was evenly dark green and
then red and had 20 percent more sugar and 20 to 30 percent more carotenoids when ripe.
But were the genetically engineered tomatoes more flavorful? Because Department of
Agriculture regulations forbid the consumption of experimental produce, no one tasted
And, Dr. Giovannoni says, do not look for those genetically engineered tomatoes at the
grocery store. Producers would not dare to make such a tomato for fear that consumers
would reject it.
But, Dr. Powell said, there is a way around the issue. Heirloom tomatoes and many wild
species do not have the uniform ripening mutation. “The idea is to get the vegetable seed
industry interested,” Dr. Powell said.
A version of this article appeared in print on June 29, 2012, on page A12 of the New York
edition with the headline: Flavor Is Price Of Scarlet Hue Of Tomatoes, Study Finds.