April 10, 2002

Tomato catch-up: discovery of ripening gene could make store-bought tomatoes as tasty as homegrown

ITHACA, N.Y. -- The fruits of genetic research are about to ripen: Scientists at the U.S. Department of Agriculture (USDA) and the Boyce Thompson Institute for Plant Research, Inc. (BTI), located on the campus of Cornell University, have discovered a gene that controls ripening in tomatoes.

This means that tastier, more-nutritious grocery-store tomatoes are not far behind, say the researchers in an article in the latest issue of the journal Science (April 12, 2002), titled "A MADS-box gene necessary for fruit ripening at the tomato ripening-inhibitor (rin ) locus."

"For understanding tomato ripening and eventually taste, this could be the Holy Grail," says Jim Giovannoni, a project scientist with the USDA and also with BTI.

MADS refers to a family of genes (the name is an acronym formed from the initials of the four original members of the family). More than 100 MADS-box sequences have been found in species of microbes, animals and plants, and most play important roles in developmental processes. Most prominent, the MADS-box genes in ßowering plants are the "molecular architects" of growth.

Giovannoni and his colleagues have found two tandem MADS-box genes, one a ripening gene, the LeMADS-RIN (or rin for short), and the other the LeMADS-MC gene, which controls the development of the sepal -- the collar of pointy green leaves at the top of tomatoes. Finding these genes provides the first molecular insight into a non-hormonal way to ripen fruit, he says.

The shelf life of tomatoes was lengthened by the discovery in the early 1960s, by Henry Munger, Cornell professor of plant breeding, of a mutant tomato plant containing what Giovannoni and his group now have shown to be a defect in the rin gene. Munger crossed this mutant plant with normal tomatoes, allowing the fruit to reach full size while slowing the ripening process. Today, this hybrid is commercially ubiquitous. But, says Giovannoni, in order to be fresh for the supermarket, these tomatoes are harvested while they are still firm and unripe so they can survive the rigors of shipping and have an extended shelf life. As a result, tomato flavors, typical of homegrown fruit, do not get a chance to develop on the vine, and consumers complain about their blandness.

The discovery of the rin gene provides a way to keep the tomato on the vine a little longer so that it develops more nutrients, color and taste, Giovannoni says. And yet it is still firm enough for shipping, and with a good shelf life. As a bonus, the longer a tomato remains on the vine, the more lycopene (an antioxidant that inhibits cancer and heart disease) is produced.

Giovannoni's research team also has been able to moderate the ripening process, creating tomatoes that ripen at fast, medium or slow speeds. Using a procedure called "antisense," the researchers take the rin gene and invert it. This effectively shuts off the normal gene and, in this case, slows the tomato's ripening process. The procedure, says Giovannoni, also should work with strawberries, bananas, bell peppers and melons, in addition to many other fruits for which shelf life and softening are problems. This, says Giovannoni, could reduce the use of ethylene to kick-start ripening after fruit has been shipped to the warehouse.

Giovannoni's co-authors of the Science paper are: Julia Vrebalov, research associate at the USDA-Agricultural Research Service's Plant, Soil and Nutrition Laboratory and at BTI; Ruth White, a researcher at the USDA and BTI; Diana Medrano, researcher, BTI; Rachel Drake, of Syngenta; Wolfgang Schuch, formerly of Syngenta, now with CellFor, Inc.; and former members of the Giovannoni lab, Diane Ruezinsky, now with Monsanto, and Veeraragavan Padmanabhan, now with Pioneer Seed.

Early work on the research was conducted by Giovannoni at the Texas Agricultural Experiment Station. The research was funded by the USDA-National Research Initiative plant genome grant, the National Science Foundation and Syngenta.

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o The Boyce Thompson Institute for Plant Research, Inc.: