Database Product Description
- Host Organism
- Solanum lycopersicum (Tomato)
- Delayed softening through suppression of polygalacturonase (PG) enzyme activity.
- Trait Introduction
- Agrobacterium tumefaciens-mediated plant transformation.
- Proposed Use
Production for human consumption.
- Product Developer
- Calgene Inc.
Summary of Regulatory Approvals
Summary of Introduced Genetic Elements Expand
Characteristics of Solanum lycopersicum (Tomato) Expand
Modification Method Expand
Characteristics of the Modification Expand
Environmental Safety Considerations Expand
Food and/or Feed Safety Considerations Expand
The tomato is a vine-like herb of the nightshade family (Solanaceae) that also includes potatoes, peppers and eggplants. Botanically this vegetable is a fruit (a berry), which although being a perennial plant in the tropics, is grown as an annual plant in northern climates. The tomato is a native of the Peru, Bolivia, and Ecuador area of the Andes Mountains. Its antiquity is uncertain in regard to cultivation but it was being cultivated when Europeans discovered America. However, it was not generally cultivated in the United States until 1835 because, until then, it was widely believed to be poisonous.
Tomatoes are propagated from seeds. In temperate regions seeds are generally started in greenhouses, hotbeds, or cold frames; the plants are set out in the fields when danger of frost is past. Fresh tomatoes are harvested by hand, while those destined for canning or for processing into soups, sauces and ketchups are harvested by machine. The numerous varieties differ greatly in plant form and fruit type, the latter ranging from a small currant size through cherry, plum, and pear forms to the large, nearly round fruits, 10 cm (4 in) or more in diameter, which are the most widely grown. All forms include red- and yellow-fruited varieties.
Tomatoes are a valuable source of food minerals and vitamins, and are low in calories. One medium-sized tomato provides 57% of the recommended daily allotment (RDA) of vitamin C, 25% RDA vitamin A, and 8% RDA iron, yet it has only 35 calories. Tomatoes are also rich in the anti-oxidant lycopene, a carotenoid that has been found to protect cells from oxidants that have been linked to cancer. In laboratory tests, lycopene was found to be twice as powerful as beta-carotene in neutralizing free radicals. Lycopene has been linked to risk reduction for a number of types of cancers, including prostate, lung and stomach, pancreatic, cervical, colorectal, oral and esophageal cancers.
In the fresh market industry the tomato fruit is often picked at the mature green or breaker stages for long-distance shipping, and is then subsequently ripened by treatment with ethylene (12 to 18 h at 20ºC). For processing tomatoes the ethylene-producing compound, ethephon or Ethrel, is applied prior to harvest when only 10% of the fruit is ripe; this accelerates and concentrates fruit-ripening and facilitates once-over machine harvest.
Pectin is a building block in plant cell walls and is what gives tomatoes their firmness. Fruit softening during ripening is due to the breakdown of cell wall pectin by an enzyme called polygalacturonase (PG). The FLAVR SAVR™ tomato line was genetically engineered to express delayed softening by insertion of an additional copy of the PG encoding gene in the “antisense” orientation, resulting in reduced translation of the endogenous PG messenger RNA (mRNA). The antisense PG gene is essentially a reverse copy of part of the native tomato PG gene that suppresses the expression of endogenous PG enzyme prior to the onset of fruit ripening. The mechanism of decreased PG activity in FLAVR SAVR™ tomato is likely linked to the hybridization of antisense and sense mRNA transcripts, resulting in a decreased amount of free positive sense mRNA available for protein translation. Reduced PG expression decreases the breakdown of pectin and leads to fruit with slowed cell wall breakdown, better viscosity characteristics and delayed softening. FLAVR SAVR™ tomatoes have improved harvest and processing properties that allow the transgenic tomatoes to remain longer on the vine to develop their natural flavour, maintain firmness for shipping and produce a thicker consistency in processing. The measured level of endogenous PG activity in transgenic FLAVR SAVR tomato was found to be less than 1% of PG activity found in the unmodified parental line.
FLAVR SAVR™ tomatoes were field tested in the United States from 1988 to 1992. Field trials demonstrated that the variation in agronomic characteristics among the FLAVR SAVR™ tomato lines did not differ significantly from the natural variation found in commercial cultivars of tomato. These reports indicated that FLAVR SAVR™ tomatoes did not exhibit weedy characteristics, and had no observable effect on nontarget organisms or the general environment. The transformed tomato line was not expected to impact on threatened or endangered species.
Cultivated tomatoes are self-fertile, and almost exclusively self-pollinating. Their unique flower and anther morphology makes tomato an essentially cleistogamous plant, in which self-pollination and fertilization occur within an unopened flower. A low crossing rate between tomato varieties was demonstrated and attributed to the limited availability of pollen and poor foraging activity of insect pollinators.
Several related species are found as weeds in tomato fields, however, commercial tomato is generally sexually incompatible with these weedy relatives. Two Solanum species, S. lycopersicoides and S. rickii, neither of which is a weed pest in the United States, can be crossed with commercial tomato only under specific, controlled conditions requiring human intervention. The cherry tomato, S. lycopersicum var. cerasiforme can be crossed with tomato. However, it would be very unlikely for the FLAVR SAVR™ tomato line to hybridize with cherry tomatoes in the United States since the rate of outcrossing in tomatoes is low and cherry tomatoes are not common in areas devoted to the large-scale cultivation of tomatoes. It was concluded that the chance of genetic exchange among tomato crops was small and outcrossing to other species, even more remote. In the event that an outcrossing event involving pollen from the transgenic FLAVR SAVR™ tomato line did occur, it was unlikely that the delayed-ripening trait would increase the plant’s weediness or probability of survival.
Tomatoes are consumed in both fresh (whole and sliced or diced in a variety of foods) and processed (soups, ketchup, paste, prepared sauces) forms, and the genetic modification introduced into the transgenic tomato line was not expected to result in any changes in consumption patterns. FLAVR SAVR™ tomatoes were expected to provide an alternate or additional choice to consumers and food manufacturers.
The analysis of nutrients from FLAVR SAVR™ tomatoes and non-transgenic control lines did not reveal any significant differences in the levels of macro- and micronutrients, pH, total acidity, total solids, or sugars. Levels of glycoalkaloids (alpha-tomatine) present in mature tomatoes from the transgenic tomato line were within the range reported for conventional tomato varieties.
As the antisense PG gene did not encode for any new protein there was no expectation of toxic or allergenic potential related to the genetic modification. Additional data from three 28-day rat feeding trials comparing transgenic and non-transgenic tomatoes demonstrated no biologically significant changes in body weight, organ weight, food consumption, hematologic parameters, and clinical chemistry findings that were specific to the transgenic line.
Links to Further Information Expand
This record was last modified on Wednesday, May 20, 2015