Database Product Description
- Host Organism
- Oryza sativa (Rice)
- Trade Name
- Phosphinothricin (PPT) herbicide tolerance, specifically glufosinate ammonium.
- Trait Introduction
- Direct DNA transfer system
- Proposed Use
Production for human food, livestock feed and industrial uses.
- Product Developer
- Aventis CropScience
Summary of Regulatory Approvals
Summary of Introduced Genetic Elements Expand
Characteristics of Oryza sativa (Rice) Expand
Donor Organism Characteristics Expand
Modification Method Expand
Characteristics of the Modification Expand
Environmental Safety Considerations Expand
Food and/or Feed Safety Considerations Expand
The major producers of rice were China, India, Indonesia, Bangladesh, Viet Nam, Thailand and Myanmar. Rice is grown primarily for its grain, which is the staple food for half of the world’s population, and has many uses in the food and industrial sectors, including use in livestock feed.
Harvested rice, or rough rice, is encased by an inedible hull or husk, which is removed before milling. The hulls are utilized as fuels, mulch, abrasives and animal feed products. Brown rice is what remains after the hulls are removed. The light brown colour of brown rice is due to the presence of bran layers and the rice germ surrounding the rice kernel. Brown rice can be milled into regular white or ‘polished rice’, where white rice is distinguished by the fact that the hulls, bran layers and rice germ are removed. The bran and rice germs are high in protein and nutrients and are used in specialty foods such as rice bran oil and also in livestock feed. Both brown and white rice kernels can be parboiled and/or milled into rice flour for use in breakfast cereals, baby foods and desserts and numerous other food products. Rice kernels are also used to produce beer and rice wine.
Weeds are a significant pest problem in rice production in the United States. The best approach to controlling weeds in rice involves a combination of good cultural (certified seed, variety selection), mechanical (crop rotations, preparation of seedbed), and chemical practices. In order to obtain high yield potential, high rates and often multiple applications of herbicides are required for weed control. Over the years, herbicide tolerant weeds have developed and resulted in the rapid decline in the effectiveness of several herbicides (e.g., Londax®; common name bensulfuron methyl) against these resistant weeds. The use of integrated weed management strategies will be the key to delaying the development of resistance in rice weeds.
Rice lines LLRICE06 and LLRICE62 were genetically engineered to express tolerance to glufosinate ammonium, the active ingredient in phosphinothricin herbicides (Basta®, Rely®, Finale®, and Liberty®). Glufosinate chemically resembles the amino acid glutamate and acts to inhibit an enzyme, called glutamine synthetase, which is involved in the synthesis of glutamine. Essentially, glufosinate acts enough like glutamate, the molecule used by glutamine synthetase to make glutamine, that it blocks the enzyme's usual activity. Glutamine synthetase is also involved in ammonia detoxification. The action of glufosinate results in reduced glutamine levels and a corresponding increase in concentrations of ammonia in plant tissues, leading to cell membrane disruption and cessation of photosynthesis resulting in plant withering and death.
Glufosinate tolerance in these rice lines is the result of introducing a gene encoding the enzyme phosphinothricin-N-acetyltransferase (PAT) isolated from the common aerobic soil actinomycete, Streptomyces hygroscopicus, the same organism from which glufosinate was originally isolated. The PAT enzyme catalyzes the acetylation of phosphinothricin, detoxifying it into an inactive compound. The PAT enzyme is not known to have any toxic properties. The PAT encoding gene (bar) was introduced into the rice genome by direct gene delivery transformation, and the resulting rice lines displayed field tolerance to phosphinothricin-containing herbicides.
LLRICE06 and LLRICE62 were tested in field trials in the United States (1997-1998). These tests demonstrated that the transformed lines did not exhibit weedy characteristics, or negatively affect beneficial or nontarget organisms, and were not expected to impact on threatened or endangered species.
Cultivated rice is primarily self-pollinating, but may cross-pollinate with other cultivated rice varieties although rates are less than one percent. Factors limiting cross-pollination in rice include flower morphology, inability of pollen to remain viable longer than a few minutes, and a lack of insect vectors for pollen spread. In the United States, the only wild species known to be compatible with cultivated rice are O. rufipogon, which has been found in a single location in the Everglades of Florida, and red rice, a wild variant of cultivated O. sativa. Due to the relative isolation of O. rufipogon, it is unlikely to hybridize with cultivated rice.
Cultivated rice may cross-pollinate with red rice, given suitable conditions, and form glufosinate-tolerant hybrids. However, the glufosinate-tolerance trait is not expected to provide a competitive advantage to hybrid plants unless grown in managed environments that are routinely subjected to glufosinate applications. In the event that a glufosinate-tolerant hybrid survived, the herbicide-tolerant individual would be easily controlled using mechanical and other available chemical means. The use of good cultural practices, crop and herbicide rotations, are also effective strategies for controlling the establishment of herbicide tolerant weeds.
The food and livestock feed safety of rice lines LLRICE06 and LLRICE62 was established based on several standard criteria. As part of the safety assessment, the nutritional composition of rice was found to be equivalent to conventional varieties as shown by the analyses of grain, straw, and various processed fractions for key nutrients including proximates (moisture, ash, fat, protein, total dietary fibre, and carbohydrates), amino acid and fatty acid profiles and mineral content (calcium, phosphorus and iron). Assays were completed for anti-nutritional factors normally concentrated in the bran fraction of rice, such as phytic acid, trypsin inhibitor, and lectins. The levels of trypsin inhibitor and lectins in LLRICE06 and conventional rice were reported to be below the limit of detection, and the phytic acid content was the same for both transgenic and conventional varieties. The nutritional equivalence of LLRICE06 and LLRICE62 and conventional rice was confirmed in a 42-day feeding trial with male broiler chickens.
The potential for toxicity and allergenicity of the PAT protein was assessed by examining its physiochemical characteristics, amino acid sequence homology to known protein allergens, and susceptibility to in vitro digestion under conditions simulating the mammalian digestive tract. In each case, the PAT protein did not exhibit the characteristics commonly associated with food allergens. There were no amino acid sequence homologies with known allergens or toxins and the protein was readily digested in simulated gastric fluids. These studies were sufficient to provide a reasonable certainty that PAT protein has no allergenic potential.
There are reports of allergenic proteins within the rice endosperm. Laboratory studies determined there were no differences in the content of these allergenic proteins between rice lines LLRICE06 and LLRICE62 and conventional rice. These transgenic rice lines were also analyzed for the Osborne fraction, which contains prolamine proteins known to be related to Celiac disease. These proteins were investigated in brown rice samples and results showed there were no differences between rice lines LLRICE06 and LLRICE62 and conventional rice.
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This record was last modified on Wednesday, September 21, 2016