Database Product Description
- Host Organism
- Oryza sativa (Rice)
- Trade Name
- Phosphinothricin (PPT) herbicide tolerance, specifically glufosinate ammonium.
- Trait Introduction
- Agrobacterium tumefaciens-mediated plant transformation.
- Proposed Use
Production for human food, livestock feed and industrial uses.
- Product Developer
- Bayer CropScience (Aventis CropScience(AgrEvo))
Summary of Regulatory Approvals
Summary of Introduced Genetic Elements Expand
Characteristics of Oryza sativa (Rice) Expand
Rice (Oryza sativa L.) was grown as a commercial crop in more than 100 countries with a combined harvest of 630 million metric tonn in 2006. 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 line LLRICE601 was 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 this rice line 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.
LLRICE601 was tested in field trials in the United States (1998-2001). 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. However a full petition for non-regulated status was not submitted at that time as the developer elected to submit two other lines for deregulation - LLRICE06 and LLRICE62. In 2006, contamination of cultivated rice with LLRICE601 was discovered and the developer elected to submit a petition for deregulation as an extension to the previously deregulated lines.
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.
Links to Further Information Expand
This record was last modified on Friday, March 26, 2010