GM Crop Database

Database Product Description

MS6 (ACS-ZMØØ5-4)
Host Organism
Zea mays (Maize)
Trade Name
InVigor™
Trait
Glufosinate ammonium herbicide tolerance and male sterility
Trait Introduction
Electroporation of immature embryos.
Proposed Use

Production for human consumption and livestock feed.

Product Developer
Bayer CropScience (Aventis CropScience(AgrEvo))

Summary of Regulatory Approvals

Country Food Feed Environment Notes
United States 2000 2000 1999

Introduction Expand

Maize line MS6 (tradename InVigor®) was developed to provide a reliable hybridization system based on nuclear male sterility. The transgenic line was produced by genetically engineering plants to be male sterile and tolerant to the herbicide glufosinate ammonium, where herbicide tolerance was used as a selectable marker to identify the male sterile plants. These transformed maize lines contain the barnase gene for male sterility, isolated from Bacillus amyloliquefaciens, a common soil bacterium that is frequently used as a source for industrial enzymes. The barnase gene encodes for a ribonuclease enzyme (RNAse) that is expressed only in the tapetum cells of the pollen sac during anther development. The RNAse affects RNA production, disrupting normal cell functioning and arresting early anther development, thus leading to male sterility.

The male sterile maize line MS6 also contained the bar gene isolated from the common soil microorganism Streptomyces hygroscopicus, for use as a selectable marker. The bar gene encodes a phosphinothricin acetyl transferase (PAT) enzyme, which, when introduced into a plant cell, confers tolerance to the herbicide glufosinate ammonium. The herbicide tolerance trait was introduced into the maize line as a selectable marker to identify transformed plants during tissue culture regeneration, and as a field selection method to identify the male sterile lines at any growth stage. Under field conditions, plants that were not male-sterile could be eliminated by application of the herbicide glufosinate ammonium. The novel hybrid system provided an efficient and effective way to identify male-sterile plants for use in hybrid seed production.

Glufosinate ammonium is the active ingredient in phosphinothricin herbicides (Basta, Rely, Finale, and Liberty) and acts by inhibiting the plant enzyme glutamine synthetase, a key enzyme in plants that detoxifies ammonia by incorporating it into glutamine. Inhibition of this enzyme leads to an accumulation of ammonia in the plant tissues, which kills the plant within hours of application. PAT catalyses the acetylation of the herbicide phosphinothricin and thus detoxifies glufosinate ammonium into an inactive compound.

In the United States, the male-sterile line MS3 was designated as the antecedent organism for MS6 for the purposes of conducting the environmental safety assessment. Maize lines MS3 and MS6 were genetically modified using the same transformation technique and the same genetic elements. Based on the similarity between MS6 and the antecedent organism MS3, and on an analysis of scientific data and field tests of MS6, the maize line MS6 was judged not to have any characteristics that would pose a greater impact on the environment or non-target organisms.

For additional information related to either the environmental or food safety assessment of the antecedent organism, MS3, the reader is referred to the description for that product.

Summary of Introduced Genetic Elements Expand

Code Name Type Promoter, other Terminator Copies Form
barnase barnase ribonuclease MS pTa 29 pollen specific promoter from Nicotiana tabacum
bar phosphinothricin N-acetyltransferase HT CaMV 35S A. tumefaciens nopaline synthase (nos) 3'-untranslated region Modified
bla beta lactamase SM bacterial promoter Fragmented copy; not expressible

Characteristics of Zea mays (Maize) Expand

Center of Origin Reproduction Toxins Allergenicity

Mesoamerican region, now Mexico and Central America

Cross-pollination via wind-borne pollen is limited, pollen viability is about 30 minutes. Hybridization reported with teosinte species and rarely with members of the genus Tripsacum.

No endogenous toxins or significant levels of antinutritional factors.

Although some reported cases of maize allergy, protein(s) responsible have not been identified.

Donor Organism Characteristics Expand

Latin Name Gene Pathogenicity
Streptomyces hygroscopicus bar S. hygroscopicus is ubiquitous in the soil and there have been no reports of adverse affects on humans, animals, or plants.

Modification Method Expand

Maize line MS6 was produced by transforming the inbred line H99 by electroporation of immature embryos in the presence of a preparation of linearized plasmid DNA. The plasmid mixture contained both genes of interest; the male sterility gene (barnase) and the herbicide resistance gene, (bar). While maize line MS6 contained fragments of the beta-lactamase encoding (bla) marker gene, it was concluded that the fragments would not produce an intact protein in either prokaryotic (bacterial) or plant expression systems.

The barnase gene encodes an RNAse enzyme that disrupts cell function during anther development and results in male sterility. The expression of the barnase gene was under control of an anther-specific promoter (pTa29), from Nicotiana tabacum, that turns on expression of the gene in the anthers where pollen is produced. The barnase gene was terminated by the 3' -polyadenylation signal of the nopaline synthase (nos) gene isolated from the Ti plasmid of Agrobacterium tumefaciens.

The bar gene encodes the PAT enzyme confering tolerance to glufosinate ammonium herbicide and was used as a selectable marker. Constitutive expression of the bar gene was under control of the cauliflower mosaic virus (CaMV) 35S promoter. Translocation of the introduced PAT enzyme to chloroplasts was accomplished by fusing sequences encoding the chloroplast transit peptide to the 5' terminus of the bar gene. Apart from the sequences encoding barnase RNAse and PAT, no other plant translatable DNA sequences were introduced into the maize plant genome.

Abstract Collapse

Maize (Zea mays L.) is grown primarily for its kernel, which is largely refined into products used in a wide range of food, medical, and industrial goods.

Only a small amount of whole maize kernel is consumed by humans. Maize oil is extracted from the germ of the maize kernel and maize is also a raw material in the manufacture of starch. A complex refining process converts the majority of this starch into sweeteners, syrups and fermentation products, including ethanol. Refined maize products, sweeteners, starch, and oil are abundant in processed foods such as breakfast cereals, dairy goods, and chewing gum.
In the United States and Canada maize is typically used as animal feed, with roughly 70% of the crop fed to livestock, although an increasing amount is being used for the production of ethanol. The entire maize plant, the kernels, and several refined products such as glutens and steep liquor, are used in animal feeds. Silage made from the whole maize plant makes up 10-12% of the annual corn acreage, and is a major ruminant feedstuff. Livestock that feed on maize include cattle, pigs, poultry, sheep, goats, fish and companion animals.

Industrial uses for maize products include recycled paper, paints, cosmetics, pharmaceuticals and car parts.

The maize line MS6 was genetically engineered to express male sterility and 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 maize 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 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 male-sterile trait was introduced by inserting the barnase gene, isolated from Bacillus amyloliquefaciens, a common soil bacterium that is frequently used as a source for industrial enzymes. The barnase gene encodes for a ribonuclease enzyme (RNAse) that is expressed only in the tapetum cells of the pollen sac during anther development. The RNAse affects RNA production, disrupting normal cell functioning and arresting early anther development, thus leading to male sterility. The PAT enzyme was used as a selectable marker enabling identification of transformed plants during tissue culture regeneration, and as a field selection method to identify the male-sterile lines prior to flowering. Under field conditions, plants that were not male-sterile could be eliminated by application of the herbicide glufosinate ammonium. The novel hybrid system provided an efficient and effective way to identify male-sterile plants for use in hybrid seed production.

In the United States, the male-sterile line MS3 was designated as the antecedent organism for MS6 for the purposes of conducting the environmental safety assessment. Maize lines MS3 and MS6 were genetically modified using the same transformation technique and the same genetic elements. Based on the similarity between MS6 and the antecedent organism MS3, and on an analysis of scientific data and field tests of MS6, the maize line MS6 was judged not to have any characteristics that would pose a greater impact on the environment or on non-target organisms.

For additional information related to either the environmental or food safety assessment of the antecedent organism, MS3, the reader is referred to the description for that product.

Links to Further Information Expand


This record was last modified on Friday, March 26, 2010