GM Crop Database

Database Product Description

T303-3 (BCS-GHØØ3-6)
Host Organism
Gossypium hirsutum (Cotton)

Herbicide Tolerance, Insect Resistance

Trait Introduction
Agrobacterium tumefaciens-mediated plant transformation.
Proposed Use

Production for fibre, livestock feed, and human consumption.

Product Developer
Bayer CropScience USA LP

Summary of Regulatory Approvals

Country Food Feed Environment Notes
United States 2012

Introduction Expand

T303 cotton (Gossypium hirsutum) plants express the insecticidal protein Cry1Ab (encoded by the cry1Ab gene) from the common soil bacterium Bacillus thuringiensis subsp. berliner (B.t. berliner) and the herbicide tolerance protein phosphinothicin acetyltransferase (PAT; encoded by the bar gene) from Streptomyces hygroscopicus.  The Cry1Ab protein is effective in controlling lepidopteran larvae such as bollworm (CBW, Helicoverpa zea) and tobacco budworm (TBW, Heliothis virescens) larvae, which are common pests of cotton.  The expression of the PAT (phosphinothricin acetyltransferase) protein provides tolerance to glufosinate ammonium herbicides by acetylating glufosinate ammonium, thus detoxifying it.  The cry1Ab and bar genes have been stably integrated into the T303 cotton genome.

T303 cotton has never been commercialized.

Summary of Introduced Genetic Elements Expand

Code Name Type Promoter, other Terminator Copies Form
cry1Ab Cry1Ab delta-endotoxin IR

P35S2 from Cauliflower mosaic virus

3’me1 from Flavia bidentis


cry1Ab coding sequence

bar phosphinothricin N-acetyltransferase HT

P35S2 (Cauliflower Mosaic Virus)

3’ untranslated region of nopaline synthase gene from Agrobacterium tumefaciens


Coding sequence of bar gene 

Characteristics of Gossypium hirsutum (Cotton) Expand

Center of Origin Reproduction Toxins Allergenicity

Believed to originate in Meso-America (Peruvian-Ecuadorian-Bolivian region).

Generally self-pollinating, but can be cross-pollinating in the presence of suitable insect pollinators (bees). In the U.S., compatible species include G. hirsutum, G. barbadense, and G. tomentosum.

Gossypol in cottonseed meal.

Cotton is not considered to be allergenic, although there are rare, anecdotal reports of allergic reactions in the literature.

Donor Organism Characteristics Expand

Latin Name Gene Pathogenicity
Bacillus thuringiensis subsp Berliner cry1Ab

While target insects are susceptible to oral doses of Bt proteins, no evidence of toxic effects in laboratory mammals or birds given up to 10 µg protein/g body weight.

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

Agrobacterium-mediated transformation of Coker 315 cotton with the T-DNA vector pTDL004 was carried out using cotyledon explants.  Following co-culture with Agrobacterium, callus formation was initiated on a specific medium containing glufosinate ammonium as the selective agent and cefotaxime to eliminate residual Agrobacterium.  Selected tissues were transferred to the appropriate regeneration medium.  The developed plantlets were transferred to the greenhouse to allow flowering and seed set.

Characteristics of the Modification Expand

Southern blot analyses determined that the inserted transgenic sequence in cotton event T303 consists of one complete copy of the T-DNA of the cry1Ab gene cassette and one copy of the bar gene cassette.

The inserted genes are inherited as a single dominant trait.  The stability of the gene insertion was demonstrated by Southern blot analyses and Mendelian inheritance analyses.  Southern analyses were conducted across four generations, three environments and four genetic backgrounds.  No differences were seen in any of the analyses. 

Phenotypic stability was demonstrated by Mendelian segregation of the T303 insert. A T0 plant was selfed to give a T1 plants.  These were again selfed to give T2 plants. The T0 was also crossed with conventional cotton, and the resulting F1 plants were evaluated in the greenhouse.  The F1 plants were selfed, resulting in the F2 generation which was evaluated in the greenhouse for herbicide tolerance.  The F1 plants were back-crossed with the conventional variety to yield the BC1F1 plants which were again back-crossed with the conventional variety to yield the BC2F1 plants.  The BC2F1 plants were selfed twice to yield the BC3F3 plants.  The results from the T1, T2, F2 and BC3F3 genetic backgrounds demonstrated Mendelian inheritance for a single gene locus and confirmed stability of the Event T303 cotton insert.

Expression analyses for Cry1Ab and PAT proteins were conducted on fuzzy seeds. The measured values, by ELISA, for Cry1Ab were 7.14 µg/g to 17.9 µg/g in seed.  Cry1Ab protein constitutes 0.0051% of the total crude protein in seed.  For PAT, the values were 56.6 µg/g to 130 µg/g in seed.  PAT protein constitutes 0.048% of the total crude protein in the T303 seed.

Environmental Safety Considerations Expand

Field Testing

T303 cotton was field tested by Bayer CropScience in 2005 to 2006. Data collected from these field trials demonstrated that T303 cotton did not exhibit weedy characteristics and had no effects on non-target organisms or the general environment.


While gene flow could occur vegetatively, by seed or pollen, only pollen flow has any potential risk for cotton.  Vegetative propagation is uncommon for cotton and seed dispersal (wind, birds, and animals) is rarely successful due to the properties of the boll structure.  Cotton pollen is not transferred by wind due to its large, heavy and sticky nature.  Natural cross-pollination results from pollen being carried by insects, bees being the most important cotton pollinators.

In the US, there are four cotton species, with two that are cultivated commercially – G. hirsutum L. and G. barbadense L. and two wild relatives – G. thurberi Todaro and G. tomentosum Nuttall ex Seemann.  Of these four species, only three Gossypium species could be recipients for G. hirsutum - G. hirsutum itself, G. barbadense and G. tomentosum. Feral populations of G. hirsutum are found only in the southern tip of Florida and in Hawaii, which is hundreds of miles from any commercial cotton fields.  G. barbadense is only found in very small commercial plots and is not found in wild environments in the US.  Thus outcrossing to wild G. hirsutum or commercial plots of G. barbadense is unlikely.

Outcrossing of the tetraploid G. hirsutum to the wild diploid G. thurberi, which occurs in Arizona, is extremely unlikely.  Crosses between these species in breeding programs have been done, but the vigor of the hybrid seed is much reduced and the plants are usually infertile.  In addition, native populations of G. thurberi reside in the higher altitudes and are thus isolated from commercial cotton production (Fryxell, 1979).  Therefore, outcrossing of commercial TwinLink cotton to G. thurberi is not a concern.

Gossypium tomentosum is only found in the Hawaiian archipelago, occurring in dry coastal areas far removed from agricultural areas.  The flowers of G. tomentosum are only receptive at night, rather than in the day as for G. hirsutum and moths, rather than bees generally pollinate them.  

Thus, it was concluded that the potential for transfer of the insect resistance, herbicide tolerance traits from the T304-40 cotton varieties to other cotton species via pollen or gene flow was negligible in managed ecosystems such as farms.

Weediness Potential

Cotton is generally considered not to be a serious, principal or common weed pest.  The largest concern is that of volunteer plants that could become weedy in subsequent years.  Volunteers are also limited by the geography in which they may exist, because cotton does not survive as a perennial where freezing temperatures are reached during the winter.  Volunteers can easily be controlled by crop rotation, tillage and/or pre- or post-emergence herbicides.  For example, T303 cotton volunteers could easily be controlled by using the herbicide glyphosate.

Secondary and Non-Target Adverse Effects

Field observations of T303 cotton concluded there was no significant impact on organisms beneficial to plants and/or agriculture or on other non-target organisms. 

The mode of action of Cry proteins in target organisms is well understood and is mediated by binding proteins in the gut, which have considerable inter-species variability.  Bacillus thuringiensis (Bt) Cry proteins (including several Cry1 proteins) have been extensively studied in laboratory assays and field tests, and cotton and corn expressing these proteins have been grown on significant acreage in globally with no reports of significant effects.  These studies indicate that Cry proteins pose no unacceptable risk for any organisms except the narrowly-targeted pest species and very close relatives. For T304-40 cotton, additional data was generated on non-target organisms such as honey bees, earthworms, springtails, etc. and no effects were identified.  

Food and/or Feed Safety Considerations Expand

Nutritional Data

Proximate analyses were carried out on seed, meal, toasted meal, hulls and linters, amino acid profiles of seed, meal and toasted meal, fatty acid profiles of seed, crude oil and deodorized oil, and levels of Cry1Ab and PAT proteins expression in whole and processed fractions. Analyses were also conducted for naturally occurring toxicants and antinutrients (gossypol, cyclopropenoid fatty acids and phytic acid), as well as Vitamin E (tocopherol) for seed (whole and delinted) and oil (crude and deodorized). T304-40 cotton was found to be substantially equivalent to other varieties of cotton.


The low potential for allergenicity of the Cry1Ab and PAT proteins has been established through amino acid sequence comparisons to known allergens, digestibility in simulated gastric and intestinal fluids, presence of glycosylation and assessment of heat stability.  The Cry1Ab and PAT proteins share no epitopes with known allergens, are not glycosylated or heat stable and degrade rapidly in  simulated gastric and intestinal fluids.  

Links to Further Information Expand

This record was last modified on Monday, May 8, 2017