What is gene stacking?
Gene stacking refers to the process of combining genes of interest into a single plant line. It is used in conventional as well as genetically modified (GM) crops to develop improved lines. A stacked GM line contains at least two novel genes.
Stacked genes are sometimes referred to as stacked events; gene stacking as gene pyramiding
How are the genes combined?
Traditional plant breeding is the most common way to stack novel genes in GM crops. Individual GM plant lines, each expressing a desired trait or multiple traits, are cross fertilised to produce a new generation of plants exhibiting the traits of the parent lines.
Examples of stacked GM lines generated using traditional breeding include:
- Roundup Ready® YieldGard® corn which is the result of crossing three different GM corn lines (MON863 x MON810 x NK603) to combine twoBtgenes (for insect protection) with one gene for herbicide tolerance (to glyphosate herbicides);
- Bollgard II® Roundup Ready Flex® cotton, which is the result of crossing two different GM cotton lines (15985 x MON88913) to combine twoBtgenes (for insect protection) with one gene for herbicide tolerance (to glyphosate herbicides); and
- SmartStax™ corn, which is the result of crossing four different GM corn lines (MON89034 x 1507 x MON88017 x DAS-59122-7) to combine two herbicide tolerance genes (conferring tolerance to glyphosate and glufosinate ammonium containing herbicides) with sixBtgenes to confer protection from certain insect pests.
Gene stacking can also be achieved using more direct methods involving gene technology, where multiple novel genes are introduced, either simultaneously or consecutively, into a single plant line.
How widespread are GM crops with stacked genes?
Plants with stacked genes now form a significant part of GM crops grown throughout the world. The main stacked traits have been insect protection and herbicide tolerance. In the future, other major traits are likely to include compositional changes, disease resistance, and tolerance to abiotic stress.
A total of approximately 51 million hectares of stacked GM crops were planted in 2014 in 13 different countries representing approximately 28% of the 181 million ha of GM crops planted worldwide.
In the past, gene stacking was confined primarily to corn and cotton varieties. Stacked commercial soybean lines are also now being planted and, for example in 2014, 5.8 million hectares of stacked soybeans were grown in Brazil, Argentina, Paraguay and Uruguay.
In the United States of America, over 70% of all GM corn lines grown in 2013 were stacked lines, and more than 65% of all GM cotton lines were-stacked lines. In Australia, 95% of all GM cotton grown in the 2010/2011 season consisted of stacked varieties.
What is the FSANZ regulatory approach to food from stacked GM plants?
No separate approval or safety assessment is necessary for foods derived from a stacked GM line that is the result of traditional breeding between a number of GM parent lines for which food has already been approved. Food from the parent lines must be listed in Schedule 26 of the Australia New Zealand Food Standards Code. For example, in the case of SmartStax™ corn (described above), foods derived from GM corn lines MON89034, 1507, MON88017 and DAS-59122-7 are already approved in the Code, therefore separate pre-market approval for SmartStax™ corn is not required. The parent lines may contain any number of different genes. If food from any of the GM parent lines has not been approved, then a full pre-market safety assessment of food from the stacked line must be undertaken.
Where a single line containing a number of genes has been produced as a result of direct gene technology methods (rather than traditional crossing) then food derived from the line must undergo a full pre-market safety assessment before approval can be given.
What is the scientific justification for this approach?
The key consideration is whether crossing two or more approved GM plant lines, using traditional plant breeding, is likely to pose any new or additional food safety risks over and above what was previously considered as part of the safety assessment of each parental GM line. While in theory new risks could arise, the novel traits themselves are important indicators of any possible interactions in the stacked variety. In terms of the current range of agronomic traits present in approved GM parent lines, such as insect protection and herbicide tolerance, there is no scientifically plausible reason to postulate that interactions between such traits would create new or altered hazards.
There is also no reason to suppose that novel GM traits would be more likely to interact because of the method used to introduce them into the parent line. Rather, possible interactions would be determined by the nature of the traits themselves. The potential food risks associated with stacked GM plant lines which are products of traditional breeding can therefore be regarded as fundamentally no different from those occurring with any other conventionally bred plant.
All new crop varieties undergo comprehensive phenotypic assessment in order to determine their commercial suitability and viability. FSANZ considers this process of examination provides additional assurance of the absence of significant unintended effects in stacked GM lines.
Is labeling required for foods derived from stacked GM lines?
Yes, foods derived from stacked lines will have the same labeling requirements as the approved GM parent lines.