Food Derived from GM Plants Containing Stacked Genes
What is gene stacking?
Gene stacking [1] 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.
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 are becoming the dominant form of GM crops grown throughout the world [2] . Currently, gene stacking is confined primarily to corn and cotton varieties where the objective has been to achieve various combinations of insect protection and herbicide tolerance traits.
A total of 26.9 million hectares of stacked GM crops were planted in 2008 in 10 different countries [3] with the total area and number of countries growing stacked GM crops expected to increase further over the next five to seven years.
In the United States of America, 78% of all GM corn lines grown in 2008 were either double- or triple-stacked lines, and more than 75% of all GM cotton lines were double-stacked lines. In Australia, 81% of all GM cotton grown in 2008 consisted of stacked varieties.
By 2015, it is estimated that for corn alone, 24 single genetic modifications may have been commercialised, and that this could equate to over 2,000 triple-stacked lines and over 12,000 quadruple-stacked lines [4] . In addition to the traits of herbicide tolerance and insect protection, other major traits are likely to include compositional changes, disease resistance, and tolerance to abiotic stress.
What is the FSANZ regulatory approach to stacked GM plants?
No separate approval is necessary for foods derived from a stacked GM line that is the result of traditional breeding between a number of approved GM parent lines. The parent lines must be listed in the Australia New Zealand Food Standards Code [5]. 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.
In contrast, a crop containing stacked genes as a result of direct gene technology methods is regarded as a new GM plant line and must undergo a 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.
[1] Stacked genes are sometimes referred to as stacked events; gene stacking as gene pyramiding
[2] James, C. (2008). Global Status of Commercialized Biotech/GM Crops: 2008. ISAAA Brief No. 39, Manila.
[3] United States of America, Canada, Philippines, Australia, Mexico, South Africa, Honduras, Chile, Colombia, and Argentina
[4] Stein, A.J.; Rodriguez-Cerezo, E. (2009). The global pipeline of new GM crops: implications of asynchronous approval for international trade. European Commission Joint Research Centre.