Jun 9, 2009
Effects of transgenic zexanthin potatoes on soil quality:
“We have not found any effects that go beyond normal varietal differences.”
A team of researchers led by the Technical University of Munich (TUM) has been investigating the effect of different potato varieties on soil quality over the past three years. They included a broad spectrum of varieties in their research: classic varieties, genetically modified (GM) lines and the relevant wild type. The GM potatoes accumulate zeaxanthin in their tubers. Zeaxanthin is a carotenoid that is thought to protect against age-related blindness. GMO Safety spoke to Michael Schloter, head of the research team, about the results and their significance for biosafety research.
Dr Michael Schloter , Helmholtz Centre Munich, Institute of Soil Ecology, head of the research team consisting of microbiologists, plant breeders, plant nutritionists and agricultural scientists
Shape and colour of tubers in the varieties investigated: the Baltica wild type, the genetically modified lines (SR47 and SR 48) and various classic varieties.
GMO Safety: What issues did your research project investigate?
Michael Schloter: Our research focused on two main questions: firstly, we wanted to know whether the genetic modification led to other unexpected changes in the plant phenotype, over and above the intended zeaxanthin accumulation. Secondly, we were interested in the effect of the genetic modification on the function of microbial communities in the root area and in the plant litter. We started from the hypothesis that a genetic modification can cause other changes to a plant’s metabolism – even if it has been targeted to affect only one gene.
We used the zeaxanthin potato as a model plant to assess potential safety risks of relevance to soil quality in conjunction with the release of transgenic plants.
GMO Safety: What are the key findings of your research work?
Michael Schloter: In greenhouse experiments we found that the genetic modification of the zeaxanthin potatoes leads to a change in the plant phenotype over and above the intended modification. This could be because the plant is trying to compensate for the modified genetic network structure through alternative metabolic pathways.
For instance, the transgenic plants and the wild type differ in terms of the expressionof several secondary metabolismgenes. But root growth and root morphologycan also differ between the wild type and transgenic lines. However, if you look at the results from a broad spectrum of classic varieties, the differences between individual varieties in terms of the traits investigated are greater than those found between the wild type and the transgenic line.
GMO Safety: What were the results of the experiments in the root area?
Michael Schloter: Among other things, the rhizosphereis significantly affected by plant root exudates and by nutrients that are released when the roots die off. This can alter conditions for the micro-organisms that live there. Micro-organisms carry out important metabolic processes in the soil, e.g. carbon and nitrogen metabolism, which means that they affect the quality of the soil. Here our hypothesis was that if other genes in the plant are affected in addition to the target gene, this could lead to changes to metabolic processes in the rhizosphere.
We were able to observe that the modified plant phenotype leads to differences in the structure and function of the soil micro-organisms in the rhizosphere and, as a result, to different material conversion rates. However, here too, the differences between the wild type and transgenic plants were much smaller than classic varietal effects. Site characteristics and the stage of development of the plants also played an important role.
GMO Safety: The varietal effect in particular is astonishingly high. Why is that?
Michael Schloter: We have discovered that a genetic modification can affect other genes as well as the target gene. But in classing breeding, entire genomes are combined. This is a fundamental intervention in a plant’s genome and it means that they react differently, especially when different environmental factors are brought into play. If you compare the transcriptionpatterns of two conventional potato varieties, e.g. Desiree and Baltica, you will see that they are very different. It is pretty amazing that they both produce potatoes. Classic breeding is nowhere near as targeted as genetic modification
GMO Safety: What is the significance of your findings for the safety assessment of transgenic plants?
Michel Schloter: Safety assessments of genetically modified plants need to look for effects that are not directly linked to the modification, especially where it is the plant’s metabolism that has been modified. These modifications can be expressed as e.g. unintended changes to the phenotype. This was the hypothesis on which our research was based.
But we also need to look at the relevance of such changes, since only differences that go beyond ‘natural’ variability are relevant from a safety point of view. This is why our research covered a range of different locations, different levels of fertilizers and pesticides and a broad range of plant varieties.
GMO Safety: You have been researching soil ecology issues for over ten years. Have you found any indications that transgenic potato plants have an impact on soil quality?
Michael Schloter: We have experience with potatoes that accumulate amylopectinand zeaxanthin. These are both substances that are produced in the potato, so no new genes have been inserted into the plant genome. Instead, existing genes have been switched off – genes that would normally ensure that these substances are wholly or partially broken down again. With these lines we have not found any effects that go beyond normal varietal differences.
In the past ten years of soil ecology we have been focusing around 75 per cent of our efforts on methodological improvements. Years ago we did not have the tools to investigate important issues relating to specific functions of the microflora. You have to know about the functions of micro-organisms in order to be able to establish their effect on soil quality. Without more fundamental research in the field of soil ecology we will be unable to answer important questions in the area of biosafety research.
GMO Safety: Thank you for talking to us.