DNA methylation pattern of organic and conventional plant samples
EpiOrg – Preventing food fraud: Epigenetic patterns of organic and conventionally grown foods
Organic food is becoming increasingly popular. Whether it is the hoped-for health benefits or the promise that its production is more environmentally friendly than conventional products, the organic sector in Germany recorded sales growth of 9.9% in 2016 alone.
The paper-based certification system is repeatedly reaching its limits. The retail price is about a third higher than for comparable conventional goods, which makes food fraud tempting. Time and again, falsely declared ‘organic goods’ are found.
To date, many attempts have been made to develop an analytical method to clearly identify a plant-based bioproduct as such. For example, vitamin assays, pesticide residues and stable isotopes have been investigated. However, large-scale classification of cultivation systems has failed due to factors such as varietal and annual variability, contamination from pesticide drift, and the possibility of using organic fertilisers in conventional farming. The idea behind stable isotope analysis was that nitrogen fertiliser obtained using the Haber-Bosch process has a different isotope composition than organic fertilisers used on organic fields, and that these ratios can be found in the plants.
A new approach to authenticating organic food could now be the investigation of epigenetic patterns. Initial transcriptome studies have shown that there are differences in gene expression between organically and conventionally grown plants. However, these differences are far too variable to be able to identify an organic product in the long term, as short-term environmental changes, such as fluctuating light conditions, heat, etc., lead to the transcription of other genome segments within a very short time. Epigenetic patterns, i.e. modifications on and in the environment of DNA that influence the activity of genome segments beyond mutations, have proven to be less dynamic but equally dependent on the environment. A distinction is made here between DNA methylation, histone positioning and modifications, and the expression of microRNA fragments that can intercept mRNA pieces before translation.
As part of a project tender by the Volkswagen Foundation, we were one of 17 projects selected for funding out of a total of 594 project applications.
The idea behind the project is that the environment of plants has a decisive influence on epigenetic gene regulation mechanisms and DNA configurations. In a first step, we now want to investigate how methylation patterns – similar to a barcode – differ between organically and conventionally grown soybeans and potato tubers. To ensure that the samples were grown in the appropriate manner, they come from one of the most extensive and elaborate field trials in this area, conducted by the Research Institute of Organic Agriculture (FIBL) in Switzerland.
Methodologically, bisulfite sequencing in cooperation with the Leibniz Institute of Plant Genetics and Crop Plant Research (IPK Gatersleben) will be used to develop an analytical protocol that will enable us to clearly identify organic foods based on their methylation patterns. We expect to find methylation differences in genome regions that are necessary for the nutrient balance and stress response of plants, as well as for their defence.
