It was thought for a long time that hybrid vigour - the phenomenon that the offspring of two different parents perform better for a given trait than the parents - is only the result of genetic differences between the parental lines. Recent research by, among others, UvA-biologists shows that not only the DNA building blocks, but also the differences in the amount of chemical modifications present can lead to better properties. The results are published in the latest issue of Plant Physiology.
Hybrid vigour, also known as heterosis, has many manifestations. It plays a role in the optimization of agricultural crops, but also in the longer life span of pet animals that are the result of crossing different breeds. The occurrence of heterosis has long been explained as a beneficial effect of combining two slightly different genomes. Hereby the less favorable features of both genomes can be compensated for by crossing.
Two parental lines differ, however, not only in the order of the DNA building blocks, but also in the existing chemical modifications of the DNA, and the proteins that are bound to the DNA (epigenetic modifications). Previous research has already shown that these modifications may also play a role in the occurrence of heterosis. However, in those studies one could not distinguish between the contribution of the genetic and epigenetic differences between the parental lines.
In the recent study, done by Kathrin Lauss, Rurika Oka and Maike Stam of the Swammerdam Institute of Life Sciences, they used a special trick, looked exclusively at the effect of differences in DNA methylation on heterosis in the scientific model plant Arabidopsis. DNA methylation is the epigenetic mechanism adding methyl groups (basic structure -CH3) to DNA molecules, resulting in a change in the accessibility of the DNA for cellular proteins. The team identified specific DNA regions that differ in the amount of DNA methylation between the parental lines and that also play a role in the observed heterosis in the offspring. These regions contain multiple genes that may play a role in heterosis.
Genome-wide data sets presented in the study also showed that there are all kinds of changes in DNA methylation and gene activity in the hybrid offspring. This is most likely due to the differences in DNA methylation between the parent lines. In conclusion, the data show that local differences in DNA methylation between parental lines have a direct or indirect effect on the occurrence of heterosis. The data thus provides a better insight into this very complex phenomenon.
The new understanding that differences in chemical modifications can be sufficient to cause heterosis can be used in the future to steer this process, and perhaps play a crucial role in further optimizing the yield of crops and fulfilling the growing demand for food. Follow-up research is aimed at examining whether the epigenetic differences between the identified candidate genes are actually sufficient to bring about heterosis. In addition, further work will be done on unraveling the mechanisms underlying the changes in DNA methylation in hybrid offspring: genome-wide, but also between specific versions of genes.
This research was done in collaboration with René Wardenaar and Frank Johannes of the University of Groningen and the Technical University in Munich, as well as the group of Joost Keurentjes at the University of Wageningen. All the experimental work and part of the data analysis has been carried out under the supervision of Maike Stam. Most data analysis was performed under supervision of Frank Johannes. The phenotypic analysis of the plants was done in a climate-controlled room with automatic camera system in Wageningen, with support of the group of Joost Keurentjes.
Kathrin Lauss, René Wardenaar, Rurika Oka, Marieke H. A. van Hulten, Victor Guryev, Joost J. B. Keurentjes, Maike Stam, Frank Johannes, 2018): 'Parental DNA Methylation States Are Associated with Heterosis in Epigenetic Hybrids' in Plant Physiology, Februari 2018. DOI: https://doi.org/10.1104/pp.17.01054