Epigenetics and symbioses. Analysis of DNA methylation pattern in Apis mellifera and Varroa destructor parasitic relationship

DNA methylation is an epigenetic mechanism which consist of the a addition of a methyle group to a cytosine in a DNA sequence. Such modifications are able to cause several changes in the regulation and expression of genes, allowing organisms to respond quickly to different kind of environmental variations. In this study, the hypothesis that such epigenetic modification and, in particular DNA methylation, for its great simplicity, plasticity and magnitude can be involved in the regulation symbiont interactions. It is infact, well known that a lot of viruses and bacteria interact with their host also by interfering with the regulation of DNA methylation. This work focused on the study of arthropod symbioses and in particluar on the case of Apis mellifera, a pollinator insect important both economically and genetically, especially since its genome has been sequenced, and Varroa destructor, an ectoparasitic mite that reproduces inside the bees’ brood cells and have recently caused the disappearance of millions A. mellifera colonies. Previous studies have shown that mite attack can cause extensive damages in bees, impairing in particular the immune system the immune system and cognitive abilities. This work focused on a three levels analysis. First the genomic DNA methylation pattern was studied. Then the DNA pattern, with gene level resolution focusing on target genes direclty involved in the interaction between mite and bees, was analyzed. Finally, all samples were screened for mite-transmitted virus presence. Result show that in there are no differences between the genomic methylation level between parasitized and non parasitized bees, reflecting the genomic constitution of bees, which are characterized by very AT rich genomes, so poor methylable genome. Gene resolution analysis shown that in every case, the DNA methylation levels are lower in parasitized non parasitized samples. Moreover, DNA methylation was shown to increase with the virus parasitization of the bees. Taken together these result indicated that DNA methylation may play a role in the regulation of honeybee and parasites relationship. Moreover, this study also support DNA methylation as a good candidate for the interaction and communications of two symbiont in a symbioses, providing DNA methylation as a good target candidate for the control of parasitic symbionts.