Arbuscular mycorrhizal fungi change host plant DNA methylation systemically

DNA methylation is an important epigenetic mechanism regulating gene expression in plants. DNA methylation has been shown to vary among species and also among plant tissues. However, no study has evaluated whether arbuscular mycorrhizal (AM) fungi affect DNA methylation levels in a tissue-specific manner. We investigated whether symbiosis with AM fungi affects DNA methylation in the host, focusing on different plant tissues (roots versus leaves) and across time. We carried out a 6-month pot experiment using Geranium robertianum in symbiosis with the AM fungus Funneliformis mosseae. Our results show that the pattern of total DNA methylation differed between leaves and roots and was related to when plants were harvested, confirming that DNA methylation is a process that occurs dynamically throughout an organism's lifetime. More importantly, the presence of AM fungus in roots of our experimental plants had a positive effect on total DNA methylation in both tissues. This study shows that colonisation by AM fungi can affect DNA methylation levels in their hosts and that plant DNA methylation varies in an age- and tissue-specific manner.