Exogenous fragmented DNA acts as a damage-associated molecular pattern (DAMP) inducing changes in CpG DNA methylation and defence-related responses in Lactuca sativa

Damage-associated molecular patterns (DAMPs) have been studied recently to understand plant self-nonself recognition in response to attack by biotic and abiotic stresses. Extracellular DNA has emerged as a possible DAMP. As a DAMP DNA seems to function depending on the phylogenetic scale and has been tested in a few plant species. This study aimed to evaluate the possible role of self DNA (sDNA) as a DAMP by analysing changes in CpG DNA methylation and defence-related responses in lettuce (Lactuca sativa L.) as a model plant. sDNA and nonself DNA (nsDNA) from Capsicum chinense Murray (both species belong to the same Glade, Asterids) stimulated aberrant seed germination and root growth in lettuce seedlings. Similar resultswere obtained with nsDNA obtained from Acaciella angustissima (Mill.) Britton & Rose plants (belonging to the Glade Rosids I), although at significantly higher concentrations. Moreover, in most cases, this behaviour was correlated with hypomethylation of CpG DNA as well as defence responses measured as altered gene expression associated with oxidative burst and production of secondary metabolites (phenylpropanoids) related to coping with stress conditions. Our results suggested that extracellular and fragmented DNA has a role as a DAMP depending on phylogenetic closeness in plants as lettuce, inducing epigenetic, genetic and biochemical changes within the plant. The importance of our results is that, for the first time, they demonstrate that sDNA acts as a DAMP in plants, changing CpG DNA methylation levels as well as increasing the production of secondary metabolites associated with defence responses to stress.