A nuclear replicating viroid antagonizes infectivity and accumulation of a geminivirus by upregulating methylation related genes and inducing hypermethylation of viral DNA
DNA methylation and post transcriptional gene silencing play critical roles in controlling infection of single stranded (ss) DNA geminiviruses and ssRNA viroids, respectively, but both pathogens can counteract these host defense mechanisms and promote their infectivity. Moreover, a specific role of DNA methylation in viroid host interactions is not yet confirmed. Here, using an experimental system where two nuclear replicating agents, the geminivirus tomato yellow leaf curl Sardinia virus (TYLCSV) and potato spindle tuber viroid (PSTVd) co infect their common host tomato, we observed that PSTVd severely interferes with TYLCSV infectivity and accumulation, most likely as a consequence of strong activation of host DNA methylation pathways. In fact, PSTVd alone or in co infection with TYLCSV significantly upregulates the expression of key genes governing DNA methylation in plants. Using methylation sensitive restriction and bisulfite conversion assays, we further showed that PSTVd infection promotes a strong hypermethylation of TYLCSV DNA, thus supporting a mechanistic link with the antagonism of the viroid on the virus in co infected tomato plants. These results describe the interaction between two nuclear replicating pathogens and show that they differentially interfere with DNA methylation pathways.
Scientific reports