Almond Grafting for Plum Pox Virus Resistance Triggers Significant Transcriptomic and Epigenetic Shifts in Peaches

Sharka disease, caused by the plum pox virus (PPV), negatively impacts stone fruit production, resulting in economic losses. It has been demonstrated that grafting the almond ( (Miller) D.A. Webb) variety 'Garrigues' into susceptible peach ( (L.) Batsch) rootstocks can result in PPV resistance. The molecular circuits related to grafting in species, however, have not been fully investigated. In this study, susceptible peach rootstocks 'GF305' were either heterografted with 'Garrigues' almond or homografted with the same cultivar. Peach samples were collected at two stages of scion development, with ungrafted plants utilized as controls. Profiles of transcripts, small RNAs (sRNAs), and DNA methylation were obtained and analyzed on a genome-wide scale. Homografting and heterografting significantly altered the transcriptome and methylome of peach rootstocks, with these modifications being more pronounced during the early stages of scion development. The profiles of sRNAs were significantly more impacted when almonds were used as a scion as opposed to peaches, likely due to the transmission of PPV-unrelated viral sequences. Gene expression differences resulting from DNA methylation alterations are more thoroughly documented at the promoter sequences of genes than within their bodies. This study suggests that the 'Garrigues' almond variety triggers a complex defense response in the peach rootstock, potentially involving the interplay of epigenetic modifications and small RNA-mediated priming of antiviral defenses, which ultimately may contribute to PPV resistance.