Gene Expression Analysis of Induced Plum Pox Virus Resistance in Peach (Prunus Persica) by Almond (P. Dulcis) Grafting

No natural sources of resistance to Plum pox virus (PPV, sharka disease) have been identified in peach. However, previous studies have demonstrated that grafting ‘Garrigues’ almond onto ‘GF305’ peach seedlings heavily infected with PPV can progressively reduce disease symptoms and virus accumulation. Furthermore, grafting ‘Garrigues’ onto ‘GF305’ has completely prevented virus infection. This study aims to analyse the rewiring of gene expression associated with this resistance to PPV transmitted by grafting through phloem using RNA-Seq and RTqPCR analysis. A total of 18 candidate genes were differentially expressed after grafting ‘Garrigues’ almond onto healthy ‘GF305’ peach. Among the up-regulated genes, a HEN1 homolog stands out, which, together with the differential expression of RDR- and DCL2-homologs in some of the conditions assayed, suggests that the RNA silencing machinery is activated by PPV infection and can contribute to the resistance induced by ‘Garrigues’ almond. Glucan endo -1,3-Beta D-Glucosidase could be also relevant for the ‘Garrigues’-induced response, since its expression is much higher in ‘Garrigues’ than in ‘GF305’. We also discuss the potential relevance of the following in PPV infection and ‘Garrigues’-induced resistance: several pathogenesis-related proteins, No apical meristem proteins, the transcription initiation factor TFIIB, the Speckle-type POZ protein and a number of proteins involved in phytohormone signalling.