Phenotypic, molecular and phytohormonal evidence of Plum pox virus silencing in susceptible apricot genotypes

Abstract

Plum pox virus (PPV; sharka disease) is the most important limiting factor for apricot production in affected areas. The generation of new resistant cultivars is the definitive solution to this problem. For this reason, resistance to PPV is one of the main objectives of breeding programmes. During the evaluation of resistance in these programmes, a reduction of sharka symptoms has been observed after the infection of virus in some susceptible cultivars. In this study, we present the results of phenotypic, gene expression and phytohormonal profile changes induced by PPV infection in susceptible apricot cultivars. At the phenotypic level, a reduction in the severity of symptoms during the second infection cycle of the study was observed. This reduction of symptoms could be explained by a silencing effect on the PPV. In line with this idea, the transcriptomic analyses revealed that the early response to PPV is associated with an induction of genes involved in pathogen resistance such as those encoding jasmonic acid, resistance proteins, chitinases, etc. However, the overexpression of the Dicer protein 2a gene in leaves with strong symptoms may indicate the suppression of a gene silencing mechanism in the plant by PPV HCPro and P1 PPV proteins. Salicylic acid appeared to be involved in susceptible infected genotypes. This could also be related to the gene silencing response elicited by the virus. The successful silencing of the virus could be the origin of the reduction in sharka symptoms observed after the infection of some susceptible cultivars.