Transcriptional analysis in Barbera and Nebbiolo grapevines recovered from flavescence dorée

Grapevine (Vitis vinifera) can be severely affected by phytoplasmas, phloem sieve restricted Mollicutes, transmitted by sap-feeding insect vectors. Flavescence dorèe (FD) is a serious threat to vineyard survival in several grape growing areas, and it is subjected to quarantine restrictions in Europe. Following initial infection and symptom expression, the disease can disappear completely in the following years, giving rise to recovery, an interesting but still largely unknown phenomenon of the plant -pathogen interaction. The biological bases of recovery were investigated in two Italian cultivars, Nebbiolo and Barbera, showing different sensitivity to phytoplasma infection and different recovery occurrence. For each cultivar, leaves of healthy and FD-recovered plants were collected at two time-points during the vegetative season (July and August)in a productive vineyard located in Piemonte and monitored for several years to estimate FD incidence and recovery rate. A list of 18 grapevine genes related to hormone signaling, oxidative response and defence pathways, possibly involved in the recovery phenomenon, was selected on the basis of the available literature and preliminary studies. Variation in mRNA level of the target genes, was evaluated by quantitative RealTime-PCR and correlated to the season and to the phytosanitary status. Despite the season had a deep impact on gene expression variation, few genes related with hydrogen peroxide production and jasmonic acid pathway could discriminate healthy from recovered samples in both cultivars, confirming a probable role for these metabolisms during FD-recovery.