Caratterizzazione del profilo metabolico e trascrizionale di una popolazione di Vitis spp. segregante per la resistenza a Plasmopara viticola

Downy mildew, caused by the oomycete Plasmopara viticola (B. et C.) Berl. et De Toni, is a common disease of grapevine. Although the exact mechanisms by which grapevine cells regulate the disease incidence upon P. viticola infection have largely lain undiscovered until now, it is known that a hypersensitive response (HR) occurs in American Vitis species. The HR to P. viticola was also associated with metabolic and transcriptional events, such as deposition of lignin and other phenolics, accumulation of stilbene phytoalexins, and activation of genes encoding for pathogenesis related proteins (Jeandet et al., 2002, Pezet et al., 2004, Kortekamp, 2006). Aim of this project was to test a possible correlation between the variability in the resistance to the fungus, in the stilbene content and in the gene expression by a targeted metabolite and transcriptional profiling of selected individuals of a population from Merzling (V. vinifera x V. rupestris x V. lincecumii) x V. vinifera ‘Teroldego’. The phenotypic characterization of the response to the fungus within the population allowed us to classify the individuals in classes from total resistance to total susceptibility. The HPLC-DAD-MS analysis performed on infected leaves collected at 6 days post infection (dpi) with the pathogen lead to three main results: it confirmed the stilbene accumulation upon P. viticola infection, it selected a 17% of individuals accumulating the five major viniferins in grapevine and it pointed our attention to the presence of a few oligostilbenes and stilbenoids still undiscovered, whose characterization was performed in the same project. The comparative transcriptional analysis was conducted on resistant and susceptible individuals by a combined approach of i) cDNA-Amplification Fragment Length Polymorphism (AFLP) and ii) oligo-array techniques. The first analysis lead to the isolation of more than 300 transcripts specifically modulated in a totally resistant offspring with respect to Merzling parental and to the discovery that these transcripts can be clustered in two groups according to their kinetics of activation. The “early modulated” were differentially expressed during the first 12 hours post infection, the “late modulated” were differentially expressed starting from 48 hpi. The second analysis allowed further investigation of these genes picking which ones were specific or common between resistant and susceptible individuals.