Characterization of 3 new partial stilbene synthase genes out of over 20 expressed in Vitis vinifera during the interaction with Plasmopara viticola

SummaryRT-PCR was used to amplify stilbene synthase (STS) transcripts expressed in the grape–downy mildew interaction. Four grape cultivars, Chasselas, IRAC-2029, IRAC-1999 and Solaris (from susceptible to resistant), were used in order to access members of the gene family and some allelic variations. Plant resistance to Plasmopara viticola was scored by quantification of stilbenes 2 days post inoculation and of sporangia at 7 days. RT-PCR products were analyzed by gel electrophoresis, cloned and 300 individual clones were sequenced. Sequences covered 1/3 (455 bp) of the coding region and up to 300 bp of the 3′ untranslated region. A cluster tree of the aligned sequences exhibits 17 main branches, most of which split again suggesting allelic variations. Quantitative real-time PCR was then performed to identify single copy genes coding for STS as well as for the closely related chalcone synthase (CHS). The analysis identified that grapes have two CHS, one CHS-like and close to 25 STS single copy genes. A comparison between a sensitive and a resistant grape to P. viticola is discussed in relation to the stilbene synthase gene family and the problematic to quantify their expression.