Characterization of differentially expressed transcripts in quercetin-treated apples by suppression subtractive hybridization

In previous trials the flavonoid quercetin proved to be effective in reducing Penicillium expansum infections and patulin accumulation in apples. Since quercetin resulted more effective in in vivo than in in vitro trials, a possible role of this substance in enhancing host resistance was hypothesized. To verify this hypothesis, a cDNA library of genes differentially expressed in response to quercetin application was constructed by using the suppression subtractive hybridization (SSH) approach. A total of 89 unique sequences were obtained. By homology search and functional analysis the identified sequences were putatively categorized as belonging to "metabolism", "subcellular localization" and "protein with binding functions or cofactor requirement" classes. Similarity was also found with genes coding proteins whose role in defence mechanisms is still unknown.