Suppression Subtractive Hybridization (SSH) was applied in a search for genes induced during the compatible interaction between Phytophthora infestans and potato. Using potato leaves that had been treated with benzo (1,2,3)thiadiazole-7-carbothioic acid S-methylester (BTH) as the control tissue, a low redundancy library with a relatively low frequency of the classic
plant Pathogenesis-Related (PR) genes was generated. 288 of the clones were screened for induced sequences using Inverse Northern analysis (hybridizing the arrayed clones with radiolabelled cDNA populations). Of the 75 clones that were detectable by this method, 43 appeared to be induced. Eleven of these clones were then analysed by total RNA blot analysis, and
elevation of transcript levels during P. infestans infection was
confirmed for 10 of them. Some of the cDNAs analysed by RNA blot analysis have homology to genes already known to be induced during infection, e.g. to β-1,3-glucanase. Another group of cDNAs have homology to enzymes involved in detoxification: gamma-glutamylcysteine synthetase, cytochrome P450, glutathione S-transferase and an MRP-type ABC transporter. Other infection induced cDNAs encode putative proteins that have not previously been reported to be induced by infection: e.g. the ER-located chaperone BiP, and a homologue of Aspergillusnidulans SudD, which was isolated as a suppressor of a mutation in chromosome disjunction. The differential library therefore presents the opportunity to analyse the metabolic changes occurring during infection, and the disease process itself in more detail.
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