cDNA cloning of sesquiterpene cyclase and squalene synthase, and expression of the genes in potato tuber infected with Phytophthora infestans.

Sesquiterpene cyclase and squalene synthase are key branch point enzymes in isoprenoid pathway for the synthesis of sesquiterpenoid phytoalexins and sterols/steroid glycoalkaloids, respectively. cDNA clones encoding these enzymes were isolated from potato. A phylogenetic tree showed that the sesquiterpene cyclase is vetispiradiene synthase. Infection of Phytophthora infestans with potato tubers caused transient increases in the transcript level of vetispiradiene synthase in a compatible and an incompatible interactions. On the other hand, wound-induced expression of the squalene synthase was suppressed in favor of the expression of vetispiradiene synthase regardless of inoculated races.