Isolation and characterization of a cDNA encoding a plant defensin-like protein from roots of Norway spruce

We are studying the interaction between the roots of Norway spruce seedlings (Picea abies L. Karst) and a highly pathogenic isolate of Pythium dimorphum. Here, we report the isolation of a cDNA from spruce roots encoding a protein with high sequence similarity to plant defensins, designated as SPI1 (Spruce Pathogen Induced No. 1). The transcript hybridizing to the SPI1 cDNA probe is highly induced in uninfected roots when the seedlings are transferred from solid to liquid incubating malt medium (hypoxic conditions). However, when the seedlings are transferred from solid to liquid malt media containing a saturating amount of P. dimorphum hyphae, the amount of transcript is unchanged the first day after infection, but then decreases on day 1, and is no longer detectable 2 days after infection. Since plant defensins may play a role in plant defence, their negative regulation upon infection might reflect a strategy employed by this pathogenic fungus to evade the effect of toxic gene products.