Evidence for Different Signaling Pathways Activated by Inducers of Acquired Resistance in Wheat

Acquired resistance (AR) of wheat (Triticum aestivum) to the powdery mildew fungus Erysiphe graminis f. sp. tritici can be induced either by inoculation with the nonhost pathogen E. graminis f. sp. hordei or by treatment with chemical substances such as benzo(1,2,3)thiodiazole-7-carbothioic acid S-methyl ester (BTH). In the dicotyledonous plants tobacco and Arabidopsis, induction of AR by pathogens and BTH is accompanied by the expression of a characteristic set of genes. Here we report that in wheat, BTH treatment failed to activate genes whose transcripts accumulate after AR induction by nonhost pathogens, whereas BTH-inducible genes were not activated by an appropriate pathogen inoculation. This suggests that at least two different pathways exist for the induction of AR in monocots.