ETR1-, JAR1- and PAD2-dependent signaling pathways are involved in C6-aldehyde-induced defense responses of Arabidopsis

C6-aldehydes [(E)-2-hexenal and (Z)-3-hexenal] induce expression of defense genes, accumulation of antifungal substances, and resistance against Botrytis cinerea with Arabidopsis. In order to elucidate the signaling pathway mediating the defense responses induced by C6-aldehydes in Arabidopsis, we compared the responses of Arabidopsis mutants deficient in the signaling pathways; i.e., etr1-1 (ethylene resistant), jar1-1 (jasmonate resistant), npr1-1 (salicylic acid insensitive), or pad2-1 (phytoalexin-deficient) with those of wild type (WT) plants. Induction of some, but not all of the defense genes in response to C6-aldehydes was significantly repressed in jar1-1, etr1-1, and pad2-1, but not at all in npr1-1. C6-aldehyde-treatment enhanced accumulation of camalexin with WT and npr1-1, but only partially with etr1-1 and jar1-1. pad2-1 showed little accumulation of camalexin. npr1-1 accumulated the antifungal substances as WT did, however, etr1-1, jar1-1 and pad2-1 exhibited only partial accumulation. The treatment enhanced resistance of etr1-1, jar1-1 and npr1-1 against B. cinerea, but failed to enhance the resistance of pad2-1. Taken together, it was suggested that ETR1-, JAR1-, and PAD2-dependent signaling pathways were simultaneously activated by C6-aldehyde-treatment. Among these, PAD2-dependent signaling appeared to be most important. In contrast, involvement of NPR1-dependent signaling was minimal.