Jasmonates differentially affect interconnected signal-transduction pathways of Pieris rapae-induced defenses in Arabidopsis thaliana

Abstract The jasmonic acid (JA) pathway is the main signal-transduction pathway induced by insect folivory. Mutant plants affected in the jasmonate pathway (18:0 and/or 16:0-oxylipin routes) were studied to assess the effects of JA and its oxylipin intermediates 12-oxophytodienoic acid (OPDA) and dinor-OPDA (dnOPDA) on interconnected signal-transduction pathways that underlie induced defenses in Arabidopsis. Our data show that the oxylipin jasmonates dnOPDA, OPDA and JA have different roles in defense signaling induced after feeding by the chewing-biting caterpillar Pieris rapae. Jasmonic acid, and not OPDA or dnOPDA, is the major signaling compound required for the induction of the defense-related genes LOX2 (Lipoxygenase 2), OPR3 (12-Oxophytodienoate reductase 3), ACX1 (Acyl-CoA oxidase 1) and PAL1 (Phenylalanine ammonia-lyase 1). Monitoring PAL1 transcript levels clearly showed that accumulation of JA upon P. rapae feeding results in the induction of the salicylic acid pathway. Furthermore, JA is the major signaling compound required for the P. rapae-induced expression of the defense-related gene HPL1 (Hydroperoxide lyase 1). The jasmonate dnOPDA influences the induction of the HPL-branch as well, yet its effect is antagonistic to the effect of JA. Our data show that these jasmonates may be used to fine-tune Arabidopsis’ herbivore-induced responses in terms of the HPL-branch from the oxylipin pathway.