Effect of Hydroxycinnamic Acid Amides, Coumaroyl Tyramine and Coumaroyl Tryptamine on Biotic Stress Response in Arabidopsis

Abstract

Coumaroyl tyramine (CT) and coumaroyl tryptamine (CTr) are neutral hydroxycinnamic acid amides (HCAAs) that accumulate in plants in response to pathogen infection. In this study, we showed that inoculation of Pseudomonas syringae pv. tomato DC3000 (Pto) and Erwinia carotovora carotovora (ECC) increased the accumulation of CT in Arabidopsis thaliana leaves at 24 h post-inoculation. Both CT and CTr increased the accumulation of PATHOGENESIS-RELATED 1 (PR1) protein. However, CT and CTr had no significant effect on resistance to biotrophic pathogens in both compatible and incompatible plant-pathogen interactions. Nonetheless, our results revealed that CTr plays a critical role in increasing plant susceptibility to the necrotrophic pathogen ECC. Exogenous application of CT and CTr increased the induction of callose deposition in both the absence and presence of ECC. Increased callose deposition was detected in salicylic acid induction-deficient Arabidopsis mutant sid2 but to a lesser extent in ethylene signaling mutants, ein2-1 and etr1. Overall, our results suggest that ethylene signaling is related to CT and CTr-induced callose deposition and contributes to plant defense against pathogens, whereas salicylic acid is not required for this response.