Tunicamycin-induced endoplasmic reticulum stress suppresses plant immunity

Abstract

Most secretory and membrane proteins are properly folded in the endoplasmic reticulum (ER) before being transferred to their functional destinations. Physiological and pathological stresses induce unfolded and misfolded protein accumulation in the ER, termed as ER stress. Under ER stress, cells initiate a protective response to maintain cellular homeostasis, which is referred as unfolded protein responses. Although protein processing in the ER has been known to regulate cell lifespan and disease, few evidences that prove the role of ER stress in plant immunity have been reported. We investigated the interaction between ER stress and pathogenicity in Arabidopsis by utilizing the N-glycosylation inhibitor, tunicamycin (TM) as an ER stress inducer. TM induced the accumulation of PR1 (pathogenesis-related protein 1) and callose in plant leaves, which are markers for PAMP-triggered immunity (PTI) activation. However, TM pre-treatment increased susceptibility of Arabidopsis to all bacterial pathogens tested. Moreover, TM resulted in cell death of plant leaves with an additive effect to hypersensitive response by bacterial effector proteins, suggesting TM-induced cell death is independent of the effector-triggered immunity. These results imply that TM-induced ER stress weakens overall immune system of plant not a specific immune pathway, probably via disruption of post-translational modification of immune-related proteins in the ER and subsequent cell death by apoptosis or autophagy. This study provides proves for the distinct suppressive effect of ER stress on the plant immune system.