Abstract: Maintenance of endoplasmic reticulum (ER) homeostasis is central for plants to survive in changing cellular and environmental conditions. Although the role of ER in plant immunity is evident, how ER homeostasis is associated with activation of the immune response remains unclear. Here, we report that StDMP2, an ER-localized member of the DOMAIN OF UNKNOWN FUNCTION 679 membrane protein (DMP) family, positively regulates resistance to Phytophthora in potato (Solanum tuberosum). Heterologous expression of StDMP2 in tobacco (Nicotiana benthamiana) also enhances resistance to Phytophthora. Furthermore, StDMP2 is involved in both chemical- and pathogen-induced ER stress responses. Notably, StDMP2 plays a crucial role in several pathogen-associated molecular pattern-triggered immunity responses, and specifically contributes to the hypersensitive response triggered by the bacterial type-III secreted effector AvrRpt2, but not the Phytophthora infestans-secreted effector Avr3a. Further investigation revealed that StDMP2 affects the ER quality control-mediated accumulation of specific pattern recognition receptors and NON-RACE SPECIFIC DISEASE RESISTANCE 1. Collectively, these findings elucidate a mechanism by which StDMP2 promotes plant immunity through modulating ER homeostasis.

Key words: DOMAIN OF UNKNOWN FUNCTION 679 membrane protein, ER quality control, ER stress, Phytophthora resistance, plant immunity, potato