Plant immunity mediated by nucleotide-binding leucine-rich repeat (NLR) receptors through specific recognition of pathogen effectors is well established, yet signaling mechanisms involving non-NLR resistance proteins remain poorly understood. Here, we uncover the mechanism of PTR, a non-NLR protein in rice that con- fers broad resistance to Magnaporthe oryzae by recognizing the effector AVR-Pita. We show that PTR functions as an endoplasmic reticulum (ER)-localized Ca²  channel, assembling into a pentam- eric, Ca² -permeable complex required for immune signaling. PTR is autoinhibited by its C-terminal tail, which undergoes farnesyla- tion in planta and this modification is both necessary and sufficient for channel inhibition. Notably, AVR-Pita cleaves the farnesylated C-terminal tail, relieving autoinhibition and activating Ca²  influx to initiate defense. Rice plants carrying PTR alleles with mutated cleavage sites exhibit enhanced susceptibility to Magnaporthe oryzae, underscoring the physiological relevance of this mecha-nism. Our findings directly connect pathogen effector recognition to calcium signaling and reveal a novel immune activation mechanism in which effector-mediated proteolysis derepresses a Ca²  channel to trigger plant immunity.