SignificancePlant diseases are a major cause of yield loss. We identified SADR1, a TIR-containing immune receptor and found that it participates in immune signaling and in a pathogen containment mechanism sufficient to prevent the spread of a virulent pathogen. SADR1 acts partially independently of EDS1, the receptor for TIR-derived signaling molecules. Inhibition of TIR enzymatic activity with nicotinamide revealed a broader function of TIR domains in immunity. TIR domains can act independently of EDS1 to potentiate immune signaling triggered by other immune receptors.