SUMMARYPlant cells possess a two‐layered immune system consisting of pattern‐triggered immunity (PTI) and effector‐triggered immunity (ETI), mediated by cell surface pattern‐recognition receptors and intracellular nucleotide‐binding leucine‐rich repeat receptors (NLRs), respectively. The CONSTITUTIVE EXPRESSION OF PR GENES 5 (CPR5) nuclear pore complex protein negatively regulates ETI, including ETI‐associated hypersensitive response. Here, we show that CPR5 is essential for the activation of various PTI responses in Arabidopsis, such as resistance to the non‐adapted bacterium Pseudomonas syringae pv. tomato DC3000 hrcC‐. In a forward‐genetic screen for suppressors of cpr5, we identified the mediator protein MED4. Mutation of MED4 in cpr5 greatly restored the defective PTI of cpr5. Our findings reveal that CPR5 plays opposite roles in regulating PTI and ETI, and genetically regulates PTI via MED4.