Disease resistance (R) protein that recognizes the AVR-Pia and AVR1-CO39 effector avirulence proteins from M.oryzae. Resistance proteins guard the plant against pathogens that contain an appropriate avirulence protein via an indirect interaction with this avirulence protein. That triggers a defense system including the hypersensitive response, which restricts the pathogen growth. Contribution of RGA4 is required to recognize the effector avirulence proteins AVR-Pia and AVR1-CO39 from M.oryzae (PubMed:21251109, PubMed:23548743). Acts as a repressor of the RGA4-mediated cell death activation. Upon infection, recognition and binding of the AVR effectors relieve the RGA5-mediated repression and triggers the hypersensitive response (PubMed:25024433). Immune response triggered by the RGA4-RGA5 -mediated recognition of AVR1-CO39 confers resistance to X.oryzae pathovars (PubMed:27289079). Forms homodimer or heterodimer with RGA4 through its coiled coil (CC) domain (PubMed:25024433). Interacts with AVR1-Pia and AVR-CO39 through its C-terminal part containing the HMA-like domain (PubMed:23548743, PubMed:28087830). Expressed in leaves. The HMA-like (RATX1) domain is responsible for the specific recognition of AVR effectors. Belongs to the disease resistance NB-LRR family.