Disease resistance (R) protein. 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 RGA5 is required to recognize the effector avirulence proteins AVR-Pia and AVR1-CO39 from M.oryzae (PubMed:21251109, PubMed:23548743). Acts as a constitutively active cell death inducer that is repressed by RGA5 (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 RGA5 through its coiled coil (CC) domain. Expressed in leaves. Belongs to the disease resistance NB-LRR family.