Secreted effector that acts as an elicitor of hypersensitive response (HR) specifically on plants carrying defense protein RPP5. Expressed in spores as well as during host plant infection. Has the canonical EER motif, but lacks the canonical translocation motif RxLR, which characterizes most oomycete effectors identified so far. The EER motif is not required to trigger an RPP5-dependent immune response. The ATR5 effector protein is a polymorphic member of the RXLR class and displays copy-number variation among different isolates of H.arabidopsidis. Belongs to the RxLR effector family.