Secreted effector that acts as an elicitor of hypersensitive response (HR) specifically on plants carrying both defense protein RPP1 from several ecotypes including RPP1-NdA, RPP1-WsB, RPP1-EstA and RPP1-ZdrA. Monomer (PubMed:21788488). Interacts with defense protein RPP1 from several ecotypes including RPP1-NdA, RPP1-WsB, RPP1-EstA and RPP1-ZdrA, via their leucine-rich repeats (LLRs) (PubMed:25671309, PubMed:26725254). The RxLR-dEER motif acts to carry the protein into the host cell cytoplasm through binding to cell surface phosphatidylinositol-3-phosphate (PIP). However ATR1 does not bind to PIPs, even though it harbors the RxLR-dEER motif at the N-terminus, suggesting that the RxLR-dEER motif is insufficient for PIP binding. The tandem repeated WY domains are involved in the recognition of the RPP1 defense proteins of the different Arabidopsis thaliana ecotypes. The ATR1 effector protein of Hyaloperonospora arabidopsidis is a polymorphic member of the RXLR class of secreted effectors. The ATR1 alleles are differentially recognized by RPP1 genes from different Arabidopsis ecotypes (Niederzenz, Wassilewskija, Estland and Zdarec). Belongs to the RxLR effector family.