Secreted effector that acts as an elicitor of hypersensitive response (HR) specifically on plants carrying defense protein RPP13. Recognition of ATR13 by RPP13 initiates defense responses that are effective against oomycete, bacterial and viral pathogens (PubMed:15591208, PubMed:18165328, PubMed:18198274, PubMed:22194907). Due to high polymorphism, ATR13-Emoy2 does not recognize RPP13-Nd, the RPP13 defense protein from Arabidopsis thaliana ecotype Niederzenz (PubMed:15591208, PubMed:18165328, PubMed:18198274, PubMed:22194684). ATR13-Emoy2 is recognized by RPP13 variants RPP13-UKID44, RPP13-UKID65 and RPP13-UKID71 (PubMed:19523099). Localizes to the cytoplasmic scaffolding and to discrete punctate spots along these strands. Has the canonical translocation motif RxLR, but lacks the canonical EER motif, which characterizes most oomycete effectors identified so far. The leucine heptad repeat region contains five protein variants with 12 amino acid polymorphisms. Leucine heptad repeats are a feature of coiled coils where the leucines are embedded in an alpha helical region. Three of the different variants were recognized by RPP13-Nd, suggesting that alteration of the amino acid sequence in this region is tolerated. All ATR13 variants contain at least one 11-amino-acid direct repeat region. This region is involved in nucleolar localization. A single repeat unit is found in ATR13-Aswa1, ATR13-Emco5, ATR13-Goco1-A and ATR13-Goco1-B (ATR13-Hind2 has one repeat unit followed by an additional 3 amino acids), preventing nucleolar localization, whereas three units are present in ATR13-Bico1, ATR13-Waco5 and ATR13-Wela3, and four units are present in ATR13-Maks9, ATR13-Hiks1, ATR13-Cala2, ATR13-Cand5, ATR13-Hind4, ATR13-Emwa1-A, ATR13-Emwa1-B, ATR13-Emoy2, ATR13-Noks1 and ATR13-Ahnd1. In addition there are 14 polymorphic positions, resulting in a total of seven variant forms within this domain. No association between the number or sequence identity of these repeats and recognition by RPP13-Nd could be detected. The highly variable C-terminus domain and is involved in the specificity for the recognition by RPP13-Nd. 'Thr-152' and 'Arg-181' are critical for recognition by A.thaliana RPP13-Nd. The ATR13 effector protein is a highly polymorphic member of the RXLR class, yet only a small subset of the polymorphic residues appear to be involved in RPP13Nd-mediated recognition. Polymorphic residues of ATR13 appear as clusters across the surface of the protein. ATR13-Emoy2 is not recognized by RPP13-Nd because it has Ile-152 and Gln-181 rather than 'Thr-152' and 'Arg-181' within the highly variable C-terminus domain. Belongs to the RxLR effector family.