ATR13 is expressed by the plant pathogen oomycete Hyaloperonospora. Such phytopathogenic oomycetes like the one that infects Arabidopsis, Hyaloperonospora arabidopsidis (Hpa), grow intercellularly, forming parasitic structures called haustoria. Haustoria play a role in feeding and suppression of host defence systems. A whole range of pathogen proteins, called effectors, are secreted across this haustorial membrane, a subset of which are further translocated across the plant plasma membrane by an unknown mechanism that is present in both plants and animals. ATR13 is an RxLR effector from the downy mildew oomycete, and is a very dynamic protein. It contains two surface-exposed patches of polymorphism, one of which is involved in the specific recognition by host R-genes. The R-gene-products detect the presence of the infection by recognising the effector proteins. Once detected, the host R-genes trigger apoptosis of the host cell. The R-gene-products carry a specific motif, RxLR, that is recognises the effector proteins [1].

1: Structural elucidation and functional characterization of the Hyaloperonospora arabidopsidis effector protein ATR13. Leonelli L, Pelton J, Schoeffler A, Dahlbeck D, Berger J, Wemmer DE, Staskawicz B; PLoS Pathog. 2011;7:e1002428. PMID:22194684