title: Structural elucidation and functional characterization of the Hyaloperonospora arabidopsidis effector protein ATR13.
abstract: The oomycete Hyaloperonospora arabidopsidis (Hpa) is the causal agent of downy mildew on the model plant Arabidopsis thaliana and has been adapted as a model system to investigate pathogen virulence strategies and plant disease resistance mechanisms. Recognition of Hpa infection occurs when plant resistance proteins (R-genes) detect the presence or activity of pathogen-derived protein effectors delivered to the plant host. This study examines the Hpa effector ATR13 Emco5 and its recognition by RPP13-Nd, the cognate R-gene that triggers programmed cell death (HR) in the presence of recognized ATR13 variants. Herein, we use NMR to solve the backbone structure of ATR13 Emco5, revealing both a helical domain and a disordered internal loop. Additionally, we use site-directed and random mutagenesis to identify several amino acid residues involved in the recognition response conferred by RPP13-Nd. Using our structure as a scaffold, we map these residues to one of two surface-exposed patches of residues under diversifying selection. Exploring possible roles of the disordered region within the ATR13 structure, we perform domain swapping experiments and identify a peptide sequence involved in nucleolar localization. We conclude that ATR13 is a highly dynamic protein with no clear structural homologues that contains two surface-exposed patches of polymorphism, only one of which is involved in RPP13-Nd recognition specificity.
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, California, United States of America.
authors.forename: Lauriebeth
authors.initials: L
authors.lastname: Leonelli
authors.forename: Jeffery
authors.initials: J
authors.lastname: Pelton
authors.forename: Allyn
authors.initials: A
authors.lastname: Schoeffler
authors.forename: Douglas
authors.initials: D
authors.lastname: Dahlbeck
authors.forename: James
authors.initials: J
authors.lastname: Berger
authors.forename: David E
authors.initials: DE
authors.lastname: Wemmer
authors.forename: Brian
authors.initials: B
authors.lastname: Staskawicz
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000469:parasitology; D029681:Arabidopsis Proteins / Q000378:metabolism; D002466:Cell Nucleolus / Q000378:metabolism; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D009868:Oomycetes / Q000235:genetics / Q000472:pathogenicity*; D017433:Protein Structure, Secondary; D014774:Virulence / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D009687:Nuclear Proteins; C408688:RPP13 protein, Arabidopsis