title: Structure and evolution of barley powdery mildew effector candidates.
abstract: BACKGROUND
  Protein effectors of pathogenicity are instrumental in modulating host immunity and disease resistance. The powdery mildew pathogen of grasses Blumeria graminis causes one of the most important diseases of cereal crops. B. graminis is an obligate biotrophic pathogen and as such has an absolute requirement to suppress or avoid host immunity if it is to survive and cause disease.
  
  
  RESULTS
  Here we characterise a superfamily predicted to be the full complement of Candidates for Secreted Effector Proteins (CSEPs) in the fungal barley powdery mildew parasite B. graminis f.sp. hordei. The 491 genes encoding these proteins constitute over 7% of this pathogen's annotated genes and most were grouped into 72 families of up to 59 members. They were predominantly expressed in the intracellular feeding structures called haustoria, and proteins specifically associated with the haustoria were identified by large-scale mass spectrometry-based proteomics. There are two major types of effector families: one comprises shorter proteins (100-150 amino acids), with a high relative expression level in the haustoria and evidence of extensive diversifying selection between paralogs; the second type consists of longer proteins (300-400 amino acids), with lower levels of differential expression and evidence of purifying selection between paralogs. An analysis of the predicted protein structures underscores their overall similarity to known fungal effectors, but also highlights unexpected structural affinities to ribonucleases throughout the entire effector super-family. Candidate effector genes belonging to the same family are loosely clustered in the genome and are associated with repetitive DNA derived from retro-transposons.
  
  
  CONCLUSIONS
  We employed the full complement of genomic, transcriptomic and proteomic analyses as well as structural prediction methods to identify and characterize the members of the CSEPs superfamily in B. graminis f.sp. hordei. Based on relative intron position and the distribution of CSEPs with a ribonuclease-like domain in the phylogenetic tree we hypothesize that the associated genes originated from an ancestral gene, encoding a secreted ribonuclease, duplicated successively by repetitive DNA-driven processes and diversified during the evolution of the grass and cereal powdery mildew lineage.
authors.affiliation: Department of Agriculture & Ecology, Plant and Soil Science, University ofCopenhagen, Copenhagen, Denmark.
authors.forename: Carsten
authors.initials: C
authors.lastname: Pedersen
authors.forename: Emiel
authors.initials: E
authors.lastname: Ver Loren van Themaat
authors.forename: Liam J
authors.initials: LJ
authors.lastname: McGuffin
authors.forename: James C
authors.initials: JC
authors.lastname: Abbott
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Burgis
authors.forename: Geraint
authors.initials: G
authors.lastname: Barton
authors.forename: Laurence V
authors.initials: LV
authors.lastname: Bindschedler
authors.forename: Xunli
authors.initials: X
authors.lastname: Lu
authors.forename: Takaki
authors.initials: T
authors.lastname: Maekawa
authors.forename: Ralf
authors.initials: R
authors.lastname: Wessling
authors.forename: Rainer
authors.initials: R
authors.lastname: Cramer
authors.forename: Hans
authors.initials: H
authors.lastname: Thordal-Christensen
authors.forename: Ralph
authors.initials: R
authors.lastname: Panstruga
authors.forename: Pietro D
authors.initials: PD
authors.lastname: Spanu
mesh_terms: D000595:Amino Acid Sequence; D001203:Ascomycota / Q000235:genetics*; D002523:Edible Grain / Q000382:microbiology; D005656:Fungal Proteins / Q000235:genetics*; D001467:Hordeum / Q000378:metabolism / Q000382:microbiology*; D054884:Host-Pathogen Interactions / Q000235:genetics; D008969:Molecular Sequence Data; D009181:Mycoses / Q000235:genetics* / Q000276:immunology*; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D040901:Proteomics; D016415:Sequence Alignment
chemical_list: D005656:Fungal Proteins