title: Discovery of a novel small secreted protein family with conserved N-terminal IGY motif in Dikarya fungi.
abstract: BACKGROUND
  Small secreted proteins (SSPs) are employed by plant pathogenic fungi as essential strategic tools for their successful colonization. SSPs are often species-specific and so far only a few widely phylogenetically distributed SSPs have been identified.
  
  
  RESULTS
  A novel fungal SSP family consisting of 107 members was identified in the poplar tree fungal pathogen Marssonina brunnea, which accounts for over 17% of its secretome. We named these proteins IGY proteins (IGYPs) based on the conserved three amino acids at the N-terminus. In spite of overall low sequence similarity among IGYPs; they showed conserved N- and C-terminal motifs and a unified gene structure. By RT-PCR-seq, we analyzed the IGYP gene models and validated their expressions as active genes during infection. IGYP homologues were also found in 25 other Dikarya fungal species, all of which shared conserved motifs and the same gene structure. Furthermore, 18 IGYPs from 11 fungi also shared similar genomic contexts. Real-time RT-PCR showed that 8 MbIGYPs were highly expressed in the biotrophic stage. Interestingly, transient assay of 12 MbIGYPs showed that the MbIGYP13 protein induced cell death in resistant poplar clones.
  
  
  CONCLUSIONS
  In total, 154 IGYPs in 26 fungi of the Dikarya subkingdom were discovered. Gene structure and genomic context analyses indicated that IGYPs originated from a common ancestor. In M. brunnea, the expansion of highly divergent MbIGYPs possibly is associated with plant-pathogen arms race.
authors.affiliation: Jiangsu Key Laboratory for Poplar Germplasm Enhancement and Variety Improvement, Nanjing Forestry University, Nanjing 210037, China. chengqiang@njfu.edu.cn.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Cheng
authors.forename: Haoran
authors.initials: H
authors.lastname: Wang
authors.forename: Bin
authors.initials: B
authors.lastname: Xu
authors.forename: Sheng
authors.initials: S
authors.lastname: Zhu
authors.forename: Lanxi
authors.initials: L
authors.lastname: Hu
authors.forename: Minren
authors.initials: M
authors.lastname: Huang
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001203:Ascomycota / Q000166:cytology / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D017124:Conserved Sequence; D005656:Fungal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D016681:Genome, Fungal / Q000235:genetics; D023281:Genomics; D008969:Molecular Sequence Data; D010802:Phylogeny; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013559:Symbiosis
chemical_list: D005656:Fungal Proteins