Powdery mildew fungal effector candidates share N-terminal Y/F/WxC-motif.
BACKGROUND
Powdery mildew and rust fungi are widespread, serious pathogens that depend on developing haustoria in the living plant cells. Haustoria are separated from the host cytoplasm by a plant cell-derived extrahaustorial membrane. They secrete effector proteins, some of which are subsequently transferred across this membrane to the plant cell to suppress defense.


RESULTS
In a cDNA library from barley epidermis containing powdery mildew haustoria, two-thirds of the sequenced ESTs were fungal and represented approximately 3,000 genes. Many of the most highly expressed genes encoded small proteins with N-terminal signal peptides. While these proteins are novel and poorly related, they do share a three-amino acid motif, which we named "Y/F/WxC", in the N-terminal of the mature proteins. The first amino acid of this motif is aromatic: tyrosine, phenylalanine or tryptophan, and the last is always cysteine. In total, we identified 107 such proteins, for which the ESTs represent 19% of the fungal clones in our library, suggesting fundamental roles in haustoria function. While overall sequence similarity between the powdery mildew Y/F/WxC-proteins is low, they do have a highly similar exon-intron structure, suggesting they have a common origin. Interestingly, searches of public fungal genome and EST databases revealed that haustoria-producing rust fungi also encode large numbers of novel, short proteins with signal peptides and the Y/F/WxC-motif. No significant numbers of such proteins were identified from genome and EST sequences from either fungi which do not produce haustoria or from haustoria-producing Oomycetes.


CONCLUSIONS
In total, we identified 107, 178 and 57 such Y/F/WxC-proteins from the barley powdery mildew, the wheat stem rust and the wheat leaf rust fungi, respectively. All together, our findings suggest the Y/F/WxC-proteins to be a new class of effectors from haustoria-producing pathogenic fungi.
Godfrey
Dale
D
Plant and Soil Science Laboratory, Department of Agricultural and Ecology, Faculty of Life Sciences, University of Copenhagen, Denmark.
Böhlenius
Henrik
H
Pedersen
Carsten
C
Zhang
Ziguo
Z
Emmersen
Jeppe
J
Thordal-Christensen
Hans
H
D020816:Amino Acid Motifs; D001203:Ascomycota / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D017124:Conserved Sequence; D020224:Expressed Sequence Tags; D005656:Fungal Proteins / Q000737:chemistry* / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal / Q000235:genetics; D010802:Phylogeny; D010935:Plant Diseases / Q000382:microbiology*; D018515:Plant Leaves / Q000502:physiology; D021382:Protein Sorting Signals / Q000235:genetics; D014908:Triticum / Q000382:microbiology
D005656:Fungal Proteins; D021382:Protein Sorting Signals