Kee Hoon Sohn,2
H. Murat Aksoy,1
Jonathan D. G. Jones,2
Eric B. Holub,1 and
1University of Warwick, School of Life Sciences CV35 9EF, U.K.; 2Sainsbury Laboratory, John Innes Centre, Norwich Research Park, Norwich NR4 7UH, U.K.; 3National Pollen and Aerobiology Research Unit, University of Worcester, Henwick Grove, Worcester WR2 6AJ, U.K.
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Accepted 23 February 2011.
RPP5 is the seminal example of a cytoplasmic NB-LRR receptor-like protein that confers downy mildew resistance in Arabidopsis thaliana. In this study, we describe the cloning and molecular characterization of the gene encoding ATR5Emoy2, an avirulence protein from the downy mildew pathogen Hyaloperonospora arabidopsidis isolate Emoy2. ATR5Emoy2 triggers defense response in host lines expressing the functional RPP5 allele from Landsberg erecta (Ler-0). ATR5Emoy2 is embedded in a cluster with two additional ATR5-like (ATR5L) genes, most likely resulting from gene duplications. ATR5L proteins do not trigger RPP5-mediated resistance and the copy number of ATR5L genes varies among H. arabidopsidis isolates. ATR5Emoy2 and ATR5L proteins contain a signal peptide, canonical EER motif, and an RGD motif. However, they lack the canonical translocation motif RXLR, which characterizes most oomycete effectors identified so far. The signal peptide and the N-terminal regions including the EER motif of ATR5Emoy2 are not required to trigger an RPP5-dependent immune response. Bioinformatics screen of H. arabidopsidis Emoy2 genome revealed the presence of 173 open reading frames that potentially encode for secreted proteins similar to ATR5Emoy2, in which they share some motifs such as EER but there is no canonical RXLR motif.
© 2011 The American Phytopathological Society