Characterization of Blumeria graminis peptides as potential effectors targeting barley RAC/ROP proteins

Small monomeric RAC/ROP GTPases are molecular switches in cell polarity and plant defence responses. In barley RACB and related RAC/ROPs function in susceptibility to the biotrophic ascomycete pathogen Blumeria graminis f.sp. hordei (Bgh). To identify RACBinteracting proteins, we have carried out yeast two hybrid screenings of a cDNA library from infected barley. This identified six fungal clones coding for to the same class of small peptides. Protein-protein interaction was confirmed in independent assays, and a GFP-fusion protein of a fungal RACB-interacting peptide labelled small structures in the cytoplasm and cell cortex and accumulated at the site of pathogen entry. Over-expression or host-induced gene silencing of two Bgh-peptides, enhanced or reduced susceptibility to fungal entry, respectively. By the use of cell-biological and genetic tools, we would like now to provide evidence that the peptides represent fungal virulence effectors that target barley RAC/ROPs for effector-triggered susceptibility.