Functional analysis of barley powdery mildew effector candidates and identification of their barley targets
A. AHMED (1), C. Pedersen (2), T. Schultz-Larsen (2), M. Kwaaitaal (3), H. Jørgensen (2), H. Thordal-Christensen (2) (1) University of California, Davis Genome center, U.S.A.; (2) University of Copenhagen, Denmark; (3) Aachen University, Germany

The genome of barley powdery mildew (Blumeria graminis f. sp. hordei, Bgh) encodes around 500 Candidate Secreted Effector Proteins (CSEPs). So far, little is known about the function in virulence of many CSEPs and the identities of their host targets. In this study, we investigated the function of nine CSEPs using host-induced gene silencing and found that CSEP0081, CSEP0105, CSEP0162 and CSEP0254 contribute to Bgh infection success. Independent silencing of these CSEPs signi?cantly reduced the fungal haustorial formation rate. These CSEPs are likely required during and after the formation of haustoria, in which their transcripts were found to be predominant, rather than in epiphytic tissue. When expressed in barley leaf epidermal cells, these CSEPs localized to the cytosol and the nucleus, suggesting that their host targets locate in these cellular compartments. Interestingly, two cytosolic barley small heat shock proteins, Hsp16.9 and Hsp17.5, were identified as interactors with both CSEP0105 and CSEP0162 in a yeast two-hybrid assay. These interactions were confirmed in planta by BiFC and co-localization studies. As predicted, the barley Hsp16.9 showed chaperone activity that prevented the aggregation of Escherichia coli proteins during thermal stress. Remarkably, CSEP0105 compromised this activity. These data suggest that CSEP0105 promotes virulence by interfering with the chaperone activity of a barley small heat shock protein essential for defense and stress responses. 

Abstract Number: C14-3, P10-340
Session Type: Concurrent