Interactions between the Powdery Mildew Effector BEC1054 and Barley Proteins Identify Candidate Host Targets

There are over 500
candidate secreted effector proteins (CSEPs)
or Blumeria effector candidates (BECs) specific to
the barley powdery mildew pathogen Blumeria graminis f.sp. hordei. The CSEP/BEC proteins are expressed
and predicted to be secreted by biotrophic feeding structures called
haustoria. Eight BECs are required for the formation of functional
haustoria. These include the RNase-like effector BEC1054 (synonym
CSEP0064). In order to identify host proteins targeted by BEC1054,
recombinant BEC1054 was expressed in E. coli, solubilized,
and used in pull-down assays from barley protein extracts. Many putative
interactors were identified by LC-MS/MS after subtraction of unspecific
binders in negative controls. Therefore, a directed yeast-2-hybrid
assay, developed to measure the effectiveness of the interactions
in yeast, was used to validate putative interactors. We conclude that
BEC1054 may target several host proteins, including a glutathione-S-transferase,
a malate dehydrogenase, and a pathogen-related-5 protein isoform,
indicating a possible role for BEC1054 in compromising well-known
key players of defense and response to pathogens. In addition, BEC1054
interacts with an elongation factor 1 gamma. This study already suggests
that BEC1054 plays a central role in barley powdery mildew virulence
by acting at several levels.