Abstract
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.
Highlights
Microbial pathogens secrete effector proteins into host tissues and cells to facilitate infection
In vitro affinity pull-down to identify barley proteins interacting with BEC1054
Additional putative interactors selected for validation using Y2H included the malate dehydrogenase (Q6YWL3), ribosomal protein 40S S16 (Q0IQF7), an elongation factor EF1A (Q9LN13) and a nucleoside diphosphate protein kinase (NDPK, Q9LKM0)
Summary
Microbial pathogens secrete effector proteins into host tissues and cells to facilitate infection Some of these effectors play a crucial role by targeting key proteins involved in host immunity. This is well documented for bacterial pathogens of plants and animals.[1] Plant pathogenic fungi produce arsenals of diverse effectors.[2] Large families of protein effectors have been described in biotrophic fungi such as Puccinia triticina wheat rust[3] and Blumeria graminis cereal powdery mildews.[4,5] These pathogens, like many biotrophs and mutualistic symbionts, develop specialized feeding structures called haustoria. It is becoming clear that, in addition to taking up nutrients from the host, haustoria play a central role in effector delivery to host cells.[6]
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