Interactions between the powdery mildew effector BEC1054 and barley proteins identify candidate host targets

Pennington, H. G., Gheorghe, D. M., Damerum, A., Pliego, C., Spanu, P. D., Cramer, R. ORCID: https://orcid.org/0000-0002-8037-2511 and Bindschedler, L. V. (2016) Interactions between the powdery mildew effector BEC1054 and barley proteins identify candidate host targets. Journal of Proteome Research, 15 (3). pp. 826-839. ISSN 1535-3907 doi: 10.1021/acs.jproteome.5b00732

Abstract/Summary

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.