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Title: Immunomodulation by the Pseudomonas syringae HopZ Type III Effector Family in Aribidopsis

item Lewis, Jennifer
item WILTON, MIKE - University Of Toronto
item MOTT, ADAM - University Of Toronto
item LU, WENWAN - University Of Toronto
item HASSAN, JANA - University Of California
item GUTTMANN, DAVID - University Of Toronto
item DESVEAUX, DARRELL - University Of Toronto

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2014
Publication Date: 12/29/2014
Citation: Lewis, J.D., Wilton, M., Mott, A.G., Lu, W., Hassan, J.A., Guttmann, D.S., Desveaux, D. 2014. Immunomodulation by the Pseudomonas syringae HopZ Type III Effector Family in Aribidopsis. PLoS One. 9(2):e116152.

Interpretive Summary: Pseudomonas syringae is a bacterial pathogen that infects more than 100 plant species. P. syringae causes disease by injecting type III effector proteins into the plant. Type III effector proteins primarily function to suppress plant immune pathways. Recognition of specific type III effector proteins results in a rapid immune response that protects the plant from further infection. We characterized the roles of the HopZ family of effector proteins to better understand their roles in suppressing plant immune pathways. This work will help identify plant genes that are targeted by pathogens and that can be protected in the plant to prevent disease.

Technical Abstract: Pseudomonas syringae employs a type III secretion system to inject 20-30 different type III effector (T3SE) proteins into plant host cells. A major role of T3SEs is to suppress plant immune responses and promote bacterial infection. The YopJ/HopZ acetyltransferases are a superfamily of T3SEs found in both plant and animal pathogenic bacteria. In P. syringae, this superfamily includes the evolutionarily diverse HopZ1, HopZ2 and HopZ3 alleles. To investigate the roles of the HopZ family in immunomodulation, we generated dexamethasone-inducible T3SE transgenic lines of Arabidopsis for HopZ family members and characterized them for immune suppression phenotypes. We show that all of the HopZ family members can actively suppress various facets of Arabidopsis immunity in a catalytic residue-dependent manner. HopZ family members can differentially suppress the activation of mitogen-activated protein (MAP) kinase cascades or the production of reactive oxygen species, whereas all members can promote the growth of non-virulent P. syringae. Localization studies show that four of the HopZ family members containing predicted myristoylation sites are localized to the plasma membrane while HopZ3 which lacks the myristoylation site is nuclear localized, indicating diversification of immunosuppressive mechanisms. Overall, we demonstrate that despite significant evolutionary diversification, all HopZ family members can suppress immunity in Arabidopsis.