HrcU and HrpP are pathogenicity factors in the fire blight pathogen Erwinia amylovora required for the type III secretion of DspA/E.

R Ryan Mcnally,George W Sundin,Quan Zeng

doi:10.1186/s12866-016-0702-y

Abstract

BackgroundMany Gram-negative bacterial pathogens mediate host-microbe interactions via utilization of the type III secretion (T3S) system. The T3S system is a complex molecular machine consisting of more than 20 proteins. Collectively, these proteins translocate effectors across extracellular space and into the host cytoplasm. Successful translocation requires timely synthesis and allocation of both structural and secreted T3S proteins. Based on amino acid conservation in animal pathogenic bacteria, HrcU and HrpP were examined for their roles in regulation of T3S hierarchy.ResultsBoth HrcU and HrpP were shown to be required for disease development in an immature pear infection model and respective mutants were unable to induce a hypersensitive response in tobacco. Using in vitro western blot analyses, both proteins were also shown to be required for the secretion of DspA/E, a type 3 effector and an important pathogenicity factor. Via yeast-two hybridization (Y2H), HrpP and HrcU were revealed to exhibit protein-protein binding. Finally, all HrcU and HrpP phenotypes identified were shown to be dependent on a conserved amino acid motif in the cytoplasmic tail of HrcU.ConclusionsCollectively, these data demonstrate roles for HrcU and HrpP in regulating T3S and represent the first attempt in understanding T3S heirarchy in E. amylovora.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-016-0702-y) contains supplementary material, which is available to authorized users.

Highlights

Many Gram-negative bacterial pathogens mediate host-microbe interactions via utilization of the type III secretion (T3S) system
HrcU exhibits a conserved Asparigine-prolinethreonine-histidine domain found in YscU/FlhB proteins (NPTH) motif required for pathogenicity in E. amylovora The NPTH motif in YscU/FlhB proteins is the site of autoproteolytic cleavage and conformational change required for protein function [4, 15]
Using T-Coffee multiple alignment software, the amino acid sequence of HrcU was compared to multiple homologs in Type III secretion (T3S) systems of plant and animal bacterial pathogens as well as in the flagellum (Table 1) [32]

Summary

Introduction

Many Gram-negative bacterial pathogens mediate host-microbe interactions via utilization of the type III secretion (T3S) system. The T3S system is a complex molecular machine consisting of more than 20 proteins. These proteins translocate effectors across extracellular space and into the host cytoplasm. Successful translocation requires timely synthesis and allocation of both structural and secreted T3S proteins. The type III secretion (T3S) system is a common feature of Gram-negative bacterial pathogens. The T3S system functions to facilitate the translocation of bacterial effector proteins into eukaryotic host cells where they suppress host defense responses, facilitate colonization, and promote disease development [1]. Because the successful translocation of bacterial effectors necessitates a functioning multipartite machine, the production of structural and secreted T3S system components has been assumed to be hierarchical. Recent analyses have confirmed the hierarchical nature of T3S in a few animal

Methods

Results

Discussion

Conclusion