title: HrcU and HrpP are pathogenicity factors in the fire blight pathogen Erwinia amylovora required for the type III secretion of DspA/E.
abstract: BACKGROUND
  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. 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.
  
  
  RESULTS
  Both 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.
  
  
  CONCLUSIONS
  Collectively, these data demonstrate roles for HrcU and HrpP in regulating T3S and represent the first attempt in understanding T3S heirarchy in E. amylovora.
authors.affiliation: Department of Plant Pathology, University of Minnesota, St. Paul, MN, 55108, USA.|Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing, MI, 48824, USA.
authors.forename: R Ryan
authors.initials: RR
authors.lastname: McNally
authors.affiliation: Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing, MI, 48824, USA.|Department of Plant Pathology and Ecology, Connecticut Agricultural Experiment Station, New Haven, CT, 06504, USA.
authors.forename: Quan
authors.initials: Q
authors.lastname: Zeng
authors.affiliation: Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing, MI, 48824, USA. sundin@msu.edu.
authors.forename: George W
authors.initials: GW
authors.lastname: Sundin
mesh_terms: D020816:Amino Acid Motifs; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D044084:Erwinia amylovora / Q000378:metabolism / Q000472:pathogenicity*; D016297:Mutagenesis, Site-Directed; D010935:Plant Diseases / Q000382:microbiology*; D031989:Pyrus / Q000382:microbiology; D016415:Sequence Alignment; D000069296:Type III Secretion Systems / Q000235:genetics / Q000378:metabolism*; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D000069296:Type III Secretion Systems; D037521:Virulence Factors
keywords: Erwinia amylovora; HrcU; HrpP; Secretion hierarchy; Substrate specificity; Type III secretion system