title: The Pseudomonas syringae HrpJ protein controls the secretion of type III translocator proteins and has a virulence role inside plant cells.
abstract: The bacterial plant pathogen Pseudomonas syringae injects effector proteins into plant cells via a type III secretion system (T3SS), which is required for pathogenesis. The protein HrpJ is secreted by P. syringae and is required for a fully functional T3SS. A hrpJ mutant is non-pathogenic and cannot inject effectors into plant cells or secrete the harpin HrpZ1. Here we show that the hrpJ mutant also cannot secrete the harpins HrpW1 and HopAK1 or the translocator HrpK1, suggesting that these proteins are required in the translocation (injection) of effectors into plant cells. Complementation of the hrpJ mutant with secretion incompetent HrpJ derivatives restores the secretion of HrpZ1 and HrpW1 and the ability to elicit a hypersensitive response, a measure of translocation. However, growth in planta and disease symptom production is only partially restored, suggesting that secreted HrpJ may have a direct role in virulence. Transgenic Arabidopsis plants expressing HrpJ-HA complemented the virulence phenotype of the hrpJ mutant expressing a secretion incompetent HrpJ derivative and were reduced in their immune responses. Collectively, these data indicate that HrpJ has a dual role in P. syringae: inside bacterial cells HrpJ controls the secretion of translocator proteins and inside plant cells it suppresses plant immunity.
authors.affiliation: Center for Plant Science Innovation, University of Nebraska, Lincoln, NE 68588-0660, USA.
authors.forename: Emerson
authors.initials: E
authors.lastname: Crabill
authors.forename: Andrew
authors.initials: A
authors.lastname: Karpisek
authors.forename: James R
authors.initials: JR
authors.lastname: Alfano
mesh_terms: D017360:Arabidopsis / Q000382:microbiology; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D005816:Genetic Complementation Test; D059828:Plant Cells / Q000382:microbiology*; D010935:Plant Diseases / Q000382:microbiology*; D044224:Pseudomonas syringae / Q000472:pathogenicity*; D014774:Virulence; D037521:Virulence Factors / Q000378:metabolism*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D037521:Virulence Factors; C083700:hrpJ protein, Pseudomonas syringae; C087295:HrpZ protein, Pseudomonas syringae