title: The pathogenicity factor HrpF interacts with HrpA and HrpG to modulate type III secretion system (T3SS) function and t3ss expression in Pseudomonas syringae pv. averrhoi.
abstract: To ensure the optimal infectivity on contact with host cells, pathogenic Pseudomonas syringae has evolved a complex mechanism to control the expression and construction of the functional type III secretion system (T3SS) that serves as a dominant pathogenicity factor. In this study, we showed that the hrpF gene of P. syringae pv. averrhoi, which is located upstream of hrpG, encodes a T3SS-dependent secreted/translocated protein. Mutation of hrpF leads to the loss of bacterial ability on elicitation of disease symptoms in the host and a hypersensitive response in non-host plants, and the secretion or translocation of the tested T3SS substrates into the bacterial milieu or plant cells. Moreover, overexpression of hrpF in the wild-type results in delayed HR and reduced t3ss expression. The results of protein-protein interactions demonstrate that HrpF interacts directly with HrpG and HrpA in vitro and in vivo, and protein stability assays reveal that HrpF assists HrpA stability in the bacterial cytoplasm, which is reduced by a single amino acid substitution at the 67th lysine residue of HrpF with alanine. Taken together, the data presented here suggest that HrpF has two roles in the assembly of a functional T3SS: one by acting as a negative regulator, possibly involved in the HrpSVG regulation circuit via binding to HrpG, and the other by stabilizing HrpA in the bacterial cytoplasm via HrpF-HrpA interaction prior to the secretion and formation of Hrp pilus on the bacterial surface.
authors.affiliation: Department of Plant Pathology, National Chung Hsing University, Taichung, 40227, Taiwan.|Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, 40227, Taiwan.
authors.forename: Yi-Chiao
authors.initials: YC
authors.lastname: Huang
authors.affiliation: Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, 40227, Taiwan.
authors.forename: Yuan-Chuen
authors.initials: YC
authors.lastname: Lin
authors.affiliation: Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, 40227, Taiwan.
authors.forename: Chia-Fong
authors.initials: CF
authors.lastname: Wei
authors.affiliation: Department of Plant Pathology, National Chung Hsing University, Taichung, 40227, Taiwan.|Agricultural Biotechnology Center, National Chung Hsing University, Taichung, 40227, Taiwan.
authors.forename: Wen-Ling
authors.initials: WL
authors.lastname: Deng
authors.affiliation: Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, 40227, Taiwan.
authors.forename: Hsiou-Chen
authors.initials: HC
authors.lastname: Huang
mesh_terms: D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D054884:Host-Pathogen Interactions; D047468:Immunoprecipitation; D050505:Mutant Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D010935:Plant Diseases / Q000382:microbiology; D011485:Protein Binding; D021381:Protein Transport; D044224:Pseudomonas syringae / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014026:Nicotiana / Q000276:immunology / Q000382:microbiology; D020798:Two-Hybrid System Techniques; D000069296:Type III Secretion Systems
chemical_list: D001426:Bacterial Proteins; D050505:Mutant Proteins; D011993:Recombinant Fusion Proteins; D000069296:Type III Secretion Systems
keywords: Pseudomonas syringae; T3SS; hrpF; t3ss regulation