title: HrpE3 is a type III effector protein required for full virulence of Xanthomonas oryzae pv. oryzicola in rice.
abstract: Xanthomonas oryzae pv. oryzicola (Xoc) is the causal agent of bacterial leaf streak, a devastating disease in rice. Xoc uses a type III secretion (T3S) system, which is encoded by the hrp-hrc-hpa (hypersensitive response and pathogenicity, hrp-conserved and hrp-associated) genes, to inject repertoires of T3S effectors (T3Es) into plant cells. Many of the hrp-hrc-hpa genes have roles in pathogenesis, but the role of hrpE3, which shows homology to hpaE in X. campestris pv. vesicatoria (Xcv), is poorly understood. In this study, hrpE3 was shown to be transcribed independent of the hrpD operon, and its expression was dependent on a promoter within hpaB. The expression of hrpE3 was positively regulated by HrpG and HrpX, a finding probably caused by an imperfect plant-inducible promoter (PIP) box (TTCGT-N16 -TTCGA) in the hrpE3 promoter. The secretion of HrpE3 was dependent on T3S, and subcellular localization of HrpE3 was cytoplasmic and nuclear in plant cells. A mutation in hrpE3 reduced the virulence of Xoc by decreasing disease lesion length and bacterial growth in planta. Full virulence was restored to the mutant when Xoc hrpE3, but not Xcv hpaE, was expressed in trans. The differences in transcription, secretion via the T3S system and bacterial virulence in plants were attributed to N-terminal amino acid differences between Xoc HrpE3 and Xcv HpaE. Collectively, the results demonstrate that hrpE3 encodes a T3E protein which is delivered into the plant cell through the T3S system, localizes to the cytoplasm and nucleus, and is required for full virulence in rice.
authors.affiliation: Department of Plant Pathology, Nanjing Agricultural University/Key Laboratory of Monitoring and Management for Plant Diseases and Insects, Ministry of Agriculture of China, Nanjing, 210095, China.
authors.forename: Yiping
authors.initials: Y
authors.lastname: Cui
authors.forename: Lifang
authors.initials: L
authors.lastname: Zou
authors.forename: Huasong
authors.initials: H
authors.lastname: Zou
authors.forename: Yurong
authors.initials: Y
authors.lastname: Li
authors.forename: Muhammad
authors.initials: M
authors.lastname: Zakria
authors.forename: Gongyou
authors.initials: G
authors.lastname: Chen
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D058947:Bacterial Secretion Systems; D001483:Base Sequence; D003593:Cytoplasm / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D054884:Host-Pathogen Interactions; D008969:Molecular Sequence Data; D012275:Oryza / Q000382:microbiology*; D011401:Promoter Regions, Genetic / Q000235:genetics; D021381:Protein Transport; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013347:Subcellular Fractions / Q000378:metabolism; D014158:Transcription, Genetic; D014774:Virulence / Q000235:genetics; D014974:Xanthomonas / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity*
chemical_list: D001426:Bacterial Proteins; D058947:Bacterial Secretion Systems