title: Identification of phenolic compounds that suppress the virulence of Xanthomonas oryzae on rice via the type III secretion system.
abstract: The targeting of bacterial type III secretion systems (T3SSs), which are critical virulence factors in most Gram-negative pathogens, is regarded as an alternative strategy for the development of novel anti-microbial drugs. Xanthomonas oryzae pv. oryzae (Xoo) and X. oryzae pv. oryzicola (Xoc) are two of the most important bacterial pathogens on rice, which cause leaf blight and leaf streak diseases, respectively. To identify potential anti-virulence drugs against these two pathogens, we screened a library of plant phenolic compounds and derivatives for their effects on the Xoo T3SS. Ten of 56 compounds significantly inhibited the promoter activity of a harpin gene, hpa1. These inhibitors were further tested for their impact on the hypersensitive response (HR) caused by Xoo on non-host tobacco plants. The results showed that pretreatment of Xoo with TS006 (o-coumaric acid, OCA), TS010, TS015 and TS018 resulted in significantly attenuated HR without affecting bacterial growth or survival. In addition, Cya translocation assays demonstrated that the translocation of two T3 effectors was suppressed by the four inhibitors. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis showed that mRNA levels of representative genes in the hrp (hypersensitive response and pathogenicity) cluster, as well as the regulatory genes hrpG and hrpX, were reduced by treatment with the four inhibitors, suggesting that expression of the Xoo T3SS was suppressed. The expression of other virulence factors was not suppressed, which indicated possible T3SS-specific inhibition. Finally, we demonstrated that these inhibitors reduced the disease symptoms of Xoo and Xoc on the rice cultivar (Oryza sativa) IR24 to varying extents.
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, 100193, China.
authors.forename: Susu
authors.initials: S
authors.lastname: Fan
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, 100193, China.
authors.forename: Fang
authors.initials: F
authors.lastname: Tian
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, 100193, China.
authors.forename: Jianyu
authors.initials: J
authors.lastname: Li
authors.affiliation: Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA.
authors.forename: William
authors.initials: W
authors.lastname: Hutchins
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, 100193, China.
authors.forename: Huamin
authors.initials: H
authors.lastname: Chen
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, 100193, China.
authors.forename: Fenghuan
authors.initials: F
authors.lastname: Yang
authors.affiliation: Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA.
authors.forename: Xiaochen
authors.initials: X
authors.lastname: Yuan
authors.affiliation: Guangdong Province Key Laboratory of Microbial Signals and Disease Control, Department of Plant Pathology, South China Agricultural University, Guangzhou, 510642, China.
authors.forename: Zining
authors.initials: Z
authors.lastname: Cui
authors.affiliation: Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA.
authors.forename: Ching-Hong
authors.initials: CH
authors.lastname: Yang
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, 100193, China.
authors.forename: Chenyang
authors.initials: C
authors.lastname: He
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D005434:Flow Cytometry; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D005798:Genes, Bacterial; D012275:Oryza / Q000187:drug effects / Q000382:microbiology*; D010636:Phenols / Q000494:pharmacology*; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014026:Nicotiana / Q000187:drug effects / Q000276:immunology / Q000382:microbiology; D000069296:Type III Secretion Systems / Q000378:metabolism*; D014774:Virulence / Q000187:drug effects / Q000235:genetics; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism; D014867:Water; D014974:Xanthomonas / Q000235:genetics / Q000254:growth & development / Q000378:metabolism* / Q000472:pathogenicity*
chemical_list: D001426:Bacterial Proteins; D010636:Phenols; D012333:RNA, Messenger; D000069296:Type III Secretion Systems; D037521:Virulence Factors; D014867:Water
keywords: HrpG; HrpX; bacterial leaf blight; bacterial leaf streak; harpin; hypersensitive response; o-coumaric acid