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Xie T, Wu X, Luo L, Qu Y, Fan R, Wu S, Long Y, Zhao Z. Natural variation in the hrpL promoter renders the phytopathogen Pseudomonas syringae pv. actinidiae nonpathogenic. MOLECULAR PLANT PATHOLOGY 2023; 24:262-271. [PMID: 36600466 PMCID: PMC9923390 DOI: 10.1111/mpp.13289] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2022] [Revised: 11/22/2022] [Accepted: 12/09/2022] [Indexed: 05/14/2023]
Abstract
The genetic basis underlying loss-of-virulence mutations that arise among natural phytopathogen populations is not well documented. In this study, we examined the virulence of 377 isolates of Pseudomonas syringae pv. actinidiae biovar 3 (Psa3) that were isolated from 76 kiwifruit orchards suffering from bacterial canker disease. Eighty-four nonpathogenic isolates were identified in 40 orchards. A nonpathogenic isolate G166 was found to be defective in hrpL transcription and the downstream type III secretion system (T3SS)-dependent phenotypes. Comparative genomics and complementary expression assay revealed that a single-base "G" insertion in the hrpL promoter blocks gene transcription by reducing promoter activity. The electrophoretic mobility shift assay showed that the genetic variation impairs σ54 /promoter binding during gene transcription under hrp-inducing conditions, resulting in lower expression of hrpL. A PCR-restriction fragment length polymorphism assay was performed to trace the evolutionary history of this mutation, which revealed the independent onset of genetic variations in natural Psa3 populations. We also found that nonpathogenic variants outperformed virulent Psa3 bacteria for both epiphytic and apoplast colonization of kiwifruit leaves in mixed inoculations. Our study highlights a novel mechanism for loss of virulence in Psa3 and provides insight into bacterial adaptive evolution under natural settings.
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Affiliation(s)
- Ting Xie
- Department of Plant Pathology, College of AgricultureGuizhou UniversityGuiyangChina
| | - Xiujiao Wu
- Department of Plant Pathology, College of AgricultureGuizhou UniversityGuiyangChina
| | - Le Luo
- Department of Plant Pathology, College of AgricultureGuizhou UniversityGuiyangChina
| | - Yuan Qu
- Department of Plant Pathology, College of AgricultureGuizhou UniversityGuiyangChina
| | - Rong Fan
- Kiwifruit Engineering & Technology Research CenterGuizhou UniversityGuiyangChina
| | - Shiping Wu
- Institute of Plant ProtectionGuizhou Academy of Agricultural SciencesGuiyangChina
| | - Youhua Long
- Kiwifruit Engineering & Technology Research CenterGuizhou UniversityGuiyangChina
| | - Zhibo Zhao
- Department of Plant Pathology, College of AgricultureGuizhou UniversityGuiyangChina
- Kiwifruit Engineering & Technology Research CenterGuizhou UniversityGuiyangChina
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Huang J, Yao C, Sun Y, Ji Q, Deng X. Virulence-related regulatory network of Pseudomonas syringae. Comput Struct Biotechnol J 2022; 20:6259-6270. [PMID: 36420163 PMCID: PMC9678800 DOI: 10.1016/j.csbj.2022.11.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2022] [Revised: 11/05/2022] [Accepted: 11/05/2022] [Indexed: 11/11/2022] Open
Abstract
Transcription factors (TFs) play important roles in regulating multiple biological processes by binding to promoter regions and regulating the global gene transcription levels. Pseudomonas syringae is a Gram-negative phytopathogenic bacterium harbouring 301 putative TFs in its genome, approximately 50 of which are responsible for virulence-related gene and pathway regulation. Over the past decades, RNA sequencing, chromatin immunoprecipitation sequencing, high-throughput systematic evolution of ligands by exponential enrichment, and other technologies have been applied to identify the functions of master regulators and their interactions in virulence-related pathways. This review summarises the recent advances in the regulatory networks of TFs involved in the type III secretion system (T3SS) and non-T3SS virulence-associated pathways, including motility, biofilm formation, quorum sensing, nucleotide-based secondary messengers, phytotoxins, siderophore production, and oxidative stress. Moreover, this review discusses the future perspectives in terms of TF-mediated pathogenesis mechanisms and provides novel insights that will help combat P. syringae infections based on the regulatory networks of TFs.
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Affiliation(s)
- Jiadai Huang
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR 999077 China
| | - Chunyan Yao
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR 999077 China
| | - Yue Sun
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR 999077 China
| | - Quanjiang Ji
- Gene Editing Center, School of Life Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Xin Deng
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR 999077 China
- Shenzhen Research Institute, City University of Hong Kong, Shenzhen 518057, China
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3
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Xie Y, Li J, Ding Y, Shao X, Sun Y, Xie F, Liu S, Tang S, Deng X. An atlas of bacterial two-component systems reveals function and plasticity in signal transduction. Cell Rep 2022; 41:111502. [DOI: 10.1016/j.celrep.2022.111502] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2022] [Revised: 08/11/2022] [Accepted: 09/22/2022] [Indexed: 11/03/2022] Open
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Sun Y, Shao X, Zhang Y, Han L, Huang J, Xie Y, Liu J, Deng X. Maintenance of tRNA and elongation factors supports T3SS proteins translational elongations in pathogenic bacteria during nutrient starvation. Cell Biosci 2022; 12:147. [PMID: 36064743 PMCID: PMC9446538 DOI: 10.1186/s13578-022-00884-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2022] [Accepted: 08/13/2022] [Indexed: 11/10/2022] Open
Abstract
Abstract
Background
Sufficient nutrition contributes to rapid translational elongation and protein synthesis in eukaryotic cells and prokaryotic bacteria. Fast synthesis and accumulation of type III secretion system (T3SS) proteins conduce to the invasion of pathogenic bacteria into the host cells. However, the translational elongation patterns of T3SS proteins in pathogenic bacteria under T3SS-inducing conditions remain unclear. Here, we report a mechanism of translational elongation of T3SS regulators, effectors and structural protein in four model pathogenic bacteria (Pseudomonas syringae, Pseudomonas aeruginosa, Xanthomonas oryzae and Ralstonia solanacearum) and a clinical isolate (Pseudomonas aeruginosa UCBPP-PA14) under nutrient-limiting conditions. We proposed a luminescence reporter system to quantitatively determine the translational elongation rates (ERs) of T3SS regulators, effectors and structural protein under different nutrient-limiting conditions and culture durations.
Results
The translational ERs of T3SS regulators, effectors and structural protein in these pathogenic bacteria were negatively regulated by the nutrient concentration and culture duration. The translational ERs in 0.5× T3SS-inducing medium were the highest of all tested media. In 1× T3SS-inducing medium, the translational ERs were highest at 0 min and then rapidly decreased. The translational ERs of T3SS regulators, effectors and structural protein were inhibited by tRNA degradation and by reduced levels of elongation factors (EFs).
Conclusions
Rapid translational ER and synthesis of T3SS protein need adequate tRNAs and EFs in nutrient-limiting conditions. Numeric presentation of T3SS translation visually indicates the invasion of bacteria and provides new insights into T3SS expression that can be applied to other pathogenic bacteria.
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Xie Y, Ding Y, Shao X, Yao C, Li J, Liu J, Deng X. Pseudomonas syringae senses polyphenols via phosphorelay crosstalk to inhibit virulence. EMBO Rep 2021; 22:e52805. [PMID: 34580996 DOI: 10.15252/embr.202152805] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2021] [Revised: 09/06/2021] [Accepted: 09/09/2021] [Indexed: 01/04/2023] Open
Abstract
Bacteria use a variety of mechanisms, such as two-component regulatory systems (TCSs), to rapidly sense and respond to distinct conditions and signals in their host organisms. For example, a type III secretion system (T3SS) is a key determinant of the virulence of the model plant pathogen Pseudomonas syringae and contains the TCS RhpRS as a key regulator. However, the plant-derived compound targeting RhpRS remains unknown. Here, we report that RhpRS directly interacts with polyphenols and responds by switching off P. syringae T3SS via crosstalk with alternative histidine kinases. We identify three natural polyphenols that induce the expression of the rhpRS operon in an RhpS-dependent manner. The presence of these three specific polyphenols inhibits the phosphatase activity of RhpS, thus suppressing T3SS activation in T3SS-inducing conditions. The Pro40 residue of RhpS is essential to respond to these polyphenols. In addition, three non-cognate histidine kinases cooperatively phosphorylate RhpR and antagonize the rhpS mutant phenotype. This work illustrates that plant polyphenols can directly target P. syringae RhpRS, which results in bacterial virulence being switched off via a phosphorylation-related crosstalk.
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Affiliation(s)
- Yingpeng Xie
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China
| | - Yiqing Ding
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China
| | - Xiaolong Shao
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China
| | - Chunyan Yao
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China
| | - Jingwei Li
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China
| | - Jingui Liu
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China
| | - Xin Deng
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China.,Shenzhen Research Institute, City University of Hong Kong, Shenzhen, China
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Yuan X, Hulin MT, Sundin GW. Effectors, chaperones, and harpins of the Type III secretion system in the fire blight pathogen Erwinia amylovora: a review. JOURNAL OF PLANT PATHOLOGY 2021; 103:25-39. [PMID: 0 DOI: 10.1007/s42161-020-00623-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Accepted: 07/23/2020] [Indexed: 05/20/2023]
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O’Malley MR, Anderson JC. Regulation of the Pseudomonas syringae Type III Secretion System by Host Environment Signals. Microorganisms 2021; 9:microorganisms9061227. [PMID: 34198761 PMCID: PMC8228185 DOI: 10.3390/microorganisms9061227] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Revised: 05/30/2021] [Accepted: 06/01/2021] [Indexed: 12/12/2022] Open
Abstract
Pseudomonas syringae are Gram-negative, plant pathogenic bacteria that use a type III secretion system (T3SS) to disarm host immune responses and promote bacterial growth within plant tissues. Despite the critical role for type III secretion in promoting virulence, T3SS-encoding genes are not constitutively expressed by P. syringae and must instead be induced during infection. While it has been known for many years that culturing P. syringae in synthetic minimal media can induce the T3SS, relatively little is known about host signals that regulate the deployment of the T3SS during infection. The recent identification of specific plant-derived amino acids and organic acids that induce T3SS-inducing genes in P. syringae has provided new insights into host sensing mechanisms. This review summarizes current knowledge of the regulatory machinery governing T3SS deployment in P. syringae, including master regulators HrpRS and HrpL encoded within the T3SS pathogenicity island, and the environmental factors that modulate the abundance and/or activity of these key regulators. We highlight putative receptors and regulatory networks involved in linking the perception of host signals to the regulation of the core HrpRS–HrpL pathway. Positive and negative regulation of T3SS deployment is also discussed within the context of P. syringae infection, where contributions from distinct host signals and regulatory networks likely enable the fine-tuning of T3SS deployment within host tissues. Last, we propose future research directions necessary to construct a comprehensive model that (a) links the perception of host metabolite signals to T3SS deployment and (b) places these host–pathogen signaling events in the overall context of P. syringae infection.
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Shao X, Tan M, Xie Y, Yao C, Wang T, Huang H, Zhang Y, Ding Y, Liu J, Han L, Hua C, Wang X, Deng X. Integrated regulatory network in Pseudomonas syringae reveals dynamics of virulence. Cell Rep 2021; 34:108920. [PMID: 33789108 DOI: 10.1016/j.celrep.2021.108920] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Revised: 02/09/2021] [Accepted: 03/09/2021] [Indexed: 02/07/2023] Open
Abstract
Pseudomonas syringae, a Gram-negative plant pathogen, expresses multitudinous transcriptional regulators to control the type III secretion system (T3SS) and response to diverse environmental challenges. Although the mechanisms of virulence-associated regulators of P. syringae have been studied for decades, the overall crosstalk underlying these regulators is still elusive. Here, we identify five T3SS regulators (EnvZ-OmpR, CbrAB2, PhoPQ, PilRS, and MgrA), and find that the two-component systems EnvZ-OmpR and CbrAB2 negatively regulate the T3SS. To elucidate crosstalk between 16 virulence-associated regulators in P. syringae, we map an online intricate network called "PSRnet" (Pseudomonas syringae regulatory network) by combining the differentially expressed genes (DEGs) of these 16 regulators by RNA sequencing (RNA-seq) and their binding loci by chromatin immunoprecipitation sequencing (ChIP-seq). Consequently, we identify 238 and 153 functional genes involved in the T3SS and other virulence-related pathways in KB and MM media, respectively. Our results provide insights into the mechanism of plant infections caused by P. syringae.
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Affiliation(s)
- Xiaolong Shao
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China
| | - Miaomiao Tan
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China
| | - Yingpeng Xie
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China
| | - Chunyan Yao
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China
| | - Tingting Wang
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China
| | - Hao Huang
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China
| | - Yingchao Zhang
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China
| | - Yiqing Ding
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China
| | - Jingui Liu
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China
| | - Liangliang Han
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China
| | - Canfeng Hua
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China
| | - Xin Wang
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China; Shenzhen Research Institute, City University of Hong Kong, Shenzhen 518057, China.
| | - Xin Deng
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong SAR, China; Shenzhen Research Institute, City University of Hong Kong, Shenzhen 518057, China.
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Xie Y, Liu W, Shao X, Zhang W, Deng X. Signal transduction schemes in Pseudomonas syringae. Comput Struct Biotechnol J 2020; 18:3415-3424. [PMID: 33294136 PMCID: PMC7691447 DOI: 10.1016/j.csbj.2020.10.039] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Revised: 10/29/2020] [Accepted: 10/31/2020] [Indexed: 11/11/2022] Open
Abstract
To cope with their continually fluctuating surroundings, pathovars of the unicellular phytopathogen Pseudomonas syringae have developed rapid and sophisticated signalling networks to sense extracellular stimuli, which allow them to adjust their cellular composition to survive and cause diseases in host plants. Comparative genomic analyses of P. syringae strains have identified various genes that encode several classes of signalling proteins, although how this bacterium directly perceives these environmental cues remains elusive. Recent work has revealed new mechanisms of a cluster of bacterial signal transduction systems that mainly include two-component systems (such as RhpRS, GacAS, CvsRS and AauRS), extracytoplasmic function sigma factors (such as HrpL and AlgU), nucleotide-based secondary messengers, methyl-accepting chemotaxis sensor proteins and several other intracellular surveillance systems. In this review, we compile a list of the signal transduction mechanisms that P. syringae uses to monitor and respond in a timely manner to intracellular and external conditions. Further understanding of these surveillance processes will provide new perspectives from which to combat P. syringae infections.
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Affiliation(s)
- Yingpeng Xie
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong 999077, Hong Kong Special Administrative Region
| | - Wenbao Liu
- College of Agricultural Sciences and Technology, Shandong Agriculture and Engineering University, Jinan 250100, China
| | - Xiaolong Shao
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong 999077, Hong Kong Special Administrative Region
| | - Weihua Zhang
- Institute of Vegetables and Flowers, Shandong Academy of Agricultural Sciences, Jinan 250100, China
| | - Xin Deng
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong 999077, Hong Kong Special Administrative Region.,Shenzhen Research Institute, City University of Hong Kong, Shenzhen 518057, China
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Turner SE, Pang YY, O'Malley MR, Weisberg AJ, Fraser VN, Yan Q, Chang JH, Anderson JC. A DeoR-Type Transcription Regulator Is Required for Sugar-Induced Expression of Type III Secretion-Encoding Genes in Pseudomonas syringae pv. tomato DC3000. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2020; 33:509-518. [PMID: 31829102 DOI: 10.1094/mpmi-10-19-0290-r] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The type III secretion system (T3SS) of plant-pathogenic Pseudomonas syringae is essential for virulence. Genes encoding the T3SS are not constitutively expressed and must be induced upon infection. Plant-derived metabolites, including sugars such as fructose and sucrose, are inducers of T3SS-encoding genes, yet the molecular mechanisms underlying perception of these host signals by P. syringae are unknown. Here, we report that sugar-induced expression of type III secretion A (setA), predicted to encode a DeoR-type transcription factor, is required for maximal sugar-induced expression of T3SS-associated genes in P. syringae DC3000. From a Tn5 transposon mutagenesis screen, we identified two independent mutants with insertions in setA. When both setA::Tn5 mutants were cultured in minimal medium containing fructose, genes encoding the T3SS master regulator HrpL and effector AvrRpm1 were expressed at lower levels relative to that of a wild-type strain. Decreased hrpL and avrRpm1 expression also occurred in a setA::Tn5 mutant in response to glucose, sucrose, galactose, and mannitol, demonstrating that setA is genetically required for T3SS induction by many different sugars. Expression of upstream regulators hrpR/S and rpoN was not altered in setA::Tn5, indicating that SetA positively regulates hrpL expression independently of increased transcription of these genes. In addition to decreased response to defined sugar signals, a setA::Tn5 mutant had decreased T3SS deployment during infection and was compromised in its ability to grow in planta and cause disease. These data suggest that SetA is necessary for P. syringae to effectively respond to T3SS-inducing sugar signals encountered during infection.
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Affiliation(s)
- Sydney E Turner
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, U.S.A
- Honors College, Oregon State University
| | - Yin-Yuin Pang
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, U.S.A
| | - Megan R O'Malley
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, U.S.A
| | - Alexandra J Weisberg
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, U.S.A
| | - Valerie N Fraser
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, U.S.A
- Molecular and Cellular Biology Program, Oregon State University
| | - Qing Yan
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, U.S.A
| | - Jeff H Chang
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, U.S.A
- Center for Genome Research and Biocomputing, Oregon State University
| | - Jeffrey C Anderson
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, U.S.A
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Horizontally Acquired Quorum-Sensing Regulators Recruited by the PhoP Regulatory Network Expand the Host Adaptation Repertoire in the Phytopathogen Pectobacterium brasiliense. mSystems 2020; 5:5/1/e00650-19. [PMID: 31992632 PMCID: PMC6989131 DOI: 10.1128/msystems.00650-19] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
In this study, we examine the impact of transcriptional network rearrangements driven by horizontal gene acquisition in PhoP and SlyA regulons using as a case study a phytopathosystem comprised of potato tubers and the soft-rot pathogen Pectobacterium brasiliense 1692 (Pb1692). Genome simulations and statistical analyses uncovered the tendency of PhoP and SlyA networks to mobilize lineage-specific traits predicted as horizontal gene transfer at late infection, highlighting the prominence of regulatory network rearrangements in this stage of infection. The evidence further supports the circumscription of two horizontally acquired quorum-sensing regulators (carR and expR1) by the PhoP network. By recruiting carR and expR1, the PhoP network also impacts certain host adaptation- and bacterial competition-related systems, seemingly in a quorum sensing-dependent manner, such as the type VI secretion system, carbapenem biosynthesis, and plant cell wall-degrading enzymes (PCWDE) like cellulases and pectate lyases. Conversely, polygalacturonases and the type III secretion system (T3SS) exhibit a transcriptional pattern that suggests quorum-sensing-independent regulation by the PhoP network. This includes an uncharacterized novel phage-related gene family within the T3SS gene cluster that has been recently acquired by two Pectobacterium species. The evidence further suggests a PhoP-dependent regulation of carbapenem- and PCWDE-encoding genes based on the synthesized products' optimum pH. The PhoP network also controls slyA expression in planta, which seems to impact carbohydrate metabolism regulation, especially at early infection, when 76.2% of the SlyA-regulated genes from that category also require PhoP to achieve normal expression levels.IMPORTANCE Exchanging genetic material through horizontal transfer is a critical mechanism that drives bacteria to efficiently adapt to host defenses. In this report, we demonstrate that a specific plant-pathogenic species (from the Pectobacterium genus) successfully integrated a population density-based behavior system (quorum sensing) acquired through horizontal transfer into a resident stress-response gene regulatory network controlled by the PhoP protein. Evidence found here underscores that subsets of bacterial weaponry critical for colonization, typically known to respond to quorum sensing, are also controlled by PhoP. Some of these traits include different types of enzymes that can efficiently break down plant cell walls depending on the environmental acidity level. Thus, we hypothesize that PhoP's ability to elicit regulatory responses based on acidity and nutrient availability fluctuations has strongly impacted the fixation of its regulatory connection with quorum sensing. In addition, another global gene regulator, known as SlyA, was found under the PhoP regulatory network. The SlyA regulator controls a series of carbohydrate metabolism-related traits, which also seem to be regulated by PhoP. By centralizing quorum sensing and slyA under PhoP scrutiny, Pectobacterium cells added an advantageous layer of control over those two networks that potentially enhances colonization efficiency.
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12
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Xie Y, Shao X, Deng X. Regulation of type III secretion system inPseudomonas syringae. Environ Microbiol 2019; 21:4465-4477. [DOI: 10.1111/1462-2920.14779] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Revised: 08/10/2019] [Accepted: 08/11/2019] [Indexed: 12/11/2022]
Affiliation(s)
- Yingpeng Xie
- Department of Biomedical SciencesCity University of Hong Kong Kowloon Tong Hong Kong SAR 999077 China
| | - Xiaolong Shao
- Department of Biomedical SciencesCity University of Hong Kong Kowloon Tong Hong Kong SAR 999077 China
| | - Xin Deng
- Department of Biomedical SciencesCity University of Hong Kong Kowloon Tong Hong Kong SAR 999077 China
- Shenzhen Research InstituteCity University of Hong Kong Shenzhen 518057 China
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13
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Li K, Zhu Y, Yan W, Deng X, Xiao Y, Song L, Fang R, Jia Y, Tang X. Two components of the rhpPC operon coordinately regulate the type III secretion system and bacterial fitness in Pseudomonas savastanoi pv. phaseolicola. PLoS Pathog 2019; 15:e1007673. [PMID: 30998769 PMCID: PMC6490944 DOI: 10.1371/journal.ppat.1007673] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2018] [Revised: 04/30/2019] [Accepted: 03/02/2019] [Indexed: 12/17/2022] Open
Abstract
Many plant bacterial pathogens including Pseudomonas species, utilize the type III secretion system (T3SS) to deliver effector proteins into plant cells. Genes encoding the T3SS and its effectors are repressed in nutrient-rich media but are rapidly induced after the bacteria enter a plant or are transferred into nutrient-deficient media. To understand how the T3SS genes are regulated, we screened for P. savastanoi pv. phaseolicola (Psph) mutants displaying diminished induction of avrPto-luc, a reporter for the T3SS genes, in Arabidopsis. A mutant carrying transposon insertion into a gene coding for a small functional unknown protein, designated as rhpC, was identified that poorly induced avrPto-luc in plants and in minimal medium (MM). Interestingly, rhpC is located immediately downstream of a putative metalloprotease gene named rhpP, and the two genes are organized in an operon rhpPC; but rhpP and rhpC displayed different RNA expression patterns in nutrient-rich King’s B medium (KB) and MM. Deletion of the whole rhpPC locus did not significantly affect the avrPto-luc induction, implying coordinated actions of rhpP and rhpC in regulating the T3SS genes. Further analysis showed that RhpC was a cytoplasmic protein that interacted with RhpP and targeted RhpP to the periplasm. In the absence of RhpC, RhpP was localized in the cytoplasm and caused a reduction of HrpL, a key regulator of the T3SS genes, and also reduced the fitness of Psph. Expression of RhpP alone in E. coli inhibited the bacterial growth. The detrimental effect of RhpP on the fitness of Psph and E. coli required metalloprotease active sites, and was repressed when RhpC was co-expressed with RhpP. The coordination between rhpP and rhpC in tuning the T3SS gene expression and cell fitness reveals a novel regulatory mechanism for bacterial pathogenesis. The function of RhpP in the periplasm remains to be studied. The induction of the type III secretion system (T3SS) is of great importance to the pathogenesis of bacterial pathogens in host plants. Pseudomonas savastanoi pv. phaseolicola (Psph) causes halo blight disease on beans. We discovered that the bicistronic genes in the rhpPC locus of Psph act coordinately to regulate the T3SS gene expression, bacterial fitness, and pathogenicity. rhpP encodes a metalloprotease that can degrade the key T3SS regulator protein HrpL and reduce bacterial fitness. rhpC encodes a chaperone that inhibits the RhpP activity and mediates translocation of RhpP to the periplasm. The level of rhpP RNA is high in KB but decreases in MM, but the rhpC RNA is low in KB but increases in MM. The elevated rhpC/rhpP transcript ratio in MM plus the inhibition of RhpC on RhpP activity in cytoplasm provide double insurance that warrants high induction of the T3SS genes in MM and bacterial fitness. The coordination between rhpP and rhpC reveals a new mechanism regulating bacterial pathogenicity, and may provide an important target for controlling bacterial pathogens.
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Affiliation(s)
- Kun Li
- Guangdong Key Lab of Biotechnology for Plant Development, School of Life Sciences, South China Normal University, Guangzhou, China
- State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
- National Plant Gene Research Center, Beijing, China
- School of Life Sciences, Capital Normal University, Beijing, China
| | - Yanan Zhu
- State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
- National Plant Gene Research Center, Beijing, China
- School of Life Sciences, Capital Normal University, Beijing, China
| | - Wei Yan
- Guangdong Key Lab of Biotechnology for Plant Development, School of Life Sciences, South China Normal University, Guangzhou, China
| | - Xin Deng
- Department of Biomedical Sciences, City University of Hong Kong, Kowloon Tong, Hong Kong
| | - Yanmei Xiao
- Department of Plant Pathology, Kansas State University, Kansas, United States of America
| | - Liyang Song
- State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
- National Plant Gene Research Center, Beijing, China
- College of Life Sciences, University of the Chinese Academy of Sciences, Beijing, China
| | - Rongxiang Fang
- State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
- National Plant Gene Research Center, Beijing, China
- * E-mail: (RF); (YJ); (XT)
| | - Yantao Jia
- State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
- National Plant Gene Research Center, Beijing, China
- * E-mail: (RF); (YJ); (XT)
| | - Xiaoyan Tang
- Guangdong Key Lab of Biotechnology for Plant Development, School of Life Sciences, South China Normal University, Guangzhou, China
- * E-mail: (RF); (YJ); (XT)
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14
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Pseudomonas savastanoi Two-Component System RhpRS Switches between Virulence and Metabolism by Tuning Phosphorylation State and Sensing Nutritional Conditions. mBio 2019; 10:mBio.02838-18. [PMID: 30890603 PMCID: PMC6426608 DOI: 10.1128/mbio.02838-18] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Pseudomonas savastanoi uses a type III secretion system (T3SS) to invade host plants. Our previous studies have demonstrated that a two-component system (TCS), RhpRS, enables P. savastanoi to coordinate the T3SS gene expression, which depends on the phosphorylation state of RhpR under different environmental conditions. Orthologues of RhpRS are distributed in a wide range of bacterial species, indicating a general regulatory mechanism. How RhpRS uses external signals and the phosphorylation state to exercise its regulatory functions remains unknown. We performed chromatin immunoprecipitation sequencing (ChIP-seq) assays to identify the specific binding sites of RhpR and RhpRD70A in either King's B medium (KB [a T3SS-inhibiting medium]) or minimal medium (MM [a T3SS-inducing medium]). We identified 125 KB-dependent binding sites and 188 phosphorylation-dependent binding sites of RhpR. In KB, RhpR directly and positively regulated cytochrome c 550 production (via ccmA) and alcohol dehydrogenase activity (via adhB) but negatively regulated anthranilate synthase activity (via trpG) and protease activity (via hemB). In addition, phosphorylated RhpR (RhpR-P) directly and negatively regulated the T3SS (via hrpR and hopR1), swimming motility (via flhA), c-di-GMP levels (via PSPPH_2590), and biofilm formation (via algD). It positively regulated twitching motility (via fimA) and lipopolysaccharide production (via PSPPH_2653). Our transcriptome sequencing (RNA-seq) analyses identified 474 and 840 new genes that were regulated by RhpR in KB and MM, respectively. We showed nutrient-rich conditions allowed RhpR to directly regulate multiple metabolic pathways of P. savastanoi and phosphorylation enabled RhpR to specifically control virulence and the cell envelope. The action of RhpRS switched between virulence and regulation of multiple metabolic pathways by tuning its phosphorylation and sensing environmental signals in KB, respectively.IMPORTANCE The plant pathogen Pseudomonas savastanoi invades host plants through a type III secretion system, which is strictly regulated by a two-component system called RhpRS. The orthologues of RhpRS are widely distributed in the bacterial kingdom. The master regulator RhpR specifically depends on the phosphorylation state to regulate the majority of the virulence-related genes. Under nutrient-rich conditions, it modulates many important metabolic pathways, which consist of one-fifth of the genome. We propose that RhpRS uses phosphorylation- and nutrition-dependent mechanisms to switch between regulating virulence and metabolism, and this functionality is widely conserved among bacterial species.
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15
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Wang J, Shao X, Zhang Y, Zhu Y, Yang P, Yuan J, Wang T, Yin C, Wang W, Chen S, Liang H, Deng X. HrpS Is a Global Regulator on Type III Secretion System (T3SS) and Non-T3SS Genes in Pseudomonas savastanoi pv. phaseolicola. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2018; 31:1232-1243. [PMID: 29717915 DOI: 10.1094/mpmi-02-18-0035-r] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The type III secretion system (T3SS) is the main machinery for Pseudomonas savastanoi and other gram-negative bacteria to invade plant cells. HrpR and HrpS form a hetero-hexamer, which activates the expression of HrpL, which induces all T3SS genes by binding to a 'hrp box' in promoters. However, the individual molecular mechanism of HrpR or HrpS has not been fully understood. Through chromatin immunoprecipitation coupled to high-throughput DNA sequencing, we found that HrpR, HrpS, and HrpL had four, 47, and 31 targets on the genome, respectively. HrpS directly bound to the promoter regions of a group of T3SS genes and non-T3SS genes. HrpS independently regulated these genes in a hrpL deletion strain. Additionally, a HrpS-binding motif (GTGCCAAA) was identified, which was verified by electrophoretic mobility shift assay and lux-reporter assay. HrpS also regulated motility and biofilm formation in P. savastanoi. The present study strongly suggests that HrpS alone can work as a global regulator on both T3SS and non-T3SS genes in P. savastanoi. [Formula: see text] Copyright © 2018 The Author(s). This is an open-access article distributed under the CC BY-NC-ND 4.0 International license .
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Affiliation(s)
- Jingru Wang
- 1 Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, TEDA Institute of Biological Sciences and Biotechnology, Nankai University, 23 Hongda Street, Tianjin, 300457, China
| | - Xiaolong Shao
- 1 Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, TEDA Institute of Biological Sciences and Biotechnology, Nankai University, 23 Hongda Street, Tianjin, 300457, China
| | - Yingchao Zhang
- 1 Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, TEDA Institute of Biological Sciences and Biotechnology, Nankai University, 23 Hongda Street, Tianjin, 300457, China
| | - Yanan Zhu
- 2 Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA, U.S.A
| | - Pan Yang
- 1 Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, TEDA Institute of Biological Sciences and Biotechnology, Nankai University, 23 Hongda Street, Tianjin, 300457, China
| | - Jian Yuan
- 1 Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, TEDA Institute of Biological Sciences and Biotechnology, Nankai University, 23 Hongda Street, Tianjin, 300457, China
| | - Tingting Wang
- 3 Department of Biomedical Sciences, City University of Hong Kong, 83 Tat Chee Rd, Kowloon Tong, Hong Kong
| | - Chunyan Yin
- 1 Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, TEDA Institute of Biological Sciences and Biotechnology, Nankai University, 23 Hongda Street, Tianjin, 300457, China
| | - Wei Wang
- 1 Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, TEDA Institute of Biological Sciences and Biotechnology, Nankai University, 23 Hongda Street, Tianjin, 300457, China
| | - Sheng Chen
- 4 Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Hong Kong; and
| | - Haihua Liang
- 5 Key Laboratory of Resources Biology and Biotechnology in Western China, Ministry of Education, College of Life Science, Northwest University, Xi'an, ShaanXi 710069, China
| | - Xin Deng
- 3 Department of Biomedical Sciences, City University of Hong Kong, 83 Tat Chee Rd, Kowloon Tong, Hong Kong
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16
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Migration of Type III Secretion System Transcriptional Regulators Links Gene Expression to Secretion. mBio 2018; 9:mBio.01096-18. [PMID: 30065089 PMCID: PMC6069116 DOI: 10.1128/mbio.01096-18] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Many plant-pathogenic bacteria of considerable economic importance rely on type III secretion systems (T3SSs) of the Hrc-Hrp 1 family to subvert their plant hosts. T3SS gene expression is regulated through the HrpG and HrpV proteins, while secretion is controlled by the gatekeeper HrpJ. A link between the two mechanisms was so far unknown. Here, we show that a mechanistic coupling exists between the expression and secretion cascades through the direct binding of the HrpG/HrpV heterodimer, acting as a T3SS chaperone, to HrpJ. The ternary complex is docked to the cytoplasmic side of the inner bacterial membrane and orchestrates intermediate substrate secretion, without affecting early substrate secretion. The anchoring of the ternary complex to the membranes potentially keeps HrpG/HrpV away from DNA. In their multiple roles as transcriptional regulators and gatekeeper chaperones, HrpV/HrpG provide along with HrpJ potentially attractive targets for antibacterial strategies. On the basis of scientific/economic importance, Pseudomonas syringae and Erwinia amylovora are considered among the top 10 plant-pathogenic bacteria in molecular plant pathology. Both employ type III secretion systems (T3SSs) of the Hrc-Hrp 1 family to subvert their plant hosts. For Hrc-Hrp 1, no functional link was known between the key processes of T3SS gene expression and secretion. Here, we show that a mechanistic coupling exists between expression and secretion cascades, through formation of a ternary complex involving the T3SS proteins HrpG, HrpV, and HrpJ. Our results highlight the functional and structural properties of a hitherto-unknown complex which orchestrates intermediate T3SS substrate secretion and may lead to better pathogen control through novel targets for antibacterial strategies.
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17
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Lee JH, Ancona V, Zhao Y. Lon protease modulates virulence traits in Erwinia amylovora by direct monitoring of major regulators and indirectly through the Rcs and Gac-Csr regulatory systems. MOLECULAR PLANT PATHOLOGY 2018; 19:827-840. [PMID: 28509355 PMCID: PMC6638003 DOI: 10.1111/mpp.12566] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2017] [Revised: 05/08/2017] [Accepted: 05/10/2017] [Indexed: 05/10/2023]
Abstract
Lon, an ATP-dependent protease in bacteria, influences diverse cellular processes by degrading damaged, misfolded and short-lived regulatory proteins. In this study, we characterized the effects of lon mutation and determined the molecular mechanisms underlying Lon-mediated virulence regulation in Erwinia amylovora, an enterobacterial pathogen of apple. Erwinia amylovora depends on the type III secretion system (T3SS) and the exopolysaccharide (EPS) amylovoran to cause disease. Our results showed that mutation of the lon gene led to the overproduction of amylovoran, increased T3SS gene expression and the non-motile phenotype. Western blot analyses showed that mutation in lon directly affected the accumulation and stability of HrpS/HrpA and RcsA. Mutation in lon also indirectly influenced the expression of flhD, hrpS and csrB through the accumulation of the RcsA/RcsB proteins, which bind to the promoter of these genes. In addition, lon expression is under the control of CsrA, possibly at both the transcriptional and post-transcriptional levels. Although mutation in csrA abolished both T3SS and amylovoran production, deletion of the lon gene in the csrA mutant only rescued amylovoran production, but not T3SS. These results suggest that CsrA might positively control both T3SS and amylovoran production partly by suppressing Lon, whereas CsrA may also play a critical role in T3SS by affecting unknown targets.
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Affiliation(s)
- Jae Hoon Lee
- Department of Crop SciencesUniversity of Illinois at Urbana‐ChampaignUrbanaIL 61801USA
| | - Veronica Ancona
- Department of Crop SciencesUniversity of Illinois at Urbana‐ChampaignUrbanaIL 61801USA
- Present address:
Texas A&M University‐Kingsville, Citrus CenterWeslacoTX 78596USA
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18
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Shopera T, Henson WR, Moon TS. Dynamics of sequestration-based gene regulatory cascades. Nucleic Acids Res 2017; 45:7515-7526. [PMID: 28525642 PMCID: PMC5499576 DOI: 10.1093/nar/gkx465] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2016] [Accepted: 05/10/2017] [Indexed: 12/21/2022] Open
Abstract
Gene regulatory cascades are ubiquitous in biology. Because regulatory cascades are integrated within complex networks, their quantitative analysis is challenging in native systems. Synthetic biologists have gained quantitative insights into the properties of regulatory cascades by building simple circuits, but sequestration-based regulatory cascades remain relatively unexplored. Particularly, it remains unclear how the cascade components collectively control the output dynamics. Here, we report the construction and quantitative analysis of the longest sequestration-based cascade in Escherichia coli. This cascade consists of four Pseudomonas aeruginosa protein regulators (ExsADCE) that sequester their partner. Our computational analysis showed that the output dynamics are controlled in a complex way by the concentration of the unbounded transcriptional activator ExsA. By systematically varying the cascade length and the synthesis rate of each regulator, we experimentally verified the computational prediction that ExsC plays a role in rapid circuit responses by sequestering the anti-activator ExsD, while ExsD increases response times by decreasing the free ExsA concentration. In contrast, when additional ExsD was introduced to the cascade via indirect negative feedback, the response time was significantly reduced. Sequestration-based regulatory cascades with negative feedback are often found in biology, and thus our finding provides insights into the dynamics of this recurring motif.
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Affiliation(s)
- Tatenda Shopera
- Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, MO, 63130, USA
| | - William R Henson
- Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, MO, 63130, USA
| | - Tae Seok Moon
- Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, MO, 63130, USA
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19
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Lee JH, Zhao Y. Integration of multiple stimuli-sensing systems to regulate HrpS and type III secretion system in Erwinia amylovora. Mol Genet Genomics 2017; 293:187-196. [PMID: 28965178 DOI: 10.1007/s00438-017-1376-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2017] [Accepted: 09/20/2017] [Indexed: 12/13/2022]
Abstract
The bacterial enhancer binding protein (bEBP) HrpS is essential for Erwinia amylovora virulence by activating the type III secretion system (T3SS). However, how the hrpS gene is regulated remains poorly understood in E. amylovora. In this study, 5' rapid amplification of cDNA ends and promoter deletion analyses showed that the hrpS gene contains two promoters driven by HrpX/HrpY and the Rcs phosphorelay system, respectively. Electrophoretic mobility shift and gene expression assays demonstrated that integration host factor IHF positively regulates hrpS expression through directly binding the hrpX promoter and positively regulating hrpX/hrpY expression. Moreover, hrpX expression was down-regulated in the relA/spoT ((p)ppGpp-deficient) mutant and the dksA mutant, but up-regulated when the wild-type strain was treated with serine hydroxamate, which induced (p)ppGpp-mediated stringent response. Furthermore, the csrA mutant showed significantly reduced transcripts of major hrpS activators, including the hrpX/hrpY, rcsA and rcsB genes, indicating that CsrA is required for full hrpS expression. On the other hand, the csrB mutant exhibited up-regulation of the rcsA and rcsB genes, and hrpS expression was largely diminished in the csrB/rcsB mutant, indicating that the Rcs system is mainly responsible for the increased hrpS expression in the csrB mutant. These findings suggest that E. amylovora recruits multiple stimuli-sensing systems, including HrpX/HrpY, the Rcs phosphorelay system and the Gac-Csr system, to regulate hrpS and T3SS gene expression.
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Affiliation(s)
- Jae Hoon Lee
- Department of Crop Sciences, University of Illinois at Urbana-Champaign, 1201 W. Gregory Dr., Urbana, IL, 61801, USA
| | - Youfu Zhao
- Department of Crop Sciences, University of Illinois at Urbana-Champaign, 1201 W. Gregory Dr., Urbana, IL, 61801, USA.
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20
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Panopoulos NJ. A Career on Both Sides of the Atlantic: Memoirs of a Molecular Plant Pathologist. ANNUAL REVIEW OF PHYTOPATHOLOGY 2017; 55:1-21. [PMID: 28777925 DOI: 10.1146/annurev-phyto-080516-035506] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
This article recounts the experiences that shaped my career as a molecular plant pathologist. It focuses primarily on technical and conceptual developments in molecular phytobacteriology, shares some personal highlights and untold stories that impacted my professional development, and describes the early years of agricultural biotechnology. Writing this article required reflection on events occurring over several decades that were punctuated by a mid-career relocation across the Atlantic. I hope it will still be useful, informative, and enjoyable to read. An extended version of the abstract is provided in the Supplemental Materials , available online.
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Affiliation(s)
- Nickolas J Panopoulos
- Professor Emeritus, Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94619
- Department of Biology, University of Crete, Heraklion, GR-71003, Greece;
- Hellenic Agricultural Academy, Agricultural University of Athens, 118 55 Athens, Greece
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21
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Jovanovic M, Waite C, James E, Synn N, Simpson T, Kotta-Loizou I, Buck M. Functional Characterization of Key Residues in Regulatory Proteins HrpG and HrpV of Pseudomonas syringae pv. tomato DC3000. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2017; 30:656-665. [PMID: 28488468 DOI: 10.1094/mpmi-03-17-0073-r] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The plant pathogen Pseudomonas syringae pv. tomato DC3000 uses a type III secretion system (T3SS) to transfer effector proteins into the host. The expression of T3SS proteins is controlled by the HrpL σ factor. Transcription of hrpL is σ54-dependent and bacterial enhancer-binding proteins HrpR and HrpS coactivate the hrpL promoter. The HrpV protein imposes negative control upon HrpR and HrpS through direct interaction with HrpS. HrpG interacts with HrpV and relieves such negative control. The sequence alignments across Hrp group I-type plant pathogens revealed conserved HrpV and HrpG amino acids. To establish structure-function relationships in HrpV and HrpG, either truncated or alanine substitution mutants were constructed. Key functional residues in HrpV and HrpG are found within their C-terminal regions. In HrpG, L101 and L105 are indispensable for the ability of HrpG to directly interact with HrpV and suppress HrpV-dependent negative regulation of HrpR and HrpS. In HrpV, L108 and G110 are major determinants for interactions with HrpS and HrpG. We propose that mutually exclusive binding of HrpS and HrpG to the same binding site of HrpV governs a transition from negative control to activation of the HrpRS complex leading to HrpL expression and pathogenicity of P. syringae.
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Affiliation(s)
- Milija Jovanovic
- 1 Imperial College London, Imperial College Road, London, SW7 2AZ, U.K
| | - Christopher Waite
- 1 Imperial College London, Imperial College Road, London, SW7 2AZ, U.K
| | - Ellen James
- 2 Trio Medicines Ltd., Hammersmith Medicines Research, Cumberland Avenue, London, NW10 7EW, U.K.; and
| | - Nicholas Synn
- 1 Imperial College London, Imperial College Road, London, SW7 2AZ, U.K
| | - Timothy Simpson
- 3 Medical School, Queen's Medical Centre, Nottingham, NG7 2UH, U.K
| | - Ioly Kotta-Loizou
- 1 Imperial College London, Imperial College Road, London, SW7 2AZ, U.K
| | - Martin Buck
- 1 Imperial College London, Imperial College Road, London, SW7 2AZ, U.K
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22
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Bartho JD, Bellini D, Wuerges J, Demitri N, Toccafondi M, Schmitt AO, Zhao Y, Walsh MA, Benini S. The crystal structure of Erwinia amylovora AmyR, a member of the YbjN protein family, shows similarity to type III secretion chaperones but suggests different cellular functions. PLoS One 2017; 12:e0176049. [PMID: 28426806 PMCID: PMC5398634 DOI: 10.1371/journal.pone.0176049] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2017] [Accepted: 04/04/2017] [Indexed: 11/18/2022] Open
Abstract
AmyR is a stress and virulence associated protein from the plant pathogenic Enterobacteriaceae species Erwinia amylovora, and is a functionally conserved ortholog of YbjN from Escherichia coli. The crystal structure of E. amylovora AmyR reveals a class I type III secretion chaperone-like fold, despite the lack of sequence similarity between these two classes of protein and lacking any evidence of a secretion-associated role. The results indicate that AmyR, and YbjN proteins in general, function through protein-protein interactions without any enzymatic action. The YbjN proteins of Enterobacteriaceae show remarkably low sequence similarity with other members of the YbjN protein family in Eubacteria, yet a high level of structural conservation is observed. Across the YbjN protein family sequence conservation is limited to residues stabilising the protein core and dimerization interface, while interacting regions are only conserved between closely related species. This study presents the first structure of a YbjN protein from Enterobacteriaceae, the most highly divergent and well-studied subgroup of YbjN proteins, and an in-depth sequence and structural analysis of this important but poorly understood protein family.
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Affiliation(s)
- Joseph D. Bartho
- Bioorganic Chemistry and Bio-Crystallography laboratory (B2Cl), Faculty of Science and Technology, Free University of Bolzano, Piazza Università 5, Bolzano, Italy
| | - Dom Bellini
- Diamond Light Source, Harwell Science and Innovation Campus, Didcot, United Kingdom
- Research Complex at Harwell, Harwell Science and Innovation Campus, Didcot, United Kingdom
| | - Jochen Wuerges
- Bioorganic Chemistry and Bio-Crystallography laboratory (B2Cl), Faculty of Science and Technology, Free University of Bolzano, Piazza Università 5, Bolzano, Italy
| | - Nicola Demitri
- Elettra–Sincrotrone Trieste, S.S 14 km 163.5 in Area Science Park, Basovizza, Trieste, Italy
| | - Mirco Toccafondi
- Bioorganic Chemistry and Bio-Crystallography laboratory (B2Cl), Faculty of Science and Technology, Free University of Bolzano, Piazza Università 5, Bolzano, Italy
| | - Armin O. Schmitt
- Bioorganic Chemistry and Bio-Crystallography laboratory (B2Cl), Faculty of Science and Technology, Free University of Bolzano, Piazza Università 5, Bolzano, Italy
- Georg-August-Universität Göttingen, Dept. Nutztierwissenschaften, Breeding informatics, Margarethe von Wrangell-Weg 7, Göttingen, Germany
| | - Youfu Zhao
- Department of Crop Sciences, University of Illinois, 1201 W. Gregory Dr., Urbana, IL, United States of America
| | - Martin A. Walsh
- Diamond Light Source, Harwell Science and Innovation Campus, Didcot, United Kingdom
- Research Complex at Harwell, Harwell Science and Innovation Campus, Didcot, United Kingdom
| | - Stefano Benini
- Bioorganic Chemistry and Bio-Crystallography laboratory (B2Cl), Faculty of Science and Technology, Free University of Bolzano, Piazza Università 5, Bolzano, Italy
- * E-mail:
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23
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Zhou T, Yin C, Zhang Y, Shi H, Wang J, Sun L, Shao X, Gao R, Wang W, Deng X. Lon Protease Is Involved in RhpRS-Mediated Regulation of Type III Secretion in Pseudomonas syringae. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2016; 29:807-814. [PMID: 27657922 DOI: 10.1094/mpmi-06-16-0114-r] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Pseudomonas syringae depends on the type III secretion system (T3SS) to directly translocate effectors into host cells. Previously, we reported a nonpathogenic rhpS mutant, suggesting that the two-component transduction system rhpRS is an important regulator of T3SS in P. syringae. rhpRS regulates itself and a variety of downstream genes under an inverted repeat element promoter in a phosphorylation-dependent manner. Here, we identify lon as a suppressor of the rhpS mutant through transposon screening. A lon/rhpS double mutant restored the phenotypes of the rhpS mutant. The expression level of lon was higher in rhpS and other T3SS-deficient mutants than the wild-type strain, suggesting a negative feedback mechanism between lon and T3SS genes. lon was also induced by a novel T3SS inhibitor, acetate, which substantially compromises the activation of T3SS genes in minimal medium and bacterial growth in host plants.
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Affiliation(s)
- Tianhong Zhou
- Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, TEDA Institute of Biological Sciences and Biotechnology, Nankai University, 23 Hongda Street, Tianjin 300457, China
| | - Chunyan Yin
- Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, TEDA Institute of Biological Sciences and Biotechnology, Nankai University, 23 Hongda Street, Tianjin 300457, China
| | - Yingchao Zhang
- Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, TEDA Institute of Biological Sciences and Biotechnology, Nankai University, 23 Hongda Street, Tianjin 300457, China
| | - Heng Shi
- Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, TEDA Institute of Biological Sciences and Biotechnology, Nankai University, 23 Hongda Street, Tianjin 300457, China
| | - Jingru Wang
- Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, TEDA Institute of Biological Sciences and Biotechnology, Nankai University, 23 Hongda Street, Tianjin 300457, China
| | - Linbo Sun
- Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, TEDA Institute of Biological Sciences and Biotechnology, Nankai University, 23 Hongda Street, Tianjin 300457, China
| | - Xiaolong Shao
- Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, TEDA Institute of Biological Sciences and Biotechnology, Nankai University, 23 Hongda Street, Tianjin 300457, China
| | - Ruxia Gao
- Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, TEDA Institute of Biological Sciences and Biotechnology, Nankai University, 23 Hongda Street, Tianjin 300457, China
| | - Wei Wang
- Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, TEDA Institute of Biological Sciences and Biotechnology, Nankai University, 23 Hongda Street, Tianjin 300457, China
| | - Xin Deng
- Key Laboratory of Molecular Microbiology and Technology, Ministry of Education, TEDA Institute of Biological Sciences and Biotechnology, Nankai University, 23 Hongda Street, Tianjin 300457, China
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24
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Rufián JS, Sánchez-Romero MA, López-Márquez D, Macho AP, Mansfield JW, Arnold DL, Ruiz-Albert J, Casadesús J, Beuzón CR. Pseudomonas syringae Differentiates into Phenotypically Distinct Subpopulations During Colonization of a Plant Host. Environ Microbiol 2016; 18:3593-3605. [PMID: 27516206 DOI: 10.1111/1462-2920.13497] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2016] [Accepted: 08/09/2016] [Indexed: 11/28/2022]
Abstract
Bacterial microcolonies with heterogeneous sizes are formed during colonization of Phaseolus vulgaris by Pseudomonas syringae. Heterogeneous expression of structural and regulatory components of the P. syringae type III secretion system (T3SS), essential for colonization of the host apoplast and disease development, is likewise detected within the plant apoplast. T3SS expression is bistable in the homogeneous environment of nutrient-limited T3SS-inducing medium, suggesting that subpopulation formation is not a response to different environmental cues. T3SS bistability is reversible, indicating a non-genetic origin, and the T3SSHIGH and T3SSLOW subpopulations show differences in virulence. T3SS bistability requires the transcriptional activator HrpL, the double negative regulatory loop established by HrpV and HrpG, and may be enhanced through a positive feedback loop involving HrpA, the main component of the T3SS pilus. To our knowledge, this is the first example of phenotypic heterogeneity in the expression of virulence determinants during colonization of a non-mammalian host.
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Affiliation(s)
- José S Rufián
- Depto. Biología Celular, Genética y Fisiología, Instituto de Hortofruticultura Subtropical y Mediterránea, Universidad de Málaga-Consejo Superior de Investigaciones Científicas (IHSM-UMA-CSIC), Málaga, E-29071, Spain
| | | | - Diego López-Márquez
- Depto. Biología Celular, Genética y Fisiología, Instituto de Hortofruticultura Subtropical y Mediterránea, Universidad de Málaga-Consejo Superior de Investigaciones Científicas (IHSM-UMA-CSIC), Málaga, E-29071, Spain
| | - Alberto P Macho
- Depto. Biología Celular, Genética y Fisiología, Instituto de Hortofruticultura Subtropical y Mediterránea, Universidad de Málaga-Consejo Superior de Investigaciones Científicas (IHSM-UMA-CSIC), Málaga, E-29071, Spain
| | - John W Mansfield
- Faculty of Natural Sciences, Imperial College, London, SW7 2AZ, UK
| | - Dawn L Arnold
- Centre for Research in Bioscience, Faculty of Health and Applied Sciences, University of the West of England, Bristol, BS16 1QY, UK
| | - Javier Ruiz-Albert
- Depto. Biología Celular, Genética y Fisiología, Instituto de Hortofruticultura Subtropical y Mediterránea, Universidad de Málaga-Consejo Superior de Investigaciones Científicas (IHSM-UMA-CSIC), Málaga, E-29071, Spain
| | - Josep Casadesús
- Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Seville, 1095, Spain
| | - Carmen R Beuzón
- Depto. Biología Celular, Genética y Fisiología, Instituto de Hortofruticultura Subtropical y Mediterránea, Universidad de Málaga-Consejo Superior de Investigaciones Científicas (IHSM-UMA-CSIC), Málaga, E-29071, Spain.
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25
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Huang YC, Lin YC, Wei CF, Deng WL, Huang HC. 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. MOLECULAR PLANT PATHOLOGY 2016; 17:1080-94. [PMID: 26638129 PMCID: PMC6638529 DOI: 10.1111/mpp.12349] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2015] [Revised: 11/05/2015] [Accepted: 11/29/2015] [Indexed: 05/08/2023]
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.
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Affiliation(s)
- Yi-Chiao Huang
- Department of Plant Pathology, National Chung Hsing University, Taichung, 40227, Taiwan
- Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, 40227, Taiwan
| | - Yuan-Chuen Lin
- Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, 40227, Taiwan
| | - Chia-Fong Wei
- Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, 40227, Taiwan
| | - Wen-Ling Deng
- Department of Plant Pathology, National Chung Hsing University, Taichung, 40227, Taiwan
- Agricultural Biotechnology Center, National Chung Hsing University, Taichung, 40227, Taiwan
| | - Hsiou-Chen Huang
- Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, 40227, Taiwan
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26
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Lee JH, Sundin GW, Zhao Y. Identification of the HrpS binding site in the hrpL promoter and effect of the RpoN binding site of HrpS on the regulation of the type III secretion system in Erwinia amylovora. MOLECULAR PLANT PATHOLOGY 2016; 17:691-702. [PMID: 26440313 PMCID: PMC6638409 DOI: 10.1111/mpp.12324] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
The type III secretion system (T3SS) is a key pathogenicity factor in Erwinia amylovora. Previous studies have demonstrated that the T3SS in E. amylovora is transcriptionally regulated by an RpoN-HrpL sigma factor cascade, which is activated by the bacterial alarmone (p)ppGpp. In this study, the binding site of HrpS, an enhancer binding protein, was identified for the first time in plant-pathogenic bacteria. Complementation of the hrpL mutant with promoter deletion constructs of the hrpL gene and promoter activity analyses using various lengths of the hrpL promoter fused to a promoter-less green fluorescent protein (gfp) reporter gene delineated the upstream region for HrpS binding. Sequence analysis revealed a dyad symmetry sequence between -138 and -125 nucleotides (TGCAA-N4-TTGCA) as the potential HrpS binding site, which is conserved in the promoter of the hrpL gene among plant enterobacterial pathogens. Results of quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR) and electrophoresis mobility shift assay coupled with site-directed mutagenesis (SDM) analysis showed that the intact dyad symmetry sequence was essential for HrpS binding, full activation of T3SS gene expression and virulence. In addition, the role of the GAYTGA motif (RpoN binding site) of HrpS in the regulation of T3SS gene expression in E. amylovora was characterized by complementation of the hrpS mutant using mutant variants generated by SDM. Results showed that a Y100F substitution of HrpS complemented the hrpS mutant, whereas Y100A and Y101A substitutions did not. These results suggest that tyrosine (Y) and phenylalanine (F) function interchangeably in the conserved GAYTGA motif of HrpS in E. amylovora.
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Affiliation(s)
- Jae Hoon Lee
- Department of Crop Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - George W Sundin
- Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing, MI, 48824, USA
| | - Youfu Zhao
- Department of Crop Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
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27
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Chatnaparat T, Li Z, Korban SS, Zhao Y. The Stringent Response Mediated by (p)ppGpp Is Required for Virulence of Pseudomonas syringae pv. tomato and Its Survival on Tomato. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2015; 28:776-789. [PMID: 25675257 DOI: 10.1094/mpmi-11-14-0378-r] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The hypersensitive response and pathogenicity (hrp) type III secretion system (T3SS) is a key pathogenicity factor in Pseudomonas syringae pv. tomato DC3000 (DC3000). In this study, the role of the second messenger (p)ppGpp on virulence and survival of DC3000 was investigated. Results have demonstrated that (p)ppGpp-deficient mutant (ppGpp(0)) of DC3000 exhibited lower levels of expression of the T3SS and genes of other virulence traits, such as coronatine toxin. The ppGpp(0) mutant of DC3000 was greatly impaired in causing disease and in growth in planta. Furthermore, (p)ppGpp was required for swarming motility, pyoverdine production, the oxidative stress response, as well as γ-amino butyric acid utilization. Screening of amino acids, major signals in activation of ppGpp biosynthesis, revealed that promoter activities of the avrPto gene could be either activated or suppressed by various amino acids in a ppGpp-dependent or -independent manner. Moreover, the ppGpp(0) mutant exhibited increased cell size and decreased survival on plant surfaces. Altogether, these findings indicate that ppGpp acts as an internal signal that regulates the T3SS as well as other virulence factors in pseudomonads and suggest that bacterial pathogens utilize intracellular messengers to sense environmental and nutritional signals for rapid, precise, and reversible control of their pathogenesis and survival.
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Affiliation(s)
- Tiyakhon Chatnaparat
- 1 Department of Crop Sciences, University of Illinois at Urbana-Champaign, Urbana, IL 61801, U.S.A
| | - Zhong Li
- 2 Metabolomics Center, Roy J. Carver Biotechnology Center, University of Illinois at-Urbana-Champaign
| | - Schuyler S Korban
- 3 Department of Natural Resources and Environmental Sciences, University of Illinois at Urbana-Champaign
- 4 Department of Biology, University of Massachusetts Boston, Boston, MA 02125, U.S.A
| | - Youfu Zhao
- 1 Department of Crop Sciences, University of Illinois at Urbana-Champaign, Urbana, IL 61801, U.S.A
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28
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Gazi AD, Charova S, Aivaliotis M, Panopoulos NJ, Kokkinidis M. HrpG and HrpV proteins from the Type III secretion system of Erwinia amylovora form a stable heterodimer. FEMS Microbiol Lett 2014; 362:1-8. [PMID: 25790492 DOI: 10.1093/femsle/fnu011] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Bacterial type III secretion systems (T3SSs) are specialized multicomponent nanomachines that mediate the transport of proteins either to extracellular locations or directly into eukaryotic host cell cytoplasm. Erwinia amylovora, the main agent of rosaceous plants fireblight disease, employs an Hrp/Hrc1 T3SS to accomplish its pathogenesis. The regulatory network that controls the activation of this T3SS is largely unknown in E. amylovora. However, in Pseudomonas syringae pathovars, the HrpG/HrpV complex has been shown to directly regulate the activity of transcription factor HrpS and consequently the upregulation of the Hrp/Hrc1 T3SS related genes. In this work, we report the successful recombinant production and purification of a stable E. amylovora HrpG/HrpV complex, using pPROpET, a bicistronic expression vector. Furthermore, we present the first solution structure of this complex based on small-angle X-ray scattering data.
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Affiliation(s)
- Anastasia D Gazi
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas (IMBB-FORTH), Nikolaou Plastira 100, GR-70013, Heraklion, Crete, Greece Biology Department, University of Crete, Vasilika Vouton, 71409 Heraklio, Crete, Greece
| | - Spyridoula Charova
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas (IMBB-FORTH), Nikolaou Plastira 100, GR-70013, Heraklion, Crete, Greece
| | - Michalis Aivaliotis
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas (IMBB-FORTH), Nikolaou Plastira 100, GR-70013, Heraklion, Crete, Greece
| | - Nicholas J Panopoulos
- Professor Emeritus, Biology Department, University of Crete, Vasilika Vouton, 71409 Heraklio, Crete, Greece Professor Emeritus, Department of Environmental Sciences, Policy, and Management, University of California, Berkeley, 130 Mulford Hall, Berkeley, CA 94720-3114, USA
| | - Michael Kokkinidis
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas (IMBB-FORTH), Nikolaou Plastira 100, GR-70013, Heraklion, Crete, Greece Biology Department, University of Crete, Vasilika Vouton, 71409 Heraklio, Crete, Greece
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29
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Deng X, Liang H, Chen K, He C, Lan L, Tang X. Molecular mechanisms of two-component system RhpRS regulating type III secretion system in Pseudomonas syringae. Nucleic Acids Res 2014; 42:11472-86. [PMID: 25249629 PMCID: PMC4191427 DOI: 10.1093/nar/gku865] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Pseudomonas syringae uses the two-component system RhpRS to regulate the expression of type III secretion system (T3SS) genes and bacterial virulence. However, the molecular mechanisms and the regulons of RhpRS have yet to be fully elucidated. Here, we show that RhpS functions as a kinase and a phosphatase on RhpR and as an autokinase upon itself. RhpR is phosphorylated by the small phosphodonor acetyl phosphate. A specific RhpR-binding site containing the inverted repeat (IR) motif GTATC-N6-GATAC, was mapped to its own promoter by a DNase I footprint analysis. Electrophoretic mobility shift assay indicated that P-RhpR has a higher binding affinity to the IR motif than RhpR. To identify additional RhpR targets in P. syringae, we performed chromatin immunoprecipitation followed by high-throughput DNA sequencing (ChIP-seq) and detected 167 enriched loci including the hrpR promoter, suggesting the direct regulation of T3SS cascade genes by RhpR. A genome-wide microarray analysis showed that, in addition to the T3SS cascade genes, RhpR differentially regulates a large set of genes with various functions in response to different growth conditions. Together, these results suggested that RhpRS is a global regulator that allows P. syringae to sense and respond to environmental changes by coordinating T3SS expression and many other biological processes.
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Affiliation(s)
- Xin Deng
- Department of Chemistry and Institute for Biophysical Dynamics, University of Chicago, Chicago, IL 60637, USA
| | - Haihua Liang
- Department of Life Science, Northwest University, Xi'an, Shaanxi 710069, China
| | - Kai Chen
- Department of Chemistry and Institute for Biophysical Dynamics, University of Chicago, Chicago, IL 60637, USA
| | - Chuan He
- Department of Chemistry and Institute for Biophysical Dynamics, University of Chicago, Chicago, IL 60637, USA
| | - Lefu Lan
- Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Pudong Zhangjiang Hi-Tech Park, Shanghai 201203, China
| | - Xiaoyan Tang
- College of Life Sciences, Capital Normal University, Beijing 100048, China
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30
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Jovanovic M, Lawton E, Schumacher J, Buck M. Interplay among Pseudomonas syringae HrpR, HrpS and HrpV proteins for regulation of the type III secretion system. FEMS Microbiol Lett 2014; 356:201-11. [PMID: 24863420 PMCID: PMC4145663 DOI: 10.1111/1574-6968.12476] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2014] [Revised: 05/15/2014] [Accepted: 05/16/2014] [Indexed: 11/28/2022] Open
Abstract
Pseudomonas syringae pv. tomato DC3000, a plant pathogenic gram-negative bacterium, employs the type III secretion system (T3SS) to cause disease in tomato and Arabidopsis and to induce the hypersensitive response in nonhost plants. The expression of T3SS is regulated by the HrpL extracytoplasmic sigma factor. Expression of HrpL is controlled by transcriptional activators HrpR and HrpS and negative regulator HrpV. In this study, we analysed the organization of HrpRS and HrpV regulatory proteins and interplay between them. We identified one key residue I26 in HrpS required for repression by HrpV. Substitution of I26 in HrpS abolishes its interaction with HrpV and impairs interactions between HrpS and HrpR and the self-association of HrpS. We show that HrpS self-associates and can associate simultaneously with HrpR and HrpV. We now propose that HrpS has a central role in the assembly of the regulatory HrpRSV complex. Deletion analysis of HrpR and HrpS proteins showed that C-terminal parts of HrpR and HrpS confer determinants indispensable for their self-assembly.
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Affiliation(s)
- Milija Jovanovic
- Department of Life Sciences, Imperial College London, London, UK
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31
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Ancona V, Li W, Zhao Y. Alternative sigma factor RpoN and its modulation protein YhbH are indispensable for Erwinia amylovora virulence. MOLECULAR PLANT PATHOLOGY 2014; 15:58-66. [PMID: 23937726 PMCID: PMC6638869 DOI: 10.1111/mpp.12065] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
In Erwinia amylovora, ECF (extracytoplasmic functions) alternative sigma factor HrpL regulates the transcription of hrp (hypersensitive response and pathogenicity)-type III secretion system (T3SS) genes by binding to a consensus sequence known as the hrp box in hrp gene promoters. In turn, the expression of hrpL has been proposed to be positively controlled by alternative sigma factor 54 (σ(54)) (RpoN) and HrpS, a member of the σ(54) enhancer-binding proteins (EBPs). However, the function of RpoN has not been characterized genetically in E. amylovora. In this study, we investigated the role of RpoN, a nitrogen limitation sigma factor, and its modulation protein YhbH, a novel ribosome-associated protein, in E. amylovora virulence. Our results showed that mutations in hrpS, hrpL, rpoN and yhbH, but not yfiA and rmf3, resulted in a nonpathogenic phenotype on immature pear fruits and apple shoots. Consistently, the expression of T3SS genes, including hrpL, dspE, hrpN and hrpA, was barely detected in hrpS, hrpL, rpoN and yhbH mutants. These mutants were also not capable of eliciting a hypersensitive response (HR) on tobacco; however, the overexpression of hrpL using an inducible promoter rescued the HR-eliciting abilities of these mutants. These results suggest that a sigma factor cascade exists in the regulatory networks of E. amylovora and regulates important virulence factors. On the basis of this study and previously reported data, a model is proposed for the regulation of T3SS in E. amylovora.
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Affiliation(s)
- Veronica Ancona
- Department of Crop Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
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32
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Lohou D, Lonjon F, Genin S, Vailleau F. Type III chaperones & Co in bacterial plant pathogens: a set of specialized bodyguards mediating effector delivery. FRONTIERS IN PLANT SCIENCE 2013; 4:435. [PMID: 24319448 PMCID: PMC3837300 DOI: 10.3389/fpls.2013.00435] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Accepted: 10/12/2013] [Indexed: 05/19/2023]
Abstract
Gram-negative plant pathogenic bacteria possess a type III secretion system (T3SS) to inject bacterial proteins, called type III effectors (T3Es), into host cells through a specialized syringe structure. T3Es are virulence factors that can suppress plant immunity but they can also conversely be recognized by the plant and trigger specific resistance mechanisms. The T3SS and injected T3Es play a central role in determining the outcome of a host-pathogen interaction. Still little is known in plant pathogens on the assembly of the T3SS and the regulatory mechanisms involved in the temporal control of its biosynthesis and T3E translocation. However, recent insights point out the role of several proteins as prime candidates in the role of regulators of the type III secretion (T3S) process. In this review we report on the most recent advances on the regulation of the T3S by focusing on protein players involved in secretion/translocation regulations, including type III chaperones (T3Cs), type III secretion substrate specificity switch (T3S4) proteins and other T3S orchestrators.
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Affiliation(s)
- David Lohou
- Institut National de la Recherche Agronomique, UMR441, Laboratoire des Interactions Plantes-MicroorganismesCastanet-Tolosan, France
- Centre National de la Recherche Scientifique, UMR2594, Laboratoire des Interactions Plantes-MicroorganismesCastanet-Tolosan, France
| | - Fabien Lonjon
- Institut National de la Recherche Agronomique, UMR441, Laboratoire des Interactions Plantes-MicroorganismesCastanet-Tolosan, France
- Centre National de la Recherche Scientifique, UMR2594, Laboratoire des Interactions Plantes-MicroorganismesCastanet-Tolosan, France
| | - Stéphane Genin
- Institut National de la Recherche Agronomique, UMR441, Laboratoire des Interactions Plantes-MicroorganismesCastanet-Tolosan, France
- Centre National de la Recherche Scientifique, UMR2594, Laboratoire des Interactions Plantes-MicroorganismesCastanet-Tolosan, France
| | - Fabienne Vailleau
- Institut National de la Recherche Agronomique, UMR441, Laboratoire des Interactions Plantes-MicroorganismesCastanet-Tolosan, France
- Centre National de la Recherche Scientifique, UMR2594, Laboratoire des Interactions Plantes-MicroorganismesCastanet-Tolosan, France
- Institut National Polytechnique, École Nationale Supérieure Agronomique de Toulouse, Université de ToulouseCastanet-Tolosan, France
- *Correspondence: Fabienne Vailleau, Institut National de la Recherche Agronomique, UMR441, Laboratoire des Interactions Plantes-Microorganismes, CS 52627, 24 Chemin de Borde Rouge-Auzeville, Castanet-Tolosan cedex 31326, France e-mail:
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33
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Protein export according to schedule: architecture, assembly, and regulation of type III secretion systems from plant- and animal-pathogenic bacteria. Microbiol Mol Biol Rev 2012; 76:262-310. [PMID: 22688814 DOI: 10.1128/mmbr.05017-11] [Citation(s) in RCA: 304] [Impact Index Per Article: 25.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Flagellar and translocation-associated type III secretion (T3S) systems are present in most gram-negative plant- and animal-pathogenic bacteria and are often essential for bacterial motility or pathogenicity. The architectures of the complex membrane-spanning secretion apparatuses of both systems are similar, but they are associated with different extracellular appendages, including the flagellar hook and filament or the needle/pilus structures of translocation-associated T3S systems. The needle/pilus is connected to a bacterial translocon that is inserted into the host plasma membrane and mediates the transkingdom transport of bacterial effector proteins into eukaryotic cells. During the last 3 to 5 years, significant progress has been made in the characterization of membrane-associated core components and extracellular structures of T3S systems. Furthermore, transcriptional and posttranscriptional regulators that control T3S gene expression and substrate specificity have been described. Given the architecture of the T3S system, it is assumed that extracellular components of the secretion apparatus are secreted prior to effector proteins, suggesting that there is a hierarchy in T3S. The aim of this review is to summarize our current knowledge of T3S system components and associated control proteins from both plant- and animal-pathogenic bacteria.
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34
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Stauber JL, Loginicheva E, Schechter LM. Carbon source and cell density-dependent regulation of type III secretion system gene expression in Pseudomonas syringae pathovar tomato DC3000. Res Microbiol 2012; 163:531-9. [PMID: 22944041 DOI: 10.1016/j.resmic.2012.08.005] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2012] [Accepted: 08/13/2012] [Indexed: 01/07/2023]
Abstract
Pseudomonas syringae utilizes a type III secretion system (T3SS) encoded by the hrp/hrc genes to translocate virulence proteins called effectors into plant cells. To ensure that the T3SS functions at appropriate times during infection, hrp/hrc and effector gene expression is modulated by environmental conditions and a complex network of transcription factors. The sigma factor HrpL activates hrp/hrc and effector genes, while σ(54) and enhancer binding proteins HrpR and HrpS regulate hrpL. To better understand how environmental conditions control the T3SS regulatory cascade in P. syringae pathovar tomato strain DC3000, we tested the effects of various growth media and carbon sources on expression of the hrpRS operon, hrpL, and the effector avrPto. Fructose optimally induced hrpRS expression, while most other carbon sources had only mild stimulatory effects. In contrast, hrpL and avrPto were highly induced by several sugars and organic acids, yet expression decreased as cultures reached higher cell densities. This cell density-dependent regulation was not due to alteration of the pH of the medium, although involvement of a quorum sensing signal was also not apparent. Our findings may explain conflicting results from previous studies and additionally indicate that culture conditions should be considered carefully when examining T3SS gene expression.
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Affiliation(s)
- Jennifer L Stauber
- Department of Biology, University of Missouri-St. Louis, St. Louis, MO 63121, USA.
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35
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Wei CF, Hsu ST, Deng WL, Wen YD, Huang HC. Plant innate immunity induced by flagellin suppresses the hypersensitive response in non-host plants elicited by Pseudomonas syringae pv. averrhoi. PLoS One 2012; 7:e41056. [PMID: 22911741 PMCID: PMC3402453 DOI: 10.1371/journal.pone.0041056] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2012] [Accepted: 06/16/2012] [Indexed: 01/04/2023] Open
Abstract
A new pathogen, Pseudomonas syringae pv. averrhoi (Pav), which causes bacterial spot disease on carambola was identified in Taiwan in 1997. Many strains of this pathovar have been isolated from different locations and several varieties of hosts. Some of these strains, such as HL1, are nonmotile and elicit a strong hypersensitive response (HR) in nonhost tobacco leaves, while other strains, such as PA5, are motile and elicit a weak HR. Based on the image from a transmission electron microscope, the results showed that HL1 is flagellum-deficient and PA5 has normal flagella. Here we cloned and analyzed the fliC gene and glycosylation island from Pav HL1 and PA5. The amino acid sequences of FliC from HL1 and PA5 are identical to P. s. pvs. tabaci (Pta), glycinea and phaseolicola and share very high similarity with other pathovars of P. syringae. In contrast to the flagellin mutant PtaΔfliC, PA5ΔfliC grows as well as wild type in the host plant, but it elicits stronger HR than wild type does in non-host plants. Furthermore, the purified Pav flagellin, but not the divergent flagellin from Agrobacterium tumefaciens, is able to impair the HR induced by PA5ΔfliC. PA5Δfgt1 possessing nonglycosylated flagella behaved as its wild type in both bacterial growth in host and HR elicitation. Flagellin was infiltrated into tobacco leaves either simultaneously with flagellum-deficient HL1 or prior to the inoculation of wild type HL1, and both treatments impaired the HR induced by HL1. Moreover, the HR elicited by PA5 and PA5ΔfliC was enhanced by the addition of cycloheximide, suggesting that the flagellin is one of the PAMPs (pathogen-associated molecular patterns) contributed to induce the PAMP-triggered immunity (PTI). Taken together, the results shown in this study reveal that flagellin in Pav is capable of suppressing HR via PTI induction during an incompatible interaction.
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Affiliation(s)
- Chia-Fong Wei
- Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan
| | - Shih-Tien Hsu
- Department of Plant Pathology, National Chung Hsing University, Taichung, Taiwan
| | - Wen-Ling Deng
- Department of Plant Pathology, National Chung Hsing University, Taichung, Taiwan
| | - Yu-Der Wen
- Department of Biology, National Changhua University of Education, Changhua, Taiwan
| | - Hsiou-Chen Huang
- Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan
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36
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Jovanovic M, James EH, Burrows PC, Rego FGM, Buck M, Schumacher J. Regulation of the co-evolved HrpR and HrpS AAA+ proteins required for Pseudomonas syringae pathogenicity. Nat Commun 2011; 2:177. [PMID: 21285955 PMCID: PMC3105312 DOI: 10.1038/ncomms1177] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2010] [Accepted: 01/05/2011] [Indexed: 11/26/2022] Open
Abstract
The bacterial AAA+ enhancer-binding proteins (EBPs) HrpR and HrpS (HrpRS) of Pseudomonas syringae (Ps) activate σ54-dependent transcription at the hrpL promoter; triggering type-three secretion system-mediated pathogenicity. In contrast with singly acting EBPs, the evolution of the strictly co-operative HrpRS pair raises questions of potential benefits and mechanistic differences this transcription control system offers. Here, we show distinct properties of HrpR and HrpS variants, indicating functional specialization of these non-redundant, tandemly arranged paralogues. Activities of HrpR, HrpS and their control proteins HrpV and HrpG from Ps pv. tomato DC3000 in vitro establish that HrpRS forms a transcriptionally active hetero-hexamer, that there is a direct negative regulatory role for HrpV through specific binding to HrpS and that HrpG suppresses HrpV. The distinct HrpR and HrpS functionalities suggest how partial paralogue degeneration has potentially led to a novel control mechanism for EBPs and indicate subunit-specific roles for EBPs in σ54-RNA polymerase activation. HrpR and HrpS enhancer-binding proteins of Pseudomonas syringae activate σ54-dependent transcription of the HrpL promoter and are required for type-three secretion pathogenicity. Here, the authors demonstrate that, despite being co-regulated, HrpR and HrpS each have distinct functions for activating σ54.
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Affiliation(s)
- Milija Jovanovic
- Division of Biology, Faculty of Natural Sciences, Sir Alexander Fleming Building, Imperial College London, London SW7 2AZ, UK
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Deng WL, Lin YC, Lin RH, Wei CF, Huang YC, Peng HL, Huang HC. Effects of galU mutation on Pseudomonas syringae-plant interactions. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2010; 23:1184-96. [PMID: 20687808 DOI: 10.1094/mpmi-23-9-1184] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Bacterial galU coding for a uridine diphosphate-glucose pyrophosphorylase plays an important role in carbohydrates biosynthesis, including synthesis of lipopolysaccharides (LPS), membrane-derived oligosaccharides, and capsular polysaccharides. In this study, we characterized the galU mutant of Pseudomonas syringae pv. syringae 61 (Psy61), a necrotizing plant pathogen whose pathogenicity depends on a functional type III secretion system (T3SS), and showed that the Psy61 galU mutant had reduced biofilm formation ability, was nonmotile, and had an assembled T3SS structure but failed to elicit hypersensitive response in resistant plants and necrotic lesions in susceptible plants. Moreover, the defective LPS and other pathogen-associated molecular patterns (PAMPs) on the surface of the Psy61 galU mutant were capable of inducing PAMP-triggered immunity, which severely compromised the ability of the Psy61 galU mutant to survive in planta. Our results demonstrated that the complete LPS protected plant-pathogenic bacteria from host innate immunity, similar to what was found in animal pathogens, prior to the translocation of T3S effectors and bacterial multiplication.
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Affiliation(s)
- Wen-Ling Deng
- Department of Plant Pathology, National Chung Hsing University, Taichung, 40224, Taiwan
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Ortiz-Martín I, Thwaites R, Mansfield JW, Beuzón CR. Negative regulation of the Hrp type III secretion system in Pseudomonas syringae pv. phaseolicola. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2010; 23:682-701. [PMID: 20367475 DOI: 10.1094/mpmi-23-5-0682] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Many plant-pathogenic bacteria require type III secretion systems (T3SS) to cause disease in compatible hosts and to induce the hypersensitive response in resistant plants. T3SS gene expression is induced within the plant and responds to host and environmental factors. In Pseudomonas syringae, expression is downregulated by the Lon protease in rich medium and by HrpV under inducing conditions. HrpV acts as an anti-activator by binding HrpS. HrpG, which can also bind HrpV, has been reported to act as an anti-anti-activator. Previous studies have used mostly in vitro inducing conditions, different pathovars, and methodology. We have used single and double lon and hrpV mutants of P. syringae pv. phaseolicola 1448a, as well as strains ectopically expressing the regulators, to examine their role in coordinating expression of the T3SS. We applied real-time polymerase chain reaction to analyze gene expression both in vitro and in planta, and assessed bacterial fitness using competitive indices. Our results indicate that i) Lon downregulates expression of the hrp/hrc genes in all conditions, probably by constitutively degrading naturally unstable HrpR; ii) HrpV and HrpT downregulate expression of the hrp/hrc genes in all conditions; and iii) HrpG has an additional, HrpV-independent role, regulating expression of the hrpC operon.
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Affiliation(s)
- Inmaculada Ortiz-Martín
- Instituto de Hortofruticultura Subtropical y Mediterranea, Universidad de Málaga-Consejo Superior De Investigaciones Científicas, Depto. Biología Celular, Genética y Fisiología, Spain
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Deng X, Xiao Y, Lan L, Zhou JM, Tang X. Pseudomonas syringae pv. phaseolicola Mutants Compromised for type III secretion system gene induction. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2009; 22:964-976. [PMID: 19589072 DOI: 10.1094/mpmi-22-8-0964] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Pseudomonas syringae bacteria utilize the type III secretion system (T3SS) to deliver effector proteins into host cells. The T3SS and T3 effector genes (together called the T3 genes hereafter) are repressed in nutrient-rich medium but rapidly induced after the bacteria are transferred into minimal medium or infiltrated into plants. The induction of the T3 genes is mediated by HrpL, an alternative sigma factor that recognizes the conserved hrp box motif in the T3 gene promoters. The induction of hrpL is mediated by HrpR and HrpS, two homologous proteins that bind the hrpL promoter. To identify additional genes involved in regulation of the T3 genes, we screened for the P. syringae pv. phaseolicola NPS3121 transposon-tagged mutants with reduced induction of avrPto-luc and hrpL-luc, reporter genes for promoters of effector gene avrPto and hrpL, respectively. Determination of the transposon-insertion sites revealed genes with putative functions in signal transduction and transcriptional regulation, protein synthesis, and basic metabolism. A transcriptional regulator (AefR(NPS3121)) was identified in our screen that is homologous to AefR of P. syringae pv. syringae strain B728a, a regulator of the quorum-sensing signal and epiphytic traits, but was not known to regulate the T3 genes. AefR(NPS3121) in P. syringae pv. phaseolicola NPS3121 and AefR in P. syringae pv. syringae B728a behave similarly in regulating the quorum-sensing signal in liquid medium but differ in regulating the epiphytic traits, including swarming motility, leaf entry, and epiphytic survival.
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Affiliation(s)
- Xin Deng
- Department of Plant Pathology, Kansas State University, Manhattan, KS 66506-5502, USA
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Ramos AR, Morello JE, Ravindran S, Deng WL, Huang HC, Collmer A. Identification of Pseudomonas syringae pv. syringae 61 type III secretion system Hrp proteins that can travel the type III pathway and contribute to the translocation of effector proteins into plant cells. J Bacteriol 2007; 189:5773-8. [PMID: 17526708 PMCID: PMC1951817 DOI: 10.1128/jb.00435-07] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Pseudomonas syringae translocates effector proteins into plant cells via an Hrp1 type III secretion system (T3SS). T3SS components HrpB, HrpD, HrpF, and HrpP were shown to be pathway substrates and to contribute to elicitation of the plant hypersensitive response and to translocation and secretion of the model effector AvrPto1.
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Affiliation(s)
- Adela R Ramos
- Department of Plant Pathology, Cornell University, Ithaca, NY 14853, USA
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Xiao Y, Lan L, Yin C, Deng X, Baker D, Zhou JM, Tang X. Two-component sensor RhpS promotes induction of Pseudomonas syringae type III secretion system by repressing negative regulator RhpR. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2007; 20:223-34. [PMID: 17378425 DOI: 10.1094/mpmi-20-3-0223] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
The Pseudomonas syringae type III secretion system (T3SS) is induced during interaction with the plant or culture in minimal medium (MM). How the bacterium senses these environments to activate the T3SS is poorly understood. Here, we report the identification of a novel two-component system (TCS), RhpRS, that regulates the induction of P. syringae T3SS genes. The rhpR and rhpS genes are organized in an operon with rhpR encoding a putative TCS response regulator and rhpS encoding a putative biphasic sensor kinase. Transposon insertion in rhpS severely reduced the induction of P. syringae T3SS genes in the plant as well as in MM and significantly compromised the pathogenicity on host plants and hypersensitive response-inducing activity on nonhost plants. However, deletion of the rhpRS locus allowed the induction of T3SS genes to the same level as in the wild-type strain and the recovery of pathogenicity upon infiltration into plants. Overexpression of RhpR in the deltarhpRS deletion strain abolished the induction of T3SS genes. However, overexpression of RhpR in the wild-type strain or overexpression of RhpR(D70A), a mutant of the predicted phosphorylation site of RhpR, in the deltarhpRS deletion strain only slightly reduced the induction of T3SS genes. Based on these results, we propose that the phosphorylated RhpR represses the induction of T3SS genes and that RhpS reverses phosphorylation of RhpR under the T3SS-inducing conditions. Epistasis analysis indicated that rhpS and rhpR act upstream of hrpR to regulate T3SS genes.
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Affiliation(s)
- Yanmei Xiao
- Department of Plant Pathology, Kansas State University, Manhattan, KS 66506-5502, USA
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Zheng Z, Chen G, Joshi S, Brutinel ED, Yahr TL, Chen L. Biochemical characterization of a regulatory cascade controlling transcription of the Pseudomonas aeruginosa type III secretion system. J Biol Chem 2006; 282:6136-42. [PMID: 17197437 DOI: 10.1074/jbc.m611664200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Many Gram-negative pathogens utilize type III secretion systems (T3SS) to translocate effector proteins into eukaryotic host cells. Expression of T3SS genes is highly regulated and is often coupled to type III secretory activity. Transcription of the Pseudomonas aeruginosa T3SS genes is coupled to secretion by a cascade of interacting regulatory proteins (ExsA, ExsD, ExsC, and ExsE). ExsA is an activator of type III gene transcription, ExsD binds ExsA to inhibit transcription, ExsC inhibits ExsD activity, and ExsE inhibits ExsC activity. The entire process is coupled to secretion by virtue of the fact that ExsE is a secreted substrate of the T3SS. Changes in the intracellular concentration of ExsE are thought to govern formation of the ExsC-ExsE, ExsC-ExsD, and ExsD-ExsA complexes. Whereas formation of the ExsC-ExsE complex allows ExsD to bind ExsA and transcription of the T3SS is repressed, formation of the ExsC-ExsD complex sequesters ExsD from ExsA and transcription of the T3SS is induced. In this study, we characterized the self-association states of ExsC, ExsD, and ExsE and the binding interactions of ExsC with ExsE and ExsD. ExsC exists as a homodimer and binds one molecule of ExsE substrate. Dimeric ExsC also interacts directly with ExsD to form a heterotetrameric complex. The difference in binding affinities between the ExsC-ExsE (K(d) 1 nm) and ExsC-ExsD (K(d) 18 nm) complexes supports a model in which ExsC preferentially binds cytoplasmic ExsE, resulting in the inhibition of T3SS gene transcription.
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Affiliation(s)
- Zhida Zheng
- Department of Biology, Iniana University, Bloomington, Indiana 47405, USA
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Tang X, Xiao Y, Zhou JM. Regulation of the type III secretion system in phytopathogenic bacteria. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2006; 19:1159-66. [PMID: 17073299 DOI: 10.1094/mpmi-19-1159] [Citation(s) in RCA: 155] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
The type III secretion system (TTSS) is a specialized protein secretion machinery used by numerous gram-negative bacterial pathogens of animals and plants to deliver effector proteins directly into the host cells. In plant-pathogenic bacteria, genes encoding the TTSS were discovered as hypersensitive response and pathogenicity (hrp) genes, because mutation of these genes typically disrupts the bacterial ability to cause diseases on host plants and to elicit hypersensitive response on nonhost plants. The hrp genes and the type III effector genes (collectively called TTSS genes hereafter) are repressed in nutrient-rich media but induced when bacteria are infiltrated into plants or incubated in nutrient-deficient inducing media. Multiple regulatory components have been identified in the plant-pathogenic bacteria regulating TTSS genes under various conditions. In Ralstonia solanacearum, several signal transduction components essential for the induction of TTSS genes in plants are dispensable for the induction in inducing medium. In addition to the inducing signals, recent studies indicated the presence of negative signals in the plant regulating the Pseudomonas syringae TTSS genes. Thus, the levels of TTSS gene expression in plants likely are determined by the interactions of multiple signal transduction pathways. Studies of the hrp regulons indicated that TTSS genes are coordinately regulated with a number of non-TTSS genes.
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Affiliation(s)
- Xiaoyan Tang
- Department of Plant Pathology, Kansas State University, Manhattan, KS 66506-5502, USA.
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Büttner D, Bonas U. Who comes first? How plant pathogenic bacteria orchestrate type III secretion. Curr Opin Microbiol 2006; 9:193-200. [PMID: 16529983 DOI: 10.1016/j.mib.2006.02.006] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2005] [Accepted: 02/23/2006] [Indexed: 12/22/2022]
Abstract
The type III secretion system (T3SS) is a key pathogenicity factor of many Gram-negative plant and animal pathogens and is also present in some symbiotic bacteria. T3SSs are highly conserved, complex molecular injection machines that translocate bacterial effector proteins directly into eukaryotic cells. Recent genetic, biochemical and structural studies revealed that the activity of the T3SS is regulated by common mechanisms in different bacterial species. In many cases, type III secretion is activated upon host cell contact and depends on specific control proteins, including transcriptional regulators and type III secretion chaperones.
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Affiliation(s)
- Daniela Büttner
- Institut für Genetik, Martin-Luther-Universität Halle-Wittenberg, D-06099 Halle (Saale), Germany
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Gürlebeck D, Thieme F, Bonas U. Type III effector proteins from the plant pathogen Xanthomonas and their role in the interaction with the host plant. JOURNAL OF PLANT PHYSIOLOGY 2006; 163:233-55. [PMID: 16386329 DOI: 10.1016/j.jplph.2005.11.011] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/15/2005] [Accepted: 11/15/2005] [Indexed: 05/05/2023]
Abstract
Pathogenicity of Xanthomonas campestris pathovar (pv.) vesicatoria and most other Gram-negative bacterial plant pathogens largely depends on a type III secretion (TTS) system which is encoded by hypersensitive response and pathogenicity (hrp) genes. These genes are induced in the plant and are essential for the bacterium to be virulent in susceptible hosts and for the induction of the hypersensitive response (HR) in resistant host and non-host plants. The TTS machinery secretes proteins into the extracellular milieu and effector proteins into the plant cell cytosol. In the plant, the effectors presumably interfere with cellular processes to the benefit of the pathogen or have an avirulence activity that betrays the bacterium to the plant surveillance system. Type III effectors were identified by their avirulence activity, co-regulation with the TTS system and homology to known effectors. A number of effector proteins are members of families, e.g., the AvrBs3 family in Xanthomonas. AvrBs3 localizes to the nucleus of the plant cell where it modulates plant gene expression. Another family that is also present in Xanthomonas is the YopJ/AvrRxv family. The latter proteins appear to act as SUMO cysteine proteases in the host. Here, we will present an overview about the regulation of the TTS system and its substrates and discuss the function of the AvrRxv and AvrBs3 family members in more detail.
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Affiliation(s)
- Doreen Gürlebeck
- Institute of Genetics, Martin-Luther University Halle-Wittenberg, Weinbergweg 10, 06120 Halle, Germany.
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