scholarly journals Regulatory Network Controlling Extracellular Proteins in Erwinia carotovora subsp. carotovora: FlhDC, the Master Regulator of Flagellar Genes, Activates rsmB Regulatory RNA Production by Affecting gacA and hexA (lrhA) Expression

2008 ◽  
Vol 190 (13) ◽  
pp. 4610-4623 ◽  
Author(s):  
Yaya Cui ◽  
Asita Chatterjee ◽  
Hailian Yang ◽  
Arun K. Chatterjee
Keyword(s):  
Plant Cell Wall ◽  
Rna Binding ◽  
Pectate Lyase ◽  
Extracellular Enzyme ◽  
Erwinia Carotovora ◽  
Homoserine Lactone ◽  
Hypersensitive Reaction ◽  
Extracellular Proteins ◽  
Cell Wall Degrading Enzymes ◽  
Negative Effect

ABSTRACT Erwinia carotovora subsp. carotovora produces an array of extracellular proteins (i.e., exoproteins), including plant cell wall-degrading enzymes and Harpin, an effector responsible for eliciting hypersensitive reaction. Exoprotein genes are coregulated by the quorum-sensing signal, N-acyl homoserine lactone, plant signals, an assortment of transcriptional factors/regulators (GacS/A, ExpR1, ExpR2, KdgR, RpoS, HexA, and RsmC) and posttranscriptional regulators (RsmA, rsmB RNA). rsmB RNA production is positively regulated by GacS/A, a two-component system, and negatively regulated by HexA (PecT in Erwinia chrysanthemi; LrhA [LysR homolog A] in Escherichia coli) and RsmC, a putative transcriptional adaptor. While free RsmA, an RNA-binding protein, promotes decay of mRNAs of exoprotein genes, binding of RsmA with rsmB RNA neutralizes the RsmA effect. In the course of studies of GacA regulation, we discovered that a locus bearing strong homology to the flhDC operon of E. coli also controls extracellular enzyme production. A transposon insertion FlhDC− mutant produces very low levels of pectate lyase, polygalacturonase, cellulase, protease, and E. carotovora subsp. carotovora Harpin (HarpinEcc) and is severely attenuated in its plant virulence. The production of these exoproteins is restored in the mutant carrying an FlhDC+ plasmid. Sequence analysis and transcript assays disclosed that the flhD operon of E. carotovora subsp. carotovora, like those of other enterobacteria, consists of flhD and flhC. Complementation analysis revealed that the regulatory effect requires functions of both flhD and flhC products. The data presented here show that FlhDC positively regulates gacA, rsmC, and fliA and negatively regulates hexA (lrhA). Evidence shows that FlhDC controls extracellular protein production through cumulative effects on hexA and gacA. Reduced levels of GacA and elevated levels of HexA in the FlhDC− mutant are responsible for the inhibition of rsmB RNA production, a condition conducive to the accumulation of free RsmA. Indeed, studies with an RsmA− FlhDC− double mutant and multiple copies of rsmB + DNA establish that the negative effect of FlhDC deficiency is exerted via RsmA. The FlhDC-mediated regulation of fliA has no bearing on exoprotein production in E. carotovora subsp. carotovora. Our observations for the first time establish a regulatory connection between FlhDC, HexA, GacA, and rsmB RNA in the context of the exoprotein production and virulence of E. carotovora subsp. carotovora.

scholarly journals Elevated Temperature Enhances Virulence of Erwinia carotovora subsp. carotovora Strain EC153 to Plants and Stimulates Production of the Quorum Sensing Signal, N-Acyl Homoserine Lactone, and Extracellular Proteins

2005 ◽  
Vol 71 (8) ◽  
pp. 4655-4663 ◽  
Author(s):  
H. Hasegawa ◽  
A. Chatterjee ◽  
Y. Cui ◽  
A. K. Chatterjee
Keyword(s):  
Quorum Sensing ◽  
Extracellular Enzymes ◽  
Rna Binding ◽  
Elevated Temperatures ◽  
Pectate Lyase ◽  
Erwinia Carotovora ◽  
Homoserine Lactone ◽  
Extracellular Proteins ◽  
Acyl Homoserine Lactone ◽  
Tissue Maceration

ABSTRACT Erwinia carotovora subsp. atroseptica, E. carotovora subsp. betavasculorum, and E. carotovora subsp. carotovora produce high levels of extracellular enzymes, such as pectate lyase (Pel), polygalacturonase (Peh), cellulase (Cel), and protease (Prt), and the quorum-sensing signal N-acyl-homoserine lactone (AHL) at 28°C. However, the production of these enzymes and AHL by these bacteria is severely inhibited during growth at elevated temperatures (31.2°C for E. carotovora subsp. atroseptica and 34.5°C for E. carotovora subsp. betavasculorum and most E. carotovora subsp. carotovora strains). At elevated temperatures these bacteria produce high levels of RsmA, an RNA binding protein that promotes RNA decay. E. carotovora subsp. carotovora strain EC153 is an exception in that it produces higher levels of Pel, Peh, Cel, and Prt at 34.5°C than at 28°C. EC153 also causes extensive maceration of celery petioles and Chinese cabbage leaves at 34.5°C, which correlates with a higher growth rate and higher levels of rRNA and AHL. The lack of pectinase production by E. carotovora subsp. carotovora strain Ecc71 at 34.5°C limits the growth of this organism in plant tissues and consequently impairs its ability to cause tissue maceration. Comparative studies with ahlI (the gene encoding a putative AHL synthase), pel-1, and peh-1 transcripts documented that at 34.5°C the RNAs are more stable in EC153 than in Ecc71. Our data reveal that overall metabolic activity, AHL levels, and mRNA stability are responsible for the higher levels of extracellular protein production and the enhanced virulence of EC153 at 34.5°C compared to 28°C.

scholarly journals RpoS (Sigma-S) Controls Expression of rsmA, a Global Regulator of Secondary Metabolites, Harpin, and Extracellular Proteins in Erwinia carotovora

1998 ◽  
Vol 180 (14) ◽  
pp. 3629-3634 ◽  
Author(s):  
Asita Mukherjee ◽  
Yaya Cui ◽  
Weilei Ma ◽  
Yang Liu ◽  
Akira Ishihama ◽  
...  
Keyword(s):  
Sigma Factor ◽  
Parent Strain ◽  
Pectate Lyase ◽  
Extracellular Enzyme ◽  
Erwinia Carotovora ◽  
Hypersensitive Reaction ◽  
Extracellular Proteins ◽  
Global Regulator ◽  
E Coli ◽  
Multiple Copies

ABSTRACT RpoS (sigma-S or sigma-38) controls a large array of genes that are expressed during stationary phase and under various stress conditions in Escherichia coli and other bacteria. We document here that plant pathogenic and epiphytic Erwinia species, such as E. amylovora; E. carotovora subsp.atroseptica, betavasculorum, andcarotovora; E. chrysanthemi;E. herbicola; E. rhapontici; andE. stewartii, possess rpoS genes and produce the alternate sigma factor. We show that rpoStranscription in E. carotovora subsp.carotovora is driven from a major promoter which resides within the nlpD gene located upstream ofrpoS as in E. coli. RpoS− E. carotovora subsp. carotovoa strain AC5061, constructed by marker exchange, is more sensitive to hydrogen peroxide, carbon starvation, and acidic pH than its RpoS+ parent strain, AC5006. The basal levels of extracellular pectate lyase, polygalacturonase, and cellulase as well as those of transcripts of E. carotovora subsp. carotovora hrpN(hrpNEcc ), the gene for the elicitor of the hypersensitive reaction, are higher in the RpoS−strain than in the RpoS+ parent. Likewise, compared to AC5006, AC5061 causes more extensive maceration of celery petioles. Our findings with the RpoS− mutant and strains carrying multiple copies rpoS + DNA reveal thatrpoS positively controls rsmA expression. We also present evidence that supports the hypothesis that the RpoS effect on extracellular enzyme levels, hrpNEcc expression, and virulence manifests itself by the modulation ofrsmA expression.

scholarly journals kdgREcc Negatively Regulates Genes for Pectinases, Cellulase, Protease, HarpinEcc, and a Global RNA Regulator in Erwinia carotovora subsp.carotovora

1999 ◽  
Vol 181 (8) ◽  
pp. 2411-2421 ◽  
Author(s):  
Yang Liu ◽  
Guoqiao Jiang ◽  
Yaya Cui ◽  
Asita Mukherjee ◽  
Wei Lei Ma ◽  
...  
Keyword(s):  
Binding Site ◽  
Binding Sites ◽  
Consensus Sequence ◽  
Pectate Lyase ◽  
Extracellular Enzyme ◽  
Erwinia Carotovora ◽  
Hypersensitive Reaction ◽  
Transcriptional Unit ◽  
Negative Effect ◽  
Transcriptional Fusions

ABSTRACT Erwinia carotovora subsp. carotovoraproduces extracellular pectate lyase (Pel), polygalacturonase (Peh), cellulase (Cel), and protease (Prt). The concerted actions of these enzymes largely determine the virulence of this plant-pathogenic bacterium. E. carotovora subsp. carotovoraalso produces HarpinEcc, the elicitor of the hypersensitive reaction. We document here that KdgREcc (Kdg, 2-keto-3-deoxygluconate; KdgR, general repressor of genes involved in pectin and galacturonate catabolism), a homolog of the E. chrysanthemi repressor, KdgREch and theEscherichia coli repressor, KdgREco, negatively controls not only the pectinases, Pel and Peh, but also Cel, Prt, and HarpinEcc production in E. carotovorasubsp. carotovora. The levels of pel-1,peh-1, celV, andhrpNEcc transcripts are markedly affected by KdgREcc. The KdgREcc − mutant is more virulent than the KdgREcc + parent. Thus, our data for the first time establish a global regulatory role for KdgREcc in E. carotovora subsp.carotovora. Another novel observation is the negative effect of KdgREcc on the transcription of rsmB(previously aepH), which specifies an RNA regulator controlling exoenzyme and HarpinEcc production. The levels of rsmB RNA are higher in the KdgREcc − mutant than in the KdgREcc + parent. Moreover, by DNase I protection assays we determined that purified KdgREccprotected three 25-bp regions within the transcriptional unit ofrsmB. Alignment of the protected sequences revealed the 21-mer consensus sequence of the KdgREcc-binding site as 5′-G/AA/TA/TGAAA[N6]TTTCAG/TG/TA-3′. Two such KdgREcc-binding sites occur inrsmB DNA in a close proximity to each other within nucleotides +79 and +139 and the third KdgREcc-binding site within nucleotides +207 and +231. Analysis of lacZtranscriptional fusions shows that the KdgR-binding sites negatively affect the expression of rsmB. KdgREcc also binds the operator DNAs of pel-1 and peh-1genes and represses expression of a pel1-lacZ and apeh1-lacZ transcriptional fusions. We conclude that KdgREcc affects extracellular enzyme production by two ways: (i) directly, by inhibiting the transcription of exoenzyme genes; and (ii) indirectly, by preventing the production of a global RNA regulator. Our findings support the idea that KdgREccaffects transcription by promoter occlusion, i.e., preventing the initiation of transcription, and by a roadblock mechanism, i.e., by affecting the elongation of transcription.

Microbiota on Spoiled Vegetables and Their Characterization

2013 ◽  
Vol 76 (8) ◽  
pp. 1350-1358 ◽  
Author(s):  
DONG HWAN LEE ◽  
JIN-BEOM KIM ◽  
MIHYUN KIM ◽  
EUNJUNG ROH ◽  
KYUSUK JUNG ◽  
...  
Keyword(s):  
Plant Cell Wall ◽  
Pectate Lyase ◽  
Homoserine Lactone ◽  
Cell Wall Degrading Enzymes ◽  
Biochemical Tests ◽  
Signal Molecule ◽  
16S Rdna Sequence ◽  
Fresh Vegetables ◽  
Spoilage Bacteria ◽  
Important Enzyme

Spoilage causes vegetables to deteriorate and develop unpleasant characteristics. Approximately 30% of fresh vegetables are lost to spoilage, mainly due to colonization by bacteria. In the present study, a total of 44 bacterial isolates were obtained from a number of spoiled vegetables. The isolates were identified and classified into 20 different species of 14 genera based on fatty acid composition, biochemical tests, and 16S rDNA sequence analyses. Pseudomonas spp. were the species most frequently isolated from the spoiled vegetables. To evaluate the spoilage ability of each species, a variety of fresh vegetables were treated with each isolate and their degree of maceration was observed. In addition, the production of plant cell wall-degrading enzymes (PCWDEs), such as cellulase, xylanase, pectate lyase, and polygalacturonase, was compared among isolates to investigate their potential associations with spoilage. Strains that produce more PCWDEs cause spoilage on more diverse plants, and pectinase may be the most important enzyme among PCWDEs for vegetable spoilage. Most gram-negative spoilage bacteria produced acylated homoserine lactone, a quorum-sensing signal molecule, suggesting that it may be possible to use this compound effectively to prevent or slow down the spoilage of vegetables contaminated with diverse bacteria.

scholarly journals Comparative Analysis of Two Classes of Quorum-Sensing Signaling Systems That Control Production of Extracellular Proteins and Secondary Metabolites in Erwinia carotovora Subspecies

2005 ◽  
Vol 187 (23) ◽  
pp. 8026-8038 ◽  
Author(s):  
Asita Chatterjee ◽  
Yaya Cui ◽  
Hiroaki Hasegawa ◽  
Nathan Leigh ◽  
Vaishali Dixit ◽  
...  
Keyword(s):  
Quorum Sensing ◽  
Secondary Metabolites ◽  
Extracellular Enzyme ◽  
Erwinia Carotovora ◽  
Homoserine Lactone ◽  
Class Ii ◽  
Extracellular Proteins ◽  
Class I ◽  
Mobility Shift ◽  
Signaling Systems

ABSTRACT In Erwinia carotovora subspecies, N-acyl homoserine lactone (AHL) controls the expression of various traits, including extracellular enzyme/protein production and pathogenicity. We report here that E. carotovora subspecies possess two classes of quorum-sensing signaling systems defined by the nature of the major AHL analog produced as well as structural and functional characteristics of AHL synthase (AhlI) and AHL receptor (ExpR). Class I strains represented by E. carotovora subsp. atroseptica strain Eca12 and E. carotovora subsp. carotovora strains EC153 and SCC3193 produce 3-oxo-C8-HL (N-3-oxooctanoyl-l-homoserine lactone) as the major AHL analog as well as low but detectable levels of 3-oxo-C6-HL (N-3-oxohexanoyl-l-homoserine lactone). In contrast, the members of class II (i.e., E. carotovora subsp. betavasculorum strain Ecb168 and E. carotovora subsp. carotovora strains Ecc71 and SCRI193) produce 3-oxo-C6-HL as the major analog. ExpR species of both classes activate rsmA (Rsm, repressor of secondary metabolites) transcription and bind rsmA DNA. Gel mobility shift assays with maltose-binding protein (MBP)-ExpR71 and MBP-ExpR153 fusion proteins show that both bind a 20-mer sequence present in rsmA. The two ExpR functions (i.e., expR-mediated activation of rsmA expression and ExpR binding with rsmA DNA) are inhibited by AHL. The AHL effects are remarkably specific in that expR effect of EC153, a strain belonging to class I, is counteracted by 3-oxo-C8-HL but not by 3-oxo-C6-HL. Conversely, the expR effect of Ecc71, a strain belonging to class II, is neutralized by 3-oxo-C6-HL but not by 3-oxo-C8-HL. The AHL responses correlated with expR-mediated inhibition of exoprotein and secondary metabolite production.

scholarly journals rsmC of the Soft-Rotting Bacterium Erwinia carotovora subsp. carotovora Negatively Controls Extracellular Enzyme and HarpinEcc Production and Virulence by Modulating Levels of Regulatory RNA (rsmB) and RNA-Binding Protein (RsmA)

1999 ◽  
Vol 181 (19) ◽  
pp. 6042-6052 ◽  
Author(s):  
Yaya Cui ◽  
Asita Mukherjee ◽  
C. Korsi Dumenyo ◽  
Yang Liu ◽  
Arun K. Chatterjee
Keyword(s):  
Extracellular Enzymes ◽  
Rna Binding ◽  
Binding Protein ◽  
Regulatory Gene ◽  
Rna Binding Protein ◽  
Extracellular Enzyme ◽  
Erwinia Carotovora ◽  
Homoserine Lactone ◽  
Regulatory Rna ◽  
Knockout Mutant

ABSTRACT Previous studies have shown that the production of extracellular enzymes (pectate lyase [Pel], polygalacturonase [Peh], cellulase [Cel], and protease [Prt]) and harpinEcc (the elicitor of hypersensitive reaction) in Erwinia carotovora subsp.carotovora is regulated by RsmA, an RNA-binding protein, and rsmB, a regulatory RNA (Rsm stands for regulator of secondary metabolites) (Y. Liu et al., Mol. Microbiol. 29:219–234, 1998). We have cloned and characterized a novel regulatory gene,rsmC, that activates RsmA production and represses extracellular enzyme and harpinEcc production,rsmB transcription, and virulence in E. carotovora subsp. carotovora. In anrsmC knockout mutant of E. carotovora subsp.carotovora Ecc71 carrying the chromosomal copy of the wild-type rsmA + allele, the basal levels of Pel, Peh, Cel, Prt, and harpinEcc as well as the amounts ofrsmB, pel-1, peh-1,celV, and hrpNEcc transcripts are high, whereas the levels of rsmA transcripts and RsmA protein are low. Furthermore, the expression of anrsmA-lacZ gene fusion is lower in the RsmC−mutant than in the RsmC+ parent. Conversely, the expression of an rsmB-lacZ operon fusion is higher in the RsmC− mutant than in the RsmC+ parent. These observations establish that RsmC negatively regulates rsmBtranscription but positively affects RsmA production. Indeed, comparative studies with an RsmC− mutant, an RsmA− mutant, and an RsmA− RsmC−double mutant have revealed that the negative effects on exoprotein production and virulence are due to the cumulative regulatory effects of RsmC on rsmA and rsmB. Exoprotein production by the RsmC− mutant is partially dependent on the quorum sensing signal,N-(3-oxohexanoyl)-l-homoserine lactone. Southern blot data and analysis of PCR products disclosed the presence of rsmC sequences in E. carotovora subsp. atroseptica, E. carotovora subsp. betavasculorum, and E. carotovora subsp. carotovora. These findings collectively support the idea that rsmA andrsmB expression in these plant pathogenicErwinia species is controlled by RsmC or a functional homolog of RsmC.

Quorum sensing in soft-rotting Erwinia carotovora

2005 ◽  
Author(s):  
◽  
Hiroaki Hasegawa
Keyword(s):  
Quorum Sensing ◽  
Rna Binding ◽  
Elevated Temperatures ◽  
Minor Component ◽  
Pectate Lyase ◽  
Erwinia Carotovora ◽  
Homoserine Lactone ◽  
Class Ii ◽  
Negative Regulator ◽  
Class I

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] The soft-rotting E. carotovora subspecies (ssp.) produces effectors and an array ofextra cellular enzymes, including pectate lyase (Pel), polygalacturonase (Peh), cellulase (Cell) and protease (Prt) that are known or predicted to function as virulence and pathogenicity factors. The production of these exoproteins is activated by quorum sensing (QS)signal, N-acyl homoserine lactone (AHL). At elevated temperatures, however, a majority of E. c. ssp. atroseptica (Eca), betavasculorum (Ecb) and carotovora (Ecc) strains produce much reduced amounts of AHL as well as those exoproteins, and activate the production of a global negative regulator, RsmA (Rsm = regulator of secondarymetabolites). Ecc strain EC153 is an exception in that it produces higher levels of exproteins as well as AHL at 34.5[degree sign]C than at 28[degree sign]C. Temperature-dependent production of virrulence factors by these strains correlates with overall metabolic activities and stabilities of ahlI (the gene for AHL synthase), pel-1 and peh-1 transcripts. EC153 also causes extensive maceration of celery and Chinese cabbage petioles at 34.5[degree sign]C, which contrasts with limited tissue maceration by Ecc strain Ecc71 at this temperature. Thus, overall metabolic activity, higher levels of AHL and greater mRNA stability of virulence activates transcription of rsmA. This activation of rsmA is prevented by AHL. Consequently, in the presence of AHL RsmA production occurs at a low level, triggering the production of virulence factors. These findings for the first time document regulation of an RNA-binding protien by ExpR and AHL, link quorum sensing system via posttransciptional regulation, and explain the basis for the pleiotropic effects of AHL in Ecc. This study also reports the existence of two classes of strains based on structural and functional characteristics of ExpR and AhlI in Erwinia carotovora subspecies. While class I strains produce 3-oxooctanoyl-L-homoserine lactone (3-oxo-C8-HL) as the major AHL analog and 3-oxohexanoyl homoserine lactone (3-oxo-C6-HL) as a minor component, the members of class II strains produce 3-oxo-C6-HL as the major analog. It has also been found that AHL synthase is responsible for biosynthetic specificity. ExpR species do not discriminate between rsmA genes of strains belonging to the two classes. However, specificity is conferred by AHL analogs in that 3-oxo-C8-HL neutralizes the actions of class II ExpRs whereas 3-oxo-C6HL neutalizes class I ExpRs.

scholarly journals Erwinia carotovora Quorum Sensing System Regulates Host-Specific Virulence Factors and Development Delay in Drosophila melanogaster

mBio ◽  
2020 ◽  
Vol 11 (3) ◽  
Author(s):  
Filipe J. D. Vieira ◽  
Pol Nadal-Jimenez ◽  
Luis Teixeira ◽  
Karina B. Xavier
Keyword(s):  
Cell Wall ◽  
Drosophila Melanogaster ◽  
Quorum Sensing ◽  
Virulence Factors ◽  
Plant Cell Wall ◽  
Erwinia Carotovora ◽  
Homoserine Lactone ◽  
Cell Wall Degrading Enzymes ◽  
Content Type ◽  
Pectolytic Enzymes

ABSTRACT Multihost bacteria have to rapidly adapt to drastic environmental changes, relying on a fine integration of multiple stimuli for an optimal genetic response. Erwinia carotovora spp. are phytopathogens that cause soft-rot disease. Strain Ecc15 in particular is a model for bacterial oral-route infection in Drosophila melanogaster as it harbors a unique gene, evf, that encodes the Erwinia virulence factor (Evf), which is a major determinant for infection of the D. melanogaster gut. However, the factors involved in the regulation of evf expression are poorly understood. We investigated whether evf could be controlled by quorum sensing as, in the Erwinia genus, quorum sensing regulates pectolytic enzymes, the major virulence factors needed to infect plants. Here, we show that transcription of evf is positively regulated by quorum sensing in Ecc15 via acyl-homoserine lactone (AHL) signal synthase ExpI and AHL receptors ExpR1 and ExpR2. We also show that the load of Ecc15 in the gut depends upon the quorum sensing-mediated regulation of evf. Furthermore, we demonstrate that larvae infected with Ecc15 suffer a developmental delay as a direct consequence of the regulation of evf via quorum sensing. Finally, we demonstrate that evf is coexpressed with plant cell wall-degrading enzymes (PCWDE) during plant infection in a quorum sensing-dependent manner. Overall, our results show that Ecc15 relies on quorum sensing to control production of both pectolytic enzymes and Evf. This regulation influences the interaction of Ecc15 with its two known hosts, indicating that quorum sensing signaling may impact bacterial dissemination via insect vectors that feed on rotting plants. IMPORTANCE Integration of genetic networks allows bacteria to rapidly adapt to changing environments. This is particularly important in bacteria that interact with multiple hosts. Erwinia carotovora is a plant pathogen that uses Drosophila melanogaster as a vector. To interact with these two hosts, Ecc15 uses different sets of virulence factors: plant cell wall-degrading enzymes to infect plants and the Erwinia virulence factor (evf) to infect Drosophila. Our work shows that, despite the virulence factors being specific for each host, both sets are coactivated by homoserine lactone quorum sensing and by the two-component GacS/A system in infected plants. This regulation is essential for Ecc15 loads in the gut of Drosophila and minimizes the developmental delay caused by the bacteria with respect to the insect vector. Our findings provide evidence that coactivation of the host-specific factors in the plant may function as a predictive mechanism to maximize the probability of transit of the bacteria between hosts.

scholarly journals A Metabolic Regulator Modulates Virulence and Quorum Sensing Signal Production in Pectobacterium atrosepticum

2013 ◽  
Vol 26 (3) ◽  
pp. 356-366 ◽  
Author(s):  
Marion F. Cubitt ◽  
Peter E. Hedley ◽  
Neil R. Williamson ◽  
Jenny A. Morris ◽  
Emma Campbell ◽  
...  
Keyword(s):  
Quorum Sensing ◽  
Plant Cell Wall ◽  
Homoserine Lactone ◽  
Insertion Mutation ◽  
Virulence Determinants ◽  
Methionine Biosynthesis ◽  
Cell Wall Degrading Enzymes ◽  
Pectobacterium Atrosepticum ◽  
Small Regulatory Rna ◽  
The Impact

Plant cell wall–degrading enzymes (PCWDE) are key virulence determinants in the pathogenesis of the potato pathogen Pectobacterium atrosepticum. In this study, we report the impact on virulence of a transposon insertion mutation in the metJ gene that codes for the repressor of the methionine biosynthesis regulon. In a mutant strain defective for the small regulatory RNA rsmB, PCWDE are not produced and virulence in potato tubers is almost totally abolished. However, when the metJ gene is disrupted in this background, the rsmB– phenotype is suppressed and virulence and PCWDE production are restored. Additionally, when metJ is disrupted, production of the quorum-sensing signal, N-(3-oxohexanoyl)-homoserine lactone, is increased. The metJ mutant strains showed pleiotropic transcriptional impacts affecting approximately a quarter of the genome. Genes involved in methionine biosynthesis were most highly upregulated but many virulence-associated transcripts were also upregulated. This is the first report of the impact of the MetJ repressor on virulence in bacteria.

scholarly journals Transgenic Plants Producing the Bacterial Pheromone N-Acyl-Homoserine Lactone Exhibit Enhanced Resistance to the Bacterial Phytopathogen Erwinia carotovora

2001 ◽  
Vol 14 (9) ◽  
pp. 1035-1042 ◽  
Author(s):  
Andres Mäe ◽  
Marcos Montesano ◽  
Viia Koiv ◽  
E. Tapio Palva
Keyword(s):  
Quorum Sensing ◽  
Transgenic Tobacco ◽  
Plant Cell Wall ◽  
Ectopic Expression ◽  
Erwinia Carotovora ◽  
Homoserine Lactone ◽  
Defense Responses ◽  
Dependent Manner ◽  
Wild Type ◽  
Enhanced Resistance

Bacterial pheromones, mainly different homoserine lactones, are central to a number of bacterial signaling processes, including those involved in plant pathogenicity. We previously demonstrated that N-oxoacyl-homoserine lactone (OHL) is essential for quorum sensing in the soft-rot phytopathogen Erwinia carotovora. In this pathogen, OHL controls the coordinate activation of genes encoding the main virulence determinants, extracellular plant cell wall degrading enzymes (PCWDEs), in a cell density-dependent manner. We suggest that E. carotovora employ quorum sensing to avoid the premature production of PCWDEs and subsequent activation of plant defense responses. To test whether modulating this sensory system would affect the outcome of a plant-pathogen interaction, we generated transgenic tobacco, producing OHL. This was accomplished by ectopic expression in tobacco of the E. carotovora gene expI, which is responsible for OHL biosynthesis. We show that expI-positive transgenic tobacco lines produced the active pheromone and partially complemented the avirulent phenotype of expI mutants. The OHL-producing tobacco lines exhibited enhanced resistance to infection by wild-type E. carotovora. The results were confirmed by exogenous addition of OHL to wild-type plants, which also resulted in increased resistance to E. carotovora.

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