Tricarboxylic Acid (TCA) Cycle Enzymes and Intermediates Modulate Intracellular Cyclic di-GMP Levels and the Production of Plant Cell Wall–Degrading Enzymes in Soft Rot Pathogen Dickeya dadantii

Dickeya dadantii is a plant-pathogenic bacterium that causes soft-rot in a wide range of plants. Although we have previously demonstrated that cyclic bis-(3′-5′)-cyclic dimeric guanosine monophosphate (c-di-GMP), a bacterial secondary messenger, plays a central role in virulence regulation in D. dadantii, the upstream signals that modulate c-di-GMP remain enigmatic. Using a genome-wide transposon mutagenesis approach of a Δhfq mutant strain that has high c-di-GMP and reduced motility, we uncovered transposon mutants that recovered the c-di-GMP-mediated repression on swimming motility. A number of these mutants harbored transposon insertions in genes encoding tricarboxylic acid (TCA) cycle enzymes. Two of these TCA transposon mutants were studied further by generating chromosomal deletions of the fumA gene (encoding fumarase) and the sdhCDAB operon (encoding succinate dehydrogenase). Disruption of the TCA cycle in these deletion mutants resulted in reduced intracellular c-di-GMP and enhanced production of pectate lyases (Pels), a major plant cell wall–degrading enzyme (PCWDE) known to be transcriptionally repressed by c-di-GMP. Consistent with this result, addition of TCA cycle intermediates such as citrate also resulted in increased c-di-GMP levels and decreased production of Pels. Additionally, we found that a diguanylate cyclase GcpA was solely responsible for the observed citrate-mediated modulation of c-di-GMP. Finally, we demonstrated that addition of citrate induced not only an overproduction of GcpA protein but also a concomitant repression of the c-di-GMP-degrading phosphodiesterase EGcpB which, together, resulted in an increase in the intracellular concentration of c-di-GMP. In summary, our report demonstrates that bacterial respiration and respiration metabolites serve as signals for the regulation of c-di-GMP signaling.

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Inactivation of pecS restores the virulence of mutants devoid of osmoregulated periplasmic glucans in the phytopathogenic bacterium Dickeya dadantii

Microbiology ◽

10.1099/mic.0.074484-0 ◽

2014 ◽

Vol 160 (4) ◽

pp. 766-777 ◽

Cited By ~ 7

Author(s):

Sébastien Bontemps-Gallo ◽

Edwige Madec ◽

Jean-Marie Lacroix

Keyword(s):

Plant Cell Wall ◽

Transcriptional Regulator ◽

Soft Rot ◽

Cellular Functions ◽

Cell Wall Degrading Enzymes ◽

Dickeya Dadantii ◽

Phytopathogenic Bacterium ◽

Wide Range ◽

Severe Reduction ◽

Rot Disease

Dickeya dadantii is a phytopathogenic enterobacterium that causes soft rot disease in a wide range of plant species. Maceration, an apparent symptom of the disease, is the result of the synthesis and secretion of a set of plant cell wall-degrading enzymes (PCWDEs), but many additional factors are required for full virulence. Among these, osmoregulated periplasmic glucans (OPGs) and the PecS transcriptional regulator are essential virulence factors. Several cellular functions are controlled by both OPGs and PecS. Strains devoid of OPGs display a pleiotropic phenotype including total loss of virulence, loss of motility and severe reduction in the synthesis of PCWDEs. PecS is one of the major regulators of virulence in D. dadantii, acting mainly as a repressor of various cellular functions including virulence, motility and synthesis of PCWDEs. The present study shows that inactivation of the pecS gene restored virulence in a D. dadantii strain devoid of OPGs, indicating that PecS cannot be de-repressed in strains devoid of OPGs.

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Activities of plant cell wall-degrading enzymes by bacterial soft rot of orchid

Archives of Phytopathology and Plant Protection ◽

10.1080/03235408.2013.838374 ◽

2013 ◽

Vol 47 (10) ◽

pp. 1239-1250 ◽

Cited By ~ 15

Author(s):

Tri Joko ◽

Ahmad Subandi ◽

Nanda Kusumandari ◽

Arif Wibowo ◽

Achmadi Priyatmojo

Keyword(s):

Cell Wall ◽

Plant Cell ◽

Plant Cell Wall ◽

Soft Rot ◽

Bacterial Soft Rot ◽

Cell Wall Degrading Enzymes ◽

Degrading Enzymes

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The Bacterial Soft Rot Pathogens, Pectobacterium carotovorum and P. atrosepticum, Respond to Different Classes of Virulence-Inducing Host Chemical Signals

Horticulturae ◽

10.3390/horticulturae6010013 ◽

2020 ◽

Vol 6 (1) ◽

pp. 13

Author(s):

Paul A. Agyemang ◽

Md Niamul Kabir ◽

Caleb M. Kersey ◽

C. Korsi Dumenyo

Keyword(s):

Cell Wall ◽

Plant Cell ◽

Plant Cell Wall ◽

Soft Rot ◽

Class Ii ◽

Chemical Signals ◽

Water Soluble ◽

Negative Regulator ◽

Class I ◽

Cell Wall Degrading Enzymes

Soft rot bacteria of the Pectobacterium and Dickeya genera are Gram-negative phytopathogens that produce and secrete plant cell wall-degrading enzymes (PCWDE), the actions of which lead to rotting and decay of their hosts in the field and in storage. Host chemical signals are among the factors that induce the bacteria into extracellular enzyme production and virulence. A class of compounds (Class I) made up of intermediate products of cell wall (pectin) degradation induce exoenzyme synthesis through KdgR, a global negative regulator of exoenzyme production. While the KdgR− mutant of P. carotovorum is no longer inducible by Class I inducers, we demonstrated that exoenzyme production is induced in this strain in the presence of extracts from hosts including celery, potato, carrot, and tomato, suggesting that host plants contain another class of compounds (Class II inducers) different from the plant cell wall-degradative products that work through KdgR. The Class II inducers are thermostable, water-soluble, diffusible, and dialysable through 1 kDa molecular weight cut off pore size membranes, and could be a target for soft rot disease management strategies.

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The Modification of Plant Cell Wall Polysaccharides in Potato Plants during Pectobacterium atrosepticum-Caused Infection

Plants ◽

10.3390/plants10071407 ◽

2021 ◽

Vol 10 (7) ◽

pp. 1407

Author(s):

Vladimir Gorshkov ◽

Ivan Tsers ◽

Bakhtiyar Islamov ◽

Marina Ageeva ◽

Natalia Gogoleva ◽

...

Keyword(s):

Cell Wall ◽

Plant Cell ◽

Plant Cell Wall ◽

Expression Profiles ◽

Soft Rot ◽

Plant Colonization ◽

Cross Linking ◽

Cell Wall Polysaccharides ◽

Pectobacterium Atrosepticum ◽

Potato Plants

Our study is the first to consider the changes in the entire set of matrix plant cell wall (PCW) polysaccharides in the course of a plant infectious disease. We compared the molecular weight distribution, monosaccharide content, and the epitope distribution of pectic compounds and cross-linking glycans in non-infected potato plants and plants infected with Pectobacterium atrosepticum at the initial and advanced stages of plant colonization by the pathogen. To predict the gene products involved in the modification of the PCW polysaccharide skeleton during the infection, the expression profiles of potato and P. atrosepticum PCW-related genes were analyzed by RNA-Seq along with phylogenetic analysis. The assemblage of P. atrosepticum biofilm-like structures—the bacterial emboli—and the accumulation of specific fragments of pectic compounds that prime the formation of these structures were demonstrated within potato plants (a natural host of P. atrosepticum). Collenchyma was shown to be the most “vulnerable” tissue to P. atrosepticum among the potato stem tissues. The infection caused by the representative of the Soft Rot Pectobacteriaceae was shown to affect not only pectic compounds but also cross-linking glycans; the content of the latter was increased in the infected plants compared to the non-infected ones.

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The Gene Encoding NAD-Dependent Epimerase/Dehydratase, wcaG, Affects Cell Surface Properties, Virulence, and Extracellular Enzyme Production in the Soft Rot Phytopathogen, Pectobacterium carotovorum

Microorganisms ◽

10.3390/microorganisms7060172 ◽

2019 ◽

Vol 7 (6) ◽

pp. 172 ◽

Cited By ~ 2

Author(s):

Rabiul Islam ◽

Shyretha Brown ◽

Ali Taheri ◽

C. Korsi Dumenyo

Keyword(s):

Escherichia Coli ◽

Cell Wall ◽

Cell Surface ◽

Surface Properties ◽

Plant Cell ◽

Plant Cell Wall ◽

Soft Rot ◽

Pectobacterium Carotovorum ◽

Cell Wall Degrading Enzymes ◽

Cell Surface Properties

Pectobacterium carotovorum is a gram-negative bacterium that, together with other soft rot Enterobacteriaceae causes soft rot disease in vegetables, fruits, and ornamental plants through the action of exoproteins including plant cell wall-degrading enzymes (PCWDEs). Although pathogenicity in these bacteria is complex, virulence levels are proportional to the levels of plant cell wall-degrading exoenzymes (PCWDEs) secreted. Two low enzyme-producing transposon Tn5 mutants were isolated, and compared to their parent KD100, the mutants were less virulent on celery petioles and carrot disks. The inactivated gene responsible for the reduced virulence phenotype in both mutants was identified as wcaG. The gene, wcaG (previously denoted fcl) encodes NAD-dependent epimerase/dehydratase, a homologue of GDP-fucose synthetase of Escherichia coli. In Escherichia coli, GDP-fucose synthetase is involved in the biosynthesis of the exopolysaccharide, colanic acid (CA). The wcaG mutants of P. carotovorum formed an enhanced level of biofilm in comparison to their parent. In the hydrophobicity test the mutants showed more hydrophobicity than the parent in hexane and hexadecane as solvents. Complementation of the mutants with extrachromosomal copies of the wild type gene restored these functions to parental levels. These data indicate that NAD-dependent epimerase/dehydratase plays a vital rule in cell surface properties, exoenzyme production, and virulence in P. carotovorum.

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Phloretin, an Apple Phytoalexin, Affects the Virulence and Fitness of Pectobacterium brasiliense by Interfering With Quorum-Sensing

Frontiers in Plant Science ◽

10.3389/fpls.2021.671807 ◽

2021 ◽

Vol 12 ◽

Author(s):

Manoj Pun ◽

Netaly Khazanov ◽

Ortal Galsurker ◽

Michal Weitman ◽

Zohar Kerem ◽

...

Keyword(s):

Cell Wall ◽

Quorum Sensing ◽

Plant Cell ◽

Plant Cell Wall ◽

Soft Rot ◽

Homoserine Lactone ◽

Cell Wall Degrading Enzymes ◽

Docking Simulations ◽

E Coli ◽

Degrading Enzymes

The effects of phloretin a phytoalexin from apple, was tested on Pectobacterium brasiliense (Pb1692), an emerging soft-rot pathogen of potato. Exposure of Pb1692 to 0.2 mM phloretin a concentration that does not affect growth, or to 0.4 mM a 50% growth inhibiting concentration (50% MIC), reduced motility, biofilm formation, secretion of plant cell wall-degrading enzymes, production of acyl–homoserine lactone (AHL) signaling molecules and infection, phenotypes that are associated with bacterial population density-dependent system known as quorum sensing (QS). To analyze the effect of growth inhibition on QS, the activity of ciprofloxacin, an antibiotic that impairs cell division, was compared to that of phloretin at 50% MIC. Unlike phloretin, the antibiotic hardly affected the tested phenotypes. The use of DH5α, a QS-negative Escherichia coli strain, transformed with an AHL synthase (ExpI) from Pb1692, allowed to validate direct inhibition of AHL production by phloretin, as demonstrated by two biosensor strains, Chromobacterium violaceaum (CV026) and E. coli (pSB401). Expression analysis of virulence-related genes revealed downregulation of QS-regulated genes (expI, expR, luxS, rsmB), plant cell wall degrading enzymes genes (pel, peh and prt) and motility genes (motA, fim, fliA, flhC and flhD) following exposure to both phloretin concentrations. The results support the inhibition of ExpI activity by phloretin. Docking simulations were used to predict the molecular associations between phloretin and the active site of ExpI, to suggest a likely mode of action for the compound’s inhibition of virulence.

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