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Frontiers in Plant Science 2018The bacterium is responsible of important economic losses in crop yield worldwide. In melon leaves, produced multiple necrotic spots surrounded by a chlorotic halo,...
The bacterium is responsible of important economic losses in crop yield worldwide. In melon leaves, produced multiple necrotic spots surrounded by a chlorotic halo, followed by necrosis of the whole infiltrated area and chlorosis in the surrounding tissues. The extent of these symptoms, as well as the day of appearance, was dose-dependent. Several imaging techniques (variable chlorophyll fluorescence, multicolor fluorescence, and thermography) provided spatial and temporal information about alterations in the primary and secondary metabolism, as well as the stomatal activity in the infected leaves. Detection of diseased leaves was carried out by using machine learning on the numerical data provided by these imaging techniques. Mathematical algorithms based on data from infiltrated areas offered 96.5 to 99.1% accuracy when classifying them as mock vs. bacteria-infiltrated. These algorithms also showed a high performance of classification of whole leaves, providing accuracy values of up to 96%. Thus, the detection of disease on whole leaves by a model trained on infiltrated areas appears as a reliable method that could be scaled-up for use in plant breeding programs or precision agriculture.
PubMed: 29491881
DOI: 10.3389/fpls.2018.00164 -
Molecular Plant Pathology Feb 2018Dickeya dadantii 3937 secretes pectate lyases (Pels) to degrade plant cell walls. Previously, we have demonstrated that EGcpB and EcpC function as bis-(3',5')-cyclic...
Dickeya dadantii 3937 secretes pectate lyases (Pels) to degrade plant cell walls. Previously, we have demonstrated that EGcpB and EcpC function as bis-(3',5')-cyclic dimeric guanosine monophosphate (c-di-GMP)-specific phosphodiesterases (PDEs) to positively regulate Pel production. However, the diguanylate cyclase (DGC) responsible for the synthesis of c-di-GMP and the dichotomous regulation of Pel has remained a mystery. Here, we identified GcpA as the dominant DGC to negatively regulate Pel production by the specific repression of pelD gene expression. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assays revealed that the expression levels of histone-like, nucleoid-structuring protein encoding gene hns and post-transcriptional regulator encoding genes rsmA and rsmB were significantly affected by GcpA. Deletion of hns or rsmB in the gcpA site-directed mutant restored its Pel production and pelD expression, demonstrating that H-NS and RsmB contribute to the GcpA-dependent regulation of Pel in D. dadantii. In addition, RsmB expression was subject to positive regulation by H-NS. Thus, we propose a novel pathway consisting of GcpA-H-NS-RsmB-RsmA-pelD that controls Pel production in D. dadantii. Furthermore, we showed that H-NS and RsmB are responsible for the GcpA-dependent regulation of motility and type III secretion system (T3SS) gene expression, respectively. Of the two PDEs involved in the regulation of Pels, only EGcpB regulates pelD expression through the same pathway as GcpA.
PubMed: 29390166
DOI: 10.1111/mpp.12665 -
Molecular Plant Pathology May 2018Bacteria from the genus Dickeya cause severe symptoms on numerous economically important plants. Dickeya solani is the Dickeya species most frequently found on infected...
Bacteria from the genus Dickeya cause severe symptoms on numerous economically important plants. Dickeya solani is the Dickeya species most frequently found on infected potato plants in Europe. D. solani strains from different countries show high genetic homogeneity, but significant differences in their virulence level. Dickeya species possess two quorum sensing (QS) mechanisms: the Exp system based on classic N-acyl-homoserine lactone (AHL) signals and a specific system depending on the production and perception of a molecule of unknown structure, Virulence Factor Modulating (VFM). To study the interplay between these two QS systems, five D. solani strains exhibiting different virulence levels were selected. Mutants were constructed by inactivating genes coding for each QS system. Double mutants were obtained by simultaneous inactivation of genes coding for both QS systems. Most of the D. solani mutants showed an attenuation of chicory maceration and a decreased production of plant cell wall-degrading enzymes (PCWDEs) and motility, but to different degrees depending on the strain. The VFM-QS system seems to regulate virulence in both D. solani and Dickeya dadantii, but the AHL-QS system has greater effects in D. solani than in D. dadantii. The inactivation of both QS systems in D. solani did not reveal any additive effect on the tested features. The inactivation of vfm genes generally has a more dominant effect relative to that of exp genes. Thus, VFM- and AHL-QS systems do not work in synergy to modulate the production of diverse virulence factors and the ability to macerate plant tissue.
Topics: 4-Butyrolactone; Cichorium intybus; Enterobacteriaceae; Genes, Bacterial; Mutation; Phenotype; Plant Diseases; Plant Leaves; Plant Tubers; Quorum Sensing; Solanum tuberosum; Virulence; Virulence Factors
PubMed: 28921772
DOI: 10.1111/mpp.12614 -
Frontiers in Plant Science 2017The production of reactive oxygen species (ROS) is one of the first defense reactions induced in in response to infection by the pectinolytic enterobacterium . Previous...
The production of reactive oxygen species (ROS) is one of the first defense reactions induced in in response to infection by the pectinolytic enterobacterium . Previous results also suggest that abscisic acid (ABA) favors multiplication and spread into its hosts. Here, we confirm this hypothesis using ABA-deficient and ABA-overproducer plants. We investigated the relationships between ABA status and ROS production in after infection and showed that ABA status modulates the capacity of the plant to produce ROS in response to infection by decreasing the production of class III peroxidases. This mechanism takes place independently of the well-described oxidative stress related to the RBOHD NADPH oxidase. In addition to this weakening of plant defense, ABA content in the plant correlates positively with the production of some bacterial virulence factors during the first stages of infection. Both processes should enhance disease progression in presence of high ABA content. Given that infection increases transcript abundance for the ABA biosynthesis genes and and triggers ABA accumulation in leaves, we propose that manipulates ABA homeostasis as part of its virulence strategy.
PubMed: 28421092
DOI: 10.3389/fpls.2017.00456 -
Frontiers in Plant Science 2017Among the most devastating bacterial diseases of plants, provoked by spp. cause crop yield losses on a large range of species with potato being the most economically...
Among the most devastating bacterial diseases of plants, provoked by spp. cause crop yield losses on a large range of species with potato being the most economically important. The use of antibiotics being prohibited in most countries in the field, identifying tolerance genes is expected to be one of the most effective alternate disease control approaches. A prerequisite for the identification of tolerance genes is to develop robust disease quantification methods and to identify tolerant plant genotypes. In this work, we investigate the feasibility of the exploitation of natural variation to find tolerant genotypes and to develop robust quantification methods. We compared different quantification methods that score either symptom development or bacterial populations . An easy to set up and reliable bacterial quantification method based on qPCR amplification of bacterial DNA was validated. This study demonstrates that it is possible to conduct a robust phenotyping of soft rot disease, and that Arabidopsis natural accessions are a relevant source of tolerance genes.
PubMed: 28400777
DOI: 10.3389/fpls.2017.00394 -
Molecular Plant Pathology Mar 2018PecS is one of the major global regulators controlling the virulence of Dickeya dadantii, a broad-host-range phytopathogenic bacterium causing soft rot on several plant...
PecS is one of the major global regulators controlling the virulence of Dickeya dadantii, a broad-host-range phytopathogenic bacterium causing soft rot on several plant families. To define the PecS regulon during plant colonization, we analysed the global transcriptome profiles in wild-type and pecS mutant strains during the early colonization of the leaf surfaces and in leaf tissue just before the onset of symptoms, and found that the PecS regulon consists of more than 600 genes. About one-half of these genes are down-regulated in the pecS mutant; therefore, PecS has both positive and negative regulatory roles that may be direct or indirect. Indeed, PecS also controls the regulation of a few dozen regulatory genes, demonstrating that this global regulator is at or near the top of a major regulatory cascade governing adaptation to growth in planta. Notably, PecS acts mainly at the very beginning of infection, not only to prevent virulence gene induction, but also playing an active role in the adaptation of the bacterium to the epiphytic habitat. Comparison of the patterns of gene expression inside leaf tissues and during early colonization of leaf surfaces in the wild-type bacterium revealed 637 genes modulated between these two environments. More than 40% of these modulated genes are part of the PecS regulon, emphasizing the prominent role of PecS during plant colonization.
Topics: Arabidopsis; Bacterial Proteins; Enterobacteriaceae; Gene Expression Profiling; Regulon; Virulence
PubMed: 28295994
DOI: 10.1111/mpp.12549 -
Infection and Immunity May 2017Type II secretion (T2S) is one means by which Gram-negative pathogens secrete proteins into the extracellular milieu and/or host organisms. Based upon recent genome... (Review)
Review
Type II secretion (T2S) is one means by which Gram-negative pathogens secrete proteins into the extracellular milieu and/or host organisms. Based upon recent genome sequencing, it is clear that T2S is largely restricted to the , occurring in many, but not all, genera in the , , , and classes. Prominent human and/or animal pathogens that express a T2S system(s) include , , , , , , , , , and T2S-expressing plant pathogens include , , , , , , and T2S also occurs in nonpathogenic bacteria, facilitating symbioses, among other things. The output of a T2S system can range from only one to dozens of secreted proteins, encompassing a diverse array of toxins, degradative enzymes, and other effectors, including novel proteins. Pathogenic processes mediated by T2S include the death of host cells, degradation of tissue, suppression of innate immunity, adherence to host surfaces, biofilm formation, invasion into and growth within host cells, nutrient assimilation, and alterations in host ion flux. The reach of T2S is perhaps best illustrated by those bacteria that clearly use it for both environmental survival and virulence; e.g., employs T2S for infection of amoebae, growth within lung cells, dampening of cytokines, and tissue destruction. This minireview provides an update on the types of bacteria that have T2S, the kinds of proteins that are secreted via T2S, and how T2S substrates promote infection.
Topics: Bacterial Proteins; Gram-Negative Bacteria; Protein Transport; Type II Secretion Systems; Virulence Factors
PubMed: 28264910
DOI: 10.1128/IAI.00014-17 -
RNA (New York, N.Y.) Apr 2017Regulation of gene expression by encoded riboswitches is a prevalent theme in bacteria. Of the hundreds of riboswitch families identified, the majority of them remain as...
Regulation of gene expression by encoded riboswitches is a prevalent theme in bacteria. Of the hundreds of riboswitch families identified, the majority of them remain as orphans, without a clear ligand assignment. The orphan family was recently characterized as guanidine-sensing riboswitches. Herein we present a 2.3 Å crystal structure of the guanidine-bound riboswitch from The riboswitch folds into a boot-shaped structure, with a coaxially stacked P1/P2 stem forming the boot, and a 3'-P3 stem-loop forming the heel. Sophisticated base-pairing and cross-helix tertiary contacts give rise to the ligand-binding pocket between the boot and the heel. The guanidine is recognized in its positively charged guanidinium form, in its sp hybridization state, through a network of coplanar hydrogen bonds and by a cation-π stacking contact on top of a conserved guanosine residue. Disruption of these contacts resulted in severe guanidinium-binding defects. These results provide the structural basis for specific guanidine sensing by riboswitches and pave the way for a deeper understanding of guanidine detoxification-a previously unappreciated aspect of bacterial physiology.
Topics: Base Pairing; Binding Sites; Crystallography, X-Ray; Enterobacteriaceae; Guanidine; Hydrogen Bonding; Ligands; Models, Molecular; Nucleic Acid Conformation; RNA, Bacterial; Riboswitch; Static Electricity; Thermodynamics
PubMed: 28096518
DOI: 10.1261/rna.060186.116 -
Frontiers in Plant Science 2016The negative impact of conventional farming on environment and human health make improvements on farming management mandatory. Imaging techniques are implemented in...
The negative impact of conventional farming on environment and human health make improvements on farming management mandatory. Imaging techniques are implemented in remote sensing for monitoring crop fields and plant phenotyping programs. The increasingly large size and complexity of the data obtained by these techniques, makes the implementation of powerful mathematical tools necessary in order to identify informative parameters and to apply them in precision agriculture. Multicolor fluorescence imaging is a useful approach for the study of plant defense responses to stress factors at bench scale. However, it has not been fully applied to plant phenotyping. This work evaluates the possible application of multicolor fluorescence imaging in combination with thermography for the particular case of zucchini plants affected by soft-rot, caused by . Several statistical models -based on logistic regression analysis (LRA) and artificial neural networks (ANN)- were obtained for the experimental system zucchini-, which classify new samples as "healthy" or "infected." The LRA worked best in identifying high dose-infiltrated leaves (in infiltrated and non-infiltrated areas) whereas ANN offered a higher accuracy at identifying low dose-infiltrated areas. To assess the applicability of these results to cucurbits in a more general way, these models were validated for melon infected by the same pathogen, achieving accurate predictions for the infiltrated areas. The values of accuracy achieved are comparable to those found in the literature for classifiers identifying other infections based on data obtained by different techniques. Thus, MCFI in combination with thermography prove useful at providing data at lab scale that can be analyzed by machine learning. This approach could be scaled up to be applied in plant phenotyping.
PubMed: 27994607
DOI: 10.3389/fpls.2016.01790 -
Molecular Plant Pathology Feb 2018Soft-rot diseases of plants attributed to Dickeya dadantii result from lysis of the plant cell wall caused by pectic enzymes released by the bacterial cell by a type II...
Soft-rot diseases of plants attributed to Dickeya dadantii result from lysis of the plant cell wall caused by pectic enzymes released by the bacterial cell by a type II secretion system (T2SS). Arabidopsis thaliana can express several lines of defence against this bacterium. We employed bacterial mutants with defective envelope structures or secreted proteins to examine early plant defence reactions. We focused on the production of AtrbohD-dependent reactive oxygen species (ROS), callose deposition and cell death as indicators of these reactions. We observed a significant reduction in ROS and callose formation with a bacterial mutant in which genes encoding five pectate lyases (Pels) were disrupted. Treatment of plant leaves with bacterial culture filtrates containing Pels resulted in ROS and callose production, and both reactions were dependent on a functional AtrbohD gene. ROS and callose were produced in response to treatment with a cellular fraction of a T2SS-negative mutant grown in a Pels-inducing medium. Finally, ROS and callose were produced in leaves treated with purified Pels that had also been shown to induce the expression of jasmonic acid-dependent defence genes. Pel catalytic activity is required for the induction of ROS accumulation. In contrast, cell death observed in leaves infected with the wild-type strain appeared to be independent of a functional AtrbohD gene. It was also independent of the bacterial production of pectic enzymes and the type III secretion system (T3SS). In conclusion, the work presented here shows that D. dadantii is recognized by the A. thaliana innate immune system through the action of pectic enzymes secreted by bacteria at the site of infection. This recognition leads to AtrbohD-dependent ROS and callose accumulation, but not cell death.
Topics: Arabidopsis; Gammaproteobacteria; Glucans; Immunity, Innate; Oligosaccharides; Polysaccharide-Lyases; Reactive Oxygen Species; Type III Secretion Systems; Virulence
PubMed: 27925401
DOI: 10.1111/mpp.12522