Biology subjects

Deflandre, B.

Publications and source records attributed to Deflandre, B..

8 recordsLinked to original sources

bioRxiv2023

Nitrogen sources enhance siderophore-mediated competition for iron between potato common scab and late blight causative agents

Withdrawal StatementThe authors have withdrawn their manuscript owing to the fact that the P. infestans strain received from third parties is not the one referred in the manuscript despite having the certificate from the providing collection. All the experiments and data are correct but not included into a proper research context. A new version of this work will be published in near future. Therefore, the authors do not wish this work to be cited as reference for the project. If you have any questions, please contact the corresponding author.

microbiology↗

bioRxiv2023

Common scab disease: structural basis of elicitor recognition in pathogenic Streptomyces species

In Streptomyces scabiei, the main causative agent of common scab disease of root and tuber crops, the interaction between the substrate-binding protein (SBP) CebE (CebEscab) and cellotriose released by the plant host (KD in the nanomolar range) is the first event for the onset of its pathogenic lifestyle. Here we report the structure of CebEscab in complex with cellotriose at a 1.55 [A] resolution, adopting a general fold of the B subcluster of SBPs. The interaction between CebEscab and cellotriose involves multiple direct or water-mediated hydrogen bonds and hydrophobic interactions, the glucose monomer at the non-reducing end occupying the most conserved part of the substrate-binding cleft. As main interactions between the two domains of CebE involve cellotriose itself, the closed conformational state of CebE is performed via an induced-fit ligand binding mechanism where cellotriose binding triggers the domain movement. Analysis of regulon predictions revealed that the signaling pathway from the CebE-mediated cellotriose transport to the transcriptional activation of thaxtomin phytotoxin biosynthesis is conserved in Streptomyces spp causing common scab, except for Streptomyces ipomoeae that specifically colonizes sweet potatoes and responds to other and yet unknown virulence elicitors. Interestingly, strains belonging to pathogenic species turgidiscabies and caniscabies have a cellotriose-binding protein orthologous to the CebE protein of the saprophytic species Streptomyces reticuli with lower affinity for its substrate (KD in the micromolar range), suggesting higher cellotriose concentrations for perception of their host. Our work also provides the structural basis for the uptake of cellobiose and cellotriose by non-pathogenic cellulose-decomposing Streptomyces species. ImportanceCommon scab is a disease caused by few Streptomyces species that affects important root and tuber crops including potato, beet, radish, and parsnip, resulting in major economic losses worldwide. In this work we unveiled the molecular basis of host recognition by these pathogens by solving the structure of the sugar-binding protein CebE of S. scabiei in complex with cellotriose, the main elicitor of the pathogenic lifestyle of these bacteria. We further revealed that the signaling pathway from CebE-mediated transport of cellotriose is conserved in all pathogenic species except S. ipomoeae that causes soft rot disease on sweet potatoes. Our work also provides the structural basis of the uptake of cellobiose and cellotriose in saprophytic Streptomyces species, the first step activating the expression of the enzymatic system degrading the most abundant polysaccharide on earth, cellulose. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=125 SRC="FIGDIR/small/540135v1_ufig1.gif" ALT="Figure 1"> View larger version (34K): org.highwire.dtl.DTLVardef@1915dd1org.highwire.dtl.DTLVardef@a65aaforg.highwire.dtl.DTLVardef@18bc293org.highwire.dtl.DTLVardef@937d2f_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LICellotriose uptake triggers common scab in tuber/root crops by Streptomyces scabiei C_LIO_LICrystal structure of CebE of S. scabiei interacting with cellotriose is solved C_LIO_LICellotriose triggers the closed conformational state of CebE C_LIO_LIThe CebE/cellotriose route to pathogenicity is conserved in Streptomyces species C_LIO_LICebE-type background may affect the cellotriose concentration eliciting virulence C_LI

microbiology↗

bioRxiv2022

Structure and function of BcpE2, the most promiscuous GH3-family beta-glucosidase for scavenging glucose from heterosides

Cellulose being the most abundant polysaccharide on earth, beta-glucosidases hydrolyzing cello-oligosaccharides are key enzymes to fuel glycolysis in microorganisms developing on plant material. In Streptomyces scabiei, the causative agent of common scab in root and tuber crops, a genetic compensation phenomenon safeguards the loss of the gene encoding the cello-oligosaccharide hydrolase BglC by awakening the expression of alternative beta-glucosidases. Here we reveal that the BglC compensating enzyme BcpE2 is the GH3-family beta-glucosidase that displays the highest reported substrate promiscuity able to release the glucose moiety of all tested types of plant-derived heterosides (aryl {beta}-glucosides, monolignol glucosides, cyanogenic glucosides, anthocyanosides, and coumarin heterosides). BcpE2 structure analysis highlighted a large cavity in the PA14 domain that covers the active site, and the high flexibility of this domain would allow proper adjustment of this cavity for disparate heterosides. The exceptional substrate promiscuity of BcpE2 provides microorganisms a versatile tool for scavenging glucose from plant-derived nutrients that widely vary in size and structure. Importantly, scopolin is the only substrate commonly hydrolyzed by both BglC and BcpE2 thereby generating the potent virulence inhibitor scopoletin. Next to fueling glycolysis, both enzymes thus also interfere with the plant defense mechanisms to fine-tune the strength of virulence.

biochemistry↗

bioRxiv2021

BglC of Streptomyces scabiei is a scopolin-hydrolyzing β-glucosidase interfering with the host defense mechanism

The beta-glucosidase BglC fulfills multiple functions in both primary metabolism and induction of pathogenicity of Streptomyces scabiei, the causative agent of the common scab disease of root and tuber crops. Indeed, this enzyme hydrolyzes cellobiose and cellotriose to directly feed glycolysis with glucose, but also modifies the intracellular concentration of these cello-oligosaccharides which are the virulence elicitors. The inactivation of bglC also led to unexpected phenotypes such as the constitutive overproduction of thaxtomin A, the main virulence determinant of S. scabiei. In this work we revealed a new target substrate of BglC, the phytoalexin scopolin. Removal of the glucose moiety of scopolin generates scopoletin, a potent inhibitor of thaxtomin A production. The hydrolysis of scopolin by BglC presents substrate inhibition kinetics which contrasts with the typical Michaelis-Menten saturation curve previously observed for the degradation of its natural substrate cellobiose. Our work therefore reveals that BglC targets both cello-oligosaccharide elicitors emanating from the hosts of S. scabiei, and the scopolin phytoalexin generated by the host defense mechanisms, thereby occupying a key position to fine-tune the production of the main virulence determinant thaxtomin A.

microbiology↗

bioRxiv2021

The virulome of Streptomyces scabiei in response to cello-oligosaccharides elicitors

2.The development of spots or lesions symptomatic of the common scab disease on root and tuber crops is caused by few pathogenic Streptomyces with Streptomyces scabiei 87-22 as the model species. Thaxtomin phytotoxins are the primary virulence determinants, mainly acting by impairing cellulose synthesis, and their production in S. scabiei is in turn boosted by the cello-oligosaccharides released from host plants. In this work we aimed to determine which molecules and which biosynthetic gene clusters (BGCs) of the specialized metabolism of S. scabiei 87-22 show a production and/or transcriptional response to cello-oligosaccharides. Comparative metabolomic and transcriptomic analyses revealed that molecules of the virulome of S. scabiei induced by cellobiose and cellotriose include i) thaxtomins and concanamycins phytotoxins (and to a lesser extent N-coronafacoyl-L-isoleucine), ii) desferrioxamines, scabichelin and turgichelin siderophores in order to acquire iron essential for housekeeping functions, iii) ectoine for protection against osmotic shock once inside the host, and iv) bottromycins and concanamycins antimicrobials possibly to prevent other microorganisms from colonizing the same niche. Importantly, both cell-oligosaccharides reduced the production of the spore germination inhibitors germicidins and the plant growth regulators rotihibins. The metabolomic study also revealed that cellotriose is in general a more potent elicitor of the virulome compared to cellobiose. This result supports an earlier hypothesis that suggested that the trisaccharide would be the real virulence-triggering factor released from the plant cell wall through the action of thaxtomins. Interestingly, except for thaxtomins, none of these BGCs expression seems to be under direct control of the cellulose utilization repressor CebR suggesting the existence of another master regulator sensing the internalization of cello-oligosaccharides. Finally, we found nine additional cryptic and orphan BGCs that have their expression awakened by cello-oligosaccharides, demonstrating that other and yet to be discovered metabolites are part of the virulome of S. scabiei. 3. Impact statementUnveiling the environmental triggers that signal proper conditions for host colonization and what is the composition of the arsenal of metabolites specialized for this task (the virulome) is key to understand host-pathogen interactions. In this work, focused on the induction of the common scab disease caused by Streptomyces species, we provided further knowledge to both aspects i.e., i) highlighting the capability of cellotriose to trigger the entire virulome and not only the production of thaxtomin phytotoxins, and ii) identifying the set of metabolites that specifically respond to cello-oligosaccharides emanating from the plant under attack. Importantly, we also revealed that the expression of nine cryptic/orphan biosynthetic gene clusters (BGCs) involved in the production of unknown compounds was drastically activated upon cello-oligosaccharides import suggesting that a significant part of the virulome of S. scabiei remains to be discovered. Finally, we unexpectedly found that the expression control of most of the known and cryptic BGCs does not depend on the cello-oligosaccharide utilization repressor CebR which suggests the existence of another and yet unknown master regulator of the virulence in S. scabiei. 4. Significance as a BioResource to the communityNot Applicable 5. OutcomeNot Applicable 6. Data summary[A section describing all supporting external data including the DOI(s) and/or accession numbers(s), and the associated URL.] The authors confirm all supporting data, code and protocols have been provided within the article or through supplementary data files. RNAseq data were publicly deposited, and our experimental and analytical pipeline were described on the GEO database repository (Accession number: GSE181490)

microbiology↗

bioRxiv2019

Bagremycin Antibiotics and Ferroverdin iron-chelators are synthetized by the Same Gene Cluster

Biosynthetic gene clusters (BGCs) are organized groups of genes involved in the production of specialized metabolites. Typically, one BGC is responsible for the production of one or several similar compounds with bioactivities that usually only vary in terms of strength and/or specificity. Here we show that the previously described ferroverdins and bagremycins, which are families of metabolites with different bioactivities, are produced from the same BGC, whereby the fate of the biosynthetic pathway depends on iron availability. Under conditions of iron depletion, the monomeric bagremycins are formed, which are amino-aromatic antibiotics resulting from the condensation of 3-amino-4-hydroxybenzoic acid with p-vinylphenol. Conversely, when iron is abundantly available, the biosynthetic pathway additionally produces a molecule based on p-vinylphenyl-3-nitroso-4-hydroxybenzoate, which complexes iron to form the trimeric ferroverdins that have anticholesterol activity. Thus our work challenges the concept that BGCs should produce a single family of molecules with one type of bioactivity, the occurrence of the different metabolites being triggered by the environmental conditions.

microbiology↗

bioRxiv2017

Contribution of the β-glucosidase BglC to the Onset of the Pathogenic Lifestyle of Streptomyces scabies

Common scab disease on root and tuber plants is caused by Streptomyces scabies and related species which use the cellulose synthase inhibitor thaxtomin A as main phytotoxin. Thaxtomin production is primarily triggered by the import of cello-oligosaccharides. Once inside the cell, the fate of the cello-oligosaccharides is dichotomized into i) fueling glycolysis with glucose for the saprophytic lifestyle through the action of {beta}-glucosidase(s) (BG), and ii) eliciting the pathogenic lifestyle by inhibiting the CebR-mediated transcriptional repression of thaxtomin biosynthetic genes. Here we investigated the role of scab57721 encoding a putative BG (BglC) in the onset of the pathogenicity of S. scabies. Enzymatic assays showed that BglC was able to release glucose from cellobiose, cellotriose and all other cello-oligosaccharides tested. Its inactivation resulted in a phenotype opposite to what was expected as we monitored reduced production of thaxtomin when the mutant was cultivated on media containing cello-oligosaccharides as unique carbon source. This unexpected phenotype could be attributed to the highly increased activity of alternative intracellular BGs, probably as a compensation of bglC inactivation, which then prevented cellobiose and cellotriose accumulation to reduce the activity of CebR. In contrast, when the bglC null mutant was cultivated on media devoid of cello-oligosaccharides it instead constitutively produced thaxtomin. This observed hypervirulent phenotype does not fit with the proposed model of the cello-oligosaccharide-mediated induction of thaxtomin production and suggests that the role of BglC in the route to the pathogenic lifestyle of S. scabies is more complex than currently presented.

microbiology↗

bioRxiv2017

Tracking the Subtle Mutations Thriving Host Sensing by the Plant Pathogen Streptomyces scabies

The acquisition of genetic material conferring the arsenal necessary for host virulence is a prerequisite on the path to become a plant pathogen. More subtle mutations are also required for perception of cues witnessing the presence of the target host and optimal conditions for colonization. The decision to activate the pathogenic lifestyle is not taken lightly and involves efficient systems monitoring environmental conditions. But how can a pathogen timely trigger the expression of virulence genes if the main signal inducing its pathogenic behavior originates from cellulose, the most abundant polysaccharide on earth? This situation is encountered by Streptomyces scabies responsible for common scab disease on tuber and root crops. We here propose a series of hypotheses of how S. scabies could optimally distinguish whether cello-oligosaccharides originate from decomposing lignocellulose (nutrient sources) or, instead, emanate from living and expanding plant tissue (virulence signals), and accordingly adapt its physiological response.

microbiology↗