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54700.9812Dual role of OhrR as a repressor and an activator in response to organic hydroperoxides in Streptomyces coelicolor. Organic hydroperoxide resistance in bacteria is achieved primarily through reducing oxidized membrane lipids. The soil-inhabiting aerobic bacterium Streptomyces coelicolor contains three paralogous genes for organic hydroperoxide resistance: ohrA, ohrB, and ohrC. The ohrA gene is transcribed divergently from ohrR, which encodes a putative regulator of MarR family. Both the ohrA and ohrR genes were induced highly by various organic hydroperoxides. The ohrA gene was induced through removal of repression by OhrR, whereas the ohrR gene was induced through activation by OhrR. Reduced OhrR bound to the ohrA-ohrR intergenic region, which contains a central (primary) and two adjacent (secondary) inverted-repeat motifs that overlap with promoter elements. Organic peroxide decreased the binding affinity of OhrR for the primary site, with a concomitant decrease in cooperative binding to the adjacent secondary sites. The single cysteine C28 in OhrR was involved in sensing oxidants, as determined by substitution mutagenesis. The C28S mutant of OhrR bound to the intergenic region without any change in binding affinity in response to organic peroxides. These results lead us to propose a model for the dual action of OhrR as a repressor and an activator in S. coelicolor. Under reduced conditions, OhrR binds cooperatively to the intergenic region, repressing transcription from both genes. Upon oxidation, the binding affinity of OhrR decreases, with a concomitant loss of cooperative binding, which allows RNA polymerase to bind to both the ohrA and ohrR promoters. The loosely bound oxidized OhrR can further activate transcription from the ohrR promoter.200717586628
80110.9810Redox-sensitive transcriptional regulator SoxR directly controls antibiotic production, development and thiol-oxidative stress response in Streptomyces avermitilis. The redox-sensitive transcriptional regulator SoxR is conserved in bacteria. Its role in mediating protective response to various oxidative stresses in Escherichia coli and related enteric bacteria has been well established. However, functions and regulatory mechanisms of SoxR in filamentous Streptomyces, which produce half of known antibiotics, are unclear. We report here that SoxR pleiotropically regulates antibiotic production, morphological development, primary metabolism and thiol-oxidative stress response in industrially important species Streptomyces avermitilis. SoxR stimulated avermectin production by directly activating ave structural genes. Four genes (sav_3956, sav_4018, sav_5665 and sav_7218) that are homologous to targets of S. coelicolor SoxR are targeted by S. avermitilis SoxR. A consensus 18-nt SoxR-binding site, 5'-VSYCNVVMHNKVKDGMGB-3', was identified in promoter regions of sav_3956, sav_4018, sav_5665, sav_7218 and target ave genes, leading to prediction of the SoxR regulon and confirmation of 11 new targets involved in development (ftsH), oligomycin A biosynthesis (olmRI), primary metabolism (metB, sav_1623, plcA, nirB, thiG, ndh2), transport (smoE) and regulatory function (sig57, sav_7278). SoxR also directly activated three key developmental genes (amfC, whiB and ftsZ) and promoted resistance of S. avermitilis to thiol-oxidative stress through activation of target trx and msh genes. Overexpression of soxR notably enhanced antibiotic production in S. avermitilis and S. coelicolor. Our findings expand our limited knowledge of SoxR and will facilitate improvement of methods for antibiotic overproduction in Streptomyces species.202233951287
54420.9808Organic Hydroperoxide Induces Prodigiosin Biosynthesis in Serratia sp. ATCC 39006 in an OhrR-Dependent Manner. The biosynthesis of prodigiosin in the model prodigiosin-producing strain, Serratia sp. ATCC 39006, is significantly influenced by environmental and cellular signals. However, a comprehensive regulatory mechanism for this process has not been well established. In the present study, we demonstrate that organic hydroperoxide activates prodigiosin biosynthesis in an OhrR-dependent manner. Specifically, the MarR-family transcriptional repressor OhrR (Ser39006_RS05455) binds to its operator located far upstream of the promoter region of the prodigiosin biosynthesis operon (319 to 286 nucleotides [nt] upstream of the transcription start site) and negatively regulates the expression of prodigiosin biosynthesis genes. Organic hydroperoxide disassociates the binding between OhrR and its operator, thereby promoting the prodigiosin production. Moreover, OhrR modulates the resistance of Serratia sp. ATCC 39006 to organic hydroperoxide by regulating the transcription of its own gene and the downstream cotranscribed ohr gene. These results demonstrate that OhrR is a pleiotropic repressor that modulates the prodigiosin production and the resistance of Serratia sp. ATCC 39006 to organic hydroperoxide stress. IMPORTANCE Bacteria naturally encounter various environmental and cellular stresses. Organic hydroperoxides generated from the oxidation of polyunsaturated fatty acids are widely distributed and usually cause lethal oxidative stress by damaging cellular components. OhrR is known as a regulator that modulates the resistance of bacteria to organic hydroperoxide stress. In the current study, organic hydroperoxide disassociates OhrR from the promoter of prodigiosin biosynthesis gene cluster, thus promoting transcription of pigA to -O genes. In this model, organic hydroperoxide acts as an inducer of prodigiosin synthesis in Serratia sp. ATCC 39006. These results improve our understanding of the regulatory network of prodigiosin synthesis and serve as an example for identifying the cross talk between the stress responses and the regulation of secondary metabolism.202235044847
54930.9806Extracytoplasmic function sigma factor σ(D) confers resistance to environmental stress by enhancing mycolate synthesis and modifying peptidoglycan structures in Corynebacterium glutamicum. Mycolates are α-branched, β-hydroxylated, long-chain fatty acid specifically synthesized in bacteria in the suborder Corynebacterineae of the phylum Actinobacteria. They form an outer membrane, which functions as a permeability barrier and confers pathogenic mycobacteria to resistance to antibiotics. Although the mycolate biosynthetic pathway has been intensively studied, knowledge of transcriptional regulation of genes involved in this pathway is limited. Here, we report that the extracytoplasmic function sigma factor σ(D) is a key regulator of the mycolate synthetic genes in Corynebacterium glutamicum in the suborder. Chromatin immunoprecipitation with microarray analysis detected σ(D) -binding regions in the genome, establishing a consensus promoter sequence for σ(D) recognition. The σ(D) regulon comprised acyl-CoA carboxylase subunits, acyl-AMP ligase, polyketide synthase and mycolyltransferases; they were involved in mycolate synthesis. Indeed, deletion or overexpression of sigD encoding σ(D) modified the extractable mycolate amount. Immediately downstream of sigD, rsdA encoded anti-σ(D) and was under the control of a σ(D) -dependent promoter. Another σ(D) regulon member, l,d-transpeptidase, conferred lysozyme resistance. Thus, σ(D) modifies peptidoglycan cross-linking and enhances mycolate synthesis to provide resistance to environmental stress.201829148103
4740.9804LTP3 contributes to disease susceptibility in Arabidopsis by enhancing abscisic acid (ABA) biosynthesis. Several plant lipid transfer proteins (LTPs) act positively in plant disease resistance. Here, we show that LTP3 (At5g59320), a pathogen and abscisic acid (ABA)-induced gene, negatively regulates plant immunity in Arabidopsis. The overexpression of LTP3 (LTP3-OX) led to an enhanced susceptibility to virulent bacteria and compromised resistance to avirulent bacteria. On infection of LTP3-OX plants with Pseudomonas syringae pv. tomato, genes involved in ABA biosynthesis, NCED3 and AAO3, were highly induced, whereas salicylic acid (SA)-related genes, ICS1 and PR1, were down-regulated. Accordingly, in LTP3-OX plants, we observed increased ABA levels and decreased SA levels relative to the wild-type. We also showed that the LTP3 overexpression-mediated enhanced susceptibility was partially dependent on AAO3. Interestingly, loss of function of LTP3 (ltp3-1) did not affect ABA pathways, but resulted in PR1 gene induction and elevated SA levels, suggesting that LTP3 can negatively regulate SA in an ABA-independent manner. However, a double mutant consisting of ltp3-1 and silent LTP4 (ltp3/ltp4) showed reduced susceptibility to Pseudomonas and down-regulation of ABA biosynthesis genes, suggesting that LTP3 acts in a redundant manner with its closest homologue LTP4 by modulating the ABA pathway. Taken together, our data show that LTP3 is a novel negative regulator of plant immunity which acts through the manipulation of the ABA-SA balance.201626123657
60950.9802A metazoan ortholog of SpoT hydrolyzes ppGpp and functions in starvation responses. In nutrient-starved bacteria, RelA and SpoT proteins have key roles in reducing cell growth and overcoming stresses. Here we identify functional SpoT orthologs in metazoa (named Mesh1, encoded by HDDC3 in human and Q9VAM9 in Drosophila melanogaster) and reveal their structures and functions. Like the bacterial enzyme, Mesh1 proteins contain an active site for ppGpp hydrolysis and a conserved His-Asp-box motif for Mn(2+) binding. Consistent with these structural data, Mesh1 efficiently catalyzes hydrolysis of guanosine 3',5'-diphosphate (ppGpp) both in vitro and in vivo. Mesh1 also suppresses SpoT-deficient lethality and RelA-induced delayed cell growth in bacteria. Notably, deletion of Mesh1 (Q9VAM9) in Drosophila induces retarded body growth and impaired starvation resistance. Microarray analyses reveal that the amino acid-starved Mesh1 null mutant has highly downregulated DNA and protein synthesis-related genes and upregulated stress-responsible genes. These data suggest that metazoan SpoT orthologs have an evolutionarily conserved function in starvation responses.201020818390
3660.9801Bacillus amyloliquefaciens SN16-1-Induced Resistance System of the Tomato against Rhizoctonia solani. Tomato (Solanum lycopersicum), as an important economical vegetable, is often infected with Rhizoctonia solani, which results in a substantial reduction in production. Therefore, the molecular mechanism of biocontrol microorganisms assisting tomato to resist pathogens is worth exploring. Here, we use Bacillus amyloliquefaciens SN16-1 as biocontrol bacteria, and employed RNA-Seq technology to study tomato gene and defense-signaling pathways expression. Gene Ontology (GO) analyses showed that an oxidation-reduction process, peptidase regulator activity, and oxidoreductase activity were predominant. Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that phenylpropanoid biosynthesis, biosynthesis of unsaturated fatty acids, aldosterone synthesis and secretion, and phototransduction were significantly enriched. SN16-1 activated defenses in the tomato via systemic-acquired resistance (which depends on the salicylic acid signaling pathway), rather than classic induction of systemic resistance. The genes induced by SN16-1 included transcription factors, plant hormones (ethylene, auxin, abscisic acid, and gibberellin), receptor-like kinases, heat shock proteins, and defense proteins. SN16-1 rarely activated pathogenesis-related proteins, but most pathogenesis-related proteins were induced in the presence of the pathogens. In addition, the molecular mechanisms of the response of tomatoes to SN16-1 and R. solani RS520 were significantly different.202135055983
1670.9801A glycoside hydrolase 30 protein BpXynC of Bacillus paralicheniformis NMSW12 recognized as A MAMP triggers plant immunity response. Bacillus spp. has been widely used as a biocontrol agent to control plant diseases. However, little is known about mechanisms of the protein MAMP secreted by Bacillus spp. Herein, our study reported a glycoside hydrolase family 30 (GH30) protein, BpXynC, produced by the biocontrol bacteria Bacillus paralicheniformis NMSW12, that can induce cell death in several plant species. The results revealed that the recombinant protein triggers cell death in Nicotiana benthamiana in a BAK1-dependent manner and elicits an early defense response, including ROS burst, activation of MAPK cascades, and upregulation of plant immunity marker genes. BpXynC was also found to be a glucuronoxylanase that exhibits hydrolysis activity on xlyan. Two mutants of BpXynC which lost the glucuronoxylanase activity still retained the elicitor activity. The qRT-PCR results of defense-related genes showed that BpXynC induces plant immunity responses via an SA-mediated pathway. BpXynC and its mutants could induce resistance in N. benthamiana against infection by Sclerotinia sclerotiorum and tobacco mosaic virus (TMV). Furthermore, BpXynC-treated tomato fruits exhibited strong resistance to the infection of Phytophthora capsica. Overall, our study revealed that GH30 protein BpXynC can induce plant immunity response as MAMP, which can be further applied as a biopesticide to control plant diseases.202438286384
54380.9798OxyR2 Modulates OxyR1 Activity and Vibrio cholerae Oxidative Stress Response. Bacteria have developed capacities to deal with different stresses and adapt to different environmental niches. The human pathogen Vibrio cholerae, the causative agent of the severe diarrheal disease cholera, utilizes the transcriptional regulator OxyR to activate genes related to oxidative stress resistance, including peroxiredoxin PrxA, in response to hydrogen peroxide. In this study, we identified another OxyR homolog in V. cholerae, which we named OxyR2, and we renamed the previous OxyR OxyR1. We found that OxyR2 is required to activate its divergently transcribed gene ahpC, encoding an alkylhydroperoxide reductase, independently of H(2)O(2) A conserved cysteine residue in OxyR2 is critical for this function. Mutation of either oxyR2 or ahpC rendered V. cholerae more resistant to H(2)O(2) RNA sequencing analyses indicated that OxyR1-activated oxidative stress-resistant genes were highly expressed in oxyR2 mutants even in the absence of H(2)O(2) Further genetic analyses suggest that OxyR2-activated AhpC modulates OxyR1 activity by maintaining low intracellular concentrations of H(2)O(2) Furthermore, we showed that ΔoxyR2 and ΔahpC mutants were less fit when anaerobically grown bacteria were exposed to low levels of H(2)O(2) or incubated in seawater. These results suggest that OxyR2 and AhpC play important roles in the V. cholerae oxidative stress response.201728138024
55690.9797An ArsR/SmtB family member regulates arsenic resistance genes unusually arranged in Thermus thermophilus HB27. Arsenic resistance is commonly clustered in ars operons in bacteria; main ars operon components encode an arsenate reductase, a membrane extrusion protein, and an As-sensitive transcription factor. In the As-resistant thermophile Thermus thermophilus HB27, genes encoding homologues of these proteins are interspersed in the chromosome. In this article, we show that two adjacent genes, TtsmtB, encoding an ArsR/SmtB transcriptional repressor and, TTC0354, encoding a Zn(2+) /Cd(2+) -dependent membrane ATPase are involved in As resistance; differently from characterized ars operons, the two genes are transcribed from dedicated promoters upstream of their respective genes, whose expression is differentially regulated at transcriptional level. Mutants defective in TtsmtB or TTC0354 are more sensitive to As than the wild type, proving their role in arsenic resistance. Recombinant dimeric TtSmtB binds in vitro to both promoters, but its binding capability decreases upon interaction with arsenate and, less efficiently, with arsenite. In vivo and in vitro experiments also demonstrate that the arsenate reductase (TtArsC) is subjected to regulation by TtSmtB. We propose a model for the regulation of As resistance in T. thermophilus in which TtSmtB is the arsenate sensor responsible for the induction of TtArsC which generates arsenite exported by TTC0354 efflux protein to detoxify cells.201728696001
669100.9795Manganese Efflux Achieved by MetA and MetB Affects Oxidative Stress Resistance and Iron Homeostasis in Riemerella anatipestifer. In bacteria, manganese homeostasis is controlled by import, regulation, and efflux. Here, we identified 2 Mn exporters, MetA and MetB (manganese efflux transporters A and B), in Riemerella anatipestifer CH-1, encoding a putative cation diffusion facilitator (CDF) protein and putative resistance-nodulation-division (RND) efflux pump, respectively. Compared with the wild type (WT), ΔmetA, ΔmetB, and ΔmetAΔmetB exhibited sensitivity to manganese, since they accumulated more intracellular Mn(2+) than the WT under excess manganese conditions, while the amount of iron in the mutants was decreased. Moreover, ΔmetA, ΔmetB, and ΔmetAΔmetB were more sensitive to the oxidant NaOCl than the WT. Further study showed that supplementation with iron sources could alleviate manganese toxicity and that excess manganese inhibited bacterial cell division. RNA-Seq showed that manganese stress resulted in the perturbation of iron metabolism genes, further demonstrating that manganese efflux is critical for iron homeostasis. metA transcription was upregulated under excess manganese but was not activated by MetR, a DtxR family protein, although MetR was also involved in manganese detoxification, while metB transcription was downregulated under iron depletion conditions and in fur mutants. Finally, homologues of MetA and MetB were found to be mainly distributed in members of Flavobacteriaceae. Specifically, MetB represents a novel manganese exporter in Gram-negative bacteria. IMPORTANCE Manganese is required for the function of many proteins in bacteria, but in excess, manganese can mediate toxicity. Therefore, the intracellular levels of manganese must be tightly controlled. Manganese efflux transporters have been characterized in some other bacteria; however, their homologues could not be found in the genome of Riemerella anatipestifer through sequence comparison. This indicated that other types of manganese efflux transporters likely exist. In this study, we characterized 2 transporters, MetA and MetB, that mediate manganese efflux in R. anatipestifer in response to manganese overload. MetA encodes a putative cation diffusion facilitator (CDF) protein, which has been characterized as a manganese transporter in other bacteria, while this is the first observation of a putative resistance-nodulation-division (RND) transporter contributing to manganese export in Gram-negative bacteria. In addition, the mechanism of manganese toxicity was studied by observing morphological changes and by transcriptome sequencing. Taken together, these results are important for expanding our understanding of manganese transporters and revealing the mechanism of manganese toxicity.202336815770
519110.9795The Ruegeria pomeroyi acuI gene has a role in DMSP catabolism and resembles yhdH of E. coli and other bacteria in conferring resistance to acrylate. The Escherichia coli YhdH polypeptide is in the MDR012 sub-group of medium chain reductase/dehydrogenases, but its biological function was unknown and no phenotypes of YhdH(-) mutants had been described. We found that an E. coli strain with an insertional mutation in yhdH was hyper-sensitive to inhibitory effects of acrylate, and, to a lesser extent, to those of 3-hydroxypropionate. Close homologues of YhdH occur in many Bacterial taxa and at least two animals. The acrylate sensitivity of YhdH(-) mutants was corrected by the corresponding, cloned homologues from several bacteria. One such homologue is acuI, which has a role in acrylate degradation in marine bacteria that catabolise dimethylsulfoniopropionate (DMSP) an abundant anti-stress compound made by marine phytoplankton. The acuI genes of such bacteria are often linked to ddd genes that encode enzymes that cleave DMSP into acrylate plus dimethyl sulfide (DMS), even though these are in different polypeptide families, in unrelated bacteria. Furthermore, most strains of Roseobacters, a clade of abundant marine bacteria, cleave DMSP into acrylate plus DMS, and can also demethylate it, using DMSP demethylase. In most Roseobacters, the corresponding gene, dmdA, lies immediately upstream of acuI and in the model Roseobacter strain Ruegeria pomeroyi DSS-3, dmdA-acuI were co-regulated in response to the co-inducer, acrylate. These observations, together with findings by others that AcuI has acryloyl-CoA reductase activity, lead us to suggest that YdhH/AcuI enzymes protect cells against damaging effects of intracellular acryloyl-CoA, formed endogenously, and/or via catabolising exogenous acrylate. To provide "added protection" for bacteria that form acrylate from DMSP, acuI was recruited into clusters of genes involved in this conversion and, in the case of acuI and dmdA in the Roseobacters, their co-expression may underpin an interaction between the two routes of DMSP catabolism, whereby the acrylate product of DMSP lyases is a co-inducer for the demethylation pathway.201222563425
546120.9794Resistance to organic hydroperoxides requires ohr and ohrR genes in Sinorhizobium meliloti. BACKGROUND: Sinorhizobium meliloti is a symbiotic nitrogen-fixing bacterium that elicits nodules on roots of host plants Medicago sativa. During nodule formation bacteria have to withstand oxygen radicals produced by the plant. Resistance to H2O2 and superoxides has been extensively studied in S. meliloti. In contrast resistance to organic peroxides has not been investigated while S. meliloti genome encodes putative organic peroxidases. Organic peroxides are produced by plants and are highly toxic. The resistance to these oxygen radicals has been studied in various bacteria but never in plant nodulating bacteria. RESULTS: In this study we report the characterisation of organic hydroperoxide resistance gene ohr and its regulator ohrR in S. meliloti. The inactivation of ohr affects resistance to cumene and ter-butyl hydroperoxides but not to hydrogen peroxide or menadione in vitro. The expression of ohr and ohrR genes is specifically induced by organic peroxides. OhrR binds to the intergenic region between the divergent genes ohr and ohrR. Two binding sites were characterised. Binding to the operator is prevented by OhrR oxidation that promotes OhrR dimerisation. The inactivation of ohr did not affect symbiosis and nitrogen fixation, suggesting that redundant enzymatic activity exists in this strain. Both ohr and ohrR are expressed in nodules suggesting that they play a role during nitrogen fixation. CONCLUSIONS: This report demonstrates the significant role Ohr and OhrR proteins play in bacterial stress resistance against organic peroxides in S. meliloti. The ohr and ohrR genes are expressed in nodule-inhabiting bacteroids suggesting a role during nodulation.201121569462
594130.9789Challenging Xanthomonas campestris with low levels of arsenic mediates cross-protection against oxidant killing. Xanthomonas encounters highly toxic reactive oxygen species (ROS) from many sources, such as those generated by plants against invading bacteria, other soil bacteria and from aerobic respiration. Thus, conditions that alter intracellular ROS levels such as exposure to toxic metalloids would have profound effects on bacterial physiology. Here, we report that exposure of Xanthomonas campestris pv. phaseoli (Xp) to low levels of arsenic induces physiological cross-protection against killing by H(2)O(2) and organic hydroperoxide but not a superoxide generator. Cross-protection against H(2)O(2) and organic hydroperoxide toxicity was due to increased expression of genes encoding major peroxide-metabolizing enzymes such as alkyl hydroperoxide reductase (AhpC), catalase (KatA) and organic hydroperoxide resistance protein (Ohr). Arsenic-induced protection against H(2)O(2) and organic hydroperoxide requires the peroxide stress response regulators, OxyR and OhrR, respectively. Moreover, analyses of double mutants of the major H(2)O(2) and organic hyproperoxide-scavenging enzymes, Xp ahpC katA and Xp ahpC ohr, respectively, suggested the existence of unidentified OxyR- and OhrR-regulated genes that are involved in arsenic-induced resistance to H(2)O(2) and organic hyproperoxide killing in Xp. These arsenic-induced physiological alterations could play an important role in bacterial survival both in the soil environment and during plant-pathogen interactions.200616907748
50140.9789OsNPR1 Enhances Rice Resistance to Xanthomonas oryzae pv. oryzae by Upregulating Rice Defense Genes and Repressing Bacteria Virulence Genes. The bacteria pathogen Xanthomonas oryzae pv. oryzae (Xoo) infects rice and causes the severe disease of rice bacteria blight. As the central regulator of the salic acid (SA) signaling pathway, NPR1 is responsible for sensing SA and inducing the expression of pathogen-related (PR) genes in plants. Overexpression of OsNPR1 significantly increases rice resistance to Xoo. Although some downstream rice genes were found to be regulated by OsNPR1, how OsNPR1 affects the interaction of rice-Xoo and alters Xoo gene expression remains unknown. In this study, we challenged the wild-type and OsNPR1-OE rice materials with Xoo and performed dual RNA-seq analyses for the rice and Xoo genomes simultaneously. In Xoo-infected OsNPR1-OE plants, rice genes involved in cell wall biosynthesis and SA signaling pathways, as well as PR genes and nucleotide-binding site-leucine-rich repeat (NBS-LRR) genes, were significantly upregulated compared to rice variety TP309. On the other hand, Xoo genes involved in energy metabolism, oxidative phosphorylation, biosynthesis of primary and secondary metabolism, and transportation were repressed. Many virulence genes of Xoo, including genes encoding components of type III and other secretion systems, were downregulated by OsNPR1 overexpression. Our results suggest that OsNPR1 enhances rice resistance to Xoo by bidirectionally regulating gene expression in rice and Xoo.202337240026
37150.9789N-3-Oxo-Octanoyl Homoserine Lactone Primes Plant Resistance Against Necrotrophic Pathogen Pectobacterium carotovorum by Coordinating Jasmonic Acid and Auxin-Signaling Pathways. Many Gram-negative bacteria use small signal molecules, such as N-acyl-homoserine lactones (AHLs), to communicate with each other and coordinate their collective behaviors. Recently, increasing evidence has demonstrated that long-chained quorum-sensing signals play roles in priming defense responses in plants. Our previous work indicated that a short-chained signal, N-3-oxo-octanoyl homoserine lactone (3OC8-HSL), enhanced Arabidopsis resistance to the hemi-biotrophic bacteria Pseudomonas syringae pv. tomato DC3000 through priming the salicylic acid (SA) pathway. Here, we found that 3OC8-HSL could also prime resistance to the necrotrophic bacterium Pectobacterium carotovorum ssp. carotovorum (Pcc) through the jasmonic acid (JA) pathway, and is dependent on auxin responses, in both Chinese cabbage and Arabidopsis. The subsequent Pcc invasion triggered JA accumulation and increased the down-stream genes' expressions of JA synthesis genes (LOX, AOS, and AOC) and JA response genes (PDF1.2 and VSP2). The primed state was not observed in the Arabidopsis coi1-1 and jar1-1 mutants, which indicated that the primed resistance to Pcc was dependent on the JA pathway. The 3OC8-HSL was not transmitted from roots to leaves and it induced indoleacetic acid (IAA) accumulation and the DR5 and SAUR auxin-responsive genes' expressions in seedlings. When Arabidopsis and Chinese cabbage roots were pretreated with exogenous IAA (10 μM), the plants had activated the JA pathway and enhanced resistance to Pcc, which implied that the JA pathway was involved in AHL priming by coordinating with the auxin pathway. Our findings provide a new strategy for the prevention and control of soft rot in Chinese cabbage and provide theoretical support for the use of the quorum-sensing AHL signal molecule as a new elicitor.202235774826
57160.9788Functional analysis of NtMPK2 uncovers its positive role in response to Pseudomonas syringae pv. tomato DC3000 in tobacco. Mitogen-activated protein kinase cascades are highly conserved signaling modules downstream of receptors/sensors and play pivotal roles in signaling plant defense against pathogen attack. Extensive studies on Arabidopsis MPK4 have implicated that the MAP kinase is involved in multilayered plant defense pathways. In this study, we identified tobacco NtMPK2 as an ortholog of AtMPK4. Transgenic tobacco overexpressing NtMPK2 markedly enhances resistance to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) virulent and avirulent strains. Transcriptome analysis of NtMPK2-dependent genes shows that possibly the basal resistance system is activated by NtMPK2 overexpression. In addition to NtMPK2-mediated resistance, multiple pathways are involved in response to the avirulent bacteria based on analysis of Pst-responding genes, including SA and ET pathways. Notably, it is possible that biosynthesis of antibacterial compounds is responsible for inhibition of Pst DC3000 avirulent strain when programmed cell death processes in the host. Our results uncover that NtMPK2 positively regulate tobacco defense response to Pst DC3000 and improve our understanding of plant molecular defense mechanism.201626482478
545170.9787Characterization of the organic hydroperoxide resistance system of Brucella abortus 2308. The organic hydroperoxide resistance protein Ohr has been identified in numerous bacteria where it functions in the detoxification of organic hydroperoxides, and expression of ohr is often regulated by a MarR-type regulator called OhrR. The genes annotated as BAB2_0350 and BAB2_0351 in the Brucella abortus 2308 genome sequence are predicted to encode OhrR and Ohr orthologs, respectively. Using isogenic ohr and ohrR mutants and lacZ promoter fusions, it was determined that Ohr contributes to resistance to organic hydroperoxide, but not hydrogen peroxide, in B. abortus 2308 and that OhrR represses the transcription of both ohr and ohrR in this strain. Moreover, electrophoretic mobility shift assays and DNase I footprinting revealed that OhrR binds directly to a specific region in the intergenic region between ohr and ohrR that shares extensive nucleotide sequence similarity with so-called "OhrR boxes" described in other bacteria. While Ohr plays a prominent role in protecting B. abortus 2308 from organic hydroperoxide stress in in vitro assays, this protein is not required for the wild-type virulence of this strain in cultured murine macrophages or experimentally infected mice.201222821968
592180.9786Metabolism of Tryptophan and Tryptophan Analogs by Rhizobium meliloti. The alfalfa symbiont Rhizobium meliloti Rm1021 produces indole-3-acetic acid in a regulated manner when supplied with exogenous tryptophan. Mutants with altered response to tryptophan analogs still produce indole-3-acetic acid, but are Fix(-) because bacteria do not fully differentiate into the nitrogen-fixing bacteriod form. These mutations are in apparently essential genes tightly linked to a dominant streptomycin resistance locus.199016667364
557190.9786Identification of a MarR Subfamily That Regulates Arsenic Resistance Genes. In this study, comprehensive analyses were performed to determine the function of an atypical MarR homolog in Achromobacter sp. strain As-55. Genomic analyses of Achromobacter sp. As-55 showed that this marR is located adjacent to an arsV gene. ArsV is a flavin-dependent monooxygenase that confers resistance to the antibiotic methylarsenite [MAs(III)], the organoarsenic compound roxarsone(III) [Rox(III)], and the inorganic antimonite [Sb(III)]. Similar marR genes are widely distributed in arsenic-resistant bacteria. Phylogenetic analyses showed that these MarRs are found in operons predicted to be involved in resistance to inorganic and organic arsenic species, so the subfamily was named MarR(ars). MarR(ars) orthologs have three conserved cysteine residues, which are Cys36, Cys37, and Cys157 in Achromobacter sp. As-55, mutation of which compromises the response to MAs(III)/Sb(III). GFP-fluorescent biosensor assays show that AdMarR(ars) (MarR protein of Achromobacter deleyi As-55) responds to trivalent As(III) and Sb(III) but not to pentavalent As(V) or Sb(V). The results of RT-qPCR assays show that arsV is expressed constitutively in a marR deletion mutant, indicating that marR represses transcription of arsV. Moreover, electrophoretic mobility shift assays (EMSAs) demonstrate that AdMarR(ars) binds to the promoters of both marR and arsV in the absence of ligands and that DNA binding is relieved upon binding of As(III) and Sb(III). Our results demonstrate that AdMarR(ars) is a novel As(III)/Sb(III)-responsive transcriptional repressor that controls expression of arsV, which confers resistance to MAs(III), Rox(III), and Sb(III). AdMarR(ars) and its orthologs form a subfamily of MarR proteins that regulate genes conferring resistance to arsenic-containing antibiotics. IMPORTANCE In this study, a MarR family member, AdMarR(ars) was shown to regulate the arsV gene, which confers resistance to arsenic-containing antibiotics. It is a founding member of a distinct subfamily that we refer to as MarR(ars), regulating genes conferring resistance to arsenic and antimony antibiotic compounds. AdMarR(ars) was shown to be a repressor containing conserved cysteine residues that are required to bind As(III) and Sb(III), leading to a conformational change and subsequent derepression. Here we show that members of the MarR family are involved in regulating arsenic-containing compounds.202134613763