Promoter Fusions Research Articles

Chloramphenicol-mobilized Bacillus subtilis transiently expresses resistance to multiple antibiotics, including the glycopeptides phleomycin and bleomycin.

Antibiotic resistance is a global crisis that stems from the use of antibiotics as an essential part of modern medicine. Understanding how antibiotic resistance is controlled among cells in bacterial populations will provide insights into how antibiotics shape microbial communities. Here, we describe patterns of B. subtilis gene expression that arise from growth on a surface either in isolation or under subinhibitory chloramphenicol exposure. We identified elevated expression of genes encoding five different antibiotic resistance functions. The expression of four of the five resistance functions is controlled by a combination of terminator attenuation and transcriptional regulation. Two of these, vmlR and tlrB provide resistance to lincosamides and tylosin, respectively. We found that bmrCD promotes resistance to glycopeptides, including phleomycin and bleomycin. Promoter fusions to luciferase were used to follow expression of bmrCD, vmlR, and tlrB. Subinhibitory chloramphenicol exposure induces sliding motility of B. subtilis, wherein the three antibiotic resistance functions are expressed heterogeneously in spatiotemporally segregated pattern. We found that their expression is transiently elevated even in the absence of antibiotic exposure. The data suggest that for some antibiotics, intrinsic resistance genes are entrained to changes in growth and metabolism. Antibiotic exposure amplifies their expression, potentially providing a subpopulation of cells elevated protection to multiple classes of antibiotic.

Response and adaptation of the transcriptional heat shock response to pressure.

The molecular mechanisms underlying pressure adaptation remain largely unexplored, despite their significance for understanding biological adaptation and improving sterilization methods in the food and beverage industry. The heat shock response leads to a global stabilization of the proteome. Prior research suggested that the heat shock regulon may exhibit a transcriptional response to high-pressure stress. In this study, we investigated the pressure-dependent heat shock response in E. coli strains using plasmid-borne green fluorescent protein (GFP) promoter fusions and fluorescence fluctuation microscopy. We quantitatively confirm that key heat shock genes-rpoH, rpoE, dnaK, and groEL - are transcriptionally upregulated following pressure shock in both piezosensitive Escherichia coli and a more piezotolerant laboratory-evolved strain, AN62. Our quantitative imaging results provide the first single cell resolution measurements for both the heat shock and pressure shock transcriptional responses, revealing not only the magnitude of the responses, but also the biological variance involved. Moreover, our results demonstrate distinct responses in the pressure-adapted strain. Specifically, PgroEL is upregulated more than PdnaK in AN62, while the reverse is true in the parental strain. Furthermore, unlike in the parental strain, the pressure-induced upregulation of PrpoE is highly stochastic in strain AN62, consistent with a strong feedback mechanism and suggesting that RpoE could act as a pressure sensor. Despite its capacity to grow at pressures up to 62 MPa, the AN62 genome shows minimal mutations, with notable single nucleotide substitutions in genes of the transcriptionally important b subunit of RNA polymerase and the Rho terminator. In particular, the mutation in RNAP is one of a cluster of mutations known to confer rifampicin resistance to E. coli via modification of RNAP pausing and termination efficiency. The observed differences in the pressure and heat shock responses between the parental MG1655 strain and the pressure-adapted strain AN62 could arise in part from functional differences in their RNAP molecules.

XylR regulates genes at xyl cluster, involved in D-xylose catabolism in Herbaspirillum seropedicae Z69.

D-xylose, one of the most abundant sugars in lignocellulosic biomass, is not widely used to produce bioproducts with added value, in part due to the absence of industrial microorganisms able to metabolize it efficiently. Herbaspirillum seropedicae Z69 is a β-proteobacterium able to accumulate poly-3-hydroxybutyrate, a biodegradable thermoplastic biopolymer, with contents higher than 50%. It metabolizes D-xylose by non-phosphorylative pathways. In the genome of Z69, we found the genes xylFGH (ABC D-xylose transporter), xylB, xylD, and xylC (superior non-phosphorylative pathway), and the transcriptional regulator xylR, forming the xyl cluster. We constructed the knock-out mutant Z69ΔxylR that has a reduced growth in D-xylose and in D-glucose, compared with Z69. In addition, we analyzed the expression of xyl genes by RT-qPCR and promoter fusion. These results suggest that XylR activates the expression of genes at the xyl cluster in the presence of D-xylose. On the other hand, XylR does not regulate the expression of xylA, mhpD (lower non-phosphorylative pathways) and araB (L-arabinose dehydrogenase) genes. The participation of D-glucose in the regulation mechanism of these genes must still be elucidated. These results contribute to the development of new strains adapted to consume lignocellulosic sugars for the production of value-added bioproducts.

Low Concentration of Wenyang Tonglin Decoction Promotes Conjugation and Transfer of Drug-Resistant Plasmids among Heterologous Strains.

To investigate the effect of low concentration of Wenyang Tonglin Decoction (WTD) on the binding conditions of R45 plasmid conjugative transfer under liquid phase conjugation and its mechanism. Escherichia coli CP9 (R45) and Staphylococcus aureus RN450RF were cultured in medium containing WTD, and their minimum inhibitory concentration (MIC) values were obtained. Using promoter fusion technology, E. coli CP9 (R45) containing a promoter fusion was obtained. β-Galactosidase activity of TrfAp and TrbBp was tested, and the mRNA expression of regulatory factors (TrbA, KorA, and KorB) was detected by real-time fluorescent quantitative polymerase chain reaction. The MIC of E. coli CP9 (R45) was 400 g/L and that of S. aureus RN450RF was 200 g/L. When the drug concentration in the culture medium was 200 g/L, the highest number of conjugants was (3.47 ±0.20) × 107 CFU/mL At 90 h of conjugation, the maximum number of conjugants was (1.15 ±0.06) × 108 CFU/mL When the initial bacterial concentration was 108 CFU/mL, the maximum number of conjugants was (3.47 ± 0.20) × 107 CFU/mL. When the drug concentration was 200 g/L, the β-galactosidase activity of TrfAp and TrbBp significantly increased; the relative quantification of TrbA, KorA and KorB were significantly inhibited. Low concentration of WTD promoted the development of bacterial resistance by affecting promoters and inhibiting the expression of regulatory factors.

Co-regulation of Thermosensor Pathogenic Factors by C-di-GMP-Related Two-Component Systems and a cAMP Receptor-like Protein (Clp) in Stenotrophomonas maltophilia.

Stenotrophomonas maltophilia is a major threat to the food industry and human health owing to its strong protease production and biofilm formation abilities. However, information regarding regulatory factors or potential mechanisms is limited. Herein, we observed that temperature differentially regulates biofilm formation and protease production, and a cAMP receptor-like protein (Clp) negatively regulates thermosensor biofilm formation, in contrast to protease synthesis. Among four c-di-GMP-related two-component systems (TCSs), promoter fusion analysis revealed that clp transcription levels were predominantly controlled by LotS/LotR, partially controlled by both RpfC/RpfG and a novel TCS Sm0738/Sm0737, with no obvious effect caused by Sm1912/Sm1911. Biofilm formation in Δclp and ΔTCSs strains suggested that LotS/LotR controlled biofilm formation in a Clp-mediated manner, whereas both RpfC/RpfG and Sm0738/Sm0737 may occur in a distinct pathway. Furthermore, enzymatic activity analysis combined with c-di-GMP level indicated that the enzymatic activity of c-di-GMP-related metabolism proteins may not be a vital contributor to changes in c-di-GMP level, thus influencing physiological functions. Our findings elucidate that the regulatory pathway of c-di-GMP-related TCSs and Clp in controlling spoilage or the formation of potentially pathogenic factors in Stenotrophomonas expand the understanding of c-di-GMP metabolism and provide clues to control risk factors of S. maltophilia in food safety.

TbsP and TrmB jointly regulate gapII to influence cell development phenotypes in the archaeon Haloferax volcanii.

Microbial cells must continually adapt their physiology in the face of changing environmental conditions. Archaea living in extreme conditions, such as saturated salinity, represent important examples of such resilience. The model salt-loving organism Haloferax volcanii exhibits remarkable plasticity in its morphology, biofilm formation, and motility in response to variations in nutrients and cell density. However, the mechanisms regulating these lifestyle transitions remain unclear. In prior research, we showed that the transcriptional regulator, TrmB, maintains the rod shape in the related species Halobacterium salinarum by activating the expression of enzyme-coding genes in the gluconeogenesis metabolic pathway. In Hbt. salinarum, TrmB-dependent production of glucose moieties is required for cell surface glycoprotein biogenesis. Here, we use a combination of genetics and quantitative phenotyping assays to demonstrate that TrmB is essential for growth under gluconeogenic conditions in Hfx. volcanii. The ∆trmB strain rapidly accumulated suppressor mutations in a gene encoding a novel transcriptional regulator, which we name trmB suppressor, or TbsP (a.k.a. "tablespoon"). TbsP is required for adhesion to abiotic surfaces (i.e., biofilm formation) and maintains wild-type cell morphology and motility. We use functional genomics and promoter fusion assays to characterize the regulons controlled by each of TrmB and TbsP, including joint regulation of the glucose-dependent transcription of gapII, which encodes an important gluconeogenic enzyme. We conclude that TrmB and TbsP coregulate gluconeogenesis, with downstream impacts on lifestyle transitions in response to nutrients in Hfx. volcanii.

Reciprocal regulation of NagC and quorum sensing systems and their roles in hmsHFRS expression and biofilm formation in Yersinia pseudotuberculosis.

Biofilm formation by Yersinia pseudotuberculosis is regulated by quorum sensing (QS) and dependent on the haemin storage locus hms, required for the extracellular polysaccharide poly-N-acetylglucosamine (poly-GlcNAc) production. In Escherichia coli NagC regulates both GlcNAc biosynthesis and metabolism with GlcNAc acting as a signal that co-ordinates these and other activities. However, the contribution of NagC and GlcNAc to biofilm development in Y. pseudotuberculosis is not known. Here we show that a Y. pseudotuberculosis nagC mutant is impaired for biofilm production on abiotic (glass) and biotic (Caenorhabitis elegans) surfaces. Genetic complementation restored poly-GlcNAc production and biofilm formation on C. elegans. Using lux-based promoter fusions, hmsHFRS expression was found to be nagC dependent. Given that NagC and QS both regulate aggregation and biofilm formation, we investigated their regulatory relationship using lux-based promoter fusions. These revealed that (i) nagC is negatively autoregulated, but expression can be partially restored in the nagC mutant by exogenous GlcNAc, (ii) NagC negatively regulates the ytbI and ypsI QS genes and (iii) nagC expression is reduced in the ytbI, ypsI and ypsR mutants but not the ytbR mutant. These data establish the existence of a reciprocal regulatory relationship between NagC and QS, which in the case of the luxRI pair ytbRI, is also GlcNAc-dependent. NagC and GlcNAc are therefore components of a regulatory system involving QS that modulates biofilm formation and aggregation.

Molecular testing raises thyroid nodule fine needle aspiration diagnostic value.

Thyroid fine needle aspiration biopsy (FNAB) remains indeterminate in 16%-24% of the cases. Molecular testing could improve the diagnostic accuracy of FNAB. This study examined the gene mutation profile of patients with thyroid nodules and analyzed the diagnostic ability of molecular testing for thyroid nodules using a self-developed 18-gene test. Between January 2019 and August 2021, 513 samples (414 FNABs and 99 formalin-fixed paraffin-embedded (FFPE) specimens) underwent molecular testing at Ruijin Hospital. Sensitivity (Sen), specificity (Spe), positive predictive value (PPV), negative predictive value (NPV), and accuracy were calculated. There were 457 mutations in 428 samples. The rates of BRAF, RAS, TERT promoter, RET/PTC, and NTRK3 fusion mutations were 73.3% (n=335), 9.6% (n=44), 2.8% (n=13), 4.8% (n=22), and 0.4% (n=2), respectively. The diagnostic ability of cytology and molecular testing were evaluated in Bethesda II and V-VI samples. For cytology alone, Sen, Spe, PPV, NPV, and accuracy were 100%, 25.0%, 97.4%, 100%, and 97.4%; these numbers were 87.5%, 50.0%, 98.0%, 12.5%, and 86.2% when considering positive mutation, and 87.5%, 75.0%, 99.0%, 17.6%, and 87.1% when considering positive cytology or and positive mutation. In Bethesda III-IV nodules, when relying solely on the presence of pathogenic mutations for diagnosis, Sen, Spe, PPV, NPV, and AC were 76.2%, 66.7%, 94.1%, 26.8%, and 75.0%, respectively. It might be necessary to analyze the molecular mechanisms of disease development at the genetic level to predict patients with malignant nodules more accurately in different risk strata and develop rational treatment strategies and definite management plans.

Comparative Proteomic Analysis Revealing ActJ-Regulated Proteins in Sinorhizobium meliloti.

To adapt to different environmental conditions, Sinorhizobium meliloti relies on finely tuned regulatory networks, most of which are unexplored to date. We recently demonstrated that deletion of the two-component system ActJK renders an acid-vulnerable phenotype in S. meliloti and negatively impacts bacteroid development and nodule occupancy as well. To fully understand the role of ActJ in acid tolerance, S. meliloti wild-type and S. meliloti ΔactJ proteomes were compared in the presence or absence of acid stress by nanoflow ultrahigh-performance liquid chromatography coupled to mass spectrometry. The analysis demonstrated that proteins involved in the synthesis of exopolysaccharides (EPSs) were notably enriched in ΔactJ cells in acid pH. Total EPS quantification further revealed that although EPS production was augmented at pH 5.6 in both the ΔactJ and the parental strain, the lack of ActJ significantly enhanced this difference. Moreover, several efflux pumps were found to be downregulated in the ΔactJ strain. Promoter fusion assays suggested that ActJ positively modulated its own expression in an acid medium but not at under neutral conditions. The results presented here identify several ActJ-regulated genes in S. meliloti, highlighting key components associated with ActJK regulation that will contribute to a better understanding of rhizobia adaptation to acid stress.

Codon-optimized TDP-43 mediates neurodegeneration in a Drosophila model of ALS/FTLD.

Transactive response DNA binding protein-43 (TDP-43) is known to mediate neurodegeneration associated with amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). The exact mechanism by which TDP-43 exerts toxicity in the brains, spinal cord, and lower motor neurons of affected patients remains unclear. In a novel Drosophila melanogaster model, we report gain-of-function phenotypes due to misexpression of insect codon-optimized version of human wild-type TDP-43 (CO-TDP-43) using both the binary GAL4/UAS system and direct promoter fusion constructs. The CO-TDP-43 model showed robust tissue specific phenotypes in the adult eye, wing, and bristles in the notum. Compared to non-codon optimized transgenic flies, the CO-TDP-43 flies produced increased amount of high molecular weight protein, exhibited pathogenic phenotypes, and showed cytoplasmic aggregation with both nuclear and cytoplasmic expression of TDP-43. Further characterization of the adult retina showed a disruption in the morphology and function of the photoreceptor neurons with the presence of acidic vacuoles that are characteristic of autophagy. Based on our observations, we propose that TDP-43 has the propensity to form toxic protein aggregates via a gain-of-function mechanism, and such toxic overload leads to activation of protein degradation pathways such as autophagy. The novel codon optimized TDP-43 model is an excellent resource that could be used in genetic screens to identify and better understand the exact disease mechanism of TDP-43 proteinopathies and find potential therapeutic targets.

Investigating the molecular mechanisms behind the transcriptional response in pressure adaptation.

Despite 80% of Earth's microbial biomass existing in high pressure habitats in the Deep Ocean and within the continental crust, the mechanisms that allow for survival and growth in these thermodynamically unfavorable environments are poorly understood. Moreover, pressure resistance in pathogenic bacteria commonly found in food, such as Listeria monocytogenes and Escherichia coli, has emerged as more foods are sterilized by high pressure, rather than high temperature. To understand pressure adaptation, we have begun studying the molecular mechanisms of transcriptional adaptation to pressure. One important pathway in the pressure response is the heat shock pathway. To compare the heat shock response to pressure and temperature, we generated green fluorescent protein (GFP) promoter fusions of the central sigma factor genes’ transcriptional promoters and those of their downstream effectors. Activity of these promoter fusions was evaluated after heat shock and after pressure shock using scanning number and brightness (sN&B) fluorescence microscopy to determine the absolute number of GFP molecules produced in single cells and compared to the absolute number of GFP molecules produced in no shock conditions. Assuming transcriptional bursting at these promoters arises from release of supercoiling tension, we calculated the burst size and burst frequency from the distribution of the number of GFP molecules produced in each cell under each condition. These studies were carried out in the mesophilic E. coli MG1655 and in a moderately piezophilic (pressure-loving) strain adapted from MG1655, AN62. Studying both strains allowed us to quantify how the transcriptional response to changes in hydrostatic pressure occurs in both mesophiles and piezophiles, providing a more holistic model of the pressure response and adaptation phenomena.

Clinico-pathological and epigenetic heterogeneity of diffuse gliomas with FGFR3::TACC3 fusion

BackgroundGliomas with FGFR3::TACC3 fusion mainly occur in adults, display pathological features of glioblastomas (GB) and are usually classified as glioblastoma, IDH-wildtype. However, cases demonstrating pathological features of low-grade glioma (LGG) lead to difficulties in classification and clinical management. We report a series of 8 GB and 14 LGG with FGFR3:TACC3 fusion in order to better characterize them.MethodsCentralized pathological examination, search for TERT promoter mutation and DNA-methylation profiling were performed in all cases. Search for prognostic factors was done by the Kaplan–Meir method.ResultsTERT promoter mutation was recorded in all GB and 6/14 LGG. Among the 7 cases with a methylation score > 0.9 in the classifier (v12.5), 2 were classified as glioblastoma, 4 as ganglioglioma (GG) and 1 as dysembryoplastic neuroepithelial tumor (DNET). t-SNE analysis showed that the 22 cases clustered into three groups: one included 12 cases close to glioblastoma, IDH-wildtype methylation class (MC), 5 cases each clustered with GG or DNET MC but none with PLNTY MC. Unsupervised clustering analysis revealed four groups, two of them being clearly distinct: 5 cases shared age (< 40), pathological features of LGG, lack of TERT promoter mutation, FGFR3(Exon 17)::TACC3(Exon 10) fusion type and LGG MC. In contrast, 4 cases shared age (> 40), pathological features of glioblastoma, and were TERT-mutated. Relevant factors associated with a better prognosis were age < 40 and lack of TERT promoter mutation.ConclusionAmong gliomas with FGFR3::TACC3 fusion, age, TERT promoter mutation, pathological features, DNA-methylation profiling and fusion subtype are of interest to determine patients’ risk.

Composite plants of cucumber and buckwheat as a tool to study auxin distribution and transport in the root system

Genetic transformation of most dicotyledonous plants by Rhizobium rhizogenes (also known as Agrobacterium rhizogenes) results in production of composite plants plants consisting of wild-type shoot and transgenic root system. Composite plants are the suitable model for investigation of hormonal mechanisms related to development of the root system as regulatory links between the root system and the shoot maintains in such plants.&#x0D; In most plants initiation of lateral root primordia occurs above the elongation zone [1]. However, in cucurbits and some other species, including important cereal crop buckwheat (Fagopyrum esculentum Moench), lateral root primordia initiation and development occurs in the apical meristem of the parental root [2, 3].&#x0D; The phytohormone auxin is a key regulator of lateral root development. Fusions of auxin-responsive promoters and reporter genes can be used to study the role of auxin in the development of root system of non-model plants such as cucumber (Cucumis sativus L.) and buckwheat [4].&#x0D; The agrobacterium mediated transformation technique of cucurbits [5] has been adapted for buckwheat. R. rhizogenes strain R1000 was used in all transformations. Set of binary vectors based on pKGW-RR-MGW or pKGW-MGW was developed to study auxin response maxima (DR5::mNeonGreen) or auxin transport (fusions of genes encoding auxin efflux proteins PIN and mNeonGreen).&#x0D; Pattern of auxin response maxima was similar in both species and included quiescent center and initial cells, columella, xylem cell files and lateral root primordia on all stages of development. Members of CsPIN1 (CsPINb and CsSoPIN1) group contributed unequally in generation of auxin maximum required for lateral root primordium initiation.&#x0D; The research was supported by the RFBR grant 20-016-00233-a.

Alterations in key signaling pathways in sinonasal tract melanoma. A molecular genetics and immunohistochemical study of 90 cases and comprehensive review of the literature

AbstractSinonasal mucosal melanoma is a rare tumor arising within the nasal cavity, paranasal sinuses, or nasopharynx (sinonasal tract). This study evaluated 90 cases diagnosed in 29 males and 61 females with median age 68 years. Most tumors involved the nasal cavity and had an epithelioid morphology. Spectrum of research techniques used in this analysis includes targeted-DNA and -RNA next-generation sequencing, Sanger sequencing, fluorescence in situ hybridization and immunohistochemistry. Sinonasal melanomas were commonly driven by RAS (38/90, 42%), especially NRAS (n = 36) mutations and rarely (4/90, 4%) displayed BRAF pathogenic variants. BRAF/RAS mutants were more frequent among paranasal sinuses (10/14, 71%) than nasal (26/64, 41%) tumors. BRAF/RAS-wild type tumors occasionally harbored alterations of the key components and regulators of Ras-MAPK signaling pathway: NF1 mutations (1/17, 6%) or NF1 locus deletions (1/25, 4%), SPRED1 (3/25, 12%), PIK3CA (3/50, 6%), PTEN (4/50, 8%) and mTOR (1/50, 2%) mutations. These mutations often occurred in a mutually exclusive manner. In several tumors some of which were NRAS mutants, TP53 was deleted (6/48, 13%) and/or mutated (5/90, 6%). Variable nuclear accumulation of TP53, mirrored by elevated nuclear MDM2 expression was seen in >50% of cases. Furthermore, sinonasal melanomas (n = 7) including RAS/BRAF-wild type tumors (n = 5) harbored alterations of the key components and regulators of canonical WNT-pathway: APC (4/90, 4%), CTNNB1 (3/90, 3%) and AMER1 (1/90, 1%). Both, TERT promoter mutations (5/53, 9%) and fusions (2/40, 5%) were identified. The latter occurred in BRAF/RAS-wild type tumors. No oncogenic fusion gene transcripts previously reported in cutaneous melanomas were detected. Eight tumors including 7 BRAF/RAS-wild type cases expressed ADCK4::NUMBL cis-fusion transcripts. In summary, this study documented mutational activation of NRAS and other key components and regulators of Ras-MAPK signaling pathway such as SPRED1 in a majority of sinonasal melanomas.

Combining Clearing and Fluorescence Microscopy for Visualising Changes in Gene Expression and Physiological Responses to &lt;em&gt;Plasmodiophora brassicae&lt;/em&gt;

Infection of Brassica crops by the soilborne protist Plasmodiophora brassicae leads to gall formation on the underground organs. The formation of galls requires cellular reprogramming and changes in the metabolism of the infected plant. This is necessary to establish a pathogen-oriented physiological sink toward which the host nutrients are redirected. For a complete understanding of this particular plant-pathogen interaction and the mechanisms by which host growth and development are subverted and repatterned, it is essential to track and observe the internal changes accompanying gall formation with cellular resolution. Methods combining fluorescent stains and fluorescent proteins are often employed to study anatomical and physiological responses in plants. Unfortunately, the large size of galls and their low transparency act as major hurdles in performing whole-mount observations under the microscope. Moreover, low transparency limits the employment of fluorescence microscopy to study clubroot disease progression and gall formation. This article presents an optimized method for fixing and clearing galls to facilitate epifluorescence and confocal microscopy for inspecting P. brassicae-infected galls. A tissue-clearing protocol for rapid optical clearing was used followed by vibratome sectioning to detect anatomical changes and localize gene expression with promoter fusions and reporter lines tagged with fluorescent proteins. This method will prove useful for studying cellular and physiological responses in other pathogen-triggered structures in plants, such as nematode-induced syncytia and root knots, as well as leaf galls and deformations caused by insects.

Combining Clearing and Fluorescence Microscopy for Visualising Changes in Gene Expression and Physiological Responses to Plasmodiophora brassicae.

Infection of Brassica crops by the soilborne protist Plasmodiophora brassicae leads to gall formation on the underground organs. The formation of galls requires cellular reprogramming and changes in the metabolism of the infected plant. This is necessary to establish a pathogen-oriented physiological sink toward which the host nutrients are redirected. For a complete understanding of this particular plant-pathogen interaction and the mechanisms by which host growth and development are subverted and repatterned, it is essential to track and observe the internal changes accompanying gall formation with cellular resolution. Methods combining fluorescent stains and fluorescent proteins are often employed to study anatomical and physiological responses in plants. Unfortunately, the large size of galls and their low transparency act as major hurdles in performing whole-mount observations under the microscope. Moreover, low transparency limits the employment of fluorescence microscopy to study clubroot disease progression and gall formation. This article presents an optimized method for fixing and clearing galls to facilitate epifluorescence and confocal microscopy for inspecting P. brassicae-infected galls. A tissue-clearing protocol for rapid optical clearing was used followed by vibratome sectioning to detect anatomical changes and localize gene expression with promoter fusions and reporter lines tagged with fluorescent proteins. This method will prove useful for studying cellular and physiological responses in other pathogen-triggered structures in plants, such as nematode-induced syncytia and root knots, as well as leaf galls and deformations caused by insects.

Use of the Iron-Responsive RBT5 Promoter for Regulated Expression in Candida albicans.

ABSTRACTEngineered conditional gene expression is used in appraisal of gene function and pathway relationships. For pathogens like the fungus Candida albicans, conditional expression systems are most useful if they are active in the infection environment and if they can be utilized in multiple clinical isolates. Here, we describe such a system. It employs the RBT5 promoter and can be implemented with a few PCRs. We validated the system with RBT5 promoter fusions to two genes that promote filamentation and polarized growth, UME6 and HGC1, and with efg1Δ/Δ mutants, which are defective in an activator of filamentous growth. An RBT5 promoter fusion to either gene enabled filamentous growth of an efg1Δ/Δ mutant of strain SC5314 in iron-limited media, including RPMI with serum and yeast extract-peptone-dextrose with bathophenanthrolinedisulfonic acid. The RBT5-UME6 fusion promoted filamentation of efg1Δ/Δ mutants in RPMI with serum of four other clinical C. albicans isolates as well. In a mouse model of disseminated candidiasis, the RBT5-UME6 fusion promoted filamentation of the SC5314 efg1Δ/Δ mutant in kidney tissue, an indication that the RBT5 promoter is active in the iron-limited host environment. The RBT5 promoter expands the conditional expression toolkit for C. albicans genetics.IMPORTANCE Genetic strategies have been vital for mechanistic analysis of biological processes. Here, we describe a genetic tool for the fungal pathogen Candida albicans.

Genome-Wide Identification of the LexA-Mediated DNA Damage Response in Streptomyces venezuelae.

ABSTRACTDNA damage triggers a widely conserved stress response in bacteria called the SOS response, which involves two key regulators, the activator RecA and the transcriptional repressor LexA. Despite the wide conservation of the SOS response, the number of genes controlled by LexA varies considerably between different organisms. The filamentous soil-dwelling bacteria of the genus Streptomyces contain LexA and RecA homologs, but their roles in Streptomyces have not been systematically studied. Here, we demonstrate that RecA and LexA are required for the survival of Streptomyces venezuelae during DNA-damaging conditions and for normal development during unperturbed growth. Monitoring the activity of a fluorescent recA promoter fusion and LexA protein levels revealed that the activation of the SOS response is delayed in S. venezuelae. By combining global transcriptional profiling and chromatin immunoprecipitation sequencing (ChIP-seq) analysis, we determined the LexA regulon and defined the core set of DNA damage repair genes that are expressed in response to treatment with the DNA-alkylating agent mitomycin C. Our results show that DNA damage-induced degradation of LexA results in the differential regulation of LexA target genes. Using surface plasmon resonance, we further confirmed the LexA DNA binding motif (SOS box) and demonstrated that LexA displays tight but distinct binding affinities to its target promoters, indicating a graded response to DNA damage.IMPORTANCE The transcriptional regulator LexA functions as a repressor of the bacterial SOS response, which is induced under DNA-damaging conditions. This results in the expression of genes important for survival and adaptation. Here, we report the regulatory network controlled by LexA in the filamentous antibiotic-producing Streptomyces bacteria and establish the existence of the SOS response in Streptomyces. Collectively, our work reveals significant insights into the DNA damage response in Streptomyces that will promote further studies to understand how these important bacteria adapt to their environment.

Abstract 5851: Negative regulation of p53 by ZnT1

Abstract Rationale and Background: p53 is a powerful tumor suppressor protein that also autorepresses by inducing expression of its own negative regulators, such as MDM2. Here we explore another potential mechanism for p53 autorepression, regulation of zinc metabolism. Proper folding of p53 requires zinc binding and cancer-associated mutations in p53 often lower the affinity of the mutant proteins for zinc. Our previous work showed that ZMC1, a zinc metallochaperone, can reactivate certain p53 mutants by raising intracellular zinc concentrations. Here we show that p53 activates transcription of ZnT1. ZnT1 can then export zinc from the cell, which in turn lowers p53 activity. Methods: To explore the relationship between ZnT1 and p53, we studied several human cancer cell lines under various conditions, including ZnT1 overexpression, ZnT1 silencing, and p53 activation. For silencing gene expression, we used CRISPR-Cas9 with a lentiviral vector to knock out ZnT1 and also employed shRNAs to knockdown expression of p53 or ZnT1. To analyze the relationship between TP53 and ZnT1 genes in clinical samples, data from cBioPortal were examined. Results: ZnT1 transcription increased after p53 was activated in several p53+ cell lines but did not increase in isogenic p53-null cell lines, suggesting that ZnT1 transcription is dependent on p53. p53 also bound to the ZnT1 promoter by chromatin immunoprecipitation assay, and activated transcription of a ZnT1/luciferase promoter fusion. Overexpression of ZnT1 decreased p21 transcription, indicating lowered p53 function; conversely, knockdown of ZnT1 increased p21 transcription. By cBioPortal analysis, ZnT1 gene amplifications were mutually exclusive with TP53 gene mutations in breast and lung tumors. Conclusion: These data suggest that autorepression of p53 occurs in part due to lowered intracellular zinc caused by upregulation of ZnT1. Citation Format: Ben Brik, Kathleen Carino, Wade Narrow, Chris R. Harris, Xin Yu, Darren R. Carpizo. Negative regulation of p53 by ZnT1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5851.

Bottom-up synthetic biology approach for improving the efficiency of menaquinone-7 synthesis in Bacillus subtilis

BackgroundMenaquinone-7 (MK-7), which is associated with complex and tightly regulated pathways and redox imbalances, is produced at low titres in Bacillus subtilis. Synthetic biology provides a rational engineering principle for the transcriptional optimisation of key enzymes and the artificial creation of cofactor regeneration systems without regulatory interference. This holds great promise for alleviating pathway bottlenecks and improving the efficiency of carbon and energy utilisation.ResultsWe used a bottom-up synthetic biology approach for the synthetic redesign of central carbon and to improve the adaptability between material and energy metabolism in MK-7 synthesis pathways. First, the rate-limiting enzymes, 1-deoxyxylulose-5-phosphate synthase (DXS), isopentenyl-diphosphate delta-isomerase (Fni), 1-deoxyxylulose-5-phosphate reductase (DXR), isochorismate synthase (MenF), and 3-deoxy-7-phosphoheptulonate synthase (AroA) in the MK-7 pathway were sequentially overexpressed. Promoter engineering and fusion tags were used to overexpress the key enzyme MenA, and the titre of MK-7 was 39.01 mg/L. Finally, after stoichiometric calculation and optimisation of the cofactor regeneration pathway, we constructed two NADPH regeneration systems, enhanced the endogenous cofactor regeneration pathway, and introduced a heterologous NADH kinase (Pos5P) to increase the availability of NADPH for MK-7 biosynthesis. The strain expressing pos5P was more efficient in converting NADH to NADPH and had excellent MK-7 synthesis ability. Following three Design-Build-Test-Learn cycles, the titre of MK-7 after flask fermentation reached 53.07 mg/L, which was 4.52 times that of B. subtilis 168. Additionally, the artificially constructed cofactor regeneration system reduced the amount of NADH-dependent by-product lactate in the fermentation broth by 9.15%. This resulted in decreased energy loss and improved carbon conversion.ConclusionsIn summary, a "high-efficiency, low-carbon, cofactor-recycling" MK-7 synthetic strain was constructed, and the strategy used in this study can be generally applied for constructing high-efficiency synthesis platforms for other terpenoids, laying the foundation for the large-scale production of high-value MK-7 as well as terpenoids.