Strain N1 Research Articles

Fine Mapping the Soybean Mosaic Virus Resistance Gene in Soybean Cultivar Heinong 84 and Development of CAPS Markers for Rapid Identification.

Heinong 84 is one of the major soybean varieties growing in Northeast China, and is resistant to the infection of all strains of soybean mosaic virus (SMV) in the region including the most prevalent strain, N3. However, the resistance gene(s) in Heinong 84 and the resistant mechanism are still elusive. In this study, genetic and next-generation sequencing (NGS)-based bulk segregation analysis (BSA) were performed to map the resistance gene using a segregation population from the cross of Heinong 84 and a susceptible cultivar to strain N3, Zhonghuang 13. Results show that the resistance of Heinong 84 is controlled by a dominant gene on chromosome 13. Further analyses suggest that the resistance gene in Heinong 84 is probably an allele of Rsv1. Finally, two pairs of single-nucleotide-polymorphism (SNP)-based primers that are tightly cosegregated with the resistance gene were designed for rapidly identifying resistant progenies in breeding via the cleaved amplified polymorphic sequence (CAPS) assay.

Bioformulation Development of Bacillus velezensis Strain N1 to Control Rice Bacterial Leaf Blight

Bacterial leaf blight is a serious disease of rice caused by Xanthomonas oryzae pv. oryzae (Xoo). The objective of this study was to develop a bioformulation of Bacillus velezensis strain N1 by using microencapsulation techniques through spray drying and to then evaluate its performance in controlling rice bacterial leaf blight under greenhouse conditions. Three formulations with a different main carrier were studied and the viability after spray drying, moisture content, characteristic of formulation powder under scanning electron microscope and storage stability were examined. The results showed that formulation 3 (10 % skimmed milk, 20 % maltodextrin, 0.06 % sodium alginate and 5 % tapioca starch) had the highest antagonistic bacterial viability after spray drying of 1.24×107 CFU/g. Formulation 2 had the highest antagonistic bacterial viability of 1.44×106 CFU/g and had the lowest viability reduction of 0.61 Log CFU/g after storage at room temperature for 3 months. Moisture content of each formulation was less than 4 %. Among the 3 formulations of strain N1 bacteria against Xoo, formula 2 was able to control rice bacterial blight disease with the highest disease reduction index (45.87 %). All the results indicated that Bacillus velezensis strain N1 can be an effective antagonist and could potentially be used to develop a more successful bioformulation against rice bacterial leaf blight.
 GRAPHICAL ABSTRACT

Development of Genetic Tools in Glucoamylase-Hyperproducing Industrial Aspergillus niger Strains.

Simple SummaryGlucoamylase is one of the most needed industrial enzymes in the food and biofuel industries. Aspergillus niger is a commonly used cell factory for the production of commercial glucoamylase. For decades, genetic manipulation has promoted significant progress in industrial fungi for strain engineering and in obtaining deep insights into their genetic features. However, genetic engineering is more laborious in the glucoamylase-producing industrial strains A. niger N1 and O1 because their fungal features of having few conidia (N1) or of being aconidial (O1) make them difficult to perform transformation on. In this study, we targeted A. niger N1 and O1 and successfully developed high-efficiency transformation tools. We also constructed a clustered regularly interspaced short palindromic repeat (CRISPR)/Cas9 editing marker-free system using an autonomously replicating plasmid to express Cas9 protein and to guide RNA and the selectable marker. By using the genetic tools developed here, we generated nine albino deletion mutants. After three rounds of sub-culturing under nonselective conditions, the albino deletions lost the autonomously replicating plasmid. Together, the tools and optimization process above provided a good reference to manipulate the tough working industrial strain, not only for the further engineering these two glucoamylase-hyperproducing strains, but also for other industrial strains.The filamentous fungus Aspergillus niger is widely exploited by the fermentation industry for the production of enzymes, particularly glucoamylase. Although a variety of genetic techniques have been successfully used in wild-type A. niger, the transformation of industrially used strains with few conidia (e.g., A. niger N1) or that are even aconidial (e.g., A. niger O1) remains laborious. Herein, we developed genetic tools, including the protoplast-mediated transformation and Agrobacterium tumefaciens-mediated transformation of the A. niger strains N1 and O1 using green fluorescent protein as a reporter marker. Following the optimization of various factors for protoplast release from mycelium, the protoplast-mediated transformation efficiency reached 89.3% (25/28) for N1 and 82.1% (32/39) for O1. The A. tumefaciens-mediated transformation efficiency was 98.2% (55/56) for N1 and 43.8% (28/64) for O1. We also developed a marker-free CRISPR/Cas9 genome editing system using an AMA1-based plasmid to express the Cas9 protein and sgRNA. Out of 22 transformants, 9 albA deletion mutants were constructed in the A. niger N1 background using the protoplast-mediated transformation method and the marker-free CRISPR/Cas9 system developed here. The genome editing methods improved here will accelerate the elucidation of the mechanism of glucoamylase hyperproduction in these industrial fungi and will contribute to the use of efficient targeted mutation in other industrial strains of A. niger.

Growth studies of dominant lactic acid bacteria in orange juice and selection of strains to ferment citric fruit juices with probiotic potential.

The study aimed to evaluate the ability of dominant lactic acid bacteria (LAB) in orange juice to growth on N-depleted MRS medium supplemented or not with cysteine (mMRS), then to select the most nutritionally promising strains for growth assays in the food matrix and evaluation of beneficial attributes for fruit juice fermentation. Levilactobacillus brevis and Lactiplantibacillus plantarum were dominant species among the total of 103 LAB isolates as confirmed by multiplex PCR and/or 16s rDNA sequence analysis. Based on growing lower than 20% and higher than 70% in mMRS (1.0g/l meat extract, without peptone and yeast extract) with and without cysteine requirement, one L. brevis (JNB23) and two L. plantarum (JNB21 and JNB25) were selected. These bacteria and the L. plantarum strains N4 and N8 (previously isolated from oranges peel) when inoculated in orange juice grew up to 1.0 log cfu/ml for 24h incubation at 30°C and mainly produced lactic acid, with strains JNB25 and JNB23 reaching the highest and lowest cell densities in agreement with their nutritional exigency. In addition, all L. plantarum strains exhibited antagonistic activity against the majority of tested bacterial pathogens (in opposition to L. brevis), ability to grow or survive to pH 3.0 for 3h, to grow with 0.5% sodium taurocholate, and a decrease after simulated gastrointestinal digestion assay which did not exceed 1.0 or 2.0 log units, depending on the strain. Thus, autochthonous L. plantarum strains with ability for overcoming nutritional limitations and beneficial attributes are promising candidates for further investigations as novel probiotic and/or preservative starters to ferment citric fruit juices.

The metabolism of pyrene by a novel Altererythrobacter sp. with in-situ co-substrates: A mechanistic analysis based on pathway, genomics, and enzyme activity

Using co-substrates to enhance the metabolic activity of microbes is an effective way for high-molecular-weight polycyclic aromatic hydrocarbons removal in petroleum-contaminated environments. However, the long degradation period and exhausting substrates limit the enhancement of metabolic activity. In this study, Altererythrobacter sp. N1 was screened from petroleum-contaminated soil in Shengli Oilfield, China, which could utilize pyrene as the sole carbon source and energy source. Saturated aromatic fractions and crude oils were used as in-situ co-substrates to enhance pyrene degradation. Enzyme activity was influenced by the different co-substrates. The highest degradation rate (75.98%) was achieved when crude oil was used as the substrate because strain N1 could utilize saturated and aromatic hydrocarbons from crude oil simultaneously to enhance the degrading enzyme activity. Moreover, the phthalate pathway was dominant, while the salicylate pathway was secondary. Furthermore, the Rieske-type aromatic cyclo-dioxygenase gene was annotated in the Altererythrobacter sp. N1 genome for the first time. Therefore, the co-metabolism of pyrene was sustained to achieve a long degradation period without the addition of exogenous substrates. This study is valuable as a potential method for the biodegradation of high-molecular-weight polycyclic aromatic hydrocarbons.

Functional identification of the DHN melanin synthesis gene cluster and its role in UV-C tolerance in citrus postharvest pathogenic fungus Penicillium digitatum

The filamentous fungus Penicillium digitatum brings out great losses in citrus fruits by causing citrus green mold disease during the postharvest period. Previously, we obtained a T-DNA insertion mutant N2130 of P. digitatum, which produced albino conidia. To understand the role of green-grey conidial pigment in P. digitatum, we identified the insertion site and deeply explored the 1,8-dihydroxynaphtsalene (DHN)-melanin synthesis gene cluster in this phytopathogen. In this study, we deleted five genes in P. digitatum, PdPksP, PdAbr1, PdArp1, PdArp2, and PdAyg1, and the experiments were further performed on phenotype analyses, including pigmentation, UV-C tolerance, virulence, growth rate, conidiation, stress (osmotic-, oxidative-, cell wall disturbing-, and high temperature-) tolerance, fungicide resistance, and conidial hydrophobicity. The results showed that the five deletion mutants (ΔPdPksP, ΔPdAbr1, ΔPdArp1, ΔPdArp2 and ΔPdAyg1) produced albino, brownish, brown, reddish-brown, and Yellowish green conidia, respectively. In addition, the survival colony forming units (CFUs) of the deletion mutants, under the treatment of UV-C radiation (261.4 mJ/cm2), were 0.3- to 0.6-fold of those surviving in wild-type strain N1. Moreover, after 522.8 mJ/cm2-UV-C-irradiation on conidia, the deletion mutants showed a larger decrease in pathogenicity on Valencia Orange fruits compared with strain N1. However, there were no significant differences among other phenotypes tested in this study. Collectively, our research reported the DHN-melanin synthesis pathway in P. digitatum for the first time, and revealed that DHN-melanin is important for P. digitatum to tolerate UV-C irradiation.

Crude oil hydrocarbon degradation efficiency of indigenous bacterial strains isolated from contaminated sites in Nigeria

The crude oil degradation potential of bacterial isolates from three contaminated sites in Nigeria were investigated. Seven bacterial isolates namely Pseudomonas aeruginosa strain W15, Pseudomonas aeruginosa strain N3R, Serratia marcescens strain N4, Providencia vermicola strain W8, Serratia marcescens strain W13, Pseudomonas aeruginosa strain W11 and Pseudomonas protegens strain P7 were isolated and identified using molecular methods. Isolates N4, N3 and W13 showed higher % total petroleum hydrocarbon (TPH) degradation of 79.26%, 78.96% and 78.69% respectively than W15, P7, W8 and W11 with % TPH degradation of 68.96%, 62.14%, 59.75% and 59.00% respectively. W13 showed the fastest degradation rate with 78.72% within the first 14 days of incubation; however, after the 14th day, there was no progressive change in % TPH. W11 showed degradation of wider range of hydrocarbon components originally in the crude oil as well as the complete degradation of most intermediates formed. The isolates showed good degradation potentials for bioremediation applications.

Antimicrobial Activities of the Secondary Metabolite Extracted from a Nocardia Strain

Background & Objective: The emergence of antibiotic-resistant bacteria and limited treatment options for these infections is a challenging problem in the world. There is increasing interest in isolating bioactive molecules from actinobacteria and elucidating their antimicrobial mechanisms at the moment. The current study aimed to investigate the antimicrobial activities of a Nocardia strain (N4) that was previously isolated from the soil samples in Tehran, Iran.
 Materials & Methods: The cultural, morphological, and physiological characteristics of the strain were determined and the identity of the strain was confirmed using 16SrRNA gene sequencing. The strain was screened for antimicrobial metabolite production. The in vitro anti-microbial activity of the extracted metabolite was assessed by agar well diffusion and minimum inhibitory concentrations methods. Finally, the structure of the extracted metabolite was confirmed by HPLC and mass spectrometry methods.
 Results: The isolate shared 99% sequence similarity with Nocardia soli. The strain showed broad-spectrum antimicrobial activities against some pathogenic bacteria (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Klebsiella pneumoniae ATCC 700603, Salmonella Typhimurium ATCC 14028 and Shigella sonnei RI366) and fungi (Aspergillus niger ATCC 1015 and Aspergillus fumigatus ATCC 1022) in the agar well diffusion method. The ethyl acetate extract of the strain exhibited the highest antimicrobial activity against E. coli (MIC= 4.67±3.055 μg/mL) and K. pneumoniae (MIC=3.33±1.155 μg/mL). The metabolite showed high similarity with C2 1H28N7 O14.
 Conclusions: The current study confirmed the presence of a bioactive metabolite in strain N4, suggesting that this may be a promising candidate for discovering bioactive components with broad antibacterial activities against a variety of pathogens.

Structure-Guided Engineering of a Family IV Cold-Adapted Esterase Expands Its Substrate Range.

Cold active esterases have gained great interest in several industries. The recently determined structure of a family IV cold active esterase (EstN7) from Bacillus cohnii strain N1 was used to expand its substrate range and to probe its commercially valuable substrates. Database mining suggested that triacetin was a potential commercially valuable substrate for EstN7, which was subsequently proved experimentally with the final product being a single isomeric product, 1,2-glyceryl diacetate. Enzyme kinetics revealed that EstN7’s activity is restricted to C2 and C4 substrates due to a plug at the end of the acyl binding pocket that blocks access to a buried water-filled cavity. Residues M187, N211 and W206 were identified as key plug forming residues. N211A stabilised EstN7 allowing incorporation of the destabilising M187A mutation. The M187A-N211A double mutant had the broadest substrate range, capable of hydrolysing a C8 substrate. W206A did not appear to have any significant effect on substrate range either alone or when combined with the double mutant. Thus, the enzyme kinetics and engineering together with a recently determined structure of EstN7 provide new insights into substrate specificity and the role of acyl binding pocket plug residues in determining family IV esterase stability and substrate range.

Synergistic effects of Cd-loving Bacillus sp. N3 and iron oxides on immobilizing Cd and reducing wheat uptake of Cd

Iron oxides and microorganisms are important soil components that profoundly affect the transformation and bioavailability of heavy metals in soils. Here, batch and pot experiments were conducted to investigate the immobilization mechanisms of Cd by Cd-loving Bacillus sp. N3 and ferrihydrite (Fh) as well as their impacts on Cd uptake by wheat and bacterial community composition in wheat rhizospheric soil. The results showed that the combination of strain N3 with Fh could immobilize more Cd compared to strain N3 and Fh, respectively. Furthermore, strain N3 facilitated Cd retention on Fh, which synergistically reduced the concentration of DTPA extracted Cd in the soil and decreased Cd content (57.1%) in wheat grains. Moreover, inoculation with strain N3 increased the complexity of the co-occurrence network of the bacterial community in rhizospheric soil, and the abundance of beneficial bacteria with multipel functions including heavy metal immobilization, dissimilatory iron reduction, and plant growth promotion. Overall, this study demonstrated the enrichment of strain N3 and iron oxides, together with increased soil pH, synergistically immobilized soil Cd, which strongly suggested inoculation with Cd-loving strains could be a promising approach to immobilize Cd and reduce wheat uptake of Cd, particular for soils rich in iron oxides.

Polyamine-producing Bacteria Regulated the Community Structure of Rhizosphere Bacteria and Reduced the Absorption of Cd in Wheat

Some functional microorganisms in the soil immobilize heavy metals by adsorption and precipitation, prevent the absorption of heavy metals by crops, and play an important role in the passivation and remediation of medium and mild heavy metal-contaminated soil. A pot experiment was conducted to study the effects of the exogenous polyamine-producing bacterium Bacillus sp. N3 on Cd uptake and the bacterial community composition and function in the rhizosphere soil. The results showed that strain N3 significantly reduced the contents of Cd (64.7%) in wheat grain and DTPA-Cd (50.1%) in rhizosphere soil and increased the pH (from 6.84 to 6.97) and polyamine content. High-throughput sequencing results showed that inoculation of strain N3 reduced the diversity of the bacterial community; however, it increased the relative abundances of β-Proteobacteria, Bacteroidetes, and Firmicutes in wheat rhizosphere soil. Meanwhile, strain N3 also increased the relative abundances of heavy metal-immobilizing bacteria and plant growth-promoting bacteria (Bacillus, Arthrobacter, Brevundimonas, Ensifer, Pedobacter, Rhizobium, Pseudomonas, Enterobacter, and Serratia) in wheat rhizosphere soil. The PICRUSt function prediction showed that strain N3 increased the copy number of genes involved in antioxidant capacity, hormone synthesis, and sulfur metabolism in wheat rhizosphere soil. These results indicated that the polyamine-producing bacteria N3 reduced the DTPA-Cd content by increasing the pH; the polyamine contents; the abundances of bacteria with heavy metal-immobilizing or plant growth-promoting traits; and the metabolic pathway involved in antioxidant capacity, hormone synthesis, and sulfur metabolism in wheat rhizosphere soil, thus inhibiting the absorption of Cd by wheat. The results provide theoretical basis and technical support for restoring farmland with excessive heavy metals and ensuring the safe production of wheat.

Pathogenicity and genome-wide sequence analysis reveals relationships between soybean mosaic virus strains.

Soybean mosaic virus (SMV) is the most prevalent viral pathogen in soybean. In China, the SMV strains SC and N are used simultaneously in SMV resistance assessments of soybean cultivars, but the pathogenic relationship between them is unclear. In this study, SMV strains N1 and N3 were found to be the most closely related to SC18. Moreover, N3 was found to be more virulent than N1. A global pathotype classification revealed the highest level of genetic diversity in China. The N3 type was the most frequent and widespread worldwide, implying that SMV possibly originated in China and spread across continents through the dissemination of infected soybean. It also suggests that the enhanced virulence of N3 facilitated its spread and adaptability in diverse geographical and ecological regions worldwide. Phylogenetic analysis revealed prominent geographical associations among SMV strains/isolates, and genomic nucleotide diversity analysis and neutrality tests demonstrated that the whole SMV genome is under negative selection, with the P1 gene being under the greatest selection pressure. The results of this study will facilitate the nationwide use of SMV-resistant soybean germplasm and could provide useful insights into the molecular variability, geographical distribution, phylogenetic relationships, and evolutionary history of SMV around the world.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00705-021-05271-z.

Manipulation of triacylglycerol biosynthesis in Nannochloropsis oceanica by overexpressing an Arabidopsis thaliana diacylglycerol acyltransferase gene

Given the depleting fossil fuel resource, oleaginous microalgae have a great potential as feedstocks for sustainable and environment-friendly biofuels. Improvement of neutral lipid, especially triacylglycerol (TAG), accumulation, without a cost of growth is considerably desirable for the commercial feasibility of microalgae-derived biofuels. Genetic engineering emerges as a feasible and effective strategy to achieve this goal. Diacylglycerol acyltransferase (DGAT) catalyzes the committed and final step in the de novo biosynthesis pathway of TAG. Nevertheless, the effectiveness of overexpression of plant-derived DGAT gene in Nannochloropsis sp. remains obscure. In this study, the type1 DGAT gene (AtDGAT) from Arabidopsis thaliana was heterogeneously expressed in Nannochloropsis oceanica by electroporation, yielding one AtDGAT transformant (N4 strain). The integration and transcription of AtDGAT in N. oceanica cells were confirmed by PCR. Results revealed that HSP70A-RBSC2 promoter could activate AtDGAT transcription in N. oceanica treated with or without heat shock. AtDGAT transcription in N4H cells (with heat shock) was 31.25 times as high as that in N4 cells (without heat shock). The overexpression of AtDGAT in N. oceanica led to a significant increase in total lipid and TAG contents without compromising algal growth. In addition, gas chromatography–mass spectrometry (GC–MS) analysis indicated that AtDGAT overexpression caused a drastic elevation in C16 (C16:0 + C16:1) but a slight decline in C18 (C18:0 + C18:1), compared to wild-type N. oceanica, and the variations were further intensified with heat shock. This study offers a valuable and rational strategy of genetic manipulation of TAG content in N. oceanica and facilitates the commercialization of microalgal biofuel. This is also the first successful attempt of overexpression of plant-derived DGAT gene in Nannochloropsis sp., providing novel insights into the genetic engineering of oleaginous microalgae.

EVALUATION OF AZO DYE ORANGE G DECOLORIZATION AND DEGRADATION BY BACTERIA ISOLATED FROM TEXTILE EFFLUENT

The bacteria were isolated and identified from textile effluent, and their ability to decolorize the hazardous azo dye Orange G was evaluated. After incubating the isolates for 24 hours in mineral salt medium supplemented with 100 ppm Direct Orange G, their decolorizing activity was measured spectrophotometrically. Lysinibacillus sp. AUBTP7 (AK1), Bacillus muralis strain1Y118 (AK2), and Bacillus thuringiensis strain N3 (AK3) were identified as the bacterial strains. Bacillus thuringiensis strain N3 (AK3) was the most efficient bacteria at decolorizing Orange G (100ppm), removing 93% of the color in 24 hours at 36ºC temperature. Study of HPLC chromatogram of Orange G and degradation products suggests the formation of new compounds. As a result of this research, it has been revealed that some bacteria live in textile effluents and use dyes as a source of energy and nourishment, implying their usefulness in the treatment of industrial effluents.

Population dynamics and crude oil degrading ability of bacterial consortia of isolates from oil-contaminated sites in Nigeria.

Application of bacterial consortium of hydrocarbon degraders to crude oil-contaminated site can enhance bioremediation. This study evaluated the population dynamics and crude oil degradation abilities of various consortia developed from bacterial strains isolated from crude oil-contaminated sites using crude oil-supplemented Bushnell Haas media. Each consortium consisted of three bacterial strains and was designated as Consortium A (Serratia marcescens strain N4, Pseudomonas aeruginosa strain N3R, Pseudomonas aeruginosa strain W11), B (Pseudomonas aeruginosa strain N3R, Pseudomonas aeruginosa strain W11, Pseudomonas protegens strain P7), C (Serratia marcescens strain N4, Pseudomonas aeruginosa strain W11, Pseudomonas protegens strain P7), and D (Pseudomonas aeruginosa strain W15, Providencia vermicola strain W8, Serratia marcescens strain W13). There was progressive decline in the populations of Serratia marcescens strains in the consortia as the incubation period progressed. This may have led to reduction in their synergistic contribution and, subsequently, total degradation ability of crude oil by the consortia. The gravimetric analyses showed that Consortium D produced the highest % crude oil degradation of 29.66% compared to Consortia A, B, and C with 23.73%, 11.86%, and 19.49% respectively. Based on gas chromatography-mass spectrometry analyses, Consortium D produced the highest percentage total petroleum hydrocarbon degradation of 73.65% compared to 68.24%, 68.94%, and 69.19% produced by Consortia A, B, and C respectively. The biodegradation potential of Consortium D also demonstrates the significance of using isolates from the same isolation site in development of consortium for bioremediation.

Influence of carbides on the strain hardening behavior of 60Si2CrVAT spring steel treated by a Q&T process

The strain hardening behavior was studied in ultra-high strength 60Si2CrVAT spring steel subjected to quenching and tempering (Q&T) treatments via tailoring the carbides precipitated during tempering at 400–530 °C. Results showed that the strain hardening characteristic of the spring steel changed from a single-n upwardly convex (tempering temperatures below 470 °C) to a double-n downwardly convex (tempering temperatures equal to or higher than 470 °C), which is more suitable for cold coiling process. For the double-n state, the value of the strain hardening exponent(n) in the low-strain region of uniform plastic strain (n1) gradually decreased while the value of n in the high-strain region of uniform plastic strain (n2) gradually increased with tempering temperature increasing. It was attributed to the continuous decrease in initial dislocation density of matrix with tempering temperature increasing and the continuous increase in geometric necessary dislocations (GNDs) during cold deformation, which was significantly affected by the quantity, size, distribution and related microscopic characteristic parameters of carbides. The strengthening effect corresponding to the high-strain region is proportional to the value of n2 and the carbide particle size parameter (f/d).

Polyamine-producing bacterium Bacillus megaterium N3 reduced Cd accumulation in wheat and increased the expression of DNA repair- and plant hormone- related proteins in wheat roots

Metal-immobilizing bacteria play an important role in reducing the metal uptake of plants. However, little research has characterized the effects of polyamine-producing bacteria on the inhibition of Cd uptake in wheat. Herein, the effects of Bacillus megaterium N3 on wheat Cd uptake and the differentially expressed proteins in wheat roots were studied using hydroponic experiments. The results showed that under 3 mg L-1 Cd stress, strain N3 reduced the Cd content in wheat roots (33.59%) and leaves (82.83%) compared with no inoculation. Strain N3 significantly reduced (24.19%-31.02%) the proportion of Cd in the organelles and the soluble fraction and increased (74.91%) the proportion of Cd in the cell walls of wheat roots. Moreover, the contents of abscisic acid and polyamines in the wheat roots and leaves also increased (22.64%-372.8%) in the presence of strain N3 under 3 mg L-1 Cd. Label-free proteomics showed that 127 and 85 proteins were up- and downregulated in the N3+Cd treatment compared with the Cd treatment. The significantly enriched items were identified as a protein-DNA complex, DNA packaging complex, intercellular transport, peroxidase activity, and transferase activity. Moreover, the expression of DNA replication, plant hormone, and Fe-Zn transporter related proteins in wheat roots was increased in the presence of strain N3 compared with uninoculated roots under Cd stress. These results provide new insights and a theoretical basis for applying polyamine-producing bacteria to safe wheat production.

H2O2 mediates transcriptome reprogramming during Soybean mosaic virus-induced callose deposition in soybean

The main defense response to Soybean mosaic virus (SMV) infection in soybean [Glycine max (L.) Merr.] is thought to be blockage of intercellular virus transport by callose deposition on plasmodesmata. But the specific regulatory mechanism remains largely unknown. In this study, we found that hydrogen peroxide (H2O2) signal downstream of NO was associated with the regulation of callose accumulation. Abundant H2O2 was produced on the cell membrane and cell wall in the incompatible combination of soybean cultivar Jidou 7 and SMV strain N3, whereas no obvious H2O2 was observed in the compatible combination of Jidou 7 and strain SC-8. When H2O2 production was inhibited, callose accumulation induced by SMV infection decreased to a level insufficient to restrict virus transport in the incompatible combination. The H2O2-associated transcriptome dynamics of soybean during SMV infection was investigated. Transcriptome and functional analysis using virus-induced gene silencing showed that GmSEOB and GmPAP27, two genes regulated by H2O2, functioned in resistance by positively regulating the accumulation of callose in response to SMV infection. These results lay a foundation for further research on the signal transduction and molecular regulation of callose deposition during soybean resistance to SMV infection.

Functional Stability and Applicability of Heavy Metal Passivators in Reducing Cd Uptake by Lettuce

The use of heavy metal passivators to prevent vegetables from absorbing heavy metals is an important measure to control heavy metal-polluted vegetable fields and to ensure the safe production of vegetables. A pot experiment of planting three times in succession was conducted to study the effects of Bacillus megaterium N3 (N3), rice husk biochar (BC), sheep manure organic fertilizer (SM), strain N3 combined with biochar (BC+N3), and strain N3 combined with sheep manure (SM+N3) on Cd uptake and the functional stability of lettuce using a heavy metal passivator only at the first planting. The comprehensive applicability of the passivation materials was evaluated by the dynamic weighted comprehensive function. The results showed that when lettuce was planted for the first time, compared with the control, all the heavy metal passivators could significantly reduce (61.2%-81%) the Cd content in the edible part of the lettuce. However, in the third cultivation of lettuce, only SM+N3 could significantly reduce the Cd uptake by lettuce, which indicated that SM+N3 had the best functional stability. The dynamic weighted comprehensive function was used to evaluate the Cd content in the edible part of fresh lettuce, available Cd content in the soil, yield, and remediation cost. The results showed that the comprehensive applicability of SM+N3 was the best, followed by that of SM, BC+N3, and BC, and the comprehensive evaluation effect of strain N3 was the worst. The results of this study provide a theoretical basis and technical support for remediation of heavy metal-contaminated vegetable fields.

Phosphate-solubilizing bacterium Burkholderia sp. strain N3 facilitates the regulation of gene expression and improves tomato seedling growth under cadmium stress

Cadmium (Cd) is among the most toxic heavy metals in soils. The ways by which tomato plants inoculated with a phosphate-solubilizing bacterium (PSB) respond to Cd and regulate gene expression remain unclear. We investigated hormone metabolism and genes involved in Cd resistance in tomato seedlings inoculated with the PSB strain N3. Cd inhibited tomato plant growth and nutrient uptake and increase in dry weight. Compared with Cd treatment, N3 inoculation inhibited the accumulation of Cd in the shoots and roots, and the root dry weight significantly increased by 30.50% (P < 0.05). The nitrogen and potassium contents in the roots of seedlings treated with N3 increased, and the phosphorus levels were the same as those in the control. N3 decreased the rate of Zn2+ absorption but increased Fe3+ absorption in the roots, and the amount of accumulated Cd increased with Zn2+ uptake. The concentrations of hormones (indole-3-acetic acid, IAA; zeatin, ZEA; and jasmonic acid, JA) increased under Cd stress, whereas inoculation with N3 reduced IAA and ZEA levels. In the comparison between N3 + Cd and Cd treatments, the highest number of up- and downregulated genes was obtained. Pathways involved in signaling response, photosynthesis, phenylpropanoid biosynthesis, and DNA replication and the photosynthesis-antenna proteins pathway play important roles in the responses and adaptation of seedlings to Cd. Inoculation with N3 alleviates Cd stress in tomato seedlings. The present study provides new insights into the differentially expressed genes related to interaction between PSB and tomato exposed to Cd in soils.