Pseudostellaria heterophylla improves intestinal microecology through modulating gut microbiota and metabolites in mice.

BACKGROUND: Pseudostellaria heterophylla is a Chinese medicine and healthy edible that is widely used to for its immunomodulatory, antioxidant, antidiabetic and antitussive properties. However, the potential function of P. heterophylla in intestinal microecology remains unclear. In this study, we investigated the impact of P. heterophylla on immune functions and evaluated its potential to regulate the gut microbiota and metabolome. RESULTS: The results showed that P. heterophylla significantly increased the content of red blood cells, total antioxidant capacity and expression of immune factors, and decreased platelet counts when compared to the control under cyclophosphamide injury. In addition, P. heterophylla altered the diversity and composition of the gut bacterial community; increased the abundance of potentially beneficial Akkermansia, Roseburia, unclassified Clostridiaceae, Mucispirillum, Anaeroplasma and Parabacteroides; and decreased the relative abundance of pathogenic Cupriavidus and Staphylococcus in healthy mice. Metabolomic analyses showed that P. heterophylla significantly increased the content of functional oligosaccharides, common oligosaccharides, vitamins and functional substances. Probiotics and pathogens were regulated by metabolites across 11 pathways in the bacterial-host co-metabolism network. CONCLUSION: We demonstrated that P. heterophylla increased the abundance of probiotics and decreased pathogens, and further stimulated host microbes to produce beneficial secondary metabolites for host health. Our studies highlight the role of P. heterophylla in gut health and provide new insights for the development of traditional Chinese medicine in the diet. © 2024 Society of Chemical Industry.

Bio-fertilizer Amendment Alleviates the Replanting Disease under Consecutive Monoculture Regimes by Reshaping Leaf and Root Microbiome.

Replanting disease is a growing problem in intensive agricultural systems. Application of bio-fertilizer containing beneficial microbes contributes to disease suppression and is a promising strategy to control replanting disease. However, the effect of both replanting disease and bio-fertilizer amendment on the assembly of crop microbiota in leaves and roots and their relationships to crop yield and quality remains elusive. In these experiments, roots and leaves of Radix pseudostellariae were collected from different consecutive monoculture and bio-fertilizer amended fields, and the associated microbiota were characterized by bacterial 16S rRNA gene sequencing and quantitative PCR. Consecutive monoculture altered the bacterial community structure and composition and significantly increased the abundance of potential pathogenic Ralstonia and Fusarium oxysporum in leaves and roots. Furthermore, bio-fertilizer application alleviated replanting disease by decreasing the pathogen load, increasing the potential beneficial genera Pseudomonas, Streptomyces, Paenibacillus, and Bradyrhizobium. The proportion of positive correlations in the co-occurrence network of bio-fertilizer application was the highest, implying that bio-fertilizer potentially enhanced ecological commensalism or mutualism of the bacterial community across the two compartments. Structural equation models indicated that bio-fertilizer had a positive and indirect effect on both yield and quality by shaping the leaf microbiota and the root microbiota. Our findings highlight the role of leaf and root microbiota on replanting disease, showing that bio-fertilizer contributes to alleviating replanting disease by improving microbe-microbe interactions.

First Report of Mucor spp. Causing Root Rot of Radix pseudstellariae in Guizhou Province of China.

Radix pseudostellariae L. is one of the most common and highly-prized Chinese medicinal plants with various pharmacological effects, and mainly produced in acid soils in the Guizhou and Fujian provinces of southwestern and southeastern China, respectively (Wu et al. 2020). However, consecutive monoculture of R. pseudostellariae results in severe root rot and decline in biomass and quality of underground tubers. Root tubers of R. pseudostellariae are typically planted in December and harvested in next June. Root rot commonly starts developing in May. The disease incidence of root rot was ranging from 37 to 46% in root portions and basal stem of R. pseudostellariae under the consecutive monoculture fields in Shibing County, Guizhou Province, China (108°12'E, 27°03'N) (Li et al. 2017). Severe root rot was observed in Shibing County in May 2018. Infected plants displayed curly, withered, and yellow leaves, blight, retarded growth, root rot, and yield losses. Abundant whitish mycelia were observed on roots and surrounding soil. Two fungal isolates, designated GZ20190123 and GZ20190124, were obtained from symptomatic roots cultured on potato dextrose agar (PDA). The optimum temperature range for growth of the two isolates was 25 to 30°C. The optimum pH range for the growth of GZ20190123 was 5 to 5.5, whereas GZ20190124 grew better between pH 5 to 8.5. The mean mycelial growth rates of GZ20190123 and GZ20190124 at 30°C were 2.1 and 1.5 cm/day, respectively. Conidia of the two isolates were ovoid or obclavate and were produced in single or branched chains. The internal transcribed spacer (ITS) region was amplified with primers ITS1 and ITS4 (White et al. 1990). The sequences were deposited in GenBank as accession No. MN726736 for GZ20190123 and MN726738 for GZ20190124. Sequence comparison revealed 99% (GZ20190123) and 97% (GZ20190124) identity with previously reported isolate xsd08071 of Mucor racemosus Bull. (accession No. FJ582639.1) and isolate BM3 of Mucor fragilis Bainier (accession No. MK910058.1), respectively, which was confirmed by phylogenetic analysis. The two isolates were tested for pathogenicity on R. pseudostellariae. Six roots of R. pseudostellariae were surface-sterilized with 75% ethanol and stab inoculated with mycelia using a sterile toothpick for each isolate. Sterile distilled water was stab inoculated to twelve roots to serve as the control. Treated roots were incubated in a greenhouse with 16 h day length [light intensity 146.5 µmol/(m2·s)] and day/night temperature 26°C/18°C. The inoculated roots showed the expected symptoms on roots and sprouts 7 days after inoculation, whereas the control roots with sprouts did not show any symptom. The fungi were re-isolated from the diseased roots and confirmed as expected M. racemosus or M. fragilis based on the ITS sequences, which satisfied Koch's postulates. Thus, isolate GZ20190123 was identified as M. racemosus and GZ20190124 as M. fragilis. Previously, M. racemosus and M. fragilis have been reported as a pathogen on tomato (Kwon and Hong 2005) and grape (Ghuffar et al. 2018), respectively. To our knowledge, this is the first report of M. racemosus and M. fragilis causing root rot of R. pseudostellariae in southwestern China, where the disease could cause a significant loss to production of this important medicinal plant.

Modification of Rhizosphere Bacterial Community Structure and Functional Potentials to Control Pseudostellaria heterophylla Replant Disease.

Replant disease caused by negative plant-soil feedback commonly occurs in a Pseudostellaria heterophylla monoculture regime. Here, barcoded pyrosequencing of 16S ribosomal DNA amplicons combined with phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) analysis was applied to study the shifts in soil bacterial community structure and functional potentials in the rhizosphere of P. heterophylla under consecutive monoculture and different soil amendments (i.e., bio-organic fertilizer application [MF] and paddy-upland rotation [PR]). The results showed that the yield of tuberous roots decreased under P. heterophylla consecutive monoculture and then increased after MF and PR treatments, which was consistent with the changes in soil bacterial diversity. Both principal coordinate analysis and the unweighted pair-group method with arithmetic means cluster analysis showed the distinct difference in bacterial community structure between the consecutively monocultured soil (relatively unhealthy soil) and other relatively healthy soils (i.e., newly planted soil, MF, and PR). Furthermore, taxonomic analysis showed that consecutive monoculture of P. heterophylla significantly decreased the relative abundances of the families Burkholderiaceae and Acidobacteriaceae (subgroup 1), whereas it increased the population density of families Xanthomonadaceae, Phyllobacteriaceae, Sphingobacteriaceae, and Alcaligenaceae, and Fusarium oxysporum. In contrast, the MF and PR treatments recovered the soil microbiome and decreased F. oxysporum abundance through the different ways; for example, the introduction of beneficial microorganisms (in MF) or the switching between anaerobic and aerobic conditions (in PR). In addition, PICRUSt analysis revealed the higher abundances of membrane transport, cell motility, and DNA repair in the consecutively monocultured soil, which might contribute to the root colonization and survival for certain bacterial pathogens under monoculture. These findings highlight the close association between replant disease of P. heterophylla and the variations in structure and potential functions of rhizosphere bacterial community.

Rhizosphere Fungal Community Dynamics Associated with Rehmannia glutinosa Replant Disease in a Consecutive Monoculture Regime.

Consecutive monoculture of Rehmannia glutinosa in the same field leads to a severe decline in both quality and yield of tuberous roots, the most useful part in traditional Chinese medicine. Fungi are an important and diverse group of microorganisms in the soil ecosystem and play crucial roles in soil health. In this study, high-throughput pyrosequencing of internal transcribed spacer 2 ribosomal DNA amplicons was applied to gain insight into how consecutive monoculture practice influence and stimulate R. glutinosa rhizosphere and bulk soil fungal communities. The results from nonmetric multidimensional scaling ordination and clustering analysis revealed distinctive differences between rhizosphere and bulk soil fungal communities. However, longer-term monocultured bulk soils were more similar to the rhizosphere soils in comparison with the shorter-term monocultured bulk soils. Moreover, consecutive monoculture caused a gradual shift in the composition and structure of the soil fungal community. The cultivation of this plant led to the appearance of some exclusive operational taxonomic units in rhizosphere or bulk soils that were assigned to the genera Fusarium, Rhizoctonia, and so on. Furthermore, the sum of the relative abundance of species of Fusarium, Cylindrocarpon, and Gibberella (belonging to the family Nectriaceae); Rhizoctonia, Thanatephorus, and Ceratobasidium (belonging to the family Ceratobasidiaceae); and Lectera and Plectosporium (belonging to the family Plectosphaerellaceae) was significantly higher in consecutively monocultured (CM) than in newly planted (NP) soil in both rhizosphere and bulk soils. In particular, Fusarium abundance was significantly higher in CM than in NP in the rhizosphere, and higher in rhizosphere soils than in bulk soils for each treatment. A pathogenicity test showed that both Fusarium strains isolated were pathogenic to R. glutinosa seedlings. In addition, the culture filtrate and mycotoxins produced by Fusarium oxysporum significantly repressed the growth of the antagonistic bacterium, Pseudomonas aeruginosa. In conclusion, consecutive monoculture of R. glutinosa restructured the fungal communities in both rhizosphere and bulk soils but bulk effects developed more slowly over time in comparison with rhizosphere effects. Furthermore, microbial interactions might lead to a reduction in the abundance of beneficial microbes.

Comparative Metagenomic Analysis of Rhizosphere Microbial Community Composition and Functional Potentials under Rehmannia glutinosa Consecutive Monoculture.

Consecutive monoculture of Rehmannia glutinosa, highly valued in traditional Chinese medicine, leads to a severe decline in both quality and yield. Rhizosphere microbiome was reported to be closely associated with the soil health and plant performance. In this study, comparative metagenomics was applied to investigate the shifts in rhizosphere microbial structures and functional potentials under consecutive monoculture. The results showed R. glutinosa monoculture significantly decreased the relative abundances of Pseudomonadaceae and Burkholderiaceae, but significantly increased the relative abundances of Sphingomonadaceae and Streptomycetaceae. Moreover, the abundances of genera Pseudomonas, Azotobacter, Burkholderia, and Lysobacter, among others, were significantly lower in two-year monocultured soil than in one-year cultured soil. For potentially harmful/indicator microorganisms, the percentages of reads categorized to defense mechanisms (i.e., ATP-binding cassette (ABC) transporters, efflux transporter, antibiotic resistance) and biological metabolism (i.e., lipid transport and metabolism, secondary metabolites biosynthesis, transport and catabolism, nucleotide transport and metabolism, transcription) were significantly higher in two-year monocultured soil than in one-year cultured soil, but the opposite was true for potentially beneficial microorganisms, which might disrupt the equilibrium between beneficial and harmful microbes. Collectively, our results provide important insights into the shifts in genomic diversity and functional potentials of rhizosphere microbiome in response to R. glutinosa consecutive monoculture.

Barcoded Pyrosequencing Reveals a Shift in the Bacterial Community in the Rhizosphere and Rhizoplane of Rehmannia glutinosa under Consecutive Monoculture.

The production and quality of Rehmannia glutinosa can be dramatically reduced by replant disease under consecutive monoculture. The root-associated microbiome, also known as the second genome of the plant, was investigated to understand its impact on plant health. Culture-dependent and culture-independent pyrosequencing analysis was applied to assess the shifts in soil bacterial communities in the rhizosphere and rhizoplane under consecutive monoculture. The results show that the root-associated microbiome (including rhizosphere and rhizoplane microbiomes) was significantly impacted by rhizocompartments and consecutive monoculture. Consecutive monoculture of R. glutinosa led to a significant decline in the relative abundance of the phyla Firmicutes and Actinobacteria in the rhizosphere and rhizoplane. Furthermore, the families Flavobacteriaceae, Sphingomonadaceae, and Xanthomonadaceae enriched while Pseudomonadaceae, Bacillaceae, and Micrococcaceae decreased under consecutive monoculture. At the genus level, Pseudomonas, Bacillus, and Arthrobacter were prevalent in the newly planted soil, which decreased in consecutive monocultured soils. Besides, culture-dependent analysis confirmed the widespread presence of Pseudomonas spp. and Bacillus spp. in newly planted soil and their strong antagonistic activities against fungal pathogens. In conclusion, R. glutinosa monoculture resulted in distinct root-associated microbiome variation with a reduction in the abundance of beneficial microbes, which might contribute to the declined soil suppressiveness to fungal pathogens in the monoculture regime.

Transcriptome analysis of Pseudostellaria heterophylla in response to the infection of pathogenic Fusarium oxysporum.

BACKGROUND: Pseudostellaria heterophylla (P. heterophylla), a herbaceous perennial, belongs to Caryophyllaceae family and is one of the Chinese herbal medicine with high pharmacodynamic value. It can be used to treat the spleen deficiency, anorexia, weakness after illness and spontaneous perspiration symptoms. Our previous study found that consecutive monoculture of Pseudostellaria heterophylla could lead to the deterioration of the rhizosphere microenvironment. The specialized forms of pathogenic fungus Fusarium oxysporum f.Sp. heterophylla (F. oxysporum) in rhizosphere soils of P. heterophylla plays an important role in the consecutive monoculture of P. heterophylla. RESULTS: In this study, F. oxysporum was used to infect the tissue culture plantlets of P. heterophylla to study the responding process at three different infection stages by using RNA-sequencing. We obtained 127,725 transcripts and 47,655 distinct unigenes by de novo assembly and obtained annotated information in details for 25,882 unigenes. The Kyoto Encyclopedia of Genes and Genomes pathway analysis and the real-time quantitative PCR results suggest that the calcium signal system and WRKY transcription factor in the plant-pathogen interaction pathway may play an important role in the response process, and all of the WRKY transcription factor genes were divided into three different types. Moreover, we also found that the stimulation of F. oxysporum may result in the accumulation of some phenolics in the plantlets and the programmed cell death of the plantlets. CONCLUSIONS: This study has partly revealed the possible molecular mechanism of the population explosion of F. oxysporum in rhizosphere soils and signal response process, which can be helpful in unraveling the role of F. oxysporum in consecutive monoculture problems of P. heterophylla.

Gold(I)-catalyzed dearomative Rautenstrauch rearrangement: enantioselective access to cyclopenta[b]indoles.

A highly enantioselective dearomative Rautenstrauch rearrangement catalyzed by cationic (S)-DTBM-Segphosgold(I) is reported. This reaction provides a straightforward method to prepare enantioenriched cyclopenta[b]indoles. These studies show vast difference in enantioselectivity in the reactions of propargyl acetates and propargyl acetals in the chiral ligand-controlled Rautenstrauch reaction.

[Analysis of heavy metals monitoring results in food in Shaoxing in 2014].

OBJECTIVE: To investigate heavy metals contamination level in food in Shaoxing, and to provide basis evidence for supervising heavy metals pollution in food and environmental pollution control in Shaoxing. METHODS: Food samples in 2014 were detected for lead, cadmium, mercury, arsenic, nickel, copper and chromium by national standard methods, and the results were evaluated by GB 2762-2012 Pollutants limits in food. RESULTS: 1384 samples from 10 food categories were collected and tested for lead, cadmium, mercury and arsenic, the over standard rates were 2.0%, 3.0%, 1.5% and 0.22%, respectively, the median were 0.019, 0.0085, 0.0024 and 0.015 mg/kg, respectively; 273 samples were collected and tested for nickel, the detection rate was 48.4%, the median was 0.010 mg/kg; 255 samples were collected and tested for chromium, the detection rate was 14.9%, the median was 0.0050 mg/kg; 486 samples were collected and tested for copper, the detection rate was 94.0%, the median was 1.34 mg/kg. The heavy metals over standard rate of aquatic products, animal internal organs and grain were relatively high, 16.9%, 7.9% and 7.3% cadmium in swimming crabs exceeded standard seriously, the over standard rate was 38.9%. CONCLUSION: The overall pollution of heavy metals in food are not high in Shaoxing in 2014, but some food (aquatic products, animal internal organs and grain) pollution are relatively outstanding, and have the over standard problems of lead, cadmium, mercury and arsenic.

Gold(I)-Catalyzed Desymmetrization of 1,4-Dienes by an Enantioselective Tandem Alkoxylation/Claisen Rearrangement.

An enantioselective alkoxylation/Claisen rearrangement reaction was achieved by a strategic desymmetrization of 1,4-dienes under the catalysis of (S)-DTBM-Segphos(AuCl)2/AgBF4. This reaction system was highly selective for the formation of 3,3-rearrangement products, providing cycloheptenes with various substitutions in good yield and good to excellent enantioselectivity. This transformation was further extended to bicyclic ring substrates, providing the opportunity to easily assemble 5,6- and 6,7-fused ring systems.

Effects of 13C isotope-labeled allelochemicals on the growth of the invasive plant Alternanthera philoxeroides.

The secondary metabolites of indigenous plants have significant allelopathic inhibitory effects on the growth and development of invasive alien plants. Methyl palmitate (MP) and methyl linolenate (ML) were used as exogenous allelopathic substances. The research investigated the differences of inhibitory effects of MP and ML on the growth of seedlings of Alternanthera philoxeroides, and calculated their morphological characteristics, biomass, physiological indicators and the response index (RI). The synthetical allelopathic index (SE) of 1 mmol/L MP was the smallest (- 0.26) and the allelopathic inhibition was the strongest; therefore, it was selected as a 13C-labeled allelochemical. The distribution of 1 mmol/L MP in different parts of A. philoxeroides and the correlation between the biomass ratios of roots, stems and leaves and the 13C content were studied by 13C stable isotope tracing experiments. Atom percent excess (APE) between roots, stems and leaves of A. philoxeroides treated with 1 mmol/L MP were significantly different in terms of magnitude, with leaves (0.17%) > roots (0.12%) > stems (0.07%). The root, stem and leaf biomass ratios of invasive weeds had great significant positive correlation with 13C content (p < 0.01, R2 between 0.96 and 0.99). This current research provides a new idea and method for the control of A. philoxeroides, but large-scale popularization remains to be studied.

Revealing Microbiome Structure and Assembly Process in Three Rhizocompartments of Achyranthes bidentata Under Continuous Monoculture Regimes.

The complex composition and interaction of root-associated microbes are critical to plant health and performance. In this study, we presented a detailed characterization of three rhizocompartment (rhizosphere, rhizoplane, and root) microbiomes of Achyranthes bidentata under different years of consecutive monoculture by deep sequencing in order to determine keystone microorganisms via co-occurrence network analysis. The network analysis showed that multiple consecutive monoculture (MCM, represented 5Y and 10Y) soils generated some distinct beneficial bacterial taxa such as Bacillus, Fictibacillus, Bradyrhizobium, Shinella, and Herbaspirillum. For fungi, Mortierella substituted for Fusarium in occupying an important position in different rhizocompartments under A. bidentate monoculture. Quantitative PCR analysis confirmed a significant increase in Bacillus, Pseudomonas, and Burkholderia spp. The results of the inoculation assay showed that addition of beneficial bacteria Bacillus subtilis 74 and Bacillus halodurans 75 significantly increased the root length and fresh weight of A. bidentata. Furthermore, three types of phytosterones, as the main allochemicals, were identified both in the rhizosphere soil and in culture medium under sterile conditions by LC-MS/MS. When looking at in vitro interactions, it was found that phytosterones displayed a positive interaction with dominant beneficial species (Bacillus amyloliquefaciens 4 and B. halodurans 75) and had a negative effect on the presence of the pathogenic fungi Fusarium solani and Fusarium oxysporum. Overall, this study demonstrated that consecutive monoculture of A. bidentata can alter the bacterial and fungal community by secreting root exudates, leading to recruitment of beneficial microbes and replacement of plant-specific pathogenic fungi with plant beneficial fungi.

Effects of different technical substitutions on reducing replant disease of Radix pseudostella-riae and the underlying mechanism.

Radix pseudostellariae is a traditional Chinese medicinical herb, with tuberous roots being used as a medicine. Serious continuous monoculture problems were suffered from process of artificial and intensive cultivation. To explore the effective technical methods to overcome the monoculture problems, the effects of different technical substitution patterns on soil environment remediation, photosynthetic physiology and yield performance of R. pseudostellariae were assessed under continuous cropping system with four technical substitution treatments in the phase between two crops after the newly harvested R. pseudostellariae (first crop): fallow (RP-F-RP), fallow treated with microbial fertilizer (RP-F-BF), water flooding (RP-WF), and water flooding treated with specific microbial fertilizer (RP-WF-BF). Results showed that RP-WF-BF pattern was the single one that could effectively restore R. pseudostellariae yield under two-year monoculture and three-year monoculture to more than 90% and 70% of the newly planted respectively. All the other patterns did not significantly improve R. pseudostellariae yield under two-year monoculture. The contents of polysaccharide and total saponin in R. pseudostellariae under RP-WF-BF treatment were significantly increased by 15.3% and 16.5% compared with those of the newly planted, respectively. The abundance of beneficial microorganisms in the rhizosphere soil of R. pseudostellariae significantly increased. A reverse pattern occurred for pathogens under RP-WF-BF pattern. Moreover, soil nitrogen cycling was improved. The expression of AOB, nosZ and nirK was increased by 931%, 124% and 100% compared with those in the RP-F-RP pattern, respectively. Soil acidification under RP-WF-BF pattern was alleviated. The alleviation of soil biological and abiotic stress enhanced the stability of the antioxidant enzyme system, thereby improving the growth and development of R. pseudostellariae at the seedling and the early expand stages. The chlorophyll content, leaf area index and photosynthesis rate of leaves were increased, with the dry matter translocation improved and accumulation of underground dry matter accelerated, which ultimately increased yield and quality under RP-WF-BF pattern. In this study, the separate water flooding treatment (RP-WF) and microbial fertilizer treatment (RP-F-BF) failed to significantly reduce the continuous cropping obstacles of R. pseudostellariae, while the combination of them could produce a multiplication effect of sustainable strengthening on rhizosphere environment. The findings suggested that effective technical substitution could reduce replant disease of R. pseudostellariae.

Antagonistic Activity of Trichoderma spp. Against Fusarium oxysporum in Rhizosphere of Radix pseudostellariae Triggers the Expression of Host Defense Genes and Improves Its Growth Under Long-Term Monoculture System.

Under consecutive monoculture, the abundance of pathogenic fungi, such as Fusarium oxysporum in the rhizosphere of Radix pseudostellariae, negatively affects the yield and quality of the plant. Therefore, it is pertinent to explore the role of antagonistic fungi for the management of fungal pathogens such as F. oxysporum. Our PCR-denatured gradient gel electrophoresis (DGGE) results revealed that the diversity of Trichoderma spp. was significantly declined due to extended monoculture. Similarly, quantitative PCR analysis showed a decline in Trichoderma spp., whereas a significant increase was observed in F. oxysporum. Furthermore, seven Trichoderma isolates from the R. pseudostellariae rhizosphere were identified and evaluated in vitro for their potentiality to antagonize F. oxysporum. The highest and lowest percentage of inhibition (PI) observed among these isolates were 47.91 and 16.67%, respectively. In in vivo assays, the R. pseudostellariae treated with four Trichoderma isolates, having PI > 30%, was used to evaluate the biocontrol efficiency against F. oxysporum in which T. harzianum ZC51 enhanced the growth of the plant without displaying any disease symptoms. Furthermore, the expression of eight defense-related genes of R. pseudostellariae in response to a combination of F. oxysporum and T. harzianum ZC51 treatment was checked, and most of these defense genes were found to be upregulated. In conclusion, this study reveals that the extended monoculture of R. pseudostellariae could alter the Trichoderma communities in the plant rhizosphere leading to relatively low level of antagonistic microorganisms. However, T. harzianum ZC51 could inhibit the pathogenic F. oxysporum and induce the expression of R. pseudostellariae defense genes. Hence, T. harzianum ZC51 improves the plant resistance and reduces the growth inhibitory effect of consecutive monoculture problem.

Stereospecific Electrophilic Fluorocyclization of α,ß-Unsaturated Amides with Selectfluor.

An efficient fluorocyclization of α,ß-unsaturated amides through a formal halocyclization process is developed. The reaction proceeds under transition-metal-free conditions and leads to the formation of fluorinated oxazolidine-2,4-diones with excellent regio- and diastereoselectivity. The evaluation of the reaction mechanism based on preliminary experiments and density functional theory calculations suggests that a synergetic syn-oxo-fluorination occurs and is followed by an anti-oxo substitution reaction. The reaction opens a new window in the field of stereospecific fluorofunctionalization.

Underlying Mechanism of Wild Radix pseudostellariae in Tolerance to Disease Under the Natural Forest Cover.

Replanting disease caused by negative plant-soil feedback in continuous monoculture of Radix pseudostellariae is a critical factor restricting the development of this common and popular Chinese medicine, although wild R. pseudostellariae plants were shown to grow well without occurrence of disease in the same site for multiple years. Therefore, we aimed to identify the changes in microbial community composition in the rhizosphere soil of wild R. pseudostellariae thus providing a potential method for controlling soil-borne diseases. We analyzed differences in soil physicochemical properties, changes in soil microbial community structure, and root exudates of wild R. pseudostellariae under different biotopes. And then, simple sequence repeats amplification was used to isolate and collect significantly different formae speciales of Fusarium oxysporum. Finally, we analyzed the pathogenicity testing and influence of root exudates on the growth of F. oxysporum. We found that the different biotopes of R. pseudostellariae had significant effects on the soil microbial diversity. The soil fungal and bacterial abundances were significantly higher and the abundance of F. oxysporum was significantly lower under the rhizosphere environment of wild R. pseudostellariae than under consecutive monoculture. The relative abundances of most genera were Penicillium, Aspergillus, Fusarium, Nitrobacter, Nitrospira, Streptomyces, Actinoplanes, and Pseudomonas. Venn diagram and LEfSe analyses indicated numerously specific microbiome across all the samples, and the numbers of specific fungi were higher than the shared ones in the four biotopes. Eight types of phenolic acids were identified across all the rhizosphere soils. Mixed phenolic acids and most of the examined single phenolic acids had negative effects on the growth of isolated pathogenic F. oxysporum strains and promoted the growth of non-pathogenic strains. Similarly, correlation analysis suggested that most of the identified phenolic acids were positively associated with beneficial Pseudomonas, Nitrobacter, Nitrospira, Streptomyces, and Bacillus. This study suggested that wild R. pseudostellariae was able to resist or tolerate disease by increasing soil microbial diversity, and reducing the accumulation of soil-borne pathogens.

Linking Short-Chain N-Acyl Homoserine Lactone-Mediated Quorum Sensing and Replant Disease: A Case Study of Rehmannia glutinosa.

Rehmannia glutinosa, a perennial medicinal plant, suffers from severe replant disease under consecutive monoculture. The rhizosphere microbiome is vital for soil suppressiveness to diseases and for plant health. Moreover, N-acyl homoserine lactone (AHL)-mediated quorum sensing (QS) regulates diverse behavior in rhizosphere-inhabiting and plant pathogenic bacteria. The dynamics of short-chain AHL-mediated QS bacteria driven by consecutive monoculture and its relationships with R. glutinosa replant disease were explored in this study. The screening of QS bacteria showed that 65 out of 200 strains (32.5%) randomly selected from newly planted soil of R. glutinosa were detected as QS bacteria, mainly consisting of Pseudomonas spp. (55.4%). By contrast, 34 out of 200 (17%) strains from the diseased replant soil were detected as QS bacteria, mainly consisting of Enterobacteriaceae (73.5%). Functional analysis showed most of the QS bacteria belonging to the Pseudomonas genus showed strong antagonistic activities against Fusarium oxysporum or Aspergillus flavus, two main causal agents of R. glutinosa root rot disease. However, the QS strains dominant in the replant soil caused severe wilt disease in the tissue culture seedlings of R. glutinosa. Microbial growth assays demonstrated a concentration-dependent inhibitory effect on the growth of beneficial QS bacteria (i.e., Pseudomonas brassicacearum) by a phenolic acid mixture identified in the root exudates of R. glutinosa, but the opposite was true for harmful QS bacteria (i.e., Enterobacter spp.). Furthermore, it was found that the population of quorum quenching (QQ) bacteria that could disrupt the beneficial P. brassicacearum SZ50 QS system was significantly higher in the replant soil than in the newly planted soil. Most of these QQ bacteria in the replant soil were detected as Acinetobacter spp. The growth of specific QQ bacteria could be promoted by a phenolic acid mixture at a ratio similar to that found in the R. glutinosa rhizosphere. Moreover, these quorum-quenching bacteria showed strong pathogenicity toward the tissue culture seedlings of R. glutinosa. In conclusion, consecutive monoculture of R. glutinosa contributed to the imbalance between beneficial and harmful short-chain AHL-mediated QS bacteria in the rhizosphere, which was mediated not only by specific root exudates but also by the QQ bacterial community.

Biochar mediates microbial communities and their metabolic characteristics under continuous monoculture.

Biochar amendment has been extensively used to improve plant performance and suppress disease in monoculture systems; however, few studies have focused on the underlying control mechanisms of replanting disease. In this study, we assessed the effects of biochar application on Radix pseudostellariae plant growth, rhizosphere soil microbial communities, and the physiological properties of microorganisms in a consecutive monoculture system. We found that biochar addition had little impact on the physiological parameters of tissue cultures of R. pseudostellaria but did significantly mediate microbial abundance in the rhizosphere soil of different consecutive monoculture years, leading to decreases in the abundance of pathogenic Fusarium oxysporum, Talaromyces helicus, and Kosakonia sacchari. Furthermore, biochar amendment had negative effects on the growth of beneficial bacteria, such as Burkholderia ambifaria, Pseudomonas chlororaphis, and Bacillus pumilus. Metabolomic analysis indicated that biochar significantly influenced the metabolic processes of F. oxysporum while inhibiting the mycelial growth and abating the virulence on plants. In summary, this study details the potential mechanisms responsible for the biochar-stimulated changes in the abundances and metabolism of rhizosphere bacteria and fungi, decreases in the contents of pathogens, and therefore improvements in the environmental conditions for plants growth. Further research is needed to evaluate the effects of biochar in long-term field trials.

The effects of chemical and organic fertilizer usage on rhizosphere soil in tea orchards.

Sustainable agriculture is an important global issue. The use of organic fertilizers can enhance crop yield and soil properties while restraining pests and diseases. The objective of this study was to assess the effects of long-term use of chemical and organic fertilizers on tea and rhizosphere soil properties in tea orchards. Inductively coupled plasma mass spectrometry (ICP-MS) and high-throughput sequencing technology analyses were used to investigate heavy metals content and bacterial composition in rhizosphere soils. Our results indicated that organic fertilizer treatment significantly decreased Cu, Pb and Cd contents in rhizosphere soil sample. The results also showed that treatment with organic fertilizer significantly decreased the contents of Cd, Pb and As in tea leaves. Furthermore, organic fertilizer significantly increased the amino acids content of tea and the pH of the soil. The use of organic fertilizer significantly increased in the relative abundance of Burkholderiales, Myxococcales, Streptomycetales, Nitrospirales, Ktedonobacterales, Acidobacteriales, Gemmatimonadales, and Solibacterales, and decreased the abundance of Pseudonocardiales, Frankiales, Rhizobiales, and Xanthomonadales. In conclusion, organic fertilizer can help to shape the microbial composition and recruit beneficial bacteria into the rhizosphere of tea, leading to improved tea quality and reduced heavy metals content in rhizosphere soil and tea leaves.