Selected Aspects of Invasive Solidago canadensis with an Emphasis on Its Allelopathic Abilities: A Review.

Solidago canadensis L., native to North America, is now an invasive plant worldwide. Its abundant seeds, rapid vegetative reproduction ability, and allelopathy to other plants are the main reasons for its successful invasion. It has negative impacts on the ecological environment of the invaded area and causes a reduction in local biodiversity and economic losses of agriculture and stock farming. Each part of the plant contains a variety of allelochemicals (terpenoids, phenolics, and flavonoids), including a large number of essential oil components. These allelochemicals can be released in various ways to inhibit the growth of adjacent plants and promote their invasion; they can also affect soil properties and soil microorganisms. This article summarizes the allelopathic effects of S. canadensis on other plant species and the interaction mechanism between it and the ecosystem.

Distinctive pattern and mechanism of precipitation changes affecting soil microbial assemblages in the Eurasian steppe.

Precipitation may increase or decrease by different intensities, but the pattern and mechanism of soil microbial community assembly under various precipitation changes remain relatively underexplored. Here, although ±30% precipitation caused a small decrease (∼19%) in the within-treatment taxonomic compositional dissimilarity through the deterministic competitive exclusion process in a steppe ecosystem, ±60% precipitation caused a large increase (∼35%) in the dissimilarity through the stochastic ecological drift process (random birth/death), which was in contrast with the traditional thought that increasing the magnitude of environmental changes (e.g., from +30% to +60%) would elevate the importance of deterministic relative to stochastic processes. The increased taxonomic dissimilarity/stochasticity under ±60% precipitation translated into functional dissimilarity/stochasticity at the gene, protein, and enzyme levels. Overall, our results revealed the distinctive pattern and mechanism of precipitation changes affecting soil microbial community assembly and demonstrated the need to integrate microbial taxonomic information to better predict their functional responses to precipitation changes.

Phthalic Acid Esters: Natural Sources and Biological Activities.

Phthalic acid esters (PAEs) are a class of lipophilic chemicals widely used as plasticizers and additives to improve various products' mechanical extensibility and flexibility. At present, synthesized PAEs, which are considered to cause potential hazards to ecosystem functioning and public health, have been easily detected in the atmosphere, water, soil, and sediments; PAEs are also frequently discovered in plant and microorganism sources, suggesting the possibility that they might be biosynthesized in nature. In this review, we summarize that PAEs have not only been identified in the organic solvent extracts, root exudates, and essential oils of a large number of different plant species, but also isolated and purified from various algae, bacteria, and fungi. Dominant PAEs identified from natural sources generally include di-n-butyl phthalate, diethyl phthalate, dimethyl phthalate, di(2-ethylhexyl) phthalate, diisobutyl phthalate, diisooctyl phthalate, etc. Further studies reveal that PAEs can be biosynthesized by at least several algae. PAEs are reported to possess allelopathic, antimicrobial, insecticidal, and other biological activities, which might enhance the competitiveness of plants, algae, and microorganisms to better accommodate biotic and abiotic stress. These findings suggest that PAEs should not be treated solely as a "human-made pollutant" simply because they have been extensively synthesized and utilized; on the other hand, synthesized PAEs entering the ecosystem might disrupt the metabolic process of certain plant, algal, and microbial communities. Therefore, further studies are required to elucidate the relevant mechanisms and ecological consequences.

Metabolomics Reveals the Allelopathic Potential of the Invasive Plant Eupatorium adenophorum.

Phytotoxic chemicals produced by alien invasive plants exert inhibitory effects on native species to facilitate their invasiveness. The allelopathic process of invaders has been hypothesized as the "Novel Weapon Hypothesis". However, this hypothesis has been controversial for decades due to lack of molecular evidence, and the underlying mechanism of allelopathy still remains ambiguous. Herein, we explore the allelopathic mechanisms of Eupatorium adenophorum, a world-widely spread noxious weed, by the methods of laboratory bioassay and metabolomics analyses in the recipient plant, Arabidopsis thaliana. The bioassay revealed significant phytotoxicity of E. adenophorum extracts. A total of 234 metabolites in A. thaliana were detected by Gas Chromatographic-Mass Spectrometric analysis. There were 48, 99 and 94 impacted metabolites in A. thaliana treated by 50, 25 and 12.5% aqueous extracts compared to control. When mapping all the impacted metabolites to the biological pathways in the KEGG (Kyoto Encyclopedia of Genes and Genomes) database, we found mineral absorption, ABC transporters, amino acid biosynthesis, metabolic pathways and biosynthesis of plant secondary metabolites were mainly impacted. Synthesized with partial least-squares discriminate analysis (PLS-DA) results of metabolic profiles in A. thaliana, we found that citrate cycle was suppressed, metabolism of amino acids was disordered and phosphate absorption was inhibited. Subsequent investigation demonstrated that the phosphorus content in A. thaliana tissues exposed in allelopathic extracts was much lower, indicating inhibition of phosphate uptake. Our study revealed by metabolomics approaches that E. adenophorum is an allelopathic species.

Chemical Profile and Phytotoxic Action of Hibiscus trionum Essential Oil.

The chemical profile and phytotoxic action of Hibiscus trionum essential oil (EO) was studied. In total 17 compounds were identified via GC/MS, representing 94.18 % of the entire oil, with phytol (40.37 %) being the dominant constituent. Bioassay revealed that the EO inhibited root elongation of Medicago sativa and Amaranthus retroflexus by 32.66 % and 61.86 % at 5 mg/mL, respectively; meanwhile, the major component phytol also exhibited significant phytotoxic activity, suppressing radical elongation of Pennisetum alopecuroides, M. sativa and A. retroflexus by 26.08 %, 27.55 % and 43.96 % at 1 mg/mL, respectively. The fact that the EO showed weaker activity than phytol implied that some constituents might trigger antagonistic action to decrease the oil's activity. Our study is the first on the chemical profile and phytotoxic effect of H. trionum EO.

Mining genes associated with furanocoumarin biosynthesis in an endangered medicinal plant, Glehnia littoralis.

The endangered medicinal plant Glehnia littoralis is one of the important natural source of furanocoumarin, which has been used as mucolytic, antitussive, antitumour and antibacterial. However, the genetic information of furanocoumarin biosynthesis in G. littoralis is scarce at present. The objective of this study was to mine the putative candidate genes involved in the biosynthesis pathwayof furanocoumarin and provide references for gene identification, and functional genomics of G. littoralis. We carried out the transcriptome analysis of leaves and roots in G. littoralis, which provided a dataset for gene mining. Psoralen, imperatorin and isoimperatorin were detected in G. littoralis by high performance liquid chromatography analysis. Candidate key genes were mined based on the annotations and local BLAST with homologous sequences using BioEdit software. The relative expression of genes was analysed using quantitative real-time polymerase chain reaction. Further, the CYP450 genes were mined using phylogenetic analyses using MEGA 6.0 software. Atotal of 156,949 unigenes were generated, of which 9021 were differentially-expressed between leaves and roots. A total of 82 unigenes encoding eight enzymes in furanocoumarin biosynthetic pathway were first obtained. Seven genes that encoded key enzymes in the downstream furanocoumarin biosynthetic pathway and expressed more in roots than leaves were screened. Twenty-six candidate CYP450 unigenes expressed abundantly in roots and were chiefly concentrated in CYP71, CYP85 and CYP72 clans. Finally, we filtered 102 differentially expressed transcription factors (TFs) unigenes. The transcriptome of G. littoralis was characterized which would help to elucidate the furanocoumarin biosynthetic pathway in G. littoralis and provide an invaluable resource for further study of furanocoumarin.

Hybrid Sequencing of Full-Length cDNA Transcripts of the Medicinal Plant Scutellaria baicalensis.

Scutellaria baicalensis is a well-known medicinal plant that produces biologically active flavonoids, such as baicalin, baicalein, and wogonin. Pharmacological studies have shown that these compounds have anti-inflammatory, anti-bacterial, and anti-cancer activities. Therefore, it is of great significance to investigate the genetic information of S. baicalensis, particularly the genes related to the biosynthetic pathways of these compounds. Here, we constructed the full-length transcriptome of S. baicalensis using a hybrid sequencing strategy and acquired 338,136 full-length sequences, accounting for 93.3% of the total reads. After the removal of redundancy and correction with Illumina short reads, 75,785 nonredundant transcripts were generated, among which approximately 98% were annotated with significant hits in the protein databases, and 11,135 sequences were classified as lncRNAs. Differentially expressed gene (DEG) analysis showed that most of the genes related to flavonoid biosynthesis were highly expressed in the roots, consistent with previous reports that the flavonoids were mainly synthesized and accumulated in the roots of S. baicalensis. By constructing unique transcription models, a total of 44,071 alternative splicing (AS) events were identified, with intron retention (IR) accounting for the highest proportion (44.5%). A total of 94 AS events were present in five key genes related to flavonoid biosynthesis, suggesting that AS may play important roles in the regulation of flavonoid biosynthesis in S. baicalensis. This study provided a large number of highly accurate full-length transcripts, which represents a valuable genetic resource for further research of the molecular biology of S. baicalensis, such as the development, breeding, and biosynthesis of active ingredients.

Authentication of commercial processed Glehniae Radix (Beishashen) by DNA barcodes.

BACKGROUND: The radix of Glehnia littoralis Fr. Schmidt ex Miq. (Beishashen), is often misidentified and adultered in Chinese medicine. Its seven common adulterants include Chuanminshen violaceum Sheh et Shan (Chuanmingshen), Changium smyrnioides Wolff (Mingdangshen), Sphallerocarpus gracilis (Bess.) K.-Pol. (Miguoqin), Adenophora polyantha Nakai (Shishashen), Silene tatarinowii Regel (Shishengyingzicao), Adenophora tetraphylla (Thunb.) Fisch (Lunyeshashen) and Adenophora stricta Miq. (Shashen). This study aims to evaluate the feasibility of the second internal transcribed spacer (ITS2) DNA barcoding to discriminate between Glehniae Radix and its common adulterants. METHODS: In this study, we collected 46 samples of G. littoralis and 59 samples of its seven common adulterants. Genomic DNA sequences were extracted from samples, including original plants and commercially processed crude drugs. The ITS2 of the ribosomal DNA sequences were amplified and sequenced bi-directionally. The sequences were assembled by CodonCode Aligner 3.5.7. The descriptive data analysis was conducted and neighbor-joining (NJ) phylogenetic tree was constructed by MEGA 5.0 in accordance with the kimura 2 -parameter (K2P) model. The identification efficiency was evaluated based on the BLAST1 methods. The ITS2 secondary structures were predicted and compared between Glehniae Radix and its adulterants by the ITS2 database. RESULTS: As the 46 ITS2 sequences of G. littoralis were identical to each other, the identification efficiency of the ITS2 region was 100 %. A NJ tree based on the ITS2 sequences, and the predicted secondary structures of ITS2, distinguished Glehniae Radix from its adulterants. CONCLUSION: DNA barcoding based on ITS2 distinguished commercial processed Glehniae Radix from common herbal adulterants.

Water content differences have stronger effects than plant functional groups on soil bacteria in a steppe ecosystem.

Many investigations across natural and artificial plant diversity gradients have reported that both soil physicochemical factors and plant community composition affect soil microbial communities. To test the effect of plant diversity loss on soil bacterial communities, we conducted a five-year plant functional group removal experiment in a steppe ecosystem in Inner Mongolia (China). We found that the number and composition type of plant functional groups had no effect on bacterial diversity and community composition, or on the relative abundance of major taxa. In contrast, bacterial community patterns were significantly structured by soil water content differences among plots. Our results support researches that suggest that water availability is the key factor structuring soil bacterial communities in this semi-arid ecosystem.

Use of the psbA-trnH region to authenticate medicinal species of Fabaceae.

Fabaceae is a huge family that contains a large number of medicinal plants, many of which are commonly used in Chinese traditional medicine. However, traditional taxonomy has not been able to meet the complicated demands of species discrimination within Fabaceae. Thus, we employed a famous DNA barcode, the psbA-trnH region, to discriminate commonly used medicinal species of the family Fabaceae. Here, the psbA-trnH regions derived from 152 samples were amplified. These samples represented 104 Fabaceae medicinal species from 60 genera, including 25 authentic Fabaceae species listed in the Chinese pharmacopoeia and common adulterant species. The results indicate that the psbA-trnH region performed well in terms of its universality and high variability in length and composition. Species discriminative power analysis of the psbA-trnH region showed that 91.3% of species could be identified successfully by the BLAST1 method in conjunction with the nearest distance method. And, the species resolution rate of the TaxonGap method exceeded 93%. The results provide support for the use of the psbA-trnH plastid region as a sensitive marker to the authentication of Fabaceae medicinal plants.

Soil biota reduce allelopathic effects of the invasive Eupatorium adenophorum.

Allelopathy has been hypothesized to play a role in exotic plant invasions, and study of this process can improve our understanding of how direct and indirect plant interactions influence plant community organization and ecosystem functioning. However, allelopathic effects can be highly conditional. For example allelopathic effects demonstrated in vivo can be difficult to demonstrate in field soils. Here we tested phytotoxicity of Eupatorium adenophorum (croftonweed), one of the most destructive exotic species in China, to a native plant species Brassica rapa both in sand and in native soil. Our results suggested that natural soils from different invaded habitats alleviated or eliminated the efficacy of potential allelochemicals relative to sand cultures. When that soil is sterilized, the allelopathic effects returned; suggesting that soil biota were responsible for the reduced phytotoxicity in natural soils. Neither of the two allelopathic compounds (9-Oxo-10,11-dehydroageraphorone and 9b-Hydroxyageraphorone) of E. adenophorum could be found in natural soils infested by the invader, and when those compounds were added to the soils as leachates, they showed substantial degradation after 24 hours in natural soils but not in sand. Our findings emphasize that soil biota can reduce the allelopathic effects of invaders on other plants, and therefore can reduce community invasibility. These results also suggest that soil biota may have stronger or weaker effects on allelopathic interactions depending on how allelochemicals are delivered.