Development of conventional and nested PCR assays for the detection of Ophiocordyceps sinensis

Effects of inoculated mycorrhizal fungi and non-mycorrhizal beneficial micro-organisms on plant traits, nutrient uptake and root-associated fungal community composition of the Cymbidium hybridum in greenhouse

AIMS

The aim of this study was to assess the effects of beneficial micro-organisms on the growth, nutrient accumulation and root-associated fungal species composition of pot orchids grown in the greenhouse.

METHODS AND RESULTS

A greenhouse pot experiment was conducted to investigate the beneficial effects of a mycorrhizal fungus, Epulorhiza repens isolate ML01, an endophytic fungus, Umbelopsis nana isolate ZH3A-3 and a mixed commercial inoculum Rem, alone or in combination. Nested PCR assays showed that both isolates ML01 and ZH3A-3 can successfully establish in inoculated soil. All the inoculants significantly increased the plant total dry weight of Cymbidium hybridum 'Golden Boy', whereas only co-inoculation with the endophytic fungus ZH3A-3 and the Rem enhanced the fresh weight and height of host plants. The mycorrhizal fungus positively affected P, K, Ca, Mg content in shoots and Zn content in roots, while the endophytic fungus improved N, P, Ca accumulation in shoots and roots. Co-inoculation with the Rem and ML01 improved root to shoot translocation of Fe and Zn. In addition, inoculation with ZH3A-3, ML01+Rem and ZH3A-3+Rem decreased the relative frequency of Fusarium sp. on orchid roots. Trichoderma sp. were isolated from the roots treated with ML01, ML01+Rem and ZH3A-3+Rem.

CONCLUSIONS

Both mycorrhizal and endophytic fungi had the potential to create favourable microflora in the orchid roots and stimulate the growth of transplanted plantlets under greenhouse condition.

SIGNIFICANCE AND IMPACT OF THE STUDY

The newly isolated endophytic strain ZH3A-3 showed significant application value in orchid production.

A simple and effective method to discern the true commercial Chinese cordyceps from counterfeits

The Chinese cordyceps, a complex of the fungus Ophiocordyceps sinensis and its species-specific host insects, is also called "DongChongXiaCao" in Chinese. Habitat degradation in recent decades and excessive harvesting by humans has intensified its scarcity and increased the prices of natural populations. Some counterfeits are traded as natural Chinese cordyceps for profit, causing confusion in the marketplace. To promote the safe use of Chinese cordyceps and related products, a duplex PCR method for specifically identifying raw Chinese cordyceps and its primary products was successfully established. Chinese cordyceps could be precisely identified by detecting an internal transcribed spacer amplicon from O. sinensis and a cytochrome oxidase c subunit 1 amplicon from the host species, at a limit of detection as low as 32 pg. Eleven commercial samples were purchased and successfully tested to further verify that the developed duplex PCR method could be reliably used to identify Chinese cordyceps. It provides a new simple way to discern true commercial Chinese cordyceps from counterfeits in the marketplace. This is an important step toward achieving an authentication method for this Chinese medicine. The methodology and the developmental strategy can be used to authenticate other traditional Chinese medicinal materials.

Establishment of a PCR Assay for the Detection and Discrimination of Authentic Cordyceps and Adulterant Species in Food and Herbal Medicines

Accurate detection and differentiation of adulterants in food ingredients and herbal medicines are crucial for the safety and basic quality control of these products. Ophiocordyceps sinensis is described as the only fungal source for the authentic medicinal ingredient used in the herbal medicine "Cordyceps", and two other fungal species, Cordyceps militaris and Isaria tenuipes, are the authentic fungal sources for food ingredients in Korea. However, substitution of these three species, and adulteration of herbal material and dietary supplements originating from Cordyceps pruinosa or Isaria cicadae, seriously affects the safety and reduces the therapeutic efficacy of these products. Distinguishing between these species based on their morphological features is very difficult, especially in commercially processed products. In this study, we employed DNA barcode-based species-specific sequence characterized amplified region (SCAR) markers to discriminate authentic herbal Cordyceps medicines and Cordyceps-derived dietary supplements from related but inauthentic species. The reliable authentication tool exploited the internal transcribed spacer (ITS) region of a nuclear ribosomal RNA gene (nrDNA). We used comparative nrDNA-ITS sequence analysis of the five fungal species to design two sets of SCAR markers. Furthermore, we used a set of species-specific SCAR markers to establish a real-time polymerase chain reaction (PCR) assay for the detection of species, contamination, and degree of adulteration. We confirmed the discriminability and reproducibility of the SCAR marker analysis and the real-time PCR assay using commercially processed food ingredients and herbal medicines. The developed SCAR markers may be used to efficiently differentiate authentic material from their related adulterants on a species level. The ITS-based SCAR markers and the real-time PCR assay constitute a useful genetic tool for preventing the adulteration of Cordyceps and Cordyceps-related dietary supplements.

Proteomic identification of marker proteins and its application to authenticate Ophiocordyceps sinensis

Ophiocordyceps sinensis (O. sinensis) is a highly valuable fungus because of its nutritious and medicinal properties. The objective of this study was to identify protein markers using a proteomics approach followed by the development of an immunoassay to authenticate O. sinensis. Four authentic O. sinensis samples collected from four production regions and four counterfeit samples were examined individually. Overall 22 characteristic proteins of O. sinensis were identified by two-dimensional electrophoresis (2-DE) coupled with the matrix-assisted laser desorption/ionization-time-of-light mass spectrometry (MALDI-TOF/MS). Three authentic O. sinensis samples and three counterfeit samples were examined by the couple of alkaline native gradient PAGE (AN-PAGE) and electrospray ionization quadrupole-time-of-light mass spectrometry (ESI-Q-TOF/MS). One distinctive protein was identified to be cyanate hydratase, which was also one of the 22 distinctively characteristic proteins of O. sinensis and termed as IP4 in 2-D gel. Due to the abundance and high specificity of IP4, it was isolated and purified. Its purity was evaluated by high performance liquid chromatography (HPLC) and identified by ESI-Q-TOF/MS. Then the purified IP4 was used to produce polyclonal antibodies in BALB/c mice. The specificity of the anti-IP4 antibody was evaluated by an association of double immunodiffusion (DID) and indirect ELISA assay. Then an indirect enzyme linked immunosorbent assay (ELISA) was preliminarily developed to authenticate O. sinensis by detecting IP4. To evaluate the feasibility and accuracy of this method, three authentic O. sinensis samples and three counterfeits were analyzed. The P/N ratios (dividing the sample OD_450nm by the OD_450nm of negative controls) of three authentic O. sinensis samples were above 8, while, those of three counterfeits were lower than 1. These results indicated that the established ELISA assay based on proteomic protocols detection of protein markers might have a great potential in the authentication and also quality assessment of O.sinensis in those commercial products.

Comparison of different sequencing and assembly strategies for a repeat-rich fungal genome, Ophiocordyceps sinensis

Ophiocordyceps sinensis is one of the most expensive medicinal fungi world-wide, and has been used as a traditional Chinese medicine for centuries. In a recent report, the genome of this fungus was found to be expanded by extensive repetitive elements after assembly of Roche 454 (223Mb) and Illumina HiSeq (10.6Gb) sequencing data, producing a genome of 87.7Mb with an N50 scaffold length of 12kb and 6972 predicted genes. To test whether the assembly could be improved by deeper sequencing and to assess the amount of data needed for optimal assembly, genomic sequencing was run several times on genomic DNA extractions of a single ascospore isolate (strain 1229) on an Illumina HiSeq platform (25Gb total data). Assemblies were produced using different data types (raw vs. trimmed) and data amounts, and using three freely available assembly programs (ABySS, SOAP and Velvet). In nearly all cases, trimming the data for low quality base calls did not provide assemblies with higher N50 values compared to the non-trimmed data, and increasing the amount of input data (i.e. sequence reads) did not always lead to higher N50 values. Depending on the assembly program and data type, the maximal N50 was reached with between 50% to 90% of the total read data, equivalent to 100× to 200× coverage. The draft genome assembly was improved over the previously published version resulting in a 114Mb assembly, scaffold N50 of 70kb and 9610 predicted genes. Among the predicted genes, 9213 were validated by RNA-Seq analysis in this study, of which 8896 were found to be singletons. Evidence from genome and transcriptome analyses indicated that species assemblies could be improved with defined input material (e.g. haploid mono-ascospore isolate) without the requirement of multiple sequencing technologies, multiple library sizes or data trimming for low quality base calls, and with genome coverages between 100× and 200×.

Application of Differential Proteomic Analysis to Authenticate Ophiocordyceps sinensis

Ophiocordyceps sinensis (Berk.) Sacc. is one of the most well-known fungi in traditional Chinese medicine and is attracting attention because of its nutritious and medicinal properties. The present study aimed to produce a proteomic map to identify common O. sinensis proteins. The caterpillar body and stroma of O. sinensis collected from five locations and four fungal specimens of similar appearance were examined by two-dimensional electrophoresis (2-DE). Five proteins were identified using MALDI-TOF--TOF/MS, and the 2-DE identification pattern was provided. OCS_04585 and β-lactamase domain-containing protein, the two abundant and characteristic proteins, were separated and purified using liquid-phase isoelectric focusing. The products were high-quality materials that can be used for future protein-function studies and immunoassay development.

Development of Ophiocordyceps sinensis through Plant-Mediated Interkingdom Host Colonization

Ophiocordyceps sinensis is a well-known entomogenous and medicinal fungus. After its anamorphs parasitize the larvae of the genus Thitarodes, fruit-bodies may form to be used as medicine. However, its developmental mechanisms remain unknown. The distribution of O. sinensis was determined in different tissues of the Thitarodes larvae and the dominant plant species using real-time quantitative polymerase chain reaction (qPCR) and fluorescence in situ hybridization (FISH) technique, respectively. We found that more fungal material was located in plants than in larvae, especially in Ranunculus tanguticus. A considerable amount was detected in larval intestinal-wall and plant roots. It is suggested that plants are the potential hosts of O. sinensis, which modifies our understanding of the life cycle of O. sinensis and indicates that the phytophagous larvae may become infected as they feed. Our research may contribute to the study of systematic evolution and population ecology of O. sinensis, elucidate its developmental mechanism and promote sustainable harvesting.

On the reliability of DNA sequences of Ophiocordyceps sinensis in public databases

Some DNA sequences in the International Nucleotide Sequence Databases (INSD) are erroneously annotated, which has lead to misleading conclusions in publications. Ophiocordyceps sinensis (syn. Cordyceps sinensis) is a fungus endemic to the Tibetan Plateau, and more than 100 populations covering almost its distribution area have been examined by us over recent years. In this study, using the data from authentic materials, we have evaluated the reliability of nucleotide sequences annotated as O. sinensis in the INSD. As of October 15, 2012, the INSD contained 874 records annotated as O. sinensis, including 555 records representing nuclear ribosomal DNA (63.5 %), 197 representing protein-coding genes (22.5 %), 92 representing random markers with unknown functions (10.5 %), and 30 representing microsatellite loci (3.5 %). Our analysis indicated that 39 of the 397 internal transcribed spacer entries, 27 of the 105 small subunit entries, and five of the 53 large subunit entries were incorrectly annotated as belonging to O. sinensis. For protein-coding sequences, all records of serine protease genes, the mating-type gene MAT1-2-1, the DNA lyase gene, the two largest subunits of RNA polymerase II, and elongation factor-1α gene were correct, while 14 of the 73 β-tubulin entries were indeterminate. Genetic diversity analyses using those sequences correctly identified as O. sinensis revealed significant genetic differentiation in the fungus although the extent of genetic differentiation varied with the gene. The relationship between O. sinensis and some other related fungal taxa is also discussed.