Cloning, expression, and characterization of two novel cuticle-degrading serine proteases from the entomopathogenic fungus Cordyceps sinensis

The invasion process of the entomopathogenic fungus Ophiocordyceps sinensis into the larvae of ghost moths (Thitarodes xiaojinensis) using a GFP-labeled strain

Chinese cordyceps is a well-known and valuable traditional Chinese medicine that forms after Ophiocordyceps sinensis parasitizes ghost moth larvae. The low natural infection rate of O. sinensis limits large-scale artificial cultivation of Chinese cordyceps, and the invasion process is unclear. To investigate the temporal and spatial regulation when O. sinensis enters ghost moths, we constructed an O. sinensis transformant that stably expresses green fluorescent protein (GFP). Inoculating Thitarodes xiaojinensis larvae with a high concentration of GFP-labeled O. sinensis, we observed that O. sinensis conidia could adhere to the host cuticle within 2 days, germinate penetration pegs within 4 days, and produce blastospores in the host hemocoel within 6 days. The reconstructed three-dimensional (3D) structures of the invasion sites showed that penetration pegs germinated directly from O. sinensis conidia at the joining site with the larval cuticle. Differentiated appressoria or hyphae along the host epicuticle are not required for O. sinensis to invade ghost moths. Overall, the specific invasion process of O. sinensis into its host is clarified, and we provided a new perspective on the invasion process of entomopathogenic fungi.

iTRAQ-based comparative proteome analyses of different growth stages revealing the regulatory role of reactive oxygen species in the fruiting body development of Ophiocordyceps sinensis

In this study, using an isobaric tags for relative and absolute quantitation (iTRAQ ) approach coupled with LC-MS / MS and bioinformatics, the proteomes were analyzed for the crucial three stages covering the fruiting body development of Ophiocordyceps sinensis, including sclerotium (ST), primordium (PR) and mature fruiting body (MF), with a focus on fruiting body development-related proteins and the potential mechanisms of the development. A total of 1,875 proteins were identified. Principal Component Analysis (PCA) demonstrated that the protein patterns between PR and MF were more similar than ST. Differentially accumulated proteins (DAPs) analysis showed that there were 510, 173 and 514 DAPs in the comparisons of ST vs. PR, PR vs. MF and ST vs. MF, respectively. A total of 62 shared DAPs were identified and primarily enriched in proteins related to ‘carbon transport and mechanism’, ‘the response to oxidative stress’, ‘antioxidative activity’ and ‘translation’. KEGG and GO databases showed that the DAPs were enriched in terms of ‘primary metabolisms (amino acid/fatty acid/energy metabolism)’, ‘the response to oxidative stress’ and ‘peroxidase’. Furthermore, 34 DAPs involved in reactive oxygen species (ROS) metabolism were identified and clustered across the three stages using hierarchical clustering implemented in hCluster R package . It was suggested that their roles and the underlying mechanisms may be stage-specific. ROS may play a role in fungal pathogenicity in ST, the fruit-body initiation in PR, sexual reproduction and highland adaptation in MF. Crucial ROS-related proteins were identified, such as superoxide dismutase (SOD, T5A6F1), Nor-1 (T5AFX3), electron transport protein (T5AHD1), histidine phosphotransferase (HPt, T5A9Z5) and Glutathione peroxidase (T5A9V1). Besides, the accumulation of ROS at the three stages were assayed using 2,7-dichlorofuorescin diacetate (DCFH-DA) stanning. A much stronger ROS accumulation was detected at the stage MF, compared to the stages of PR and ST. Sections of ST and fruit-body part of MF were stained by DCFH-DA and observed under the fluorescencemicroscope, showing ROS was distributed within the conidiospore and ascus. Besides, SOD activity increased across the three stages, while CAT activity has a strong increasement in MF compared to the stages of ST and PR. It was suggested that ROS may act in gradient-dependent manner to regulate the fruiting body development. The coding region sequences of six DAPs were analyzed at mRNA level by quantitative real-time PCR (qRT-PCR). The results support the result of DAPs analysis and the proteome sequencing data. Our findings offer the perspective of proteome to understand the biology of fruiting body development and highland adaptation in O. sinensis, which would inform the big industry of this valuable fungus.

Proteome sequencing and analysis of Ophiocordyceps sinensis at different culture periods

Background

Ophiocordyceps sinensis is an important traditional Chinese medicine for its comprehensive active ingredients, such as cordycepin, cordycepic acid, and Cordyceps polysaccharide. O. sinensis zjut, a special strain isolated from O. sinensis, has similar pharmacological functions to wild O. sinensis. Currently, O. sinensis with artificial cultivation has been widely studied, but systematic fundamental research at protein levels has not been determined.

Results

Proteomes of O. sinensis zjut at different culture periods (growth period, 3rd day; pre-stable period, 6th day; and stable period, 9th day) were relatively quantified by relative isotope markers and absolute quantitative technology. In total, 4005 proteins were obtained and further annotated with Gene Ontology, Kyoto Encyclopedia of Genes and Genomes database. Based on the result of the annotations, metabolic pathways of active ingredients, amino acids and fatty acid were constructed, and the related enzymes were exhibited. Subsequently, comparative proteomics of O. sinensis zjut identified the differentially expressed proteins (DEPs) by growth in different culture periods, to find the important proteins involved in metabolic pathways of active ingredients. 605 DEPs between 6d-VS-3d, 1188 DEPs between 9d-VS-3d, and 428 DEPs between 9d-VS-6d were obtained, respectively.

Conclusion

This work provided scientific basis to study protein profile and comparison of protein expression levels of O. sinensis zjut, and it will be helpful for metabolic engineering works to active ingredients for exploration, application and improvement of this fungus.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-020-07298-z.

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.

GC-MS Profiling of Volatile Components in Different Fermentation Products of Cordyceps Sinensis Mycelia

The fermentation products of Cordyceps sinensis (C. sinensis) mycelia are sustainable substitutes for natural C. sinensis. However, the volatile compositions of the commercial products are still unclear. In this paper, we have developed a simultaneous distillation-extraction (SDE) and gas chromatography-mass spectrometry (GC-MS) method for the profiling of volatile components in five fermentation products. A total of 64, 39, 56, 52, and 44 components were identified in the essential oils of Jinshuibao capsule (JSBC), Bailing capsule (BLC), Zhiling capsule (ZLC), Ningxinbao capsule (NXBC), and Xinganbao capsule (XGBC), respectively. 5,6-Dihydro-6-pentyl-2H-pyran-2-one (massoia lactone) was first discovered as the dominant component in JSBC volatiles. Fatty acids including palmitic acid (C16:0) and linoleic acid (C18:2) were also found to be major volatile compositions of the fermentation products. The multivariate partial least squares-discriminant analysis (PLS-DA) showed a clear discrimination among the different commercial products as well as the counterfeits. This study may provide further chemical evidences for the quality evaluation of the fermentation products of C. sinensis mycelia.

Potential molecular mechanisms for fruiting body formation of Cordyceps illustrated in the case of Cordyceps sinensis

The fruiting body formation mechanisms of Cordyceps sinensis are still unclear. To explore the mechanisms, proteins potentially related to the fruiting body formation, proteins from fruiting bodies, and mycelia of Cordyceps species were assessed by using two-dimensional fluorescence difference gel electrophoresis, and the differential expression proteins were identified by matrix-assisted laser desorption/ionisation tandem time of flight mass spectrometry. The results showed that 198 differential expression proteins (252 protein spots) were identified during the fruiting body formation of Cordyceps species, and 24 of them involved in fruiting body development in both C. sinensis and other microorganisms. Especially, enolase and malate dehydrogenase were first found to play an important role in fruiting body development in macro-fungus. The results implied that cAMP signal pathway involved in fruiting body development of C. sinensis, meanwhile glycometabolism, protein metabolism, energy metabolism, and cell reconstruction were more active during fruiting body development. It has become evident that fruiting body formation of C. sinensis is a highly complex differentiation process and requires precise integration of a number of fundamental biological processes. Although the fruiting body formation mechanisms for all these activities remain to be further elucidated, the possible mechanism provides insights into the culture of C. sinensis.

Entomopathogenicity and Biological Attributes of Himalayan Treasured Fungus Ophiocordyceps sinensis (Yarsagumba)

Members of the entomophagous fungi are considered very crucial in the fungal domain relative to their natural phenomenon and economic perspectives; however, inadequate knowledge of their mechanisms of interaction keeps them lagging behind in parallel studies of fungi associated with agro-ecology, forest pathology and medical biology. Ophiocordyceps sinensis (syn. Cordyceps sinensis), an intricate fungus-caterpillar complex after it parasitizes the larva of the moth, is a highly prized medicinal fungus known widely for ages due to its peculiar biochemical assets. Recent technological innovations have significantly contributed a great deal to profiling the variable clinical importance of this fungus and other related fungi with similar medicinal potential. However, a detailed mechanism behind fungal pathogenicity and fungal-insect interactions seems rather ambiguous and is poorly justified, demanding special attention. The goal of the present review is to divulge an update on the published data and provides promising insights on different biological events that have remained underemphasized in previous reviews on fungal biology with relation to life-history trade-offs, host specialization and selection pressures. The infection of larvae by a fungus is not a unique event in Cordyceps; hence, other fungal species are also reviewed for effective comparison. Conceivably, the rationale and approaches behind the inheritance of pharmacological abilities acquired and stored within the insect framework at a time when they are completely hijacked and consumed by fungal parasites, and the molecular mechanisms involved therein, are clearly documented.

A novel serine protease, Sep1, from Bacillus firmus DS-1 has nematicidal activity and degrades multiple intestinal-associated nematode proteins

Plant-parasitic nematodes (PPNs) cause serious harm to agricultural production. Bacillus firmus shows excellent control of PPNs and has been produced as a commercial nematicide. However, its nematicidal factors and mechanisms are still unknown. In this study, we showed that B. firmus strain DS-1 has high toxicity against Meloidogyne incognita and soybean cyst nematode. We sequenced the whole genome of DS-1 and identified multiple potential virulence factors. We then focused on a peptidase S8 superfamily protein called Sep1 and demonstrated that it had toxicity against the nematodes Caenorhabditis elegans and M. incognita. The Sep1 protein exhibited serine protease activity and degraded the intestinal tissues of nematodes. Thus, the Sep1 protease of B. firmus is a novel biocontrol factor with activity against a root-knot nematode. We then used C. elegans as a model to elucidate the nematicidal mechanism of Sep1, and the results showed that Sep1 could degrade multiple intestinal and cuticle-associated proteins and destroyed host physical barriers. The knowledge gained in our study will lead to a better understanding of the mechanisms of B. firmus against PPNs and will aid in the development of novel bio-agents with increased efficacy for controlling PPNs.

Nutritional effects on the mycelial growth and enzymatic activity of Isaria farinosa, and Hepialus larvae growth

AIMS

To investigate the nutritional requirements of the mycelial growth and pathogenesis-related enzymatic activity on Isaria farinosa and the nutritional effect of fungus on its host Hepialus larvae.

METHODS AND RESULTS

Sixteen carbon sources, 16 nitrogen sources and 9 vitamin combinations were tested. The nutritional conditions that significantly prevented I. farinosa pathogenesis were selected as feed additives for rearing Hepialus larvae. Citric acid significantly inhibited the growth of I. farinosa and the activity of three enzymes. l-histidine and l-aspartic acid significantly reduced the dry weights of mycelia and their protease and lipase activities. Vitamin combination that lacked VB 1 significantly increased the growth of I. farinosa and enhanced its chitinase and lipase activities. l-aspartic acid, VB 1 or a combination of them were beneficial for maintaining the larvae survival rate and decreasing the disease rate. The result provides new insight to develop a nutrition-based strategy to control fungal epidemics during insect rearing.

CONCLUSIONS

The ability of some specific nutrients to inhibit mycelial growth and enzymatic activity can prevent epidemics of fungal disease.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results will aid in the development of nutrition-based strategies to control entomopathogenic fungal epidemics during the large-scale rearing of insects.

The intronic minisatellite OsMin1 within a serine protease gene in the Chinese caterpillar fungus Ophiocordyceps sinensis

Repetitive DNA sequences make up a significant portion of all genomes and may occur in intergenic, regulatory, coding, or even intronic regions. Partial sequences of a serine protease gene csp1 was previously used as a population genetic marker of the Chinese caterpillar fungus Ophiocordyceps sinensis, but its first intron region was excluded due to ambiguous alignment. Here in this study, we report the presence of a minisatellite OsMin1 within this intron, where a 20(19)-bp repeat motif is duplicated two to six times in different isolates. Fourteen intron alleles and 13 OsMin1 alleles were identified among 125 O. sinensis samples distributed broadly on the Tibetan Plateau. Two OsMin1 alleles were prevalent, corresponding to either two or five repeats of the core sequence motif. OsMin1 appears to be a single locus marker in the O. sinensis genome, but its origin is undetermined. Abundant recombination signals were detected between upstream and downstream flanking regions of OsMin1, suggesting that OsMin1 mutate by unequal crossing over. Geographic distribution, fungal phylogeny, and host insect phylogeny all significantly affected intron distribution patterns but with the greatest influence noted for fungal genotypes and the least for geography. As far as we know, OsMin1 is the first minisatellite found in O. sinensis and the second found in fungal introns. OsMin1 may be useful in designing an efficient protocol to discriminate authentic O. sinensis from counterfeits.

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.

A biotechnology perspective of fungal proteases

Proteases hydrolyze the peptide bonds of proteins into peptides and amino acids, being found in all living organisms, and are essential for cell growth and differentiation. Proteolytic enzymes have potential application in a wide number of industrial processes such as food, laundry detergent and pharmaceutical. Proteases from microbial sources have dominated applications in industrial sectors. Fungal proteases are used for hydrolyzing protein and other components of soy beans and wheat in soy sauce production. Proteases can be produced in large quantities in a short time by established methods of fermentation. The parameters such as variation in C/N ratio, presence of some sugars, besides several other physical factors are important in the development of fermentation process. Proteases of fungal origin can be produced cost effectively, have an advantage faster production, the ease with which the enzymes can be modified and mycelium can be easily removed by filtration. The production of proteases has been carried out using submerged fermentation, but conditions in solid state fermentation lead to several potential advantages for the production of fungal enzymes. This review focuses on the production of fungal proteases, their distribution, structural-functional aspects, physical and chemical parameters, and the use of these enzymes in industrial applications.

Identification of the Genes Involved in the Fruiting Body Production and Cordycepin Formation of Cordyceps militaris Fungus

A mutant library of Cordyceps militaris was constructed by improved Agrobacterium tumefaciens-mediated transformation and screened for degradation features. Six mutants with altered characters in in vitro and in vivo fruiting body production, and cordycepin formation were found to contain a single copy T-DNA. T-DNA flanking sequences of these mutants were identified by thermal asymmetric interlaced-PCR approach. ATP-dependent helicase, cytochrome oxidase subunit I and ubiquitin-like activating enzyme were involved in in vitro fruiting body production, serine/threonine phosphatase involved in in vivo fruiting body production, while glucose-methanol-choline oxidoreductase and telomerase reverse transcriptase involved in cordycepin formation. These genes were analyzed by bioinformatics methods, and their molecular function and biology process were speculated by Gene Ontology (GO) analysis. The results provided useful information for the control of culture degeneration in commercial production of C. militaris.

Transcriptome sequencing and analysis of the entomopathogenic fungus Hirsutella sinensis isolated from Ophiocordyceps sinensis

BACKGROUND

Ophiocordyceps sinensis, a worm and fungus combined mixture which Hirsutella sinensis is parasitic on the caterpillar body, has been used as a traditional medicine or healthy food in China for thousands of years. H. sinensis is reported as the only correct anamorph of O. sinensis and its main active ingredients are similar to the natural O. sinensis.

RESULTS

H. sinensis L0106, asexual strain of O. sinensis, was isolated and identified in this study. Three transcriptomes of H. sinensis at different cultivation periods (growth period 3d, pre-stable period 6d and stable period 9d) were sequenced for the first time by RNA-Seq method, and 25,511 unigenes (3d), 25,214 unigenes (6d) and 16,245 unigenes (9d) were assembled and obtained, respectively. These unigenes of the three samples were further assembled into 20,822 unigenes (All), and 62.3 percent of unigenes (All) could be annotated based on protein databases. Subsequently, the genes and enzymes involved in the biosynthesis of the active ingredients according to the sequencing and annotation results were predicted. Based on the predictions, we further investigated the interaction of different pathway networks and the corresponding enzymes. Furthermore, the differentially expressed genes (DEGs) of H. sinensis grown during different developmental stages (3d-VS-6d, 3d-VS-9d and 6d-VS-9d) were globally detected and analyzed based on the data from RNA-Seq, and 764 DEGs between 3d and 6d, 1,869 DEGs between 3d and 9d, and 770 DEGs between 6d and 9d were found, respectively.

CONCLUSIONS

This work presented here would aid in understanding and carrying out future studies on the genetic basis of H. sinensis and contribute to the further artificial production and application of this organism. This study provided a substantial contribution and basis to further characterize the gene expression profiles of H. sinensis in the metabolic pathways of active ingredients.

Pharmacological and therapeutic potential of Cordyceps with special reference to Cordycepin

An entomopathogenic fungus, Cordyceps sp. has been known to have numerous pharmacological and therapeutic implications, especially, in terms of human health making it a suitable candidate for ethno-pharmacological use. Main constituent of the extract derived from this fungus comprises a novel bio-metabolite called as Cordycepin (3′deoxyadenosine) which has a very potent anti-cancer, anti-oxidant and anti-inflammatory activities. The current review discusses about the broad spectrum potential of Cordycepin including biological and pharmacological actions in immunological, hepatic, renal, cardiovascular systems as well as an anti-cancer agent. The article also reviews the current efforts to delineate the mechanism of action of Cordycepin in various bio-molecular processes. The study will certainly draw the attention of scientific community to improve the bioactivity and production of Cordycepin for its commercial use in pharmacological and medical fields.

A real-time qPCR assay to quantify Ophiocordyceps sinensis biomass in Thitarodes larvae

Ophiocordyceps sinensis, an entomogenous fungus parasitic in the larvae of moths (Lepidoptera), is one of the most valuable medicinal fungi, and it only distributed naturally on the Tibetan Plateau. The parasitical amount of O. sinensis in various tissues of the host Thitarodes larvae has an important role in study the occurrence and developmental mechanisms of O. sinensis, but there no an effective method to detect the fungal anamorph. A real-time quantitative PCR (qPCR) system, including a pair of species-specific ITS primers and its related program, was developed for O. sinensis assay with high reliability and efficiency. A calibration curve was established and exhibited a very good linear correlation between the fungal biomass and the C T values (R (2)=0.999419) by the qPCR system. Based on this method, O. sinensis was detected rapidly in four tissues of its host caterpillars, and the results were shown as following: the maximum content of O. sinensis parasitized in the fat-body, and next came body-wall; both of them were much larger than that observed in the haemolymph and intestinal-wall. Taken together, these results show that qPCR assays may become useful tools for study on developmental mechanism of O. sinensis.

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.

Determining novel molecular markers in the Chinese caterpillar fungus Ophiocordyceps sinensis by screening a shotgun genomic library

The Chinese caterpillar fungus Ophiocordyceps sinensis, endemic to alpine regions on the Tibetan Plateau, is one of the most valuable medicinal fungi in the world. Genetic differentiation within this fungus was observed; however, due to lack of highly efficient molecular markers, the overall genetic structure of this fungus has not been clarified. In this study, a shotgun genomic library of O. sinensis was constructed, and >181,848 nt were analyzed from >250 random clones. Primers from 33 sequenced fragments were then designed to amplify O. sinensis samples collected from widely separated regions on the Tibetan Plateau. Ten of the 33 fragments had no amplification or poor sequencing quality from all or certain samples. Sequence variations of the remaining 23 fragments among different samples were investigated in detail. Three fragments (OSRC14, OSRC19, and OSRC32) were the most variable with 7-43 single-nucleotide polymorphism (SNP) sites, representing the SNP frequency of 1.2-6.7 % per nucleotide site. These three fragments have the potential to be useful molecular markers for studying the population genetics of O. sinensis. These results also showed that constructing and screening a shotgun genomic library was an efficient approach to identify novel molecular markers from non-model organisms.

Cloning and analysis of the MAT1-2-1 gene from the traditional Chinese medicinal fungus Ophiocordyceps sinensis

The entomopathogenic fungus Ophiocordyceps sinensis has been important in traditional Chinese medicine but has yet to be commercially cultivated. One bottleneck is the very low frequency of stromata formation from artificially infected moth larvae. The mating system of fungi is the determining factor for sexual reproduction, but mating-type genes of O. sinensis have not been previously investigated. In this study, the putative mating-type gene MAT1-2-1 within the MAT1-2 idiomorph was amplified by polymerase chain reaction (PCR) and was determined to consist of 859 nucleotides that encode 249 amino acids; genes within the MAT1-1 idiomorph, however, were not determined. The MAT1-2-1 gene contained the conserved high-mobility group (HMG) box, and MAT1-2-1 flanking sequences were subsequently obtained. Although no putative open reading frames of the MAT1-1 idiomorph were detected within the ca. 8-kb flanking sequences of MAT1-2-1, a putative DNA lyase gene (which is present next to both idiomorphs in some heterothallic fungi) was found ca. 3.0 kb downstream of MAT1-2-1. The intervening distance between MAT1-2-1 and the DNA lyase gene in O. sinensis is larger than that in Cordyceps militaris and Cordyceps takaomontana. In addition, O. sinensis showed low sequence similarities with C. militaris and C. takaomontana in both MAT1-2-1 and the DNA lyase gene. In the phylogenetic tree, different MAT1-2-1 haplotypes of O. sinensis clustered together with high bootstrap support. As a single-copy gene, MAT1-2-1 was detected in all examined O. sinensis isolates including tissue cultures and single-ascospore cultures. This report describes, for the first time, a mating-type gene of O. sinensis.

A simple method of genomic DNA extraction suitable for analysis of bulk fungal strains

AIMS

A simple and rapid method (designated thermolysis) for extracting genomic DNA from bulk fungal strains was described.

METHODS AND RESULTS

In the thermolysis method, a few mycelia or yeast cells were first rinsed with pure water to remove potential PCR inhibitors and then incubated in a lysis buffer at 85 degrees C to break down cell walls and membranes. This method was used to extract genomic DNA from large numbers of fungal strains (more than 92 species, 35 genera of three phyla) isolated from different sections of natural Ophiocordyceps sinensis specimens. Regions of interest from high as well as single-copy number genes were successfully amplified from the extracted DNA samples. The DNA samples obtained by this method can be stored at -20 degrees C for over 1 year.

CONCLUSIONS

The method was effective, easy and fast and allowed batch DNA extraction from multiple fungal isolates.

SIGNIFICANCE AND IMPACT OF STUDY

Use of the thermolysis method will allow researchers to obtain DNA from fungi quickly for use in molecular assays. This method requires only minute quantities of starting material and is suitable for diverse fungal species.

New insights into the evolution of subtilisin-like serine protease genes in Pezizomycotina

Background

Subtilisin-like serine proteases play an important role in pathogenic fungi during the penetration and colonization of their hosts. In this study, we perform an evolutionary analysis of the subtilisin-like serine protease genes of subphylum Pezizomycotina to find if there are similar pathogenic mechanisms among the pathogenic fungi with different life styles, which utilize subtilisin-like serine proteases as virulence factors. Within Pezizomycotina, nematode-trapping fungi are unique because they capture soil nematodes using specialized trapping devices. Increasing evidence suggests subtilisin-like serine proteases from nematode-trapping fungi are involved in the penetration and digestion of nematode cuticles. Here we also conduct positive selection analysis on the subtilisin-like serine protease genes from nematode-trapping fungi.

Results

Phylogenetic analysis of 189 subtilisin-like serine protease genes from Pezizomycotina suggests five strongly-supported monophyletic clades. The subtilisin-like serine protease genes previously identified or presumed as endocellular proteases were clustered into one clade and diverged the earliest in the phylogeny. In addition, the cuticle-degrading protease genes from entomopathogenic and nematode-parasitic fungi were clustered together, indicating that they might have overlapping pathogenic mechanisms against insects and nematodes. Our experimental bioassays supported this conclusion. Interestingly, although they both function as cuticle-degrading proteases, the subtilisin-like serine protease genes from nematode-trapping fungi and nematode-parasitic fungi were not grouped together in the phylogenetic tree. Our evolutionary analysis revealed evidence for positive selection on the subtilisin-like serine protease genes of the nematode-trapping fungi.

Conclusions

Our study provides new insights into the evolution of subtilisin-like serine protease genes in Pezizomycotina. Pezizomycotina subtilisins most likely evolved from endocellular to extracellular proteases. The entomopathogenic and nematode-parasitic fungi likely share similar properties in parasitism. In addition, our data provided better understanding about the duplications and subsequent functional divergence of subtilisin-like serine protease genes in Pezizomycotina. The evidence of positive selection detected in the subtilisin-like serine protease genes of nematode-trapping fungi in the present study suggests that the subtilisin-like serine proteases may have played important roles during the evolution of pathogenicity of nematode-trapping fungi against nematodes.