Decrypting the Polyporus dictyopus complex: Recovery of Atroporus Ryvarden and segregation of Neodictyopus gen. nov. (Polyporales, Basidiomyocta)

Polyporus dictyopus, with a large number of heterotypic synonyms, has been traditionally considered a species complex, characterized by wide morphological variation and geographic distribution. Thus, neotropical specimens previously identified as P. dictyopus from Amazonia, Cerrado and Atlantic Forest biomes were studied based on detailed macro- and micromorphological examination and phylogenetic analyses, using distinct ribosomal and protein-coding genomic regions: the nuclear ribosomal internal transcribed spacer (nrITS), nuclear ribosomal large subunit (nrLSU), and RNA polymerase II second subunit (RPB2). Two unrelated generic lineages, each one represented by different species, are reported: Atroporus is recovered and re-circumscribed to include A. diabolicus and A. rufoatratus comb. nov.; Neodictyopus gen. nov. is proposed to accommodate N. dictyopus comb. nov. and two new species, N. atlanticae and N. gugliottae. Our study showed that at least five distinct species were hidden under the name P. dictyopus. Detailed descriptions, pictures, illustrations, and a key are provided for Atroporus and Neodictyopus species.

[Molecular cloning and prokaryotic expression of a type II ribosome inactivating protein from Polyporus umbellatus]

A type Ⅱ ribosome inactivating protein (RIP) gene was cloned from Polyporus umbellatus sclerotia by RT-PCR method. The full open reading frame cDNA sequence of this gene was 873 bp in length and encoded a 290-aa protein with a molecular weight of 32.33 kDa and an isoelectric point of 5.58. Multiple sequence alignment revealed that the deduced amino acids possessed conserved domains of RICIN superfamily protein. A neighbor joining phylogenetic analysis suggests that PuRIP was closely related to RIP in Marasmius oreades. Real time PCR results showed that this gene expressed in all tested tissues of P. umbellatus. Meanwhile, the expression of this gene was significantly up-regulated in the part infected by Armillaria mellea. This result suggested that this PuRIP might played important role with potential biotic stress tolerance of P. umbellatus. Otherwise, we successfully constructed the pET15b-PuRIP plasmid, produced and purified the His-PuRIP fusion protein, which would provide the basic material for polyclonal antibody preparation and gene function research.

[Molecular cloning and characterization of two oxidative stress related genes from medicinal fungus Polyporus umbellatus]

OBJECTIVE

To clone the NADPH gene (PuNOX) and Glyoxal oxidase gene (PuGLOX) from a medicinal fungus Polyporus umbellatus, and to carry out the bioinformatic analysis.

METHODS

We used the Rapid Amplification of cDNA ends (RACE) technique to obtain the full length cDNA of these two genes. We used a series of bioinformatic tools to characterize physiochemical properties of the two deduced protein. The analyses of multiple alignment and phylogenetic trees were performed using Bioeditor and MEGA 5.0 softwares.

RESULTS

The entire cDNA of PuNOX and PuGLOX were 1674 bp, 1723 bp in length and encoded a 557-amino acid protein and 515-amino acid protein with a molecular weight of 63.845 kDa and 55.891 kDa and the isoelectric point of 5.58 and 4.82, respectively. PuNOX had high identities (74 to 80%) with NADPH peroxidase from other fungus. From the evolutionary tree, PuNOX was closely related to that of Pleurotus ostreatus. PuGLOX had high identities (> 50%) with Glyoxal oxidases from various fungus. Phylogenetic tree analysis suggested that PuGLOX was closely related to that of Phanerochaete chrysosporium.

CONCLUSION

Molecular characterization of the two oxidative stress related genes will be useful for further functional determination of the genes involved in the sclerotium development of Polyporus umbellatus.

[Molecular cloning and characterization of four small GTPase genes from medicinal fungus Polyporus umbellatus]

Four small GTPase genes which may be relative to sclerotial development were firstly cloned from medicinal fungus Polyporus umbellatus using rapid amplification of cDNA end PCR (RACE) method. The results showed that full-length cDNA of PuRhoA was 698 bp contained 585 bp ORF, which was predicted to encode a 194 amino acid protein with a molecular weight of 21.75 kD with an isoelectric point (pI) of 6.44; the full length cDNA of PuRhoA2 was 837 bp in length and encoded a 194 amino acid protein with a molecular weight of 21.75 kD and an isoelectric point (pI) of 6.33; the full length cDNA of Puypt1 was 896 bp in length and encoded a 204-aa protein with a molecular weight of 22.556 kD and an isoelectric point (pI) of 5.75; the full length cDNA of PuRas was 803 bp in length and encoded a 212-aa protein with a molecular weight of 23.821 kD and an isoelectric point (pI) of 5.2. There are fani acyl transferase enzyme catalytic site and myrcene-transferase enzyme catalytic site in PuRhoA1 while the PuRhoA2 only possess myrcene-transferase enzyme catalytic site. Puypt1 contains the Rab1-Ypt1 conserved domain of small GTPase family and PuRas contains the fani acyl transferase enzyme catalytic site. According to the phylogenetic analysis all these four small GTPase clustered with basidiomycete group. Quantitative real-time PCR analysis revealed that Puypt1, PuRas and PuRhoA1 transcripts were significantly higher in the beginning of sclerotial formation than that in the mycelia, whereas the transcripts levels of PuRhoA2 gene were particularly lower in sclerotia than that in mycelia, suggesting that these four genes might be involved in P umbellatus selerotial development.

Development of Microsatellite Markers Derived from Expressed Sequence Tags of Polyporales for Genetic Diversity Analysis of Endangered Polyporus umbellatus

A large scale of EST sequences of Polyporales was screened in this investigation in order to identify EST-SSR markers for various applications. The distribution of EST sequences and SSRs in five families of Polyporales was analyzed, respectively. Mononucleotide was the most abundant type, followed by trinucleotide. Among five families, Ganodermataceae occupied the most SSR markers, followed by Coriolaceae. Functional prediction of SSR marker-containing EST sequences in Ganoderma lucidum obtained three main groups, namely, cellular component, biological process, and molecular function. Thirty EST-SSR primers were designed to evaluate the genetic diversity of 13 natural Polyporus umbellatus accessions. Twenty one EST-SSRs were polymorphic with average PIC value of 0.33 and transferability rate of 71%. These 13 P. umbellatus accessions showed relatively high genetic diversity. The expected heterozygosity, Nei's gene diversity, and Shannon information index were 0.41, 0.39, and 0.57, respectively. Both UPGMA dendrogram and principal coordinate analysis (PCA) showed the same cluster result that divided the 13 accessions into three or four groups.

ESTs analysis of putative genes engaged in Polyporus umbellatus sclerotial development

Polyporus umbellatus is one of the most widely used and precious medicinal fungi and the underground sclerotia are known to be with great medicinal value. However, the molecular mechanisms involved in sclerotial development are poorly understood. In the present study, we constructed a forward suppression subtractive hybridization (SSH) cDNA library of Polyporus umbellatus to identify genes expressing differently between mycelium and sclerotia. In this library, a total of 1202 clones were sequenced, assembled into 222 contigs and 524 singletons which were further searched against the NCBI nonredundant (NR) protein database (E-value cutoff, 10⁻⁵). Based on sequence similarity with known proteins, 378 sequences between mycelium and sclerotial were identified and classified into different functional categories through Gene Ontology (GO), Clusters of orthologous Groups of proteins (COGs). We have finally identified a majority of differentially expressed genes (constituting 5.6% of the present library) between the two different periods. An expression level of 32 selected expressed sequence tags (ESTs) generated from the above SSH cDNA library was studied through RT-PCR. This study provides the first global overview of genes putatively involved in Polyporus umbellatus sclerotial development and provides a preliminary basis for further functional research in terms of regulated gene expression in sclerotial production.

Nox gene expression and cytochemical localization of hydrogen peroxide in Polyporus umbellatus sclerotial formation

The effect of temperature shift on Polyporus umbellatus sclerotial development was investigated. Micromorphology of the sclerotia was observed by using scanning electron microscopy (SEM). The cytochemical localization of H2O2 expressed as CeCl3 deposition at the subcellular level was observed by using transmission electron microscopy (TEM). Nox gene expression in sclerotia and mycelia was detected by quantitative real-time PCR (qRT-PCR) analysis. In addition, superoxide dismutase (SOD) and catalase (CAT) specific activities increased during sclerotial development and decreased after the antioxidant diphenyleneiodonium (DPI) was used. Results indicated that the temperature shift treatment induced P. umbellatus sclerotial formation. Compared with the mycelia, the Nox gene was respectively upregulated by 10.577-, 30.984- and 25.469-fold in the sclerotia of SI, SD and SM stages respectively. During the sclerotial formation, H2O2 accumulation was observed in the cell walls or around the organelle membranes of the mycelial cells. The antioxidant DPI decreased the generation of H2O2 in mycelial cells. The specific activity of SOD and CAT levels was decreased significantly by DPI. The activity of the two antioxidant enzymes in the mycelia increased much more during sclerotial formation (p < 0.05). Oxidative stress was closely associated with sclerotial development in P. umbellatus induced by temperature shift treatment.

Genetic diversity and evolution of Chinese traditional medicinal fungus Polyporus umbellatus (Polyporales, Basidiomycota)

BACKGROUND

Polyporus umbellatus is an important medicinal fungus distributed throughout most area of China. Its wide distribution may have resulted in substantial intraspecific genetic diversity for the fungus, potentially creating variation in its medical value. To date, we know little about the intraspecific genetic diversity of P. umbellatus.

METHODOLOGY/PRINCIPAL FINDINGS

The objective of this research was to assess genetic differences of P. umbellatus from geographically diverse regions of China based on nrDNA ITS and 28S rRNA (LSU, large subunit) sequences. Significant sequence variations in the ITS and LSU sequences were detected. All sclerotial samples were clustered into four clades based on phylogenetic analysis of ITS, LSU and a combined data set of both regions. Heterogeneity of ITS and LSU sequences was detected in 5 and 7 samples respectively. All clone sequences clustered into the same clade except for one LSU clone sequences (from Henan province) which clustered into two clades (Clade I and Clade II). Significant genetic divergence in P. umbellatus was observed and the genetic diversification was greater among sclerotial samples from Shaanxi, Henan and Gansu provinces than among other provinces. Polymorphism of ITS and LSU sequences indicated that in China, P. umbellatus may spread from a center (Shaanxi, Henan and Gansu province) to other regions.

CONCLUSIONS/SIGNIFICANCE

We found sclerotial samples of P. umbellatus contained levels of intraspecific genetic diversity. These findings suggested that P. umbellatus populations in Shaanxi, Henan and Gansu are important resources of genetic diversity and should be conserved accordingly.