Dynamics of fungal communities during Gastrodia elata growth

Gastrodin prevents stress-induced synaptic plasticity impairment and behavioral dysfunction via cAMP/PKA/CREB signaling pathway

BACKGROUND

Chronic stress is widely recognized as a critical factor that impairs synaptic plasticity dependent brain function and behavior, contributing to the onset of depression and anxiety disorders, which subsequently undermine learning and memory processes. Gastrodin (GAS), a prominent bioactive constituent of Gastrodiae Rhizoma exhibiting notable neuroprotective properties, holds significant potential for the prevention and treatment of stress-induced neurological dysfunction. However, the protective effects of GAS on stress-induced synaptic plasticity impairment and the underlying mechanisms have yet to be fully elucidated.

OBJECTIVES

To investigate the potential of GAS in protecting synaptic plasticity from chronic stress and its underlying cellular and molecular mechanisms.

METHOD

A chronic stress model was constructed in C57BL/6J mice, and the effects of GAS on synaptic plasticity were examined using Golgi staining and immunohistochemistry. Systematic behavioral analysis was employed to assess the impact of GAS on depressive- and anxiety-like behaviors and cognitive function of mice. Metabolomics, transcriptomics, Western blotting, immunolocalization, enzyme-linked immunosorbent assay, and the administration of signal blockers were utilized to investigate the cellular and molecular pathways via which GAS safeguards synaptic plasticity.

RESULTS

The results showed that chronic stress exposure reduces the dendritic arbor complexity, density of dendritic spines, proportion of mushroom spines of hippocampal neurons, as well as disrupts synaptic function, impairs cognitive function and induces depressive-like behaviors. Importantly, impairment of hippocampal synaptic plasticity, anxiety- and depressive-like behaviors, and cognitive decline induced by chronic stress were significantly ameliorated following GAS treatment. Moreover, we identified the cAMP/PKA/CREB signaling in hippocampal neurons as a potential mechanism through which GAS prevents synaptic plasticity impairment from chronic stress exposure. Blockade of cAMP/PKA/CREB signaling abolished the protective effects of GAS on synaptic plasticity of hippocampal neurons and behaviors in stress-exposed mice.

CONCLUSION

This study is the first to identify GAS as a potential natural compound for alleviating stress-induced synaptic plasticity impairment and behavioral dysfunction by activating the cAMP/PKA/CREB signaling pathway in hippocampal neurons, offering a promising strategy for stress-induced neurological disorders.

Bioactive Metabolites from the Dusty Seeds of Gastrodia elata Bl., Based on Metabolomics and UPLC-Q-TOF-MS Combined with Molecular Network Strategy

Orchids produce tiny, light seeds (dust-like seeds without endosperm) that rely on specific symbiotic fungi for successful germination. Plant roots often release small signaling molecules or bioactive compounds to attract arbuscular mycorrhizal (AM) fungi, promoting fungal growth and hyphal branching. However, until now, no such bioactive or signaling molecules have been identified in orchids that help recruit fungi for seed germination. In this study, we used metabolomics and UPLC-Q-TOF-MS/MS, combined with a molecular network approach, to explore potential bioactive/signaling molecules in the seeds of the achlorophyllous orchid Gastrodia elata Bl. Our analysis revealed the presence of amino acids, nucleotides, lipids, organic acids, saccharides, phospholipids, and lignanamides. Specifically, organic acids, saccharides, and lignanamides were shown to promote the growth of Mycena osmundicola, a fungus important for seed germination. Additionally, lignanamides inhibited the plant pathogen Fusarium oxysporum and exhibited strong antioxidant and anti-inflammatory activities. This is the first systematic identification of bioactive/signaling molecules in G. elata Bl. seeds, providing new insights into the symbiotic relationship between orchids and fungi.

Drastic mycorrhizal community shifts in Sceptridium ferns during the generation transition from fully mycoheterotrophic gametophytes to photosynthetic sporophytes

Many plant species experience a prolonged subterranean phase during which they rely entirely on mycorrhizal fungi for carbon. While this mycoheterotrophic strategy spans liverworts, lycophytes, and ferns, most empirical research has centered on angiosperms. This study explores the fungal associations of Sceptridium (Ophioglossaceae), an early-diverging fern with mycoheterotrophic gametophytes. We analyzed germination patterns and fungal associations in Sceptridium gametophytes, comparing them to the distribution and mycorrhizal partners of photosynthetic sporophytes. High-throughput sequencing data reveal that mycoheterotrophic gametophytes consistently associate with a single Entrophospora fungus in the order Entrophosporales (Glomeromycotina), while photosynthetic sporophytes primarily partner with fungi from Glomeraceae (Glomerales, Glomeromycotina). Consequently, gametophytes exhibit spatial clustering without association with adult plants. This is the first documentation of an association between Entrophosporaceae (and the order Entrophosporales) and mycoheterotrophic plants. The drastic shifts in Sceptridium mycorrhizal communities across life stages likely reflect changing physiological needs during development. Further research is essential to determine whether the association with Entrophosporaceae is widespread among mycoheterotrophic species and to elucidate the functional and physiological mechanisms underlying these mycorrhizal shifts.

Mode of carbon gain and fungal associations of Neuwiedia malipoensis within the evolutionarily early-diverging orchid subfamily Apostasioideae

BACKGROUND AND AIMS

The earliest-diverging orchid lineage, Apostasioideae, consists only of two genera: Apostasia and Neuwiedia. Previous reports of Apostasia nipponica indicated a symbiotic association with an ectomycorrhiza-forming Ceratobasidiaceae clade and partial utilization of fungal carbon during the adult stage. However, the trophic strategy of Neuwiedia throughout its development remains unidentified. To further improve our understanding of mycoheterotrophy in the Apostasioideae, this study focused on Neuwiedia malipoensis examining both the mycorrhizal association and the physiological ecology of this orchid species across various development stages.

METHODS

We identified the major mycorrhizal fungi of N. malipoensis protocorm, leafy seedling and adult stages using molecular barcoding. To reveal nutritional resources utilized by N. malipoensis, we compared stable isotope natural abundances (δ13C, δ15N, δ2H, δ18O) of different developmental stages with those of autotrophic reference plants.

KEY RESULTS

Protocorms exhibited an association with saprotrophic Ceratobasidiaceae rather than ectomycorrhiza-forming Ceratobasidiaceae and the 13C signature was characteristic of their fully mycoheterotrophic nutrition. Seedlings and adults were predominantly associated with saprotrophic fungi belonging to the Tulasnellaceae. While 13C and 2H stable isotope data revealed partial mycoheterotrophy of seedlings, it is unclear to what extent the fungal carbon supply is reduced in adult N. malipoensis. However, the 15N enrichment of mature N. malipoensis suggests partially mycoheterotrophic nutrition. Our data indicated a transition in mycorrhizal partners during ontogenetic development with decreasing dependency of N. malipoensis on fungal nitrogen and carbon.

CONCLUSIONS

The divergence in mycorrhizal partners between N. malipoensis and A. nipponica indicates different resource acquisition strategies and allows various habitat options in the earliest-diverging orchid lineage, Apostasioideae. While A. nipponica relies on the heterotrophic carbon gain from its ectomycorrhizal fungal partner and thus on forest habitats, N. malipoensis rather relies on own photosynthetic carbon gain as an adult, allowing it to establish in habitats as widely distributed as those where Rhizoctonia fungi occur.

Diverse Mycena Fungi and Their Potential for Gastrodia elata Germination

It remains to be determined whether there is a geographical distribution pattern and phylogenetic signals for the Mycena strains with seed germination of the orchid plant Gastrodia elata. This study analyzed the community composition and phylogenetics of 72 Mycena strains associated with G. elata varieties (G. elata. f. glauca and G. elata. f. viridis) using multiple gene fragments (ITS+nLSU+SSU). We found that (1) these diverse Mycena phylogenetically belong to the Basidiospore amyloid group. (2) There is a phylogenetic signal of Mycena for germination of G. elata. Those strains phylogenetically close to M. abramsii, M. polygramma, and an unclassified Mycena had significantly higher germination rates than those to M. citrinomarginata. (3) The Mycena distribution depends on geographic site and G. elata variety. Both unclassified Mycena group 1 and the M. abramsii group were dominant for the two varieties of G. elata; in contrast, the M. citrinomarginata group was dominant in G. elata f. glauca but absent in G. elata f. viridis. Our results indicate that the community composition of numerous Mycena resources in the Zhaotong area varies by geographical location and G. elata variety. Importantly, our results also indicate that Mycena's phylogenetic status is correlated with its germination rate.

Composition and diversity of soil microbial communities change by introducing Phallus impudicus into a Gastrodia elata Bl.-based soil

BACKGROUND

The Gastrodia elata Bl. is an orchid, and its growth demands the presence of Armillaria species. The strong competitiveness of Armillaria species has always been a concern of major threat to other soil organisms, thus disrupting the equilibrium of soil biodiversity. Introducing other species to where G. elata was cultivated, could possibly alleviate the problems associated with the disequilibrium of soil microenvironment; however, their impacts on the soil microbial communities and the underlying mechanisms remain unclear. To reveal the changes of microbial groups associated with soil chemical properties responding to different cultivation species, the chemical property measurements coupled with the next-generation pyrosequencing analyses were applied with soil samples collected from fallow land, cultivation of G. elata and Phallus impudicus, respectively.

RESULTS

The cultivation of G. elata induced significant increases (p < 0.05) in soil pH and NO3-N content compared with fallow land, whereas subsequent cultivation of P. impudicus reversed these G. elata-induced increases and was also found to significantly increase (p < 0.05) the content of soil NH4+-N and AP. The alpha diversities of soil microbial communities were significantly increased (p < 0.01) by cultivation of G. elata and P. impudicus as indicated with Chao1 estimator and Shannon index. The structure and composition of soil microbial communities differed responding to different cultivation species. In particular, the relative abundances of Bacillus, norank_o_Gaiellales, Mortierella and unclassified_k_Fungi were significantly increased (p < 0.05), while the abundances of potentially beneficial genera such as Acidibacter, Acidothermus, Cryptococcus, and Penicillium etc., were significantly decreased (p < 0.05) by cultivation of G. elata. It's interesting to find that cultivation of P. impudicus increased the abundances of these genera that G. elata decreased before, which contributed to the difference of composition and structure. The results of CCA and heatmap indicated that the changes of soil microbial communities had strong correlations with soil nutrients. Specifically, among 28 genera presented, 50% and 42.9% demonstrated significant correlations with soil pH and NO3-N in response to cultivation of G. elata and P. impudicus.

CONCLUSIONS

Our findings suggested that the cultivation of P. impudicus might have potential benefits as result of affecting soil microorganisms coupled with changes in soil nutrient profile.

Distinct orchid mycorrhizal fungal communities among co-occurring Vanilla species in Costa Rica: root substrate and population-based segregation

Despite being the second largest family of flowering plants, orchids represent community structure variation in plant-microbial associations, contributes to niche partitioning in metacommunity assemblages. Yet, mycorrhizal communities and interactions remain unknown for orchids that are highly specialized or even obligated in their associations with their mycorrhizal partners. In this study, we sought to compare orchid mycorrhizal fungal (OMF) communities of three co-occurring hemiepiphytic Vanilla species (V. hartii, V. pompona, and V. trigonocarpa) in tropical forests of Costa Rica by addressing the identity of their OMF communities across species, root types, and populations, using high-throughput sequencing. Sequencing the nuclear ribosomal internal transcribed spacer (nrITS) yielded 299 fungal Operational Taxonomic Units (OTUs) from 193 root samples. We showed distinct segregation in the putative OMF (pOMF) communities of the three coexisting Vanilla hosts. We also found that mycorrhizal communities associated with the rare V. hartii varied among populations. Furthermore, we identified Tulasnellaceae and Ceratobasidiaceae as dominant pOMF families in terrestrial roots of the three Vanilla species. In contrast, the epiphytic roots were mainly dominated by OTUs belonging to the Atractiellales and Serendipitaceae. Furthermore, the pOMF communities differed significantly across populations of the widespread V. trigonocarpa and showed patterns of distance decay in similarity. This is the first report of different pOMF communities detected in roots of wild co-occurring Vanilla species using high-throughput sequencing, which provides evidence that three coexisting Vanilla species and their root types exhibited pOMF niche partitioning, and that the rare and widespread Vanilla hosts displayed diverse mycorrhizal preferences.

Discovery of seed germinating fungi (Mycetinis scorodonius) from Gastrodia elata Bl. f. glauca S. chow in Changbai Mountain and examination of their germination ability

Multi-generational asexual reproduction of Gastrodia elata Bl. will cause seedling species degeneration. Sexual reproduction of Gastrodia elata Bl. seed is an effective method to solve the problem of degeneration. The development of Gastrodia elata Bl. seeds cannot be separated from the germination fungus. However, there are few strains of germination fungus in production, and there is also the problem of species degradation in application for many years. It is very important for the sexual reproduction of Gastrodia elata Bl. to isolate more new strains of excellent germination fungus from the origin. This study used the Gastrodia elata Bl. f. glauca S. chow seeds germination vegetative propagation corms capture method to isolate its symbiotic germination fungus, and comprehensively identified the species of germination fungus by colony morphology, ITS, sporocarps regeneration and germination function, and compared the growth characteristics and germination ability with other germination fungus (Mycena purpureofusca, Mycena dendrobii and Mycena osmundicola). The germination fungus was isolated from the vegetative propagation corms of Gastrodia elata Bl. f. glauca S. chow seeds and named GYGL-1. After comprehensive identification, GYGL-1 was Mycetinis scorodonius. Compared with other germination fungus, GYGL-1 has fast germination speed, vigorous growth, and high germination ability for Gastrodia elata Bl. f. glauca S. chow seeds. Innovated the isolation method of Gastrodia elata Bl. seeds germination fungus, obtained the regenerated sporocarps of the germination fungus, and discovered that Mycetinis scorodonius has a new function of germinating Gastrodia elata Bl. f. glauca S. chow seeds, enriching the resource library of Gastrodia elata Bl. germination fungus.

Coriolopsis strumosa as an Orchid Endophytic Fungus and Its Spatial Distribution in Epidendrum sp. (Orchidaceae)

Coriolopsis spp. are wood-decaying fungi that inhabit forests. They are mainly distributed in tropical and subtropical areas. Strain Epi910 was isolated from the asymbiotically germinated protocorm of Epidendrum sp. and identified as Coriolopsis strumosa. Symbiotic germination and high-throughput sequencing of the endophytic fungal communities of different parts were performed to characterize the function and spatial distribution of the Epi910 isolate. Under symbiotic germination, Epi910 promoted seed germination and seedling formation as an endophytic native fungus of Epidendrum sp. Endophytic fungal communities from seven different parts of Epidendrum sp. were characterized. In total, 645 OTUs were identified; 30 OTUs were shared among all seven parts. The internal transcribed spacer sequence of Epi910 was identical to that of a dominant shared OTU (OTU6). The relative abundance of OTU6 in the seven parts was identified as follows: capsule pericarp > seed > root > asymbiotically germinated protocorm > epiphytic root > ovary > rachis. Our results suggest that the isolate belonging to Coriolopsis strumosa could promote the germination of Epidendrum sp. There may, therefore, be endophytic fungi other than common orchid mycorrhizal fungi with the ability to enhance germination in orchids.

Variable, life stage-dependent mycorrhizal specificity and its developmental consequences in the fully myco-heterotrophic orchid Cyrtosia septentrionalis

The degree of specificity between fully myco-heterotrophic (MH) orchids and mycorrhizal fungi is regarded as high, but some species undergo a mycobiont shift as they transition from juvenile to adult plant. We investigated morphological and physiological aspects of the interaction between the fully MH Cyrtosia septentrionalis and its four known mycobionts to elucidate developmental consequences of variable, life-stage-dependent specificity. Of five randomly sampled germinated seeds co-cultured with each mycobiont, Physisporinus sp. 'TK-10' colonized all, Armillaria gallica and Desarmillaria tabescens colonized one, and A. mellea subsp. nipponica colonized none. Whereas 16.2% of aseptically germinated seeds exhibited onward growth when co-cultured with TK-10, just 1.5-2.6% did so with the other species. Even so, A. gallica colonized and formed internal rhizomorphs within rhizomes established with TK-10, suggesting that this mycobiont can replace and potentially can oust the latter. We infer that the orchid can associate with Armillaria and Desarmillaria mycobionts throughout its life, but that TK-10 enhances early growth. However, because TK-10 has a higher wood-rotting capacity than A. gallica, rapid resource exhaustion may cause nutrient supply shortages. We hypothesize that secondary colonization by Armillaria or Desarmillaria species triggers TK-10 displacement and that this mycobiont shift sustains orchid growth for longer.

The role of symbiotic fungi in the life cycle of Gastrodia elata Blume (Orchidaceae): a comprehensive review

Gastrodia elata Blume, a fully mycoheterotrophic perennial plant of the family Orchidaceae, is a traditional Chinese herb with medicinal and edible value. Interestingly, G. elata requires symbiotic relationships with Mycena and Armillaria strains for seed germination and plant growth, respectively. However, there is no comprehensive summary of the symbiotic mechanism between fungi and G. elata. Here, the colonization and digestion of hyphae, the bidirectional exchange of nutrients, the adaptation of fungi and G. elata to symbiosis, and the role of microorganisms and secondary metabolites in the symbiotic relationship between fungi and G. elata are summarized. We comprehensively and deeply analyzed the mechanism of symbiosis between G. elata and fungi from three perspectives: morphology, nutrition, and molecules. The aim of this review was to enrich the understanding of the mutualistic symbiosis mechanisms between plants and fungi and lay a theoretical foundation for the ecological cultivation of G. elata.

Gut microbiota deficiency ameliorates multiple myeloma and myeloma-related bone disease by Th17 cells in mice models

Purpose: Multiple myeloma, the second most common hematological tumor, is currently incurable. Multiple myeloma-related bone disease is a characteristic clinical symptom that seriously affects the survival and prognosis of patients. In recent years, gut microbiota has been shown to play an important role in the occurrence and development of multiple myeloma. However, whether and how it affects the development of myelomatous bone disease is unclear. Methods: To investigate the mechanism and influence of the microbiota on multiple myeloma and myeloma bone disease, a myeloma-gut microbiota deletion mice model was established. 16S rRNA sequencing was used to analysis of bacterial flora changes. Histochemical staining and bone micro-CT were used to assess the severity of bone disease. Bone marrow tumor load and spleen Th17 cells were detected by flow cytometry. Results: Histochemical staining revealed a reduced tumor burden after eliminating gut microbial communities in mice by administering a mixture of antibiotics. According to the 16S rRNA sequencing of intestinal contents, antibiotic treatment resulted in a significant change in the microbiota of the mice. Bone micro-CT demonstrated that antibiotic treatment could reduce bone lesions caused by myeloma while increasing mineral density, bone volume fraction, trabecular bone thickness, and trabecular number. Meanwhile, histochemical staining of the bone found that the enhanced bone resorption was weakened by the change of flora. These results were consistent with the concentration of IL17 in serum and the frequency of Th17 cells in spleen. Conclusions: Herein, the effects of the gut microbiome on myeloma bone disease are investigated for the first time, providing new insight into its pathogenesis and suggesting that gut microbiota may serve as a therapeutic target in multiple myeloma-associated bone diseases.

Bioactivity Profiling and Quantification of Gastrodin in Gastrodia elata Cultivated in the Field versus Facility via Hyphenated High-Performance Thin-Layer Chromatography

Gastrodia elata (Orchidaceae) is native to mountainous areas of Asia and is a plant species used in traditional medicine for more than two thousand years. The species was reported to have many biological activities, such as neuroprotective, antioxidant, and anti-inflammatory activity. After many years of extensive exploitation from the wild, the plant was added to lists of endangered species. Since its desired cultivation is considered difficult, innovative cultivation methods that can reduce the costs of using new soil in each cycle and at the same time avoid contamination with pathogens and chemicals are urgently needed on large scale. In this work, five G. elata samples cultivated in a facility utilizing electron beam-treated soil were compared to two samples grown in the field concerning their chemical composition and bioactivity. Using hyphenated high-performance thin-layer chromatography (HPTLC) and multi-imaging (UV/Vis/FLD, also after derivatization), the chemical marker compound gastrodin was quantified in the seven G. elata rhizome/tuber samples, which showed differences in their contents between facility and field samples and between samples collected during different seasons. Parishin E was also found to be present. Combining HPTLC with on-surface (bio)assays, the antioxidant activity and inhibition of acetylcholinesterase as well as the absence of cytotoxicity against human cells were demonstrated and compared between samples.

GelFAP v2.0: an improved platform for Gene functional analysis in Gastrodia elata

BACKGROUND

Gastrodia elata (tianma), a well-known medicinal orchid, is widely used to treat various kinds of diseases with its dried tuber. In recent years, new chromosome-level genomes of G.elata have been released in succession, which offer an enormous resource pool for understanding gene function. Previously we have constructed GelFAP for gene functional analysis of G.elata. As genomes are updated and transcriptome data is accumulated, collection data in GelFAP cannot meet the need of researchers.

RESULTS

Based on new chromosome-level genome and transcriptome data, we constructed co-expression network of G. elata, and then we annotated genes by aligning with sequences from NR, TAIR, Uniprot and Swissprot database. GO (Gene Ontology) and KEGG (Kyoto Encylopaedia of Genes and Genomes) annotations were predicted by InterProScan and GhostKOALA software. Gene families were further predicted by iTAK (Plant Transcription factor and Protein kinase Identifier and Classifier), HMMER (hidden Markov models), InParanoid. Finally, we developed an improved platform for gene functional analysis in G. elata (GelFAP v2.0) by integrating new genome, transcriptome data and processed functional annotation. Several tools were also introduced to platform including BLAST (Basic Local Alignment Search Tool), GSEA (Gene Set Enrichment Analysis), Heatmap, JBrowse, Motif analysis and Sequence extraction. Based on this platform, we found that the flavonoid biosynthesis might be regulated by transcription factors (TFs) such as MYB, HB and NAC. We also took C4H and GAFP4 as examples to show the usage of our platform.

CONCLUSION

An improved platform for gene functional analysis in G. elata (GelFAP v2.0, www.gzybioinformatics.cn/Gelv2 ) was constructed, which provides better genome data, more transcriptome resources and more analysis tools. The updated platform might be preferably benefit researchers to carry out gene functional research for their project.

An exploration of mechanism of high quality and yield of Gastrodia elata Bl. f. glauca by the isolation, identification and evaluation of Armillaria

BACKGROUND

Gastrodia elata Bl. f. glauca, a perennial herb of G.elata Bl. in Orchidaceae, is one of the most valuable traditional Chinese medicines. G. elata Bl. is a chlorophyll-free myco-heterotrophic plant, which must rely on the symbiotic growth of Armillaria, but not all Armillaria strains can play the symbiotic role. Additionally, Armillaria is easy to degenerate after multiple generations, and the compatibility between the strains from other areas and G. elata Bl. f. glauca in Changbai Mountain is unstable. Therefore, it is incredibly significant to isolate, identify and screen the symbiotic Armillaria suitable for the growth of G. elata Bl. f. glauca in Changbai Mountain, and to explore the mechanism by which Armillaria improves the production performance of G. elata Bl. f. glauca.

RESULTS

Firstly, G. elata Bl. f. glauca tubers, and rhizomorphs and fruiting bodies of Armillaria were used for the isolation and identification of Armillaria. Five Armillaria isolates were obtained in our laboratory and named: JMG, JMA, JMB, JMC and JMD. Secondly, Armillaria was selected based on the yield and the effective component content of G. elata Bl. f. glauca. It was concluded that the yield and quality of G. elata Bl. f. glauca co-planted with JMG is the highest. Finally, the mechanism of its high quality and yield was explored by investigating the effects of different Armillaria strains on the soil, its nutrition element contents and the soil microbial diversity around G. elata Bl. f. glauca in Changbai Mountain.

CONCLUSIONS

Compared with commercial strains, JMG significantly increased the content of Na, Al, Si, Mn, Fe, Zn, Rb and the absorption of C, Na, Mg, Ca, Cr, Cu, Zn and Rb in G. elata Bl. f. glauca; it improved the composition, diversity and metabolic functions of soil microbial communities around G. elata Bl. f. glauca at phylum, class and genus levels; it markedly increased the relative abundance of bacteria such as Chthoniobacter and Armillaria in the dominant populations, and enhanced such functions as Cell motility, amino acid metabolism and Lipid metabolism; it dramatically decreased the relative abundance of Bryobacter and other fungi in the dominant populations, and reduced such functions as microbial energy metabolism, translation and carbohydrate metabolism. This is the main reason why excellent Armillaria strains promote the high quality and yield of G. elata Bl. f. glauca in Changbai Mountain.

Epidendrumradicans Fungal Community during Ex Situ Germination and Isolation of Germination-Enhancing Fungi

Orchids exhibit varying specificities to fungi in different microbial environments. This pilot study investigated the preference of fungal recruitment during symbiotic germination of Epidendrum radicans Pav. ex Lindl. Two different orchid substrates were used for ex situ seed baiting: pine bark and rotten oak leaf, with Basidiomycota and Ascomycota as the respective dominant groups. Both substrates promoted seed germination, with a higher protocorm formation rate on pine bark (65.75%). High-throughput sequencing characterized the fungal communities of germinated protocorms. Basidiomycota was the dominant group in protocorms that symbiotically germinated on both substrates. The family-level community structures of endophytic fungi in protocorms that symbiotically germinated on both substrates were close to those of protocorms that germinated in vitro on MS1 medium. For protocorms, the dominant fungal groups recruited from substrates differed at the genus level; from pine bark, they were genera belonging to unclassified Sebacinales (41.34%), Thanatephorus (14.48%) and Fusarium (7.35%), while, from rotten oak leaf, they were Rhizoctonia (49.46%), Clitopilus (34.61%), and Oliveonia (7.96%). Four fungal isolates were successfully obtained and identified as belonging to the family Tulasnellaceae, genera Ceratobasidium and Peniophora, which could promote seed germination to the seedling stage. The data indicate that endophytic fungi for E. radicans germination on two different substrates are affected at the genus level by the substrate, with a degree of specificity at the family level.

Mesoamerican Cypripedium: Mycorrhizal Contributions to Promote Their Conservation as Critically Endangered Species

In the valuable orchid genus Cypripedium, the section Irapeana consists of a distinctive group of Mesoamerican species that is formed by Cypripedium dickinsonianum Hágsater, C. irapeanum Lex., and C. molle Lindl. All lady slipper orchids exhibit different distributions and abundances. Data analysis that used herbarium accessions and field investigations indicated that the habitats of these three species have been dramatically reduced. Prospecting for suitable habitats based on climatic, vegetation, and soil parameters allows us to predict potential distributions. Conservation strategies, such as ex situ propagation by asymbiotic and symbiotic approaches, have indicated that the culture media used are a determining factor for seedling development. Mycorrhizal isolates play a main role in the compatibility and further development of germinated seeds. The fungi isolated from adult plants belong to two different families, which makes it possible that widely distributed C. irapeanum populations will be fungal-specific as well as restricted for C. molle. Root mycorrhization patterns occur high on the secondary roots. In contrast with other species of the genus, in situ germination can occur over a short period of two months, but we have documented periods as long as ten years. Cypripedium is a highly problematic genus for ex situ conservation because the germination requirements and cultures are poorly documented, and there is great urgency for in situ conservation to develop strategies for identifying hotspot habitats and actualize the protection status to avoid extinction of this genus.

Fungal association and root morphology shift stepwise during ontogenesis of orchid Cremastra appendiculata towards autotrophic nutrition

The chlorophyllous, terrestrial orchid Cremastra appendiculata from East Asia is unique concerning its fungal mycorrhiza partners. The initially mycoheterotrophic protocorms exploit rather specialized non-rhizoctonia saprotrophic Psathyrellaceae. Adult individuals of this orchid species are either linked to Psathyrellaceae being partially mycoheterotrophic or form mycorrhiza with fungi of the ubiquitous saprotrophic rhizoctonia group. This study provides new insights on nutrition mode, subterranean morphology and fungal partners across different life stages of C. appendiculata. We compared different development stages of C. appendiculata to surrounding autotrophic reference plants based on multi-element natural abundance stable isotope analyses (δ¹³C, δ¹⁵N, δ²H, δ¹⁸O) and total N concentrations. Site- and sampling-time-independent enrichment factors of stable isotopes were used to reveal trophic strategies. We determined mycorrhizal fungi of C. appendiculata protocorm, seedling and adult samples using high-throughput DNA sequencing. We identified saprotrophic non-rhizoctonia Psathyrellaceae as dominant mycorrhizal fungi in protocorm and seedling rhizomes. In contrast, the roots of seedlings and mature C. appendiculata were mainly colonized with fungi belonging to the polyphyletic assembly of rhizoctonia (Ceratobasidium, Thanatephorus and Serendipitaceae). Mature C. appendiculata did not differ in isotopic signature from autotrophic reference plants suggesting a fully autotrophic nutrition mode. Characteristic of orchid specimens entirely relying on fungal nutrition, C. appendiculata protocorms were enriched in ¹⁵N, ¹³C and ²H compared to reference plants. Seedlings showed an intermediate isotopic signature, underpinning the differences in the fungal community depending on their subterranean morphology. In contrast to the suggestion that C. appendiculata is a partially mycoheterotrophic orchid species, we provide novel evidence that mature C. appendiculata with rhizoctonia mycobionts can be entirely autotrophic. Besides an environmentally driven variability among populations, we suggest high within-individual flexibility in nutrition and mycobionts of C. appendiculata, which is subject to the ontogenetic development stage.

Mycorrhizosphere Bacteria, Rahnella sp. HPDA25, Promotes the Growth of Armillaria gallica and Its Parasitic Host Gastrodia elata

Gastrodia elata is an entirely heterotrophic plant, the growth of which is completely reliant on Armillaria gallica, an orchid mycorrhizal fungus. To avoid damaging ecosystems, G. elata cultivation is shifting from woodland to farmland. However, whether the microbial community structure remains stable during this conversation is unknown. Here, we cultivated G. elata in woodland or farmland and found that woodland-cultivated G. elata produced a greater yield and larger tuber size. The relative abundance of Rahnella was 22.84- and 122.25-fold higher in woodland- and farmland-cultivated soil samples, respectively, than that in uncultivated soil samples. To investigate how Rahnella impacts the growth of G. elata and establishes symbiosis with Armillaria gallica, three Rahnella spp. strains (HPDA25, SBD3, and SBD11) were isolated from mycorrhizosphere soil samples. It was found that these strains, especially HPDA25, promoted the growth of A. gallica. Ultra-performance liquid chromatography coupled to a triple quadrupole mass spectrometry analysis detected the indole-3-acetic acid with 16.24 ng/ml in HPDA25 fermentation solution. Co-culturing with the strain HPDA25 or exogenous indole-3-acetic acid increased the branching and fresh weight of rhizomorphs and the growth rate and extracellular laccase activity of A. gallica, compared with A. gallica cultured alone. The results of RNA-seq and quantitative real-time polymerase chain reaction analysis showed that co-culturing A. gallica with HPDA25 increased the expression level of the genes including hydrophobin, SUR7/PalI family, and pectin methylesterase, whereas decreased the expression levels of glycolysis-related genes. Furthermore, co-culturing with the strain HPDA25, A. gallica promotes the growth of G. elata and enhances the tuber size of G. elata. These results provide new insights into an orchid mycorrhizal symbiosis and the cultivation of G. elata.

Mycorrhizal Switching and the Role of Fungal Abundance in Seed Germination in a Fully Mycoheterotrophic Orchid, Gastrodia confusoides

Mycorrhizal associations are essential for orchid germination and seedling establishment, and thus may constrain the distribution and abundance of orchids under natural conditions. Previous studies have shown that germination and seedling establishment in several orchids often decline with increasing distance from adult plants, resulting in non-random spatial patterns of seedling establishment. In contrast, individuals of the fully mycoheterotrophic orchid Gastrodia confusoides often tend to have random aboveground spatial patterns of distribution within bamboo forests. Since G. confusoides is parasitic on litter-decaying fungi, its random spatial patterns of distribution may be due to highly scattered patterns of litter-decaying fungi within bamboo forests. To test this hypothesis, we first identified the main mycorrhizal fungi associating with developing seeds and adult plants at a bamboo forest site in Taiwan using Miseq high-throughput DNA sequencing. Next, we combined seed germination experiments with quantitative PCR (qPCR) analyses to investigate to what extent the abundance of mycorrhizal fungi affected spatial patterns of seed germination. Our results show that seed germination and subsequent growth to an adult stage in G. confusoides required a distinct switch in mycorrhizal partners, in which protocorms associated with a single Mycena OTU, while adults mainly associated with an OTU from the genus Gymnopus. A strong, positive relationship was observed between germination and Mycena abundance in the litter, but not between germination and Gymnopus abundance. Fungal abundance was not significantly related to the distance from the adult plants, and consequently germination was also not significantly related to the distance from adult plants. Our results provide the first evidence that the abundance of litter-decaying fungi varies randomly within the bamboo forest and independently from G. confusoides adults.

Mycorrhizal Fungal Partners Remain Constant during a Root Lifecycle of Pleione bulbocodioides (Orchidaceae)

Mycorrhizal mutualisms are vital for orchids through germination to adulthood. Fungal species diversity and community composition vary across seasons and plant development stages and affect plant survival, adaptation, and community maintenance. Knowledge of the temporal turnover of mycorrhizal fungi (OMF) remains poorly understood in the eco-physiologically diverse orchids (especially in epiphytic orchids), although it is important to understand the function and adaptation of mycorrhizae. Some species of Pleione are epiphytic plants with annual roots and may recruit different fungal partners during their root lifecycle. Based on continuous samplings of Pleione bulbocodioides during a whole root lifecycle, we characterized the fungal temporal dynamics using Illumina sequencing of the ITS2 region. Our data showed that the plants of P. bulbocodioides were quickly colonized by OMF at root emergence and had a constant OMF composition throughout one root lifecycle, although the OMF richness declined with root aging after a peak occurrence during root elongation. In contrast, the richness of root-inhabiting fungal endophytes kept increasing with root aging and more drastic turnovers were found in their species compositions. Our findings of OMF temporal turnover contribute to further understanding of mycorrhizal associations and adaptation of Orchidaceae and will benefit orchid resource conservation and utilization.

Endophytic fungi stimulate the concentration of medicinal secondary metabolites in houttuynia cordata thunb

Endophytic fungi usually establish a symbiotic relationship with the host plant and affect its growth. In order to evaluate the impact of endophytic fungi on the Chinese herbal medicinal plant Houttuynia cordata Thunb., three endophytes isolated from the rhizomes of H. cordata, namely Ilyonectria liriodendra (IL), unidentified fungal sp. (UF), and Penicillium citrinum (PC), were co-cultured individually with H. cordata in sterile soil for 60 days. Analysis of the results showed that the endophytes stimulated the host plant in different ways: IL increased the growth of rhizomes and the accumulation of most of the phenolics and volatiles, UF promoted the accumulation of the medicinal compounds afzelin, decanal, 2-undecanone, and borneol without influencing host plant growth, and PC increased the fresh weight, total leaf area and height of the plants, as well as the growth of the rhizomes, but had only a small effect on the concentration of major secondary metabolites. Our results proved that the endophytic fungi had potential practical value in terms of the production of Chinese herbal medicines, having the ability to improve the yield and accumulation of medicinal metabolites.

Comparative transcriptome analysis of tubers, stems, and flowers of Gastrodia elata Blume reveals potential genes involved in the biosynthesis of phenolics

Orchidaceae, well known for its fascinating flowers, is one of the largest and most diverse families of flowering plants. There are many kinds of plants in this family; these are distributed practically globally and have high ornamental and medicinal values. Gastrodia elata Blume, a traditional Chinese medicinal herb, is a rootless and leafless achlorophyllous orchid. Phenolic compounds are considered to be the major bioactive constituents in G. elata, with antioxidant, antiangiogenic, neuroprotective, antidepressant, anxiolytic, and sedative activities. In this study, we determined the contents of six main phenolic components in tubers, stems and flowers from G. elata. Meanwhile, the transcriptomes of the tuber, stem and flower tissues of G. elata were obtained using the BGISEQ-500 platform. A total of 58.29 Gb of data and 113,067 unigenes were obtained, of which 74,820 unigenes were functionally annotated against seven public databases. Differentially expressed genes between tuber, stem and flower tissues were identified. A total of 76 DEGs encoding eight key enzymes were identified as candidate genes involved in the biosynthesis of phenolics in G. elata. For further validation, the expression levels of unigenes were measured using quantitative real-time PCR. Our results greatly enrich the transcriptomic data of G. elata and provide valuable information for the identification of candidate genes involved in the biosynthesis of secondary metabolites.

Transcriptome Reveals Roles of Lignin-Modifying Enzymes and Abscisic Acid in the Symbiosis of Mycena and Gastrodia elata

Gastrodia elata is a well-known medicinal and heterotrophic orchid. Its germination, limited by the impermeability of seed coat lignin and inhibition by abscisic acid (ABA), is triggered by symbiosis with fungi such as Mycena spp. However, the molecular mechanisms of lignin degradation by Mycena and ABA biosynthesis and signaling in G. elata remain unclear. In order to gain insights into these two processes, this study analyzed the transcriptomes of these organisms during their dynamic symbiosis. Among the 25 lignin-modifying enzyme genes in Mycena, two ligninolytic class II peroxidases and two laccases were significantly upregulated, most likely enabling Mycena hyphae to break through the lignin seed coats of G. elata. Genes related to reduced virulence and loss of pathogenicity in Mycena accounted for more than half of annotated genes, presumably contributing to symbiosis. After coculture, upregulated genes outnumbered downregulated genes in G. elata seeds, suggesting slightly increased biological activity, while Mycena hyphae had fewer upregulated than downregulated genes, indicating decreased biological activity. ABA biosynthesis in G. elata was reduced by the downregulated expression of 9-cis-epoxycarotenoid dioxygenase (NCED-2), and ABA signaling was blocked by the downregulated expression of a receptor protein (PYL12-like). This is the first report to describe the role of NCED-2 and PYL12-like in breaking G. elata seed dormancy by reducing the synthesis and blocking the signaling of the germination inhibitor ABA. This study provides a theoretical basis for screening germination fungi to identify effective symbionts and for reducing ABA inhibition of G. elata seed germination.

Temporal turnover in mycorrhizal interactions: a proof of concept with orchids

Temporal turnover events in biotic interactions involving plants are rarely assessed, although such changes might afford a considerable acclimation potential to the plant. This could enable fairly rapid responses to short-term fluctuations in growth conditions as well as lasting responses to long-term climatic trends. Here, we present a classification of temporal turnover encompassing 11 possible scenarios. Using orchid mycorrhiza as a study model, we show that temporal changes are common, and discuss under which conditions temporal turnover of fungal symbiont is expected. We provide six research questions and identify technical challenges that we deem most important for future studies. Finally, we discuss how the same framework can be applied to other types of biotic interactions.

Evolutionary histories and mycorrhizal associations of mycoheterotrophic plants dependent on saprotrophic fungi

Mycoheterotrophic plants (MHPs) are leafless, achlorophyllous, and completely dependent on mycorrhizal fungi for their carbon supply. Mycorrhizal symbiosis is a mutualistic association with fungi that is undertaken by the majority of land plants, but mycoheterotrophy represents a breakdown of this mutualism in that plants parasitize fungi. Most MHPs are associated with fungi that are mycorrhizal with autotrophic plants, such as arbuscular mycorrhizal (AM) or ectomycorrhizal (ECM) fungi. Although these MHPs gain carbon via the common mycorrhizal network that links the surrounding autotrophic plants, some mycoheterotrophic lineages are associated with saprotrophic (SAP) fungi, which are free-living and decompose leaf litter and wood materials. Such MHPs are dependent on the forest carbon cycle, which involves the decomposition of wood debris and leaf litter, and have a unique biology and evolutionary history. MHPs associated with SAP fungi (SAP-MHPs) have to date been found only in the Orchidaceae and likely evolved independently at least nine times within that family. Phylogenetically divergent SAP Basidiomycota, mostly Agaricales but also Hymenochaetales, Polyporales, and others, are involved in mycoheterotrophy. The fungal specificity of SAP-MHPs varies from a highly specific association with a single fungal species to a broad range of interactions with multiple fungal orders. Establishment of symbiotic culture systems is indispensable for understanding the mechanisms underlying plant-fungus interactions and the conservation of MHPs. Symbiotic culture systems have been established for many SAP-MHP species as a pure culture of free-living SAP fungi is easier than that of biotrophic AM or ECM fungi. Culturable SAP-MHPs are useful research materials and will contribute to the advancement of plant science.

In Vitro Symbiotic Germination: A Revitalized Heuristic Approach for Orchid Species Conservation

As one of the largest families of flowering plants, Orchidaceae is well-known for its high diversity and complex life cycles. Interestingly, such exquisite plants originate from minute seeds, going through challenges to germinate and establish in nature. Alternatively, orchid utilization as an economically important plant gradually decreases its natural population, therefore, driving the need for conservation. As with any conservation attempts, broad knowledge is required, including the species' interaction with other organisms. All orchids establish mycorrhizal symbiosis with certain lineages of fungi to germinate naturally. Since the whole in situ study is considerably complex, in vitro symbiotic germination study is a promising alternative. It serves as a tool for extensive studies at morphophysiological and molecular levels. In addition, it provides insights before reintroduction into its natural habitat. Here we reviewed how mycorrhiza contributes to orchid lifecycles, methods to conduct in vitro study, and how it can be utilized for conservation needs.

Identification and expression of DoCCaMK during Sebacina sp. symbiosis of Dendrobium officinale

Dendrobium officinale Kimura et Migo is a famous precious medicinal plant in China. Seed and seedling were cultivated with the mycorrhizal fungus Sebacina sp. CCaMK was initially cloned from D. officinale based on a SSH cDNA library of symbiotically germinated seeds with Sebacina sp. Phylogenetic analysis was performed among DoCCaMK and other CCaMKs. The particle bombardment technique was used to visualize DoCCaMK-GFP. qRT-PCR and western blot analysis were conducted to determine the tissue expression patterns of DoCCaMK with (SGS) and without (UGS) Sebacina sp. Furthermore, the effect of KN-93 on CCaMK expression was also examined. Using NMT the net Ca²⁺ fluxes and the CCaMK concentration were measured during D. officinale seed germination. DoCCaMK had the highest homology with Lilium longiflorum CCaMK. The DoCCaMK-GFP protein localized in the nucleus and cell membrane. CCaMK expression was significantly upregulated after symbiosis with Sebacina sp. KN-93 could be used as an inhibitor of CCaMK to inhibit D. officinale seed germination. Ca²⁺ influx and the concentration of the CCaMK in the SGS group was significantly more than that of the UGS group. The characterization of CCaMK provides certain genetic evidence for the involvement of this gene during seed germination and mycorrhizal cultivation in D. officinale.

Insight to shape of soil microbiome during the ternary cropping system of Gastradia elata

Background

The ternary cropping system of Gastradia elata depends on a symbiotic relationship with the mycorrhizal fungi Armillaria mellea, which decays wood to assimilate nutrition for the growth of G. elata. The composition of microbe flora as key determinants of rhizoshere and mycorrhizoshere soil fertility and health was investigated to understand how G. elata and A. mellea impacted on its composition. The next generation pyrosequencing analysis was applied to assess the shift of structure of microbial community in rhizoshere of G. elata and mycorrhizoshere of A. mellea compared to the control sample under agriculture process.

Results

The root-associated microbe floras were significantly impacted by rhizocompartments (including rhizoshere and mycorrhizoshere) and agriculture process. Cropping process of G. elata enhanced the richness and diversity of the microbial community in rhizoshere and mycorrhizoshere soil. Furthermore, planting process of G. elata significantly reduced the abundance of phyla Basidiomycota, Firmicutes and Actinobacteria, while increased the abundance of phyla Ascomycota, Chloroflexi, Proteobacteria, Planctomycetes, and Gemmatimonadetes in rhizoshere and mycorrhizoshere. Besides, A. mellea and G. elata significantly enriched several members of saprophytoic and pathogenic fungus (i.e., Exophiala, Leptodontidium, Cosmospora, Cercophora, Metarhizium, Ilyonectria, and Sporothrix), which will enhance the possibility of G. elata disease incidence. At the same time, the ternary cropping system significantly deterred several members of beneficial ectomycorrhizal fungus (i.e., Russula, Sebacina, and Amanita), which will reduce the ability to protect G. elata from diseases.

Conclusions

In the ternary cropping system of G. elata, A. mellea and G. elata lead to imbalance of microbial community in rhizoshere and mycorrhizoshere soil, suggested that further studies on maintaining the balance of microbial community in A. mellea mycorrhizosphere and G. elata rhizosphere soil under field conditions may provide a promising avenue for high yield and high quality G. elata.