Biodiversity of Fungi in Freshwater Ecosystems of Italy

Fungal biodiversity is still mostly unknown and their presence in particular ecosystems such as freshwater habitats is often underestimated. The ecological role that these fungi play in freshwater environments mainly concerns their activity as decomposers of litter and plant material. At present, it is estimated that 3870 species belong to the ecological group of freshwater fungi (13 phyla and 45 classes). In this survey, we provide an overview of the Italian freshwater fungal diversity on the basis of the field and literature data. In the literature, data on freshwater fungi are fragmentary and not updated, focusing mainly on northern Italy where the most important lakes and rivers are present, while data from central and southern Italy (including Sicily and Sardinia) are almost completely ineffective. In particular, Ascomycota are reported in only 14 publications, most of which concern the freshwater environments of Lombardia, Piemonte, and Veneto. Only one publication explores the biodiversity of freshwater Basidiomycota in the wetlands of the Cansiglio forest (Veneto). The field observation allowed for us to identify 38 species of Basidiomycota growing in riparian forest of Italy. However, the number of fungi in freshwater habitats of Italy is strongly underestimated and many species are still completely unknown.

Pathogenicity of Aspergillus Airborne Fungal Species Collected from Indoor and Outdoor Public Areas in Tianjin, China

Airborne fungi play an important role in air pollution and may have various negative effects on human health. In particular, Aspergillus fungi are pathogenic to humans and several domestic animals. In this work, Aspergillus strains isolated from airborne fungal communities sampled from different indoor and outdoor environments in Tianjin University were tested for pathogenicity on Drosophila melanogaster. Airborne fungi were sampled using an HAS-100B air sampler, over a one-year sampling period. Isolated fungal strains were identified based on morphological and molecular analysis. The Aspergillus-centered study was conducted as part of a larger work focusing on the total airborne fungal community in the analyzed environments, which yielded 173 fungal species. In this context, the genus Aspergillus showed the second-highest species richness, with 14 isolated species. Pathogenicity tests performed on male adults of Drosophila melanogaster through a bodily contact bioassay showed that all analyzed airborne Aspergillus species were pathogenic to fruit flies, with high insect mortality rates and shortened lifespan. All the studied fungi induced 100% mortality of fruit flies within 30 culture days, with one exception constituted by A. creber (39 days), while the shortest lifespan (17 days) was observed in fruit flies treated with A. tubingensis. Our results allow us to hypothesize that the studied airborne fungal species may have a pathogenic effect on humans, given the affinity between fruit flies and the human immune system, and may help to explain the health risk linked with Aspergillus fungi exposure in densely populated environments.

Analysis of Airborne Fungal Communities on Pedestrian Bridges in Urban Environments

Airborne fungal spores constitute an important type of bioaerosol and are responsible for a number of negative effects on human health, including respiratory diseases and allergies. We investigated the diversity and concentration of culturable airborne fungi on pedestrian bridges in Tianjin, China, using an HAS-100B air sampler. We compared the airborne fungal communities at the top central area of the selected pedestrian bridges and along the corresponding sidewalk, at ground level. A total of 228 fungal strains belonging to 96 species and 58 genera of Ascomycota (68.86%), Basidiomycota (30.26%), and Mucoromycota (0.88%) were isolated and identified using morphological and molecular analysis. Alternaria was the dominant genus (20.61%), followed by Cladosporium (11.48%), Schizophyllum (6.14%), Sporobolomyces (5.70%), and Sporidiobolus (4.82%). Alternaria alternata was the most frequently occurring fungal species (6.58%), followed by Schizophyllum commune (5.26%), Alternaria sp. (4.82%), Sporobolomyces carnicolor (4.39%), and Cladosporium cladosporioides (3.95%). The recorded fungal concentration ranged from 10 to 180 CFU/m3. Although there was no significant difference in the distribution and abundance of the dominant airborne fungal taxa between the two investigated bridges' sites, numerous species detected with a low percentage of abundance belonging to well-known pathogenic fungal genera, including Alternaria, Aspergillus, Aureobasidium, Cladosporium, Penicillium, and Trichoderma, were exclusively present in one of the two sites. The relative humidity showed a stronger influence compared to the temperature on the diversity and concentration of airborne fungi in the investigated sites. Our results may provide valuable information for air quality monitoring and for assessing human health risks associated with microbial pollution.

Seasonal variation of airborne fungal diversity and community structure in urban outdoor environments in Tianjin, China

Airborne fungi are ubiquitous in human living environments and may be a source of respiratory problems, allergies, and other health issues. A 12 months study was performed to investigate the diversity, concentration and community structure of culturable airborne fungi in different outdoor environments of Tianjin City, using an HAS-100B air sampler. A total of 1,015 fungal strains belonging to 175 species and 82 genera of Ascomycota 92.5%, Basidiomycota 7%, and Mucoromycota 0.3% were isolated and identified using morphological and molecular analysis. The most abundant fungal genera were Alternaria 35%, Cladosporium 18%, Penicillium 5.6%, Talaromyces 3.9%, Didymella 3%, and Aspergillus 2.8%, while the most frequently occurring species were A. alternata (24.7%), C. cladosporioides (11%), A. tenuissima (5.3%), P. oxalicum (4.53%), and T. funiculosus (2.66%). The fungal concentration ranged from 0 to 340 CFU/m³ during the whole study. Environmental factors, including temperature, relative humidity, wind speed, and air pressure exerted a varying effect on the presence and concentration of different fungal taxa. The four analyzed seasons showed significantly different airborne fungal communities, which were more strongly influenced by air temperature and relative humidity in spring and summer, whereas wind speed and air pressure had a stronger effect in autumn and winter. Fungal communities from green and busy sites did not show significant differences over the four analyzed seasons, which may be due to the effect of the surrounding environments characterized by high human activities on the air of the relatively small parks present in Tianjin. The present study provided valuable information on the seasonal dynamics and the environmental factors shaping the diversity and concentration of the analyzed outdoor airborne fungal communities, which can be of help for air quality monitoring, microbial contamination control, and health risk assessment in urban environments.

Cold stress regulates accumulation of flavonoids and terpenoids in plants by phytohormone, transcription process, functional enzyme, and epigenetics

Plants make different defense mechanisms in response to different environmental stresses. One common way is to produce secondary metabolites. Temperature is the main environmental factor that regulates plant secondary metabolites, especially flavonoids and terpenoids. Stress caused by temperature decreasing to 4-10 °C is conducive to the accumulation of flavonoids and terpenoids. However, the accumulation mechanism under cold stress still lacks a systematic explanation. In this review, we summarize three aspects of cold stress promoting the accumulation of flavonoids and terpenoids in plants, that is, by affecting (1) the content of endogenous plant hormones, especially jasmonic acid and abscisic acid; (2) the expression level and activity of important transcription factors, such as bHLH and MYB families. This aspect also includes post-translational modification of transcription factors caused by cold stress; (3) key enzyme genes expression and activity in the biosynthesis pathway, in addition, the rate-limiting enzyme and glycosyltransferases genes are responsive to cold stress. The systematic understanding of cold stress regulates flavonoids, and terpenoids will contribute to the future research of genetic engineering breeding, metabolism regulation, glycosyltransferases mining, and plant synthetic biology.

Environmental Factors Shaping the Diversity and Spatial-Temporal Distribution of Indoor and Outdoor Culturable Airborne Fungal Communities in Tianjin University Campus, Tianjin, China

Airborne fungi have significant influence on air quality and may pose adverse effects on human health due to their allergenic and pathogenic effect. We carried out a 1-year survey on the airborne fungal diversity and concentration of indoor and outdoor environments, within the Tianjin University campus. Airborne fungi were sampled using an HAS-100B air sampler. Isolated fungal strains were identified based on morphological and molecular analysis. A total of 641 fungal strains belonging to 173 species and 74 genera were identified in this study. The dominant fungal genera were Cladosporium (29.49%), Alternaria (25.9%), and Epicoccum (6.24%), while the most frequently occurring species were A. alternata (15.44%), C. cladosporioides (11.86%), and E. nigrum (5.77%). The mean fungal concentration at different sites ranged from 0 to 420 CFU/m³, which is lower than the permissive standard level. There was a seasonal variation in the airborne fungal community, while temperature and relative humidity were positively correlated with the fungal concentration and diversity at almost all the sites. Higher fungal diversity was recorded in peak period of human traffic at the two canteens, whereas the two dormitories showed higher fungal diversity in off-peak period. Our study provides the first report on the diversity and concentration of airborne fungal species within different Tianjin University campus environments and clarifies the role played by environmental factors on the analyzed fungal community. Our results may represent valuable information for air quality monitoring and microbial pollution control in densely populated human living environments.

Biosynthesis Pathways, Transport Mechanisms and Biotechnological Applications of Fungal Siderophores

Iron (Fe) is the fourth most abundant element on earth and represents an essential nutrient for life. As a fundamental mineral element for cell growth and development, iron is available for uptake as ferric ions, which are usually oxidized into complex oxyhydroxide polymers, insoluble under aerobic conditions. In these conditions, the bioavailability of iron is dramatically reduced. As a result, microorganisms face problems of iron acquisition, especially under low concentrations of this element. However, some microbes have evolved mechanisms for obtaining ferric irons from the extracellular medium or environment by forming small molecules often regarded as siderophores. Siderophores are high affinity iron-binding molecules produced by a repertoire of proteins found in the cytoplasm of cyanobacteria, bacteria, fungi, and plants. Common groups of siderophores include hydroxamates, catecholates, carboxylates, and hydroximates. The hydroxamate siderophores are commonly synthesized by fungi. L-ornithine is a biosynthetic precursor of siderophores, which is synthesized from multimodular large enzyme complexes through non-ribosomal peptide synthetases (NRPSs), while siderophore-Fe chelators cell wall mannoproteins (FIT1, FIT2, and FIT3) help the retention of siderophores. S. cerevisiae, for example, can express these proteins in two genetically separate systems (reductive and nonreductive) in the plasma membrane. These proteins can convert Fe (III) into Fe (II) by a ferrous-specific metalloreductase enzyme complex and flavin reductases (FREs). However, regulation of the siderophore through Fur Box protein on the DNA promoter region and its activation or repression depend primarily on the Fe availability in the external medium. Siderophores are essential due to their wide range of applications in biotechnology, medicine, bioremediation of heavy metal polluted environments, biocontrol of plant pathogens, and plant growth enhancement.

Molecular and Biochemical Characterization, Antimicrobial Activity, Stress Tolerance, and Plant Growth-Promoting Effect of Endophytic Bacteria Isolated from Wheat Varieties

Endophytic bacteria have been utilized as an alternative source to chemical fertilizers and pesticides to enhance plant productivity and defense mechanisms against biotic and abiotic stress. Five endophytic bacterial strains were isolated from the seeds of three different Pakistani wheat varieties (Ghaneemat-e-IBGE, Atta-Habib, and Siren). The isolated strains AH-1, S-5, S-7, GI-1, and GI-6 showed phylogenetic similarity with Bacillus altitudinis, B. aryabhattai, B. wiedmannii, Pseudomonas aeruginosa, and Burkholderia gladioli, respectively. All strains showed catalase activity (except AH-1) and Indole-3-acetic acid production, with the highest concentration (16.77 μg·mL^-1) found for GI-6, followed by S-5 (11.5 μg·mL^-1), nitrogen assimilation (except S-7), phosphorus solubilization (except S-7 and AH-1), and ability to produce siderophores, with maximum productions for GI-6 (31 ± 3.5 psu) and GI-1 (30 ± 2.9 psu). All five analyzed strains possessed antimicrobial activity, which was particularly strong in GI-6 and S-5 against Klebsiella pneumonia, Escherichia coli, and Bacillus subtilis. Increasing salinity stress with NaCl negatively affected the bacterial growth of all isolates. However, strains GI-6 and S-5 showed salt tolerance after three days of incubation. A drought tolerance test resulted in a negative impact of poly ethylene glycol on bacterial growth, which was, however, less pronounced in GI-6 strain. The GI-6 strain revealed growth-promoting effects on inoculated wheat plants.

Diversity and Co-Occurrence Patterns of Fungal and Bacterial Communities from Alkaline Sediments and Water of Julong High-Altitude Hot Springs at Tianchi Volcano, Northeast China

The Julong high-altitude volcanic hot springs in northeast China are of undeniable interest for microbiological studies due to their unique, extreme environmental conditions. The objective of this study was to provide a comprehensive analysis of the unexplored fungal and bacterial community composition, structure and networks in sediments and water from the Julong hot springs using a combination of culture-based methods and metabarcoding. A total of 65 fungal and 21 bacterial strains were isolated. Fungal genera Trichoderma and Cladosporium were dominant in sediments, while the most abundant fungi in hot spring water were Aspergillus and Alternaria. Bacterial communities in sediments and water were dominated by the genera Chryseobacterium and Pseudomonas, respectively. Metabarcoding analysis revealed significant differences in the microorganism communities from the two hot springs. Results suggested a strong influence of pH on the analyzed microbial diversity, at least when the environmental conditions became clearly alkaline. Our analyses indicated that mutualistic interactions may play an essential role in shaping stable microbial networks in the studied hot springs. The much more complicated bacterial than fungal networks described in our study may suggest that the more flexible trophic strategies of bacteria are beneficial for their survival and fitness under extreme conditions.

Analysis of culturable airborne fungi in outdoor environments in Tianjin, China

Background

Fungal spores dispersed in the atmosphere may become cause of different pathological conditions and allergies for human beings. A number of studies have been performed to analyze the diversity of airborne fungi in different environments worldwide, and in particular in many urban areas in China. We investigated, for the first time, the diversity, concentration and distribution of airborne fungi in Tianjin city. We sampled 8 outdoor environments, using open plate method, during a whole winter season. Isolated fungi were identified by morphological and molecular analysis. Environmental factors which could influence the airborne fungi concentration (temperature, humidity, wind speed, and air pressure) were monitored and analyzed. The effect of different urban site functions (busy areas with high traffic flow and commercial activities vs. green areas) on airborne fungal diversity was also analyzed.

Results

A total of 560 fungal strains, belonging to 110 species and 49 genera of Ascomycota (80 %), Basidiomycota (18 %), and Mucoromycota (2 %) were isolated in this study. The dominant fungal genus was Alternaria (22 %), followed by Cladosporium (18.4 %), Naganishia (14.1 %), Fusarium (5.9 %), Phoma (4.11 %), and Didymella (4.8 %). A fungal concentration ranging from 0 to 3224.13 CFU m^− 3 was recorded during the whole study. Permutational multivariate analysis showed that the month was the most influential factor for airborne fungal community structure, probably because it can be regarded as a proxy of environmental variables, followed by wind speed. The two analyzed environments (busy vs. green) had no detectable effect on the air fungal community, which could be related to the relatively small size of parks in Tianjin and/or to the study season.

Conclusions

Our study shed light on the highly diverse community of airborne fungi characterizing the outdoor environments of Tianjin, and clarified the role that different environmental factors played in shaping the analyzed fungal community. The dominant presence of fungi with potential hazardous effect on human health, such as Alternaria, Cladosporium and Naganishia, deserves further attention. Our results may represent a valuable source of information for air quality monitoring, microbial pollution control, and airborne diseases prevention.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02205-2.

Nanoparticle conjugation of ginsenoside Rb3 inhibits myocardial fibrosis by regulating PPARα pathway

BACKGROUND

Cardiac fibrosis occurs in ischemic and non-ischemic heart failure, hereditary cardiomyopathy, diabetes and aging. Energy metabolism, which serves a crucial function in the course and treatment of cardiovascular diseases, might have therapeutic benefits for myocardial fibrosis. Ginsenoside Rb3 (G-Rb3) is one of the main components of Ginseng and exhibits poor oral bioavailability but still exerts regulate energy metabolism effects in some diseases. Therefore, the study investigated the effect of chitosan (CS) @ sodium tripolyphosphate (TPP) nanoparticles conjugation with ginsenoside Rb3 (NpRb3) on myocardial fibrosis and studied its possible mechanisms. The results showed that NpRb3 directly participates in the remodeling of myocardial energy metabolism and the regulation of perixisome proliferation-activated receptor alpha (PPARα), thereby improving the degree of myocardial fibrosis. The study also verifies the protective effect of NpRb3 on energy metabolism and mitochondrial function by targeting the PPARα pathway. Therefore, the prepared nanodrug carrier may be a potential solution for the delivery of G-Rb3, which is a promising platform for oral treatment of myocardial fibrosis.

Bioprocessing of waste biomass for sustainable product development and minimizing environmental impact

Growing concerns around the generation of biomass waste have triggered conversation around sustainable utilization of these seemingly waste materials as feedstock towards energy generation and production of chemicals and other value-added products. Thus, biotechniques such as utilization of microbes and enzymes derived thereof have become important avenues for green pretreatment and conversion of biomass wastes. Although the products of these bioconversions are greener at an overall level, their consumption and utilization still impact the environment. Hence it is important to understand the overall impact from cradle to grave through lifecycle assessment (LCA) techniques and find avenues of process optimization and better utilization of all the materials and products involved. Another factor to consider is overall cost optimization to make the process economically feasible, profitable and increase industrial adoption. This review brings forward these critical aspects to provide better understanding for the advancement of bioeconomy.

Genome-based engineering of ligninolytic enzymes in fungi

Background

Many fungi grow as saprobic organisms and obtain nutrients from a wide range of dead organic materials. Among saprobes, fungal species that grow on wood or in polluted environments have evolved prolific mechanisms for the production of degrading compounds, such as ligninolytic enzymes. These enzymes include arrays of intense redox-potential oxidoreductase, such as laccase, catalase, and peroxidases. The ability to produce ligninolytic enzymes makes a variety of fungal species suitable for application in many industries, including the production of biofuels and antibiotics, bioremediation, and biomedical application as biosensors. However, fungal ligninolytic enzymes are produced naturally in small quantities that may not meet the industrial or market demands. Over the last decade, combined synthetic biology and computational designs have yielded significant results in enhancing the synthesis of natural compounds in fungi.

Main body of the abstract

In this review, we gave insights into different protein engineering methods, including rational, semi-rational, and directed evolution approaches that have been employed to enhance the production of some important ligninolytic enzymes in fungi. We described the role of metabolic pathway engineering to optimize the synthesis of chemical compounds of interest in various fields. We highlighted synthetic biology novel techniques for biosynthetic gene cluster (BGC) activation in fungo and heterologous reconstruction of BGC in microbial cells. We also discussed in detail some recombinant ligninolytic enzymes that have been successfully enhanced and expressed in different heterologous hosts. Finally, we described recent advance in CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)-Cas (CRISPR associated) protein systems as the most promising biotechnology for large-scale production of ligninolytic enzymes.

Short conclusion

Aggregation, expression, and regulation of ligninolytic enzymes in fungi require very complex procedures with many interfering factors. Synthetic and computational biology strategies, as explained in this review, are powerful tools that can be combined to solve these puzzles. These integrated strategies can lead to the production of enzymes with special abilities, such as wide substrate specifications, thermo-stability, tolerance to long time storage, and stability in different substrate conditions, such as pH and nutrients.

The Role of Medicinal Mushrooms in Brain Cancer Therapies: Review

Medicinal mushrooms are considered an unlimited source of polysaccharides (mainly β-glucans) and polysaccharide-protein complexes and possess various immunological and anticancer properties. In addition, their use in integrative medicine leads to a clear reduction of side effects in patients undergoing chemotherapy or radiotherapy. The literature reports a number of beneficial effects of using mushrooms as health supplements in patients affected by high-grade glioma. The effects of medicinal mushrooms on side effects in patients with brain cancer and a case study report are also described in this review.

Species Diversity With Comprehensive Annotations of Wood-Inhabiting Poroid and Corticioid Fungi in Uzbekistan

Uzbekistan, located in Central Asia, harbors high diversity of woody plants. Diversity of wood-inhabiting fungi in the country, however, remained poorly known. This study summarizes the wood-inhabiting basidiomycte fungi (poroid and corticoid fungi plus similar taxa such as Merismodes, Phellodon, and Sarcodon) (Agaricomycetes, Basidiomycota) that have been found in Uzbekistan from 1950 to 2020. This work is based on 790 fungal occurrence records: 185 from recently collected specimens, 101 from herbarium specimens made by earlier collectors, and 504 from literature-based records. All data were deposited as a species occurrence record dataset in the Global Biodiversity Information Facility and also summarized in the form of an annotated checklist in this paper. All 286 available specimens were morphologically examined. For 138 specimens, the 114 ITS and 85 LSU nrDNA sequences were newly sequenced and used for phylogenetic analysis. In total, we confirm the presence of 153 species of wood-inhabiting poroid and corticioid fungi in Uzbekistan, of which 31 species are reported for the first time in Uzbekistan, including 19 that are also new to Central Asia. These 153 fungal species inhabit 100 host species from 42 genera of 23 families. Polyporales and Hymenochaetales are the most recorded fungal orders and are most widely distributed around the study area. This study provides the first comprehensively updated and annotated the checklist of wood-inhabiting poroid and corticioid fungi in Uzbekistan. Such study should be expanded to other countries to further clarify species diversity of wood-inhabiting fungi around Central Asia.

Hydrocarbon Degradation and Enzyme Activities of Aspergillus oryzae and Mucor irregularis Isolated from Nigerian Crude Oil-Polluted Sites

Many free-living saprobic fungi are nature recruited organisms for the degradation of wastes, ranging from lignocellulose biomass to organic/inorganic chemicals, aided by their production of enzymes. In this study, fungal strains were isolated from contaminated crude-oil fields in Nigeria. The dominant fungi were selected from each site and identified as Aspergillus oryzae and Mucor irregularis based on morphological and molecular characterization, with site percentage incidences of 56.67% and 66.70%, respectively. Selected strains response/tolerance to complex hydrocarbon (used engine oil) was studied by growing them on Bushnell Haas (BH) mineral agar supplemented with the hydrocarbon at different concentrations, i.e., 5%, 10%, 15%, and 20%, with a control having dextrose. Hydrocarbon degradation potentials of these fungi were confirmed in BH broth culture filtrates pre-supplemented with 1% engine oil after 15 days of incubation using GC/MS. In addition, the presence of putative enzymes, laccase (Lac), manganese peroxidase (MnP), and lignin peroxidase (LiP) was confirmed in culture filtrates using appropriate substrates. The analyzed fungi grew in hydrocarbon supplemented medium with no other carbon source and exhibited 39.40% and 45.85% dose inhibition response (DIR) respectively at 20% hydrocarbon concentration. An enzyme activity test revealed that these two fungi produced more Lac than MnP and LiP. It was also observed through the GC/MS analyses that while A. oryzae acted on all hydrocarbon components in the used engine oil, M. irregularis only degraded the long-chain hydrocarbons and BTEX. This study confirms that A. oryzae and M. irregularis have the potential to be exploited in the bio-treatment and removal of hydrocarbons from polluted soils.

Hymenoptera venom allergy among children in Italy: time for pediatricians to take action

Hymenoptera venom allergy (HVA) is one of the most frequent causes of anaphylaxis following a bee, vespid or ant sting. Real-life data regarding the management of HVA in children are lacking. To address this unmet need, we carried out a survey defining the current management of HVA in children among pediatric allergists in Italy. Educational investments on the improvement of the management of pediatric patients with HVA are urgently needed, and our analysis represents a relevant instrument in targeting a roadmap with this aim. The time for pediatric allergists to take action has come, and a task force from the Rare Allergic Diseases Commission of the Italian Society of Pediatric Allergy and Immunology is working on the topic to improve pediatricians' knowledge and optimize the care of these patients.

Molecular evidence supports simultaneous association of the achlorophyllous orchid Chamaegastrodia inverta with ectomycorrhizal Ceratobasidiaceae and Russulaceae

BACKGROUND

Achlorophyllous orchids are mycoheterotrophic plants, which lack photosynthetic ability and associate with fungi to acquire carbon from different environmental sources. In tropical latitudes, achlorophyllous forest orchids show a preference to establish mycorrhizal relationships with saprotrophic fungi. However, a few of them have been recently found to associate with ectomycorrhizal fungi and there is still much to be learned about the identity of fungi associated with tropical orchids. The present study focused on mycorrhizal diversity in the achlorophyllous orchid C. inverta, an endangered species, which is endemic to southern China. The aim of this work was to identify the main mycorrhizal partners of C. inverta in different plant life stages, by means of morphological and molecular methods.

RESULTS

Microscopy showed that the roots of analysed C. inverta samples were extensively colonized by fungal hyphae forming pelotons in root cortical cells. Fungal ITS regions were amplified by polymerase chain reaction, from DNA extracted from fungal mycelia isolated from orchid root samples, as well as from total root DNA. Molecular sequencing and phylogenetic analyses showed that the investigated orchid primarily associated with ectomycorrhizal fungi belonging to a narrow clade within the family Ceratobasidiaceae, which was previously detected in a few fully mycoheterotrophic orchids and was also found to show ectomycorrhizal capability on trees and shrubs. Russulaceae fungal symbionts, showing high similarity with members of the ectomycorrhizal genus Russula, were also identified from the roots of C. inverta, at young seedling stage. Ascomycetous fungi including Chaetomium, Diaporthe, Leptodontidium, and Phomopsis genera, and zygomycetes in the genus Mortierella were obtained from orchid root isolated strains with unclear functional role.

CONCLUSIONS

This study represents the first assessment of root fungal diversity in the rare, cryptic and narrowly distributed Chinese orchid C. inverta. Our results provide new insights on the spectrum of orchid-fungus symbiosis suggesting an unprecedented mixed association between the studied achlorophyllous forest orchid and ectomycorrhizal fungi belonging to Ceratobasidiaceae and Russulaceae. Ceratobasidioid fungi as dominant associates in the roots of C. inverta represent a new record of the rare association between the identified fungal group and fully mycoheterotrophic orchids in nature.

Fungal networks and orchid distribution: new insights from above- and below-ground analyses of fungal communities

Orchids are critically dependent on fungi for seedling establishment and growth, so the distribution and diversity of orchids might depend on the associated fungal communities. We characterised the communities associated with eight orchid species in three Mediterranean protected areas, using a combination of above-ground analyses of sporophores and below-ground molecular analyses of orchid root samples. In three years of sporophore collection in 25 plots around flowering orchid plants, 268 macrofungal species belonging to 84 genera were observed. Statistical analyses indicated a correlation between macrofungal diversity and orchid community variation, regardless of the effect of environmental and spatial factors characterizing the investigated orchid sites. Fungal ITS-DNA PCR amplification, cloning, and sequencing revealed Rhizoctonia-like fungi belonging to Ceratobasidiaceae (26 %), Tulasnellaceae (22.5 %), and Sebacinaceae (3.5 %), as well as other basidiomycetes and ascomycetes, in the roots of 99 orchid plants. Mycorrhizal specificity was low but co-occurring orchid species showed preferences for different partners. The diverse macrofungal communities found in the sites may contribute to orchid community variation without colonizing the orchid roots. Molecular analyses revealed a segregation of associated fungi, which may contribute to Mediterranean orchid coexistence in nature.

Host preference and network properties in biotrophic plant-fungal associations

Analytical methods can offer insights into the structure of biological networks, but mechanisms that determine the structure of these networks remain unclear. We conducted a synthesis based on 111 previously published datasets to assess a range of ecological and evolutionary mechanisms that may influence the plant-associated fungal interaction networks. We calculated the relative host effect on fungal community composition and compared nestedness and modularity among different mycorrhizal types and endophytic fungal guilds. We also assessed how plant-fungal network structure was related to host phylogeny, environmental and sampling properties. Orchid mycorrhizal fungal communities responded most strongly to host identity, but the effect of host was similar among all other fungal guilds. Community nestedness, which did not differ among fungal guilds, declined significantly with increasing mean annual precipitation on a global scale. Orchid and ericoid mycorrhizal fungal communities were more modular than ectomycorrhizal and root endophytic communities, with arbuscular mycorrhizal fungi in an intermediate position. Network properties among a broad suite of plant-associated fungi were largely comparable and generally unrelated to phylogenetic distance among hosts. Instead, network metrics were predominantly affected by sampling and matrix properties, indicating the importance of study design in properly inferring ecological patterns.

The Apostasia genome and the evolution of orchids

WebComparing the whole genome sequence of Apostasia shenzhenica with transcriptome and genome data from five orchid subfamilies permits the reconstruction of an ancestral gene toolkit, providing insight into orchid origins, evolution and diversification.

Around 10 per cent of flowering plant species are orchids, with a broad diversity in both morphology and lifestyle. Apostasia is one of the earliest-diverging genera of Orchidaceae. To study the evolution and diversity of Orchidaceae, Zhong-Jian Liu, Yves Van de Peer and colleagues sequenced the genome of Apostasia shenzhenica, a self-pollinating species found in southeast China. The authors also report improved genomes for two species of Epidendroideae, Phalaenopsis equestris and Dendrobium catenatum, as well as transcriptome analysis of representatives of subfamilies of Orchidaceae. Their analyses provide insights into orchid origins, genome evolution, adaptation and diversification.

Constituting approximately 10% of flowering plant species, orchids (Orchidaceae) display unique flower morphologies, possess an extraordinary diversity in lifestyle, and have successfully colonized almost every habitat on Earth^1,2,3. Here we report the draft genome sequence of Apostasia shenzhenica⁴, a representative of one of two genera that form a sister lineage to the rest of the Orchidaceae, providing a reference for inferring the genome content and structure of the most recent common ancestor of all extant orchids and improving our understanding of their origins and evolution. In addition, we present transcriptome data for representatives of Vanilloideae, Cypripedioideae and Orchidoideae, and novel third-generation genome data for two species of Epidendroideae, covering all five orchid subfamilies. A. shenzhenica shows clear evidence of a whole-genome duplication, which is shared by all orchids and occurred shortly before their divergence. Comparisons between A. shenzhenica and other orchids and angiosperms also permitted the reconstruction of an ancestral orchid gene toolkit. We identify new gene families, gene family expansions and contractions, and changes within MADS-box gene classes, which control a diverse suite of developmental processes, during orchid evolution. This study sheds new light on the genetic mechanisms underpinning key orchid innovations, including the development of the labellum and gynostemium, pollinia, and seeds without endosperm, as well as the evolution of epiphytism; reveals relationships between the Orchidaceae subfamilies; and helps clarify the evolutionary history of orchids within the angiosperms.