Author Correction: The Apostasia genome and the evolution of orchids.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

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.

The Apostasia genome and the evolution of orchids.

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. Here we report the draft genome sequence of Apostasia shenzhenica, 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.

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.

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. 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.

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.

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.

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.

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.

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.

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.

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.

Environmental Factors Affecting Diversity, Structure, and Temporal Variation of Airborne Fungal Communities in a Research and Teaching Building of Tianjin University, China.

Airborne fungi are widely distributed in the environment and may have adverse effects on human health. A 12-month survey on the diversity and concentration of culturable airborne fungi was carried out in a research and teaching building of Tianjin University. Indoor and outdoor environments were analyzed using an HAS-100B air sampler. A total of 667 fungal strains, belonging to 160 species and 73 genera were isolated and identified based on morphological and molecular analysis. The most abundant fungal genera were Alternaria (38.57%), Cladosporium (21.49%), and Aspergillus (5.34%), while the most frequently appearing species was A. alternata (21%), followed by A. tenuissima (12.4%), and C. cladosporioides (9.3%). The concentration of fungi in different environments ranged from 0 to 150 CFU/m3 and was significantly higher outdoor than indoor. Temperature and sampling month were significant factors influencing the whole building fungal community, while relative humidity and wind speed were highly correlated with fungal composition outdoor. Variations in the relative abundance of major airborne fungal taxa at different heights above-ground could lead to different community structures at different floors. Our results may provide valuable information for air quality monitoring and microbial pollution control in university building environments.

Analysis of Soil Fungal and Bacterial Communities in Tianchi Volcano Crater, Northeast China.

High-altitude volcanoes, typical examples of extreme environments, are considered of particular interest in biology as a possible source of novel and exclusive microorganisms. We analyzed the crater soil microbial diversity of Tianchi Volcano, northeast China, by combining molecular and morphological analyses of culturable microbes, and metabarcoding based on Illumina sequencing, in order to increase our understanding of high-altitude volcanic microbial community structure. One-hundred and seventeen fungal strains belonging to 51 species and 31 genera of Ascomycota, Basidiomycota and Mucoromycota were isolated. Penicillium, Trichoderma, Cladosporium, Didymella, Alternaria and Fusarium dominated the culturable fungal community. A considerable number of isolated microbes, including filamentous fungi, such as Aureobasidium pullulans and Epicoccum nigrum, yeasts (Leucosporidium creatinivorum), and bacteria (Chryseobacterium lactis and Rhodococcus spp.), typical of high-altitude, cold, and geothermal extreme environments, provided new insights in the ecological characterization of the investigated environment, and may represent a precious source for the isolation of new bioactive compounds. A total of 1254 fungal and 2988 bacterial operational taxonomic units were generated from metabarcoding. Data analyses suggested that the fungal community could be more sensitive to environmental and geographical change compared to the bacterial community, whose network was characterized by more complicated and closer associations.

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.

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.

The Role of Medicinal Mushrooms in Brain Cancer Therapies: Review.

Medicinal mushrooms are considered an unlimited source of polysaccharides (mainly ß-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.

Plant Growth Promoting Rhizobacteria, Arbuscular Mycorrhizal Fungi and Their Synergistic Interactions to Counteract the Negative Effects of Saline Soil on Agriculture: Key Macromolecules and Mechanisms.

Soil saltiness is a noteworthy issue as it results in loss of profitability and development of agrarian harvests and decline in soil health. Microorganisms associated with plants contribute to their growth promotion and salinity tolerance by employing a multitude of macromolecules and pathways. Plant growth promoting rhizobacteria (PGPR) have an immediate impact on improving profitability based on higher crop yield. Some PGPR produce 1-aminocyclopropane-1-carboxylic (ACC) deaminase (EC 4.1.99.4), which controls ethylene production by diverting ACC into α-ketobutyrate and ammonia. ACC deaminase enhances germination rate and growth parameters of root and shoot in different harvests with and without salt stress. Arbuscular mycorrhizal fungi (AMF) show a symbiotic relationship with plants, which helps in efficient uptake of mineral nutrients and water by the plants and also provide protection to the plants against pathogens and various abiotic stresses. The dual inoculation of PGPR and AMF enhances nutrient uptake and productivity of several crops compared to a single inoculation in both normal and stressed environments. Positively interacting PGPR + AMF combination is an efficient and cost-effective recipe for improving plant tolerance against salinity stress, which can be an extremely useful approach for sustainable agriculture.

Phylogenetic Relationships, Speciation, and Origin of Armillaria in the Northern Hemisphere: A Lesson Based on rRNA and Elongation Factor 1-Alpha.

Armillaria species have a global distribution and play various roles in the natural ecosystems, e.g., pathogens, decomposers, and mycorrhizal associates. However, their taxonomic boundaries, speciation processes, and origin are poorly understood. Here, we used a phylogenetic approach with 358 samplings from Europe, East Asia, and North America to delimit the species boundaries and to discern the evolutionary forces underpinning divergence and evolution. Three species delimitation methods indicated multiple unrecognized phylogenetic species, and biological species recognition did not reflect the natural evolutionary relationships within Armillaria; for instance, biological species of A. mellea and D. tabescens are divergent and cryptic species/lineages exist associated with their geographic distributions in Europe, North America, and East Asia. While the species-rich and divergent Gallica superclade might represent three phylogenetic species (PS I, PS II, and A. nabsnona) that undergo speciation. The PS II contained four lineages with cryptic diversity associated with the geographic distribution. The genus Armillaria likely originated from East Asia around 21.8 Mya in early Miocene when Boreotropical flora (56-33.9 Mya) and the Bering land bridge might have facilitated transcontinental dispersal of Armillaria species. The Gallica superclade arose at 9.1 Mya and the concurrent vicariance events of Bering Strait opening and the uplift of the northern Tibetan plateau might be important factors in driving the lineage divergence.

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.