Paradigms of actinorhizal symbiosis under the regime of global climatic changes: New insights and perspectives.

Nitrogen occurs as inert and inaccessible dinitrogen gaseous form (N2 ) in the atmosphere. Biological nitrogen fixation is a chief process that makes this dinitrogen (N2 ) accessible and bioavailable in the form of ammonium (NH4 + ) ions. The key organisms to fix nitrogen are certain prokaryotes, called diazotrophs either in the free-living form or establishing significant mutual relationships with a variety of plants. On such examples is ~95-100 MY old incomparable symbiosis between dicotyledonous trees and a unique actinobacterial diazotroph in diverse ecosystems. In this association, the root of the certain dicotyledonous tree (~25 genera and 225 species) belonging to three different taxonomic orders, Fagales, Cucurbitales, and Rosales (FaCuRo) known as actinorhizal trees can host a diazotroph, Frankia of order Frankiales. Frankia is gram-positive, branched, filamentous, sporulating, and free-living soil actinobacterium. It resides in the specialized, multilobed, and coralloid organs (lateral roots but without caps), the root nodules of actinorhizal tress. This review aims to provide systematic information on the distribution and the phylogenetic diversity of hosts from FaCuRo and their micro-endosymbionts (Frankia spp.), colonization mechanisms, and signaling pathways. We also aim to provide details on developmental and physiological imperatives for gene regulation and functional genomics of symbiosis, phenomenal restoration ecology, influences of contemporary global climatic changes, and anthropogenic impacts on plant-Frankia interactions for the functioning of ecosystems and the biosphere.

Structural variability and niche differentiation of the rhizosphere and endosphere fungal microbiome of Casuarina equisetifolia at different ages.

BACKGROUND: Casuarina equisetifolia is one of the most important artificially planted protective forests along the coast in southern China for windbreaks, soil erosion, and sand dune stabilization. Self-renewing of C. equisetifolia is very limited, which might be caused by low soil nutrient levels and reduced microbial activity. METHODS: Use of high-throughput sequencing of the 18S rDNA to investigate the microbial communities from the rhizosphere and root endosphere of C. equisetifolia in young-aged, intermediate-aged, and mature-aged forests. RESULTS: Our results indicate that the diversity of rhizosphere fungal microbiomes in field-grown C. equisetifolia is much lower than that of the endosphere microbiomes. Bioinformatic analysis showed that rhizocompartments produce the strongest differentiation of rhizosphere and endosphere communities. Notably, the distribution of rhizosphere fungi communities was significantly influenced by the environmental factors, not by forest ages. CONCLUSIONS: The presented study suggests that the rhizocompartments and environmental factors, rather than forest ages, determine the diversities of fungal community.

A Homeotic Mutation Changes Legume Nodule Ontogeny into Actinorhizal-Type Ontogeny.

Some plants fix atmospheric nitrogen by hosting symbiotic diazotrophic rhizobia or Frankia bacteria in root organs known as nodules. Such nodule symbiosis occurs in 10 plant lineages in four taxonomic orders: Fabales, Fagales, Cucurbitales, and Rosales, which are collectively known as the nitrogen-fixing clade. Nodules are divided into two types based on differences in ontogeny and histology: legume-type and actinorhizal-type nodules. The evolutionary relationship between these nodule types has been a long-standing enigma for molecular and evolutionary biologists. Recent phylogenomic studies on nodulating and nonnodulating species in the nitrogen-fixing clade indicated that the nodulation trait has a shared evolutionary origin in all 10 lineages. However, this hypothesis faces a conundrum in that legume-type and actinorhizal-type nodules have been regarded as fundamentally different. Here, we analyzed the actinorhizal-type nodules formed by Parasponia andersonii (Rosales) and Alnus glutinosa (Fagales) and found that their ontogeny is more similar to that of legume-type nodules (Fabales) than generally assumed. We also show that in Medicago truncatula, a homeotic mutation in the co-transcriptional regulator gene NODULE ROOT1 (MtNOOT1) converts legume-type nodules into actinorhizal-type nodules. These experimental findings suggest that the two nodule types have a shared evolutionary origin.

Rhizobioaugmentation of Casuarina glauca with N-fixing actinobacteria Frankia decreases enzymatic activities in wastewater irrigated soil: effects of Frankia on C. glauca growth.

The use of wastewater for irrigation in agroforestry is cost-effective for water management. It is well established that rhizospheric microorganisms such as N2-fixing bacteria are able to modulate rhizobioaugmention and to boost phyoremediation process. To date, no study has been conducted to evaluate biological effects of rhizobioaugmentation in Casuarina glauca trees induced by their symbiont N-fixing actinobacteria of the genus Frankia. The objective of the present study was to evaluate the main effects of rhizobioaugmentation on the biological activity in the C. glauca's rhizosphere and on C. glauca growth in soils irrigated with industrial wastewater. Two Frankia strains (BMG5.22 and BMG5.23) were used in a single or dual inoculations of C. glauca seedlings irrigated with industrial wastewater. Soil enzymes activity related to carbon, phosphorus, sulfur and nitrogen cycling were measured. Results revealed that the BMG5.22 Frankia strain increases significantly the size (dry weight) of C. glauca shoots and roots while dual inoculation increased significantly the root length. Surprisingly, ß-glucosidase (BG), cellobiohydrolase (CBH), ß-N-acetylglucosaminidase (NAGase), aryl sulfatase (AS), acid phosphatase (AP), alkaline phosphatase (AlP), glycine aminopeptidase (GAP), leucine aminopeptidase (LAP), and peroxidase (PER) activity in the rhizosphere decreased significantly in soils treated with the two strains of symbionts. This suggests no positive correlations between enzymatic activity and C. glauca growth.

Cortinarius section Thaumasti in South American Nothofagaceae forests.

We studied the South American species of Cortinarius section Thaumasti based on morphological and molecular data. Members of this group can easily be identified in the field because the basidiomata are small and Phlegmacium-like with a bulbous stipe and the universal veil in most species forms a distinct volva at the base of the stipe. The phylogenetic delimitation of the clade was mostly in concordance with the earlier, morphology-based grouping of the South American taxa except that C. chrysophaeus was resolved outside of the clade. Altogether nine species were recognized in the section. Four species, C. chlorophanus, C. coleopus, C. cosmoxanthus, and C. vaginatus, were previously described by other authors, whereas three species, C. chlorosplendidus, C. olivaceovaginatus, and C. subcosmoxanthus, are described here as new. We were able to identify two remaining taxa, but we do not have sufficient morphological data to allow for a formal description. All of the species in C. section Thaumasti form ectomycorrhizal associations with Nothofagaceae. They have been documented from South America and New Zealand. The Patagonian species are considered endemic to the region. A key to the described species is provided.

Traditional mycological knowledge and processes of change in Mapuche communities from Patagonia, Argentina: A study on wild edible fungi in Nothofagaceae forests.

Practices, perceptions, beliefs, and other forms of relationships between rural inhabitants and fungi have scarcely been studied in Patagonia. In this work, we analyze species richness, cultural importance, and modes of use of wild edible fungi in five Mapuche communities in northwest Patagonia of Argentina. Through an ethnobiological approach, we carried out semistructured interviews, walks in forests, and participant observations. Data were analyzed qualitative and quantitatively. Community members collected 17 species in environments with different degrees of human disturbance that they consumed fresh in situ, after some processing or stored for later consumption or trade. Indigenous morels such as Morchella aff. tridentina, M. aff. septimelata, and an unidentified species of Morchella had the greatest cultural importance at the regional level, followed by the exotic Suillus luteus and the native Cyttaria hariotti. Most of these species were frequently mentioned as having commercial value, continuity of use over time, and outstanding organoleptic properties. The remaining species currently have occasional use. The differential use of edible fungi, practices, transferences, and resignifications, as well as new technologies for storage, were analyzed. Regional knowledge about fungi reflects important features of Mapuche tradition but also the process of change in responding to complex and dynamic socioeconomic and ecological contexts.

Chitotetraose activates the fungal-dependent endosymbiotic signaling pathway in actinorhizal plant species.

Mutualistic plant-microbe associations are widespread in natural ecosystems and have made major contributions throughout the evolutionary history of terrestrial plants. Amongst the most remarkable of these are the so-called root endosymbioses, resulting from the intracellular colonization of host tissues by either arbuscular mycorrhizal (AM) fungi or nitrogen-fixing bacteria that both provide key nutrients to the host in exchange for energy-rich photosynthates. Actinorhizal host plants, members of the Eurosid 1 clade, are able to associate with both AM fungi and nitrogen-fixing actinomycetes known as Frankia. Currently, little is known about the molecular signaling that allows these plants to recognize their fungal and bacterial partners. In this article, we describe the use of an in vivo Ca2+ reporter to identify symbiotic signaling responses to AM fungi in roots of both Casuarina glauca and Discaria trinervis, actinorhizal species with contrasting modes of Frankia colonization. This approach has revealed that, for both actinorhizal hosts, the short-chain chitin oligomer chitotetraose is able to mimic AM fungal exudates in activating the conserved symbiosis signaling pathway (CSSP) in epidermal root cells targeted by AM fungi. These results mirror findings in other AM host plants including legumes and the monocot rice. In addition, we show that chitotetraose is a more efficient elicitor of CSSP activation compared to AM fungal lipo-chitooligosaccharides. These findings reinforce the likely role of short-chain chitin oligomers during the initial stages of the AM association, and are discussed in relation to both our current knowledge about molecular signaling during Frankia recognition as well as the different microsymbiont root colonization mechanisms employed by actinorhizal hosts.

Genomic content of a novel yeast species Hanseniaspora gamundiae sp. nov. from fungal stromata (Cyttaria) associated with a unique fermented beverage in Andean Patagonia, Argentina.

A novel yeast species was isolated from the sugar-rich stromata of Cyttaria hariotii collected from two different Nothofagus tree species in the Andean forests of Patagonia, Argentina. Phylogenetic analyses of the concatenated sequence of the rRNA gene sequences and the protein-coding genes for actin and translational elongation factor-1α indicated that the novel species belongs to the genus Hanseniaspora. De novo genome assembly of the strain CRUB 1928T yielded a 10.2-Mbp genome assembly predicted to encode 4452 protein-coding genes. The genome sequence data were compared to the genomes of other Hanseniaspora species using three different methods, an alignment-free distance measure, Kr, and two model-based estimations of DNA-DNA homology values, of which all provided indicative values to delineate species of Hanseniaspora. Given its potential role in a rare indigenous alcoholic beverage in which yeasts ferment sugars extracted from the stromata of Cytarria sp., we searched for the genes that may suggest adaptation of novel Hanseniaspora species to fermenting communities. The SSU1-like gene encoding a sulfite efflux pump, which, among Hanseniaspora, is present only in close relatives to the new species, was detected and analyzed, suggesting that this gene might be one factor that characterizes this novel species. We also discuss several candidate genes that likely underlie the physiological traits used for traditional taxonomic identification. Based on these results, a novel yeast species with the name Hanseniaspora gamundiae sp. nov. is proposed with CRUB 1928T (ex-types: ZIM 2545T = NRRL Y-63793T = PYCC 7262T; MycoBank number MB 824091) as the type strain. Furthermore, we propose the transfer of the Kloeckera species, K. hatyaiensis, K. lindneri and K. taiwanica to the genus Hanseniaspora as Hanseniaspora hatyaiensis comb. nov. (MB 828569), Hanseniaspora lindneri comb. nov. (MB 828566) and Hanseniaspora taiwanica comb. nov. (MB 828567).

The role of Frankia inoculation in casuarina plantations in China.

Casuarina trees are planted along the coast from Hainan province in South China to the Zhoushan Islands of Zhejiang province in Southeastern China. Three key species, Casuarina equisetifolia, Casuarina cunninghamiana and Casuarina glauca, are used as windbreaks, in agroforestry systems, and for the production of timber and fuel wood. Frankia have been studied in China since 1984. Today, Frankia research fields are very wide, and cover morphology, physiology and genetic diversity, and the application of inocula for specific purposes on poor quality sites. In this paper, we review the role of Frankia inoculations in nurseries and casuarina plantations in China and discuss the benefits of inoculation.

The plant-growth-promoting actinobacteria of the genus Nocardia induces root nodule formation in Casuarina glauca.

Actinorhizal plants form a symbiotic association with the nitrogen-fixing actinobacteria Frankia. These plants have important economic and ecological benefits including land reclamation, soil stabilization, and reforestation. Recently, many non-Frankia actinobacteria have been isolated from actinorhizal root nodules suggesting that they might contribute to nodulation. Two Nocardia strains, BMG51109 and BMG111209, were isolated from Casuarina glauca nodules, and they induced root nodule-like structures in original host plant promoting seedling growth. The formed root nodule-like structures lacked a nodular root at the apex, were not capable of reducing nitrogen and had their cortical cells occupied with rod-shaped Nocardiae cells. Both Nocardia strains induced root hair deformation on the host plant. BMG111209 strain induced the expression of the ProCgNin:Gus gene, a plant gene involved in the early steps of the infection process and nodulation development. Nocardia strain BMG51109 produced three types of auxins (Indole-3-acetic acid [IAA], Indole-3-Byturic Acid [IBA] and Phenyl Acetic Acid [PAA]), while Nocardia BMG111209 only produced IAA. Analysis of the Nocardia genomes identified several important predicted biosynthetic gene clusters for plant phytohormones, secondary metabolites, and novel natural products. Co-infection studies showed that Nocardia strain BMG51109 plays a role as a "helper bacteria" promoting an earlier onset of nodulation. This study raises many questions on the ecological significance and functionality of Nocardia bacteria in actinorhizal symbioses.

Isolation and molecular characterization of Frankia strains resistant to some heavy metals.

Frankia strains isolated from Saudi Arabia, reported for the first time, were identified based on the morphological and molecular tools compared to those isolated from Egypt. All strains displayed typical morphological characterization of Frankia strains represented by branched hyphae, production of vesicles and sporangia. The phylogenetic analysis and relationships among Frankia strains were investigated by comparing 16S rRNA gene sequences. The analysis revealed three genetic groups which formed two clusters. The first cluster was composed of eight Frankia strains subdivided into two genetic groups (one group containing five strains; CgIT3 L2 , CgIS3 N2 , CgIS1 N1, CgIT7N2, and G5; the other group included of three strains: CgIT5L3, CgIS1 N2 , and CcI13). The second cluster was composed of only one genetic group of Frankia strain CgIS3 N1 . The strains in each genetic group exhibited similar genetic distances. All Frankia strains were able to reinfect their host of Casuarina species. For ability of these strains to resist heavy metals, our results proved that all Frankia strains isolated can resist Cu, Co, and Zn at low concentration except Pb which exhibit highly toxic effect at the same concentration used. Frankia strain G5 was proved to be the most resistant strain for heavy metals tested.

Frankia Diversity in Host Plant Root Nodules Is Independent of Abundance or Relative Diversity of Frankia Populations in Corresponding Rhizosphere Soils.

Actinorhizal plants form nitrogen-fixing root nodules in symbiosis with soil-dwelling actinobacteria within the genus Frankia, and specific Frankia taxonomic clusters nodulate plants in corresponding host infection groups. In same-soil microcosms, we observed that some host species were nodulated (Alnus glutinosa, Alnus cordata, Shepherdia argentea, Casuarina equisetifolia) while others were not (Alnus viridis, Hippophaë rhamnoides). Nodule populations were represented by eight different sequences of nifH gene fragments. Two of these sequences characterized frankiae in S. argentea nodules, and three others characterized frankiae in A. glutinosa nodules. Frankiae in A. cordata nodules were represented by five sequences, one of which was also found in nodules from A. glutinosa and C. equisetifolia, while another was detected in nodules from A. glutinosa Quantitative PCR assays showed that vegetation generally increased the abundance of frankiae in soil, independently of the target gene (i.e., nifH or the 23S rRNA gene). Targeted Illumina sequencing of Frankia-specific nifH gene fragments detected 24 unique sequences from rhizosphere soils, 4 of which were also found in nodules, while the remaining 4 sequences in nodules were not found in soils. Seven of the 24 sequences from soils represented >90% of the reads obtained in most samples; the 2 most abundant sequences from soils were not found in root nodules, and only 2 of the sequences from soils were detected in nodules. These results demonstrate large differences between detectable Frankia populations in soil and those in root nodules, suggesting that root nodule formation is not a function of the abundance or relative diversity of specific Frankia populations in soils.IMPORTANCE The nitrogen-fixing actinobacterium Frankia forms root nodules on actinorhizal plants, with members of specific Frankia taxonomic clusters nodulating plants in corresponding host infection groups. We assessed Frankia diversity in root nodules of different host plant species, and we related specific populations to the abundance and relative distribution of indigenous frankiae in rhizosphere soils. Large differences were observed between detectable Frankia populations in soil and those in root nodules, suggesting that root nodule formation is not a function of the abundance or relative diversity of specific Frankia populations in soils but rather results from plants potentially selecting frankiae from the soil for root nodule formation. These data also highlight the necessity of using a combination of different assessment tools so as to adequately address methodological constraints that could produce contradictory data sets.

A systematic overview of Descolea (Agaricales) in the Nothofagaceae forests of Patagonia.

The descolea clade includes species of ectomycorrhizal basidiomycetes in the genera Descolea, Setchelliogaster, Descomyces, and Timgrovea that are known primarily from the Southern Hemisphere. Taxa in this group produce basidiomes that range in morphology from typical epigeous mushrooms (Descolea) and secotioid taxa (Setchelliogaster) to fully gasteroid species (Descomyces and Timgrovea). High intraspecific morphological variation has been reported in several species within this clade, suggesting that careful morphological and molecular studies are needed to refine species concepts. Molecular analyses of fresh Patagonian collections in conjunction with taxonomic studies have confirmed high variability in key morphological features, including overall sporocarp form, spore shape and dimensions, universal veil remnants, and cuticle configuration. Based on our synthesis, we emend the genus Descolea to include sequestrate species. We describe the new sequestrate taxon Descolea inferna sp. nov. from Nothofagaceae forests in Patagonia and we propose Cortinarius squamatus as a synonym of our new combination Descolea brunnea. We also formalize the identity of Descolea pallida as a synonym of Descolea antarctica and provide new specimens of Cortinarius archeuretus, a species that has not been encountered since the original discovery during the expeditions of Roland Thaxter in 1905-1906. Here we re-describe and transfer this species to Descolea as D. archeureta. We also discuss diagnostic features that can be used to delimitate the four known South American taxa in the descolea clade.

Genomic, transcriptomic, and proteomic approaches towards understanding the molecular mechanisms of salt tolerance in Frankia strains isolated from Casuarina trees.

BACKGROUND: Soil salinization is a worldwide problem that is intensifying because of the effects of climate change. An effective method for the reclamation of salt-affected soils involves initiating plant succession using fast growing, nitrogen fixing actinorhizal trees such as the Casuarina. The salt tolerance of Casuarina is enhanced by the nitrogen-fixing symbiosis that they form with the actinobacterium Frankia. Identification and molecular characterization of salt-tolerant Casuarina species and associated Frankia is imperative for the successful utilization of Casuarina trees in saline soil reclamation efforts. In this study, salt-tolerant and salt-sensitive Casuarina associated Frankia strains were identified and comparative genomics, transcriptome profiling, and proteomics were employed to elucidate the molecular mechanisms of salt and osmotic stress tolerance. RESULTS: Salt-tolerant Frankia strains (CcI6 and Allo2) that could withstand up to 1000 mM NaCl and a salt-sensitive Frankia strain (CcI3) which could withstand only up to 475 mM NaCl were identified. The remaining isolates had intermediate levels of salt tolerance with MIC values ranging from 650 mM to 750 mM. Comparative genomic analysis showed that all of the Frankia isolates from Casuarina belonged to the same species (Frankia casuarinae). Pangenome analysis revealed a high abundance of singletons among all Casuarina isolates. The two salt-tolerant strains contained 153 shared single copy genes (most of which code for hypothetical proteins) that were not found in the salt-sensitive(CcI3) and moderately salt-tolerant (CeD) strains. RNA-seq analysis of one of the two salt-tolerant strains (Frankia sp. strain CcI6) revealed hundreds of genes differentially expressed under salt and/or osmotic stress. Among the 153 genes, 7 and 7 were responsive to salt and osmotic stress, respectively. Proteomic profiling confirmed the transcriptome results and identified 19 and 8 salt and/or osmotic stress-responsive proteins in the salt-tolerant (CcI6) and the salt-sensitive (CcI3) strains, respectively. CONCLUSION: Genetic differences between salt-tolerant and salt-sensitive Frankia strains isolated from Casuarina were identified. Transcriptome and proteome profiling of a salt-tolerant strain was used to determine molecular differences correlated with differential salt-tolerance and several candidate genes were identified. Mechanisms involving transcriptional and translational regulation, cell envelop remodeling, and previously uncharacterized proteins appear to be important for salt tolerance. Physiological and mutational analyses will further shed light on the molecular mechanism of salt tolerance in Casuarina associated Frankia isolates.

The Gondwanan connection - Southern temperate Amanita lineages and the description of the first sequestrate species from the Americas.

Amanita is a diverse and cosmopolitan genus of ectomycorrhizal fungi. We describe Amanita nouhrae sp. nov., a new hypogeous ('truffle-like') species associated with Nothofagus antarctica in northern Patagonia. This constitutes the first report of a sequestrate Amanita from the Americas. Thick-walled basidiospores ornamented on the interior spore wall ('crassospores') were observed consistently in A. nouhrae and its sister epigeous taxon Amanita morenoi, a rarely collected but apparently common species from northern Patagonia that has sometimes been misidentified as the Australian taxon Amanita umbrinella. Nuclear 18S and 28S ribosomal DNA and mitochondrial 16S and 26S DNA placed these two species in a southern temperate clade within subgenus Amanita, together with other South American and Australian species. Based on a dated genus-level phylogeny, we estimate that the southern temperate clade may have originated near the Eocene/Oligocene boundary (ca. 35 Ma ± 10 Ma). This date suggests a broadly distributed ancestor in the Southern Hemisphere, which probably diversified as a result of continental drift, as well as the initiation of the Antarctic glaciation. By comparison, we show that this clade follows an exceptional biogeographic pattern within a genus otherwise seemingly dominated by Northern Hemisphere dispersal.

New species of Tomentella (Thelephorales) from the Patagonian Andes forests.

The genus Tomentella forms abundant ectomycorrhizae in coniferous and deciduous forests worldwide. Molecular identification of root tips suggests undescribed species in the Nothofagus forests of Patagonia, Argentina. Tomentella tenuissima, T. pulvinulata and T. patagonica are described here as new to science based on morphological and molecular analyses. Their host range is addressed using available soil sequences. The identity of previous records of T. galzinii and T. radiosa are discussed with morphological and molecular evidence.

Gymnopanella nothofagi, a new genus and species of gymnopoid fungi (Omphalotaceae) from Chilean Nothofagus forest.

A novel, lignicolous agaric from Nothofagus forests of southern Chile is described as a new genus and species, Gymnopanella nothofagi This taxon falls within the family Omphalotaceae as a sister group to Gymnopus in phylogenetic analyses based on sequences spanning the internal transcribed spacer region and D1/D2 region of nuclear 28S rDNA. Morphologically it is characterized by convex to flabellate basidiomata with distinctly gelatinized trama, pileipellis in the form of a cutis with erect fascicles of cylindrical, spirally incrusted hyphae and nonamyloid, broadly ellipsoid basidiospores. This combination of features, in particular the lack of a rameales structure, serve to distinguish Gymnopanella from Gymnopus, Marasmiellus and other similar genera of the Omphalotaceae or Marasmiaceae. The new taxon is known only from Chilean Nothofagus forests at approximately 45-46° south latitude, but concerted searching in similar habitats in surrounding areas or in New Zealand may extend the known range considerably.