Prevalence of interspecific hybrids amongst asexual fungal endophytes of grasses

Epichloë endophytes are fungal symbionts of grasses that span a continuum including asexual mutualists that are vertically transmitted, obligately sexual pathogens that are horizontally transmitted, and mixed‐strategy symbionts with both mutualistic and pathogenic capabilities. Here we show that processes of genome evolution differ markedly for the different symbiont types. Genetic and phylogenetic analysis was conducted of a broad taxonomic, ecological and geographical sample of sexual and asexual isolates, in which were identified and sequenced alleles of genes for β‐tubulin (tub2) and translation elongation factor 1‐α (tef1), and microsatellite alleles were identified by length polymorphisms. The majority of asexual isolates had two or three alleles of most loci, but every sexual isolate had only single alleles for each locus. Phylogenetic analysis of tub2 and tef1 indicated that in all instances of multiple alleles in an isolate, the alleles were derived from different sexual species. It is concluded that, whereas horizontally transmissible species had haploid genomes and speciation occurred cladistically, most of the strictly seedborne mutualists were interspecific hybrids with heteroploid (aneuploid or polyploid) genomes. Furthermore, the phylogenetic evidence indicated that, in at least some instances, hybridization followed rather than caused evolution of the strictly seedborne habit. Therefore, the abundance of hybrid species among grass endophytes, and their prevalence in many host populations suggests a selective advantage of hybridization for the mutualistic endophytes.     

Asexual Neotyphodium endophytes in a native grass reduce competitive abilities

Asexual, vertically transmitted endophytes are well known for increasing competitive abilities of agronomic grasses, but little is known about endophyte–host interactions in native grasses. We tested whether the asexual Neotyphodium endophyte enhances competitive abilities in a native grass, Arizona fescue, in a field experiment pairing naturally infected (E+) and uninfected (E?) plants, and in a greenhouse experiment pairing E+ and E? (experimentally removed) plants, under varying levels of soil water and nutrients. In the field experiment, E? plants had greater vegetative, but not reproductive, growth than E+ plants. In the greenhouse experiment, where plant genotype was strictly controlled, E? plants consistently outperformed their E+ counterparts in terms of root and shoot biomass. Thus, Neotyphodium infection decreases host fitness via reduced competitive properties, at least in the short term. These findings contrast starkly with most endophyte studies involving introduced, agronomic grasses where infection increases competitive abilities, and the interaction is viewed as highly mutualistic.     

Genetic diversity of invasive and native Cichla (Pisces: Perciformes) populations in Brazil with evidence of interspecific hybridization

Invasive and native populations of the Amazonian fishes 'peacock bass' Cichla monoculus and of a not yet described species 'blue tucunaré' here referred as Cichla sp. 'Azul' were analysed for genetic diversity using the hypervariable domain of the mitochondrial DNA (mtDNA) control region plus steady diagnostic random amplified polymorphic DNA loci. There is no detailed historical record of the introduction of Cichla species into the Upper Paraná River basin, where they became invasive and a potential threat to local ichthyofauna. Genetic diversity among invasive populations confirmed the hypothesis of multiple introductions in this hydrographic basin. Moreover, a large and previously unknown population of natural fertile hybrids between C. cf. monoculus and Cichla sp. 'Azul' was identified in the Itaipu hydroelectric reservoir and in the floodplain of the Upper Paraná River. Crossbred morphotypes were similar to C. cf. monoculus , but their morphological identification was not unequivocal. This hybrid population was characterized by high genetic diversity and it was composed of hybrids possessing concurrently nuclear DNA fragments specific for C. cf. monoculus as well as fragments specific for Cichla sp. 'Azul'. The nuclear DNA markers indicated that reproductive isolation between C. cf. monoculus and Cichla sp. 'Azul' has broken down in the new environment, and mtDNA sequences revealed that both species can be the female donor in the interspecific crosses. The data presented herein are potentially useful for future taxonomic, genetic and evolutionary studies in the complex Cichla group, for monitoring of invasive populations, and for further development of ecological guidelines.     

Comparison of the diversity,composition, and host recurrence of xylariaceous endophytes in subtropical,cool temperate,and subboreal regions in Japan

The diversity, composition, and host recurrence of endophytic fungi in the Xylariaceae were compared in subtropical (ST), cool temperate (CT), and subboreal forests (SB) in Japan based on the 28S ribosomal DNA sequences from fungal isolates. A total of 610 isolates were obtained from the leaves of 167 tree species in three sites, which were classified into 42 operational taxonomic units (OTUs) at the 99 % similarity level of the 28S rDNA sequence. ST, CT, and SB yielded 31, 13, and three OTUs, respectively. The OTU richness, diversity, and evenness of fungal communities were in the order: ST > CT > SB. The 42 OTUs were assigned to nine genera in the Xylariaceae: Xylaria, Annulohypoxylon, Anthostomella, Biscogniauxia, Nemania, Hypoxylon, Muscodor, Daldinia, and Rosellinia. Xylarioid isolates in the subfamily Xylarioideae outnumbered Hypoxyloid isolates in the subfamily Hypoxyloideae in ST and CT, whereas the opposite was found in SB. Sørensen’s quotient of similarity was generally low between the three sites. Host recurrence of fungal OTUs was evaluated with the degree of specialization of interaction network between xylariaceous endophytes and plant species and compared between the three sites. We found that the networks in the three sites showed a significantly higher degree of specialization than simulated networks, where partners were associated randomly. Permutational multivariate analyses of variance indicated that plant family and leaf trait significantly affected the OTU composition in ST, which can account for the specialization of interaction network and host recurrence of xylariaceous endophytes.     

Endophytic fungi alter relationships between diversity and ecosystem properties

Recent studies have expanded research on biodiversity by investigating whether the effects of diversity on ecosystem functioning hinge on the presence of symbiotic microorganisms. Cool‐season grasses commonly harbour endophytic fungi that can enhance plant resistance to herbivory, drought and competition. We address whether these endosymbionts modify relationships between diversity and two ecosystem properties: productivity and invasibility. We develop a graphical model that predicts endophyte infection of a grass host will weaken correlations between diversity and ecosystem properties. We then use a long‐term field experiment to test this prediction by manipulating symbiosis in tall fescue grass (Festuca arundinacea), a common and invasive species in the US. As predicted, endophyte infection reduced the strength of correlations between diversity and both primary productivity and the invasiveness of tall fescue. By altering relationships between diversity and ecosystem functioning, endophytic fungi may contribute more to the dynamics of communities than previously supposed.     

Distribution and diversity of endophytes in seagrasses

The rhizome and leaf tissues of 10 seagrass species (seven of the family Cymodoceaceae and three of the family Hydrocharitaceae) collected along the coast of Tamilnadu state, southern India were sampled for the presence of fungal endophytes. A culture-based study revealed that the colonization frequency (CF%) of the endophytes was generally lower than that reported for terrestrial plants and that members of Eurotiomycetes dominate the endophyte assemblage in these marine angiosperms. The CF% of the endophytes was more for the rhizome than for the leaves. Species of Aspergillus, Paecilomyces and Penicillium occurred in high CF% and could be isolated from both the tissue types of seagrasses belonging to both the families.     

Detecting ancient codispersals and host shifts by double dating of host and parasite phylogenies: Application in proctophyllodid feather mites associated with passerine birds

Inferring cophylogeographic events requires matching the timing of these events on both host and symbiont (e.g., parasites) phylogenies because divergences of hosts and their symbionts may not temporally coincide, and host switches may occur. We investigate a large radiation of birds (Passeriformes) and their permanent symbionts, the proctophyllodid feather mites (117 species from 116 bird species; six genes, 11,468 nt aligned) using two time‐calibration strategies for mites: fossils only and host phylogeography only. Out of 10 putative cophylogeographic events 4 agree in timing for both symbiont and host events being synchronous co‐origins or codispersals; three were based on host shifts, but agree in timing being very close to the origin of modern hosts; two disagree; and one large basal mite split was seemingly independent from host phylogeography. Among these events was an ancient (21–25.3 Mya), synchronous codispersal from the Old World leading to the origin and diversifications of New World emberizoid passerids and their mites, the thraupis + quadratus species groups of Proctophyllodes. Our framework offers a more robust detection of host and symbiont cophylogeographic events (as compared to host‐symbiont reconciliation analysis and using host phylogeography for time‐calibration) and provides independent data for testing alternative hypotheses on timing of host diversification and dispersal.     

Genome differentiation in Magonoliaceae as revealed from meiotic pairing in interspecific and intergeneric hybrids

The cross compatibility within and between Yulania Spach and Michelia L.(Magnoliaceae) is relatively good and various such hybrids,obtained by conventional artificial hybridization,are available.The aim of the present study was to determine the extent of genome differentiation between the species involved in these crosses through the observation of chromosome pairing during meiosis in pollen mother cells (PMCs) of the hybrids.Chromosome pairing behavior was studied in five species (2n =38) and two interspecific hybrids of Michelia,eight species (2n =38,76 and 114) and 10 interspecific hybrids of Yulania,and three intergeneric hybrids between Michelia and Yulania.The results showed that chromosome pairing was normal with bivalent formation in diploid parental species and in interspecific hybrids.In addition to bivalents,multivalents were encountered in polyploid parental species and polyploid interspecific hybrids.In the intergeneric hybrids between a tetraploid Yulania and two diploid Michelia,19 chromosomes,most likely originating from Michelia,were unable to synapse from zygotene to metaphase I.Meiotic chromosome pairing indicated a high degree of homology between species within Michelia and Yulania and less homology between the genomes of these two genera.The differentiation of morphological characters and the distinctness of natural distribution also support the conclusion that these two genera are likely independent monophyletic groups.This suggests that the two genera were split at early evolution of Magnoliaceae and the overlapping characteristics in external morphology and internal structures of the two genera may be the result of parallel evolution or ancient common ancestry.     

Three symbionts involved in interspecific plant-soil feedback: epichloid endophytes and mycorrhizal fungi affect the performance of rhizobia-legume symbiosis

Aims

Plants interact by modifying soil conditions in plant-soil feedback processes. Foliar endophytes of grasses exert multiple effects on host rhizosphere with potential consequences on plant-soil feedback. Here, we hypothesize that the grass-endophyte symbiosis impairs soil symbiotic potential, and in turn influences legume performance and nitrogen acquisition.

Methods

Soil was conditioned in pots, growing Lolium multiflorum with or without the fungal endophyte Epichloë and with or without arbuscular mycorrhizal fungi (AMF). Then, Trifolium repens grew in all types of conditioned soils with high or low rhizobia availability.

Results

Endophyte soil conditioning reduced AMF spores number and rhizobial nodules (?27 % and ?38 %, respectively). Seedling survival was lower in endophyte-conditioned soil and higher in mycorrhizal soils (?27 % and +24 %, respectively). High rhizobia-availability allowed greater growth and nitrogen acquisition, independent of soil conditioning. Low rhizobia-availability allowed both effects only in endophyte-conditioned soil.

Conclusion

Endophyte-induced changes in soil (i) hindered symbiotic potential by reducing AMF spore availability or rhizobia nodulation, (ii) impaired legume survival irrespective of belowground symbionts presence, but (iii) mimicked rhizobia effects, enhancing growth and nitrogen fixation in poorly nodulated plants. Our results show that shoot and root symbionts can be interactively involved in interspecific plant-soil feedback.

     

Differential growth promotion of poplar and birch inoculated with three dark septate endophytes in two trace element-contaminated soils

Dark septate endophytes (DSEs) are abundant in stressful environments, including trace element (TE)-enriched soils. However, knowledge about the effects of DSEs on plant growth in such soils is poor compared to the well-known mycorrhizal fungi. The aim of this work was to evaluate the effects of three DSE strains isolated from TE-contaminated soils on the growth and mineral nutrition of Betula pendula and Populus tremula x alba grown on two contrasting TE-polluted soils. The three DSEs evenly colonized the two plant species in both soils. Nevertheless, plant responses to DSE inoculation varied from neutral to beneficial depending on soil properties. Depending on fungal strain and plant species, different factors seemed to contribute to plant growth promotion. Phialophora mustea Pr27 and Leptodontidium Pr30 decreased lipid peroxidation in birch shoots. Chlorophyll, K, and P concentrations increased in the shoots of Leptodontidium Pr30-inoculated trees, whereas Cd concentration decreased in Cadophora Fe06-inoculated birch. The absence of a general DSE-mediated plant growth–promoting behavior could represent a limiting factor for a generic use of DSEs in the tree-based phytomanagement of TE-contaminated soils. Our results suggest that the selection of strains adapted to particular edaphic conditions should not be overlooked within the framework of phytomanagement.     

Patterns of association between crucifers and their flower-mimic pathogens: host jumps are more common than coevolution or cospeciation

Morphological and molecular phylogenies of animal parasites have often shown parallel cladogenesis, supporting hypotheses of coevolution. Few studies of the phylogenetic history for plants and their pathogens exist. Gene-for-gene interactions suggest that plant pathogens ought to have similar phylogenetic histories as their hosts. However, high dispersability combined with an inability to choose to leave if an inappropriate host has been landed on could increase the likelihood of host jumps and thus decrease phylogenetic congruence between plant pathogens and their hosts. In this study, I examined the pattern of association between the flower-mimicking crucifer rusts and their hosts by comparing independent host phylogenies (based on both cpDNA trnL-F introns and nuclear internal transcribed spacer [ITS] sequences) with that of their rust pathogens (based on ITS sequences). The expectation was that if the pathogens coevolved or cospeciated with their hosts, then their phylogenies should be congruent. Host-tracking coevolution can be differentiated from cospeciation by examining the times of divergence: If the pathogens are younger than the hosts, then it is likely that host tracking has occurred. For the crucifer rusts and their hosts, there was little evidence of parallel cladogenesis, suggesting that both cospeciation and coevolutionary tracking are rare. Instead, the most common pattern was one of host jumps to geographically associated taxa. There are at least three factors that may have contributed to the geographic structuring of the data. First, along the east-west transect stretching from the Rocky Mountains to California, large differences in rainfall and the timing of rainfall may reduce long-distance gene flow. Second, although dispersal of infectious spores is by wind, sexual reproduction of these fungi depends on insects, which move short distances. Third, host shifts are most likely to occur to geographically available taxa. Any species that grows adjacent to infected plants will be exposed to millions of spores, and the probability of eventual infection by a new mutant increases with greater exposure. Thus, patterns of association between the crucifers and their flower-mimic pathogens reflect jumps to geographically available hosts, which are not necessarily those that are most closely related.     

Epichloë fungal endophytes and the formation of synthetic symbioses in Hordeeae (=Triticeae) grasses

This review examines two classes of organism that live in symbiosis; grasses, and fungi. Specifically it deals with grasses of the tribe Hordeeae (formerly Triticeae) of the subfamily Poöideae and the Epichloë fungi of family Clavicipitaceae. Epichloë endophytes, particularly asexual forms, have important roles in pastoral agricultural systems in the Americas, Australia, and New Zealand. Selected strains add value to some grass-based forage systems by providing both biotic and abiotic stress resistance. The importance of cereal grasses such as wheat, barley, rye, and oats to human and animal nutrition and indeed to the foundation and maintenance of human civilization is well documented. Both organism classes, Epichloë endophytes and cereal grasses, are of great importance in their own contexts. Here, we seek to review these two classes of organism and examine the possibility of bringing them together in symbiosis with the ultimate goal of improving cereal production systems.     

Genetic diversity of root-associated fungal endophytes from Calluna vulgaris at contrasting field sites

A total of 107 putative ericoid mycorrhizal endophytes were isolated from hair roots of Calluna vulgaris from two abandoned arsenic/copper mine sites and a natural heathland site in southwest England. The endophytes were initially grouped as 14 RFLP types, based on the results of ITS-RFLP analysis using the restriction endonucleases Hin f I, Rsa I and Hae III. ITS sequences were obtained for representative isolates from each RFLP type and compared phylogenetically with sequences for known ericoid mycorrhizal endophytes and selected ascomycetes. The majority of endophyte isolates (62–92%) from each site were identified as Hymenoscyphus ericae , but a number of other less common mycorrhizal RFLP types were also identified, all of which appear to have strong affinities with the order Leotiales. None of the less common RFLP types was isolated from C. vulgaris at more than one field site. Neighbour-joining analysis indicated similarities between the endophytes from C. vulgaris and mycorrhizal endophytes isolated from other Ericaceae and Epacridaceae hosts in North America and Australia.     

Seasonality of arbuscular mycorrhizal symbiosis and dark septate endophytes in a grassland site in southwest China

Arbuscular mycorrhizal and dark septate endophytic fungal colonization in a grassland in Kunming, southwest China, was investigated monthly over one year. All plant roots surveyed were co-colonized by arbuscular mycorrhizal and dark septate endophytic fungi in this grassland. Both arbuscular mycorrhizal and dark septate endophytic fungal colonization fluctuated significantly throughout the year, and their seasonal patterns were different in each plant species. The relationships between environmental (climatic and edaphic) factors and fungal colonization were also studied. Correlation analysis demonstrated that arbuscular mycorrhizal colonization was significantly correlative with environmental factors (rainfall, sunlight hours, soil P, etc.), but dark septate endophytic fungal colonization was only correlative with relative humidity and sunlight hours.     

Diversity of fungal endophytes in some medicinal plants of Himachal Pradesh,India

Fungal endophytes were isolated from surface sterilised leaf segments of five medicinal plants collected from Mandi district, Himachal Pradesh, India. A total of 373 fungal strains belonging to 15 fungal genera and 18 species, Aspergillus niger, A. flavus, A. clavatus, A. variecolor, Penicillium chrsogenum, Alternaria alternata, Curvularia lunata, Haplosporium sp., Phoma sp., Nigrospora sp., Colletotrichum sp., Cladosporium sp., Stemphylium sp., Fusarium sp., Geotrichum sp., Phomopsis sp., Trichoderma sp., Rhizopus sp. and some sterile mycelium were isolated from all the plants. The relative frequency, isolation rate and colonisation rates of endophytes were used to study the endophytic diversity. The results showed that the highest colonisation rate (93.05%) was observed in Adhathoda vasica, while it was 91.66% in Ocimum sanctum, 85% in Viola odorata, 82.81% Cannabis sativa and lowest (61.11%) in Withania somnifera. Moreover, reading the richness and diversity of the endophytic fungi, the highest was obtained for O. sanctum, W. somnifera and C. sativa having eight species each, while lowest (6 and 4) was obtained from A. vasica and V. odorata, respectively. As the role of endophytic organisms in defensive mechanisms of plants is now well established, the present study is an important step to find new and interesting endophytes among the medicinal plants.     

Higher host plant specialization of root‐associated endophytes than mycorrhizal fungi along an arctic elevational gradient

How community‐level specialization differs among groups of organisms, and changes along environmental gradients, is fundamental to understanding the mechanisms influencing ecological communities. In this paper, we investigate the specialization of root‐associated fungi for plant species, asking whether the level of specialization varies with elevation. For this, we applied DNA barcoding based on the ITS region to root samples of five plant species equivalently sampled along an elevational gradient at a high arctic site. To assess whether the level of specialization changed with elevation and whether the observed patterns varied between mycorrhizal and endophytic fungi, we applied a joint species distribution modeling approach. Our results show that host plant specialization is not environmentally constrained in arctic root‐associated fungal communities, since there was no evidence for changing specialization with elevation, even if the composition of root‐associated fungal communities changed substantially. However, the level of specialization for particular plant species differed among fungal groups, root‐associated endophytic fungal communities being highly specialized on particular host species, and mycorrhizal fungi showing almost no signs of specialization. Our results suggest that plant identity affects associated mycorrhizal and endophytic fungi differently, highlighting the need of considering both endophytic and mycorrhizal fungi when studying specialization in root‐associated fungal communities.