Biotic and abiotic constraints that facilitate host exclusivity of Gondwanamyces and Ophiostoma on Protea

Estimations of global fungal diversity are hampered by a limited understanding of the forces that dictate host exclusivity in saprobic microfungi. To consider this problem for Gondwanamyces and Ophiostoma found in the flower heads of Protea in South Africa, we determined the role of various factors thought to influence their host exclusivity. Results showed that various biotic and abiotic factors influence the growth and survival of these fungi in vitro. Monitoring temperature and relative humidity (RH) fluctuations within infructescences in vivo revealed considerable microclimatic differences between different Protea spp. Fungal growth and survival at different RH levels experienced in the field suggested that this factor does not play a major role in host exclusivity of these fungi. Maximum temperatures within infructescences and host preferences of the vectors of Gondwanamyces and Ophiostoma appear to play a substantial part in determining colonisation of Protea in general. However, these factors did not explain host exclusivity of specific fungal species towards particular Protea hosts. In contrast, differential growth of fungal species on media containing macerated tissue of Protea showed that Gondwanamyces and Ophiostoma grow best on tissue from their natural hosts. Thus, host chemistry plays a role in host exclusivity of these fungi, although some species grew vigorously on tissue of Protea spp. with which they are not naturally associated. A combination of host chemistry and temperature partially explains host exclusivity, but the relationship for these factors on the tested saprobic microfungi and their hosts is clearly complex and most likely includes combinations of various biotic and abiotic factors including those emerging from this study.     

Powdery mildew susceptibility and biotrophic infection strategies

Plants are resistant to most potentially pathogenic microbes. This forces plant pathogens to develop sophisticated strategies to overcome basic plant resistance, either by masking intrusion or by suppression of host defences. This is particularly true for fungal pathogens, which establish long lasting interactions with living host tissue, without causing visible damage to invaded cells. The interactions of cereal crops and Arabidopsis with powdery mildew fungi are model systems for understanding host resistance. Currently, these systems are also promoting the understanding of fungal infection by identifying fungal pathogenicity and virulence factors and host target sites. This minireview focuses on recent findings about host susceptibility and the way powdery mildew fungi might induce it.     

High diversity and low specificity of fungi associated with seedless epiphytic plants

Epiphytes, which grow on other plants for support, make up a large portion of Earth's plant diversity. Like other plants, their surfaces and interiors are colonized by diverse assemblages of fungi that can benefit their hosts by increasing tolerance for abiotic stressors and resistance to disease or harm them as pathogens. Fungal communities associated with epiphytic plants and the processes that structure these communities are poorly known. To address this, we sampled seven epiphytic seedless plant taxa in a Costa Rican rainforest and examined the effects of host identity and microhabitat on external and endophytic fungal communities. We found low host specificity for both external and endophytic fungi and weak differentiation between epiphytic and neighboring epilithic plant hosts. High turnover in fungi within and between hosts and habitats reveals that epiphytic plant-associated fungal communities are highly diverse and suggests that they are structured by stochastic processes.     

Differentially regulated high‐affinity iron assimilation systems support growth of the various cell types in the dimorphic pathogen Talaromyces marneffei

Iron is a key trace element important for many biochemical processes and its availability varies with the environment. For human pathogenic fungi iron acquisition can be particularly problematical because host cells sequester free iron as part of the acute‐phase response to infection. Fungi rely on high‐affinity iron uptake systems, such as reductive iron assimilation (RIA) and siderophore‐mediated iron uptake (non‐RIA). These have been extensively studied in pathogenic fungi that exist outside of host cells, but much less is known for intracellular fungal pathogens. Talaromyces marneffei is a dimorphic fungal pathogen endemic to Southeast Asia. In the host T. marneffei resides within macrophages where it grows as a fission yeast. T. marneffei has genes of both iron assimilation systems as well as a paralogue of the siderophore biosynthetic gene sidA, designated sidX. Unlike other fungi, deletion of sidA or sidX resulted in cell type‐specific effects. Mutant analysis showed that T. marneffei yeast cells also employ RIA for iron acquisition, providing an additional system in this cell type that differs substantially from hyphal cells. These data illustrate the specialized iron acquisition systems used by the different cell types of a dimorphic fungal pathogen and highlight the complexity in siderophore‐biosynthetic pathways amongst fungi.     

Fungal communities associated with roots of two closely related Juglandaceae species with a disjunct distribution in the tropics

We studied the biogeography and community structure of root-associated and ectomycorrhizal fungal communities in two related species of tropical Juglandaceae that have disjunct distributions in Asia and Mesoamerica. We tested the effects of environmental and dispersal factors in structuring root-associated fungi at a regional scale. We used Illumina sequencing to document fungi on the roots of Oreomunnea mexicana in Panama and Mexico and Alfaropsis roxburghiana in China. Ectomycorrhizal fungi dominated the communities with both hosts but we detected a more diverse root-associated fungal community in Alfaropsis but higher ectomycorrhizal fungi richness in Oreomunnea. Geographic distance was the best predictor of variation in fungal species composition, when including both hosts and when analyzing each host independently. However, our results showed a high correlation between geographic distance and abiotic variables, and therefore we were not able to determine if the observed changes in fungal community composition were explained also by spatially structured environmental or phylogenetic factors.     

Changes in ectomycorrhizal fungal community composition and declining diversity along a 2‐million‐year soil chronosequence

Ectomycorrhizal (ECM) fungal communities covary with host plant communities along soil fertility gradients, yet it is unclear whether this reflects changes in host composition, fungal edaphic specialization or priority effects during fungal community establishment. We grew two co‐occurring ECM plant species (to control for host identity) in soils collected along a 2‐million‐year chronosequence representing a strong soil fertility gradient and used soil manipulations to disentangle the effects of edaphic properties from those due to fungal inoculum. Ectomycorrhizal fungal community composition changed and richness declined with increasing soil age; these changes were linked to pedogenesis‐driven shifts in edaphic properties, particularly pH and resin‐exchangeable and organic phosphorus. However, when differences in inoculum potential or soil abiotic properties among soil ages were removed while host identity was held constant, differences in ECM fungal communities and richness among chronosequence stages disappeared. Our results show that ECM fungal communities strongly vary during long‐term ecosystem development, even within the same hosts. However, these changes could not be attributed to short‐term fungal edaphic specialization or differences in fungal inoculum (i.e. density and composition) alone. Rather, they must reflect longer‐term ecosystem‐level feedback between soil, vegetation and ECM fungi during pedogenesis.     

Unraveling the role of fungal symbionts in plant abiotic stress tolerance

Fungal symbionts have been found to be associated with every plant studied in the natural ecosystem, where they colonize and reside entirely or partially in the internal tissues of their host plant. Fungal endophytes can express/form a range of different lifestyle/relationships with different host including symbiotic, mutualistic, commensalistic and parasitic in response to host genotype and environmental factors. In mutualistic association fungal endophyte can enhance growth, increase reproductive success and confer biotic and abiotic stress tolerance to its host plant. Since abiotic stress such as, drought, high soil salinity, heat, cold, oxidative stress and heavy metal toxicity is the common adverse environmental conditions that affect and limit crop productivity worldwide. It may be a promising alternative strategy to exploit fungal endophytes to overcome the limitations to crop production brought by abiotic stress. There is an increasing interest in developing the potential biotechnological applications of fungal endophytes for improving plant stress tolerance and sustainable production of food crops. Here we have described the fungal symbioses, fungal symbionts and their role in abiotic stress tolerance. A putative mechanism of stress tolerance by symbionts has also been covered.Key words: abiotic stress, endophytes, fungal symbiont, mycorrhizal fungus, Piriformospora indica, stress tolerance, symbiosis     

Spatial patterns and determinants of common root-associated fungi in a subtropical forest of China

Aims Spatial patterns of fungal populations are affected by plant distribution, abiotic factors, fungal dispersal ability and inter-species interactions. While several studies have addressed spatial patterns of some mycorrhizal, saprotrophic and pathogenic fungi, the method based on fruit-body surveys is not efficient and unreliable to study the spatial pattern of root-associated fungal species because most fungi in plant roots do not have sporocarps and cannot be identified based only on morphological traits. Our aims are (i) to determine the spatial pattern of common root-associated fungi; (ii) to evaluate whether the abundance and spatial pattern of root-associated fungi and categories of fungi, reflect their biotic and abiotic niche constraints.     

Gene expression systems for filamentous fungi.

The extraordinary capacity of filamentous fungi to produce large quantities of extracellular protein, together with the advent of DNA-mediated fungal transformation, has resulted in rapid advances in the development of gene expression systems for filamentous fungi. This review focuses on recent developments in the expression of both fungal and non-fungal genes and improvements to the host.     

More than 400 million years of evolution and some plants still can't make it on their own: plant stress tolerance via fungal symbiosis

All plants in natural ecosystems are thought to be symbioticwith mycorrhizal and/or endophytic fungi. Collectively, thesefungi express different symbiotic lifestyles ranging from parasitismto mutualism. Analysis of Colletotrichum species indicates thatindividual isolates can express either parasitic or mutualisticlifestyles depending on the host genotype colonized. The endophytecolonization pattern and lifestyle expression indicate thatplants can be discerned as either disease, non-disease, or non-hosts.Fitness benefits conferred by fungi expressing mutualistic lifestylesinclude biotic and abiotic stress tolerance, growth enhancement,and increased reproductive success. Analysis of plant–endophyteassociations in high stress habitats revealed that at leastsome fungal endophytes confer habitat-specific stress toleranceto host plants. Without the habitat-adapted fungal endophytes,the plants are unable to survive in their native habitats. Moreover,the endophytes have a broad host range encompassing both monocotsand eudicots, and confer habitat-specific stress tolerance toboth plant groups. Key words: Colletotrichum, fungal endophytes, stress tolerance, symbiosis, symbiotic lifestyle Received 19 June 2007; Revised 25 November 2007 Accepted 30 November 2007     

Fungal functional diversity inferred along Ellenberg's abiotic gradients: Palynological evidence from different soil microbiota

The aim of this paper is to analyse whether the functional diversity of the fungal community follows the environmental gradients as much as vascular plants. After determination of the Ellenberg's indicator values on the basis of 602 cormophyte species occurring in 110 permanent plots across Central Europe, the relation between soil fungi and the abiotic factors as defined by Ellenberg's indicators has been evaluated. The palynological assessment proves that not the fungal occurrence, but the concentration of fungal remains is the most appropriate tool to unravel causal links between the belowground microflora and the soil abiotic factors. The analyses show a striking dichotomy within the fungal community. First, the logarithms of fungal diversity and hyphal density show close but opposite relationships with light, moisture, soil reaction and nitrogen availability. Second, fungal functional groups show parallel, decreasing trends for soil reaction and nitrogen availability. Aside from the mycorrhizal network as a whole (ericoid, EM and AM), we demonstrate that the degree of ecological information supplied by the different trophic levels (litter-related fungi, fimicolous fungi, wood-related fungi and strictly ericoid mycorrhizal fungi) is much greater than expected from previous studies.     

Local adaptation to soil hypoxia determines the structure of an arbuscular mycorrhizal fungal community in roots from natural CO₂ springs

The processes responsible for producing and maintaining the diversity of natural arbuscular mycorrhizal (AM) fungal communities remain largely unknown. We used natural CO(2) springs (mofettes), which create hypoxic soil environments, to determine whether a long-term, directional, abiotic selection pressure could change AM fungal community structure and drive the selection of particular AM fungal phylotypes. We explored whether those phylotypes that appear exclusively in hypoxic soils are local specialists or widespread generalists able to tolerate a range of soil conditions. AM fungal community composition was characterized by cloning, restriction fragment length polymorphism typing, and the sequencing of small subunit rRNA genes from roots of four plant species growing at high (hypoxic) and low (control) geological CO(2) exposure. We found significant levels of AM fungal community turnover (β diversity) between soil types and the numerical dominance of two AM fungal phylotypes in hypoxic soils. Our results strongly suggest that direct environmental selection acting on AM fungi is a major factor regulating AM fungal communities and their phylogeographic patterns. Consequently, some AM fungi are more strongly associated with local variations in the soil environment than with their host plant's distribution.     

Fungal growth promotor endophytes: a pragmatic approach towards sustainable food and agriculture

Agricultural productivity suffers a heavy loss due to plant pathogens, insect pests and various abiotic stresses. Agriculture being the world’s largest economic sector, it is the need of time to find and establish the ideal strategy for sustainable agriculture and improvement in crop growth. Endophytes are microorganisms that asymptomatically grow within the plant tissues without causing any disease to the host. Endophytic fungi live in symbiotic association with plants and play an important role in plant growth promotion, higher seed yield and plants resistant to various biotic, abiotic stresses and diseases. Many are able to produce antimicrobial compounds, plant growth hormones and various agrochemical bioactive metabolites. These mycoendophytes hold enormous potential for the development of eco-friendly and economically viable agricultural products. In this review we focused on the endophytic fungi recovered from different medicinal plants, their active principles involved in plant growth enhancement and the applications of fungal endophytes in agriculture. Moreover, we also discussed about endophytic fungi and their pragmatic approach towards sustainable food and agriculture.     

Spatio-temporal,environmental factors,and host identity shape culturable-epibiotic fungi of seaweeds in the Red Sea,Egypt

The study of fungal species diversity from marine algae is in its infancy; as now no studies have been carried out on the distribution and diversity of fungi on the surfaces of marine macroalgae where all fungal–algal interactions tend to begin. The aim of this study was to isolate and describe the culturable part of mycobiota associated with the surface of benthic marine macroalgae (epiphytic or epibiotic fungi). This is an important step in understanding their abundance, diversity and factors influencing their variability and composition. The fungal community was dominated by Ascomycetes (89%) with Eurotiales as the most abundant fungal order followed by Capnodiales, Pleosporales, and Hypocreales, while Zygomycetes was less frequent. The nature of occurrence of fungal genera on different macroalgal hosts suggests that a mix of generalists’ framework applies to fungal epiphytes of seaweeds, but the abundance of fungal taxa varied among ecological functional groups of algae, as well as macroalgal taxonomic groups, which imply host filtering. The fungal assemblages were also characterized by temporal variation with variation in temperature, pH, and salinity as the most important abiotic factors. The structure of fungal assemblages showed high beta diversity and low similarity between hosts.     

Heterogeneity in arbuscular mycorrhizal fungal communities may contribute to inconsistent plant-soil feedback in a Neotropical forest

Background and aims

Plant-soil feedback may vary across host species and environmental gradients. The relative importance of these biotic versus abiotic drivers of feedback will determine the stability of plant and microbial communities across environments. If plant hosts are the main driver of soil microbial communities, plant-soil feedback may be stable across changing environments. However, if microbial communities vary with environmental gradients, feedback may also vary, limiting its capacity to predict plant distributions.

Methods

We characterized arbuscular mycorrhizal (AM) fungi across tree plantations and a primary Neotropical rainforest. We then performed a plant-soil feedback pot experiment of AM fungi from these plantations on three plant species and related feedback and AM fungal communities in the field.

Results

In the field, temporal and spatial variation in AM fungal composition was similar in magnitude to variation across plant host species. Composition of AM fungi in the pot experiment significantly differed from the field plots. Furthermore, differential feedback was explained by shifts in AM fungal composition only for one plant host species (Hyeronima alchorneoides) in the pot experiment.

Conclusions

Natural AM fungal communities were temporally and spatially heterogeneous and AM fungal communities in the greenhouse did not reflect natural soils. These factors led to heterogeneous and unpredictable feedback responses, which suggests that applying greenhouse derived plant-soil feedback trends to predict plant coexistence in natural systems may be misleading.

     

Geographic structure in a widespread plant-mycorrhizal interaction: pines and false truffles

Mutualistic interactions are likely to exhibit a strong geographic mosaic in their coevolutionary dynamics, but the structure of geographic variation in these interactions is much more poorly characterized than in host-parasite interactions. We used a cross-inoculation experiment to characterize the scales and patterns at which geographic structure has evolved in an interaction between three pine species and one ectomycorrhizal fungus species along the west coast of North America. We found substantial and contrasting patterns of geographic interaction structure for the plants and fungi. The fungi exhibited a clinal pattern of local adaptation to their host plants across the geographic range of three coastal pines. In contrast, plant growth parameters were unaffected by fungal variation, but varied among plant populations and species. Both plant and fungal performance measures varied strongly with latitude. This set of results indicates that in such widespread species interactions, interacting species may evolve asymmetrically in a geographic mosaic because of differing evolutionary responses to clinally varying biotic and abiotic factors.     

Role of Diverse Non-Systemic Fungal Endophytes in Plant Performance and Response to Stress: Progress and Approaches

Plant–fungal symbiotic associations are ubiquitously distributed in natural plant communities. Besides the well-studied mycorrhizal symbiosis and grass systemic clavicipitaceous endophytes, recently, nonsystemic and horizontally transmitted fungal endophytes serving as plant symbionts have been increasingly recognized. Pure culture isolation and culture-independent molecular methods indicate that all parts of healthy plant tissues potentially harbor diverse and previously unknown fungal lineages. Limited evidence also supports a hypothesis that endophytic mycobiota dynamics may have a role in evolution of plants. High variability or “balanced antagonism” can be generally characterized with host–endophyte interactions, which implies that the outcome of symbiotic interactions can fall within a continuum ranging from mutualism to commensalism, and ultimately pathogenicity. Despite this complicated system, admittedly, fungal endophytes really endow the host with an extended phenotype. Accumulating facts illustrate that plant nutrition acquisition, metabolism, and stress tolerance may be strengthened or modulated via fungal symbionts. Piriformospora indica, a member of the order Sebacinales, simultaneously confers host resistance to biotic and abiotic stress. The ecological relevance of other fungal groups, including foliar endophytes, root dark septate endophytes (DSEs), some opportunistic and avirulent microsymbionts (for example, Trichoderma and Fusarium), and even uncultured fungi structurally and physiologically integrated with host tissues, are also being deeply exploited. Production of bioactive metabolites by fungi, overexpression of stress-related enzymes, and induced resistance in hosts upon fungal colonization are responsible for direct or indirect beneficial effects to hosts. More knowledge of endophyte-mediated enhancement of host performance and fitness will offer alternatively valuable strategies for plant cultivation and breeding. Meanwhile, with unprecedented loss of biodiversity, discovery of indigenously novel symbiotic endophytes from natural habitats is urgently needed. In addition, we present some approaches and suggestions for studying host–endophyte interactions.     

丛枝菌根真菌与深色有隔内生真菌生态修复功能与作用

生态修复是目前全球关注的热点问题,如何增加植被的覆盖度及生态修复效率是目前研究的重点。丛枝菌根真菌(arbuscular mycorrhiza fungi,AMF)和深色有隔内生真菌(dark septate endophyte,DSE)均是自然界植物根际分布广泛的一类内生真菌,均能与植物形成菌根共生体,具有一定的促进植物生长、抵抗逆境及修复污染土壤等功能与作用,在生态修复中具有广泛的应用潜力。本文综述了AMF及DSE两种微生物的功能、作用及其在生态修复应用中的研究进展,并进一步对AMF和DSE在生态修复中存在的问题和前景进行展望。     

Resistance and resilience of root fungal communities to water limitation in a temperate agroecosystem

Understanding crop resilience to environmental stress is critical in predicting the consequences of global climate change for agricultural systems worldwide, but to date studies addressing crop resiliency have focused primarily on plant physiological and molecular responses. Arbuscular mycorrhizal fungi (AMF) form mutualisms with many crop species, and these relationships are key in mitigating the effects of abiotic stress in many agricultural systems. However, to date there is little research examining whether (1) fungal community structure in agroecosystems is resistant to changing environmental conditions, specifically water limitation and (2) resilience of fungal community structure is moderated by agricultural management systems, namely the integration of trees into cropping systems. Here, we address these uncertainties through a rainfall reduction field experiment that manipulated short‐term water availability in a soybean‐based (Glycine max L. Merr.) agroforest in Southern Ontario, Canada. We employed terminal restriction fragment length polymorphism analysis to determine the molecular diversity of both general fungal and AMF communities in soybean roots under no stress, stress (rainfall shelters added), and poststress (rainfall shelters removed). We found that general fungal and AMF communities sampled from soybean roots were resistant to rainfall reduction in a monoculture, but not in an agroforest. While AMF communities were unchanged after stress removal, general fungal communities were significantly different poststress in the agroforest, indicating a capacity for resiliency. Our study indicates that generalist fungi and AMF are responsive to changes in environmental conditions and that agroecosystem management plays a key role in the resistance and resilience of fungal communities to water limitation.     

Differential expression of β-glucosidase in tomato — stress stimuli systems

In the present work the responses of β-glucosidase in leaves of tomato plants subjected to various stress factors of both pathogenic (fungi, bacteria, viruses) and abiotic origin (heat shock) were studied. Biochemical and cytochemical methods were applied. It was established that an increase of β-glucosidase activity is induced uniquely by fungal pathogens. The cytochemical tests confirm the finding. Hence, the conclusion can be drawn that β-glucosidase response is a specific character of fungal pathogenesis in tomato; probably, the enzyme is involved in plant — fungi recognition. The data are in accordance with our previous results on tobacco and wheat — stress stimuli systems.