Epichloë endophyte affects the ability of powdery mildew (Blumeria graminis) to colonise drunken horse grass (Achnatherum inebrians)

Interactions between Epichloë endophyte and the plant microbiome impact nitrogen responses in host Achnatherum inebrians plants

The clavicipitaceous fungus Epichloë gansuensis forms symbiotic associations with drunken horse grass (Achnatherum inebrians), providing biotic and abiotic stress protection to its host. However, it is unclear how E. gansuensis affects the assembly of host plant-associated bacterial communities after ammonium nitrogen (NH4+-N) treatment. We examined the shoot- and root-associated bacterial microbiota and root metabolites of A. inebrians when infected (I) or uninfected (F) with E. gansuensis endophyte. The results showed more pronounced NH4+-N-induced microbial and metabolic changes in the endophyte-infected plants compared to the endophyte-free plants. E. gansuensis significantly altered bacterial community composition and β-diversity in shoots and roots and increased bacterial α-diversity under NH4+-N treatment. The relative abundance of 117 and 157 root metabolites significantly changed with E. gansuensis infection under water and NH4+-N treatment compared to endophyte-free plants. Root bacterial community composition was significantly related to the abundance of the top 30 metabolites [variable importance in the projection (VIP) > 2 and VIP > 3] contributing to differences between I and F plants, especially alkaloids. The correlation network between root microbiome and metabolites was complex. Microorganisms in the Proteobacteria and Firmicutes phyla were significantly associated with the R00693 metabolic reaction of cysteine and methionine metabolism. Co-metabolism network analysis revealed common metabolites between host plants and microorganisms.IMPORTANCEOur results suggest that the effect of endophyte infection is sensitive to nitrogen availability. Endophyte symbiosis altered the composition of shoot and root bacterial communities, increasing bacterial diversity. There was also a change in the class and relative abundance of metabolites. We found a complex co-occurrence network between root microorganisms and metabolites, with some metabolites shared between the host plant and its microbiome. The precise ecological function of the metabolites produced in response to endophyte infection remains unknown. However, some of these compounds may facilitate plant-microbe symbiosis by increasing the uptake of beneficial soil bacteria into plant tissues. Overall, these findings advance our understanding of the interactions between the microbiome, metabolome, and endophyte symbiosis in grasses. The results provide critical insight into the mechanisms by which the plant microbiome responds to nutrient stress in the presence of fungal endophytes.

Exogenous inoculation of endophyte Penicillium sp. alleviated pineapple internal browning during storage

Pineapple is ranked sixth in terms of global fruit production and the most traded tropical fruit worldwide. Internal browning (IB), a physiological disorder of pineapple fruit after harvest, limits the export and industry development of pineapple. Evidence confirmed that endophyte played a pivotal role in plant disease. This study investigated the relationship between endophyte fungi community structure, population abundance in healthy and IB pineapple fruit; as well as the effect of endophyte Penicillium sp. inoculation on pineapple IB. Intended to explore a new effective measure for controlling IB and reducing postharvest losses in pineapple by an economical and environmentally friendly approach. We found the abundance of endophyte fungi in healthy pineapple fruit was different from that in IB fruit by high-throughput sequencing. The results emphasized that the endophyte Penicillium sp. inoculation dramatically alleviated pineapple IB intensity and severity, delayed crown withering and fruit yellowing, and maintained the exterior quality traits during the postharvest period at 20 °C. Penicillium sp. retarded H₂O₂ accumulation and increased the total phenols level in pineapple. Application of Penicillium sp. also maintained the higher antioxidant capacity by increasing antioxidant enzyme activity and ascorbic acids levels, regulated of the homeostasis of endogenous hormones, and increased the abundance of Penicillium sp. in the fruit. In summary, Penicillium sp. retarded the occurrence of IB and enhanced the storability of pineapple at postharvest, and this economical and environmentally friendly technology is convenient to spread in agriculture.

Integrated microbiological and metabolomics analyses to understand the mechanism that allows modified biochar to affect the alkalinity of saline soil and winter wheat growth

In order to understand the mechanism that allows modified biochar (BC) to enhance the salt tolerance and growth of crops in saline-alkali soil, we tested the effects of ordinary BC, nanoparticle-size BC, acidified BC (HBC), and acidified nanoparticle-size BC on winter wheat growth and the soil properties by combining microbiological and metabolomics analyses. The results showed that compared with the control with no BC, the plant height increased by 17.33 % under HBC and the proportion of large soil aggregates increased by 1.25-2.83 times. HBC increased the relative abundances of some dominant genera of bacteria (e.g., Streptococcus) and fungi (e.g., Mycothermus), as well as functions such as bacterial metabolic genetic information processing and cellular processes, and reduced the abundance of pathotrophic fungi. Metabolomics analysis showed that HBC upregulated various metabolites (including amino acids and their derivatives, lipids, flavonoids, and organic acids) and five main metabolic pathways. Among the KEGG pathways, the pyrimidine metabolism pathway was significantly upregulated, as well as crop leaf metabolism, β-alanine metabolism, and valine, leucine, and isoleucine metabolism, and the antioxidant levels and resistance to salt-alkali stress were enhanced in winter wheat leaves. Partial least squares-path modeling suggested that HBC affected the growth of winter wheat by significantly changing the soil physicochemical properties and microbial structure (path coefficients of 0.566 and 0.512, respectively).

Effect of Epichloë gansuensis Endophyte on Seed-Borne Microbes and Seed Metabolites in Achnatherum inebrians

The seed-borne microbiota and seed metabolites of the grass Achnatherum inebrians, either host to Epichloë gansuensis (endophyte infected [EI]) or endophyte free (EF), were investigated. This study determined the microbial communities both within the seed (endophytic) and on the seed surface (epiphytic) and of the protective glumes by using Illumina sequencing technology. Epichloë gansuensis decreased the richness of the seed-borne microbiota except for the epiphytic fungi of glumes and also decreased the diversity of seed-borne microbiota. In addition, metabolites of seeds and glumes were detected using liquid chromatography-mass spectrometry (LC-MS). Unlike with the seeds of EF plants, the presence of E. gansuensis resulted in significant changes in the content of 108 seed and 31 glume metabolites. A total of 319 significant correlations occurred between seed-borne microbiota and seed metabolites; these correlations comprised 163 (147 bacterial and 16 fungal) positive correlations and 156 (136 bacterial and 20 fungal) negative correlations. Meanwhile, there were 42 significant correlations between glume microbiota and metabolites; these correlations comprised 28 positive (10 bacterial and 18 fungal) and 14 negative (9 bacterial and 5 fungal) correlations. The presence of E. gansuensis endophyte altered the communities and diversities of seed-borne microbes and altered the composition and content of seed metabolites, and there were many close and complex relationships between microbes and metabolites. IMPORTANCE The present study was to investigate seed-borne microbiota and seed metabolites in Achnatherum inebrians using high-throughput sequencing and LC-MS technology. Epichloë gansuensis decreased the richness of the seed-borne microbiota except for the epiphytic fungi of glumes and also decreased the diversity of seed-borne microbiota. Compared with endophyte-free plants, the content of 108 seed and 31 glume metabolites of endophyte-infected plants was significantly changed. There were 319 significant correlations between seed-borne microbiota and seed metabolites and 42 significant correlations between glume microbiota and metabolites.

Transcriptomic Analyses Reveals Molecular Regulation of Photosynthesis by Epichloë endophyte in Achnatherum inebrians under Blumeria graminis Infection

Photosynthesis is essential for the growth of all green plants, and the presence of an Epichloë endophyte enhances the photosynthesis of Achnatherum inebrians (drunken horse grass, DHG), including when it is under attack by fungal pathogens. However, few studies have examined the mechanism of the increased photosynthetic activity at the molecular level of A. inebrians when it is under pathogen stress. The present study investigated the effects of the presence of the Epichloë endophyte on the net photosynthetic rate, intercellular CO2 concentration, stomatal conductance, and transpiration rate of DHG plants under a Blumeria graminis infection condition, and we compared the transcriptomes using RNA sequencing. The results showed that the photosynthetic rate of Epichloë endophyte-infected (E+) plants was higher under the B. graminis infection condition, and also without this pathogen, when it was compared with Epichloë endophyte-free (E-) plants. The E+ plants uninfected with B. graminis had 15 up-regulated unigenes that are involved in photosynthesis which were compared to the E- plants that were uninfected with this pathogen. This suggests that the presence of an Epichloë endophyte up-regulates the genes that are involved in the process of photosynthesis.

Infection by Endophytic Epichloë sibirica Was Associated with Activation of Defense Hormone Signal Transduction Pathways and Enhanced Pathogen Resistance in the Grass Achnatherum sibiricum

Epichloë endophytes can improve the resistance of host grasses to pathogenic fungi, but the underlying mechanisms remain largely unknown. Here, we used phytohormone quantifications, gene expression analysis, and pathogenicity experiments to investigate the effect of Epichloë sibirica on the resistance of Achnatherum sibiricum to Curvularia lunata pathogens. Comparison of gene expression patterns between endophyte-infected and endophyte-free leaves revealed that endophyte infection was associated with significant induction of 1,758 and 765 differentially expressed genes in the host before and after pathogen inoculation, respectively. Functional analysis of the differentially expressed genes suggested that endophyte infection could activate the constitutive resistance of the host by increasing photosynthesis, enhancing the ability to scavenge reactive oxygen species, and actively regulating the expression of genes with function related to disease resistance. We found that endophyte infection was associated with induction of the expression of genes involved in the biosynthesis pathways of jasmonic acid, ethylene, and pipecolic acid and amplified the defense response of the jasmonic acid/ethylene co-regulated EIN/ERF1 transduction pathway and Pip-mediated TGA transduction pathway. Phytohormone quantifications showed that endophyte infection was associated with significant accumulation of jasmonic acid, ethylene, and pipecolic acid after pathogen inoculation. Exogenous phytohormone treatments confirmed that the disease index of plants was negatively related to both jasmonic acid and ethylene concentrations. Our results demonstrate that endophyte infection can not only improve the constitutive resistance of the host to phytopathogens before pathogen inoculation but also be associated with enhanced systemic resistance of the host to necrotrophs after C. lunata inoculation.

Abscisic Acid May Play a Critical Role in the Moderating Effect of Epichloë Endophyte on Achnatherum inebrians under Drought Stress

Water scarcity is a major constraint that adversely affects plant development and growth. Abscisic acid (ABA) is a plant stress hormone that is rapidly synthesized and can induce stomatal closure to conserve water, thereby alleviating the drought stress of plants. The Epichloë endophyte enhances the drought tolerance of Achnatherum inebrians (drunken horse grass, DHG). To better understand how the Epichloë endophyte enhances drought tolerance, DHG plants without (EF) and with (EI), an Epichloë endophyte, were grown under 20% and 60% soil water conditions (SWC), and the leaves of the three treatments of EF and EI plants were sprayed with ABA solution (1 mg/L); fluridone (FLU), the ABA biosynthesis inhibitor solution (1 mg/L); and distilled water, respectively. Four-weeks later, the results indicated that the exogenous ABA application promoted plant growth, stomatal conductance, and photosynthetic rate, while the opposite effect occurred with plants sprayed with FLU. The differences between EI and EF plants in tiller number, height, chlorophyll content, stomata conductance, and photosynthetic rate were highest when sprayed with ABA. Thus, it is concluded that ABA might be involved in the moderating effect of Epichloë endophytes on DHG plants exposed to drought by maintaining growth and improving photosynthetic efficiency.

Epichloë endophytes improved Leymus chinensis tolerance to both neutral and alkali salt stresses

Symbiotic relationships with microbes may influence how plants respond to environmental change. In the present study, we tested the hypothesis that symbiosis with the endophytes promoted salt tolerance of the native grass. In the field pot experiment we compared the performance of endophyte-infected (E+) and endophyte-uninfected (E-) Leymus chinensis, a dominant species native to the Inner Mongolia steppe, under altered neutral and alkaline salt stresses. The results showed that under both neutral and alkaline salt stresses, endophyte infection significantly increased plant height, leaf length and fibrous root biomass. Under neutral salt stress, endophyte infection decreased Na⁺ content and Na⁺/K⁺ ratio (p=0.066) in the leaf sheath while increased Ca²⁺ and Mg²⁺ content in the rhizome. Under alkali salt stress, endophyte infection tended to increase K⁺ content in the fibrous root, enhance Mg²⁺ content in the fibrous root while reduce Na⁺/K⁺ ratio in the leaf blade in the 100 mmol/L alkali salt treatment. Although endophyte-infected L. chinensis cannot accumulate Na⁺ high enough to be halophytes, the observed growth promotion and stress tolerance give endophyte/plant associations the potential to be a model for endophyte-assisted phytoremediation of saline-alkaline soils.

Endophytes and their potential in biotic stress management and crop production

Biotic stress is caused by harmful microbes that prevent plants from growing normally and also having numerous negative effects on agriculture crops globally. Many biotic factors such as bacteria, fungi, virus, weeds, insects, and nematodes are the major constrains of stress that tends to increase the reactive oxygen species that affect the physiological and molecular functioning of plants and also led to the decrease in crop productivity. Bacterial and fungal endophytes are the solution to overcome the tasks faced with conventional farming, and these are environment friendly microbial commodities that colonize in plant tissues without causing any damage. Endophytes play an important role in host fitness, uptake of nutrients, synthesis of phytohormone and diminish the injury triggered by pathogens via antibiosis, production of lytic enzymes, secondary metabolites, and hormone activation. They are also reported to help plants in coping with biotic stress, improving crops and soil health, respectively. Therefore, usage of endophytes as biofertilizers and biocontrol agent have developed an eco-friendly substitute to destructive chemicals for plant development and also in mitigation of biotic stress. Thus, this review highlighted the potential role of endophytes as biofertilizers, biocontrol agent, and in mitigation of biotic stress for maintenance of plant development and soil health for sustainable agriculture.

Aphids and Mycorrhizal Fungi Shape Maternal Effects in Senecio vulgaris

Plant performance in any one generation is affected not only by the prevailing environmental conditions, but also by the conditions experienced by the parental generation of those plants. These maternal effects have been recorded in a many plant species, but the influence of external biotic (as opposed to abiotic) factors on shaping maternal effects have been rarely examined. Furthermore, almost all previous studies have taken place over one plant generation, rather than across multiple generations. Here, we studied the influence of insect herbivory and arbuscular mycorrhizal (AM) fungal colonisation on the shaping of maternal effects in the annual forb Senecio vulgaris. We grew plants with and without aphids (Myzus persicae) and AM fungi (hereafter termed ‘induction events’) over four successive generations, wherein seeds from plants in any one treatment were used to grow plants of the same treatment in the next generation, all in identical environmental conditions. We found strong evidence of maternal effects in the second plant generation, i.e., after one induction event. These plants took longer to germinate, flowered in a shorter time, produced lighter seeds and were shorter and of lower biomass than their parents. Aphid attack tended to enhance these effects, whereas AM fungi had little influence. However, thereafter there was a gradual recovery in these parameters, so that plants experiencing three inductions showed similar life history parameters to those in the original generation. We conclude that experiments investigating maternal effects need to be performed over multiple plant generations and that biotic factors such as insects and mycorrhizas must also be taken into account, along with abiotic factors, such as nutrient and water availability.

Cuticular Wax Modification by Epichloë Endophyte in Achnatherum inebrians under Different Soil Moisture Availability

The cuticular wax serves as the outermost hydrophobic barrier of plants against nonstomatal water loss and various environmental stresses. An objective of this study was to investigate the contribution of the mutualistic fungal endophyte Epichloë gansuensis to leaf cuticular wax of Achnatherum inebrians under different soil moisture availability. Through a pot experiment and gas chromatography−mass spectrometry (GC−MS) analysis, our results indicated that the hydrocarbons were the dominant components of leaf cuticular wax, and the proportion of alcohols, aldehydes, amines, and ethers varied with the presence or absence of E. gansuensis and different soil moisture availability. Amines and ethers are unique in endophyte-free (EF) A. inebrians plants and endophyte-infected (EI) A. inebrians plants, respectively. By transcriptome analysis, we found a total of 13 differentially expressed genes (DEGs) related to cuticular biosynthesis, including FabG, desB, SSI2, fadD, BiP, KCS, KAR, FAR, and ABCB1. A model is proposed which provides insights for understanding cuticular wax biosynthesis in the association of A. inebrians plants with E. gansuensis. These results may help guide the functional analyses of candidate genes important for improving the protective layer of cuticular wax of endophyte-symbiotic plants.

The effect of Epichloë endophyte on phyllosphere microbes and leaf metabolites in Achnatherum inebrians

Upon exposure to the prevailing environment, leaves become increasingly colonized by fungi and bacteria located on the surface (epiphytic) or within (endophytic) the leaves. Many cool season grasses, including Achnatherum inebrians, host a seed-borne, intercellular, mutualistic Epichloë fungal endophyte, the growth of which is synchronized with the host grass. A study utilizing illumina sequencing was used to examine the epiphytic and endophytic microbial communities in Epichloë endophyte-infected and endophyte-free A. inebrians plants growing under hot dry field conditions. The presence of Epichloë endophyte increased the Shannon and decreased Simpson diversity of bacterial and fungal communities. Sphingomonas and Hymenobacter bacteria and Filobasidium and Mycosphaerella fungi were growing largely epiphytically, whereas Methylobacterium, Escherichia-Shigella, and the fungus Blumeria were mostly found within leaves with the location of colonization influenced by the Epichloë endophyte. In addition, leaf metabolites in Epichloë-infected and Epichloë-free leaves were examined using LC/MS. Epichloë was significantly correlated with 132 metabolites.

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Epichloë altered the composition and diversity of phyllosphere microbial communities

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414 detected metabolites were annotated, of which the 132 differential metabolites

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There were 229 significant correlations between metabolites and microbial phyla

Antagonism to Plant Pathogens by Epichloë Fungal Endophytes-A Review

Epichloë is a genus of filamentous fungal endophytes that has co-evolved with cool-season grasses with which they form long-term, symbiotic associations. The most agriculturally important associations for pasture persistence for grazing livestock are those between asexual vertically transmitted Epichloë strains and the pasture species, perennial ryegrass, and tall fescue. The fungus confers additional traits to their host grasses including invertebrate pest deterrence and drought tolerance. Selected strains of these mutualistic endophytes have been developed into highly efficacious biocontrol products and are widely utilized within the Americas, Australia, and New Zealand for pasture persistence. Less publicized is the antagonism Epichloë endophytes display towards multiple species of saprophytic and pathogenic microbes. This opinion piece will review the current literature on antimicrobial properties exhibited by this genus of endophyte and discuss the reasons why this trait has historically remained a research curiosity rather than a trait of commercial significance.

Transcriptome Analysis Revealed Plant Hormone Biosynthesis and Response Pathway Modification by Epichloëgansuensis in Achnatheruminebrians under Different Soil Moisture Availability

The present study was designed to explore the effects of the endophyte Epichloë gansuensis on gene expression related to plant hormone biosynthesis and response pathways and the content of salicylic acid (SA) and jasmonic acid (JA) hormones of Achnatherum inebrians, under different moisture conditions. Through a pot experiment and transcriptome analysis, we found a total of 51 differentially expressed genes (DEGs) related to hormone biosynthesis and response pathways, including 12 auxin related genes, 8 cytokinin (CTK) related genes, 3 gibberellin (GA) related genes, 7 abscisic acid (ABA) related genes, 7 ethylene (ET) related genes, 12 JA related genes and 4 SA related genes. Furthermore, key genes of JA and SA biosynthesis and response pathways, such as LOX2S, AOS, OPR, ACX, JMT, JAZ, PAL, NPR1, TGA and PR-1, showed different degrees of upregulation or downregulation. Under 60% soil moisture content, the JA content of endophyte-free (EF) A. inebrians was significantly (p < 0.05) higher than that of endophyte-infected (EI) A. inebrians. Under 30% and 60% soil moisture content, the SA content of EF A. inebrians was significantly (p < 0.05) higher than that of EI A. inebrians. SA content of EI A. inebrians under 30% and 60% soil moisture content was significantly (p < 0.05) higher than that under 15% soil moisture content. With both EI and EF plants, the SA and JA levels, respectively, are very similar at 15% soil moisture content. This study has revealed that E. gansuensis differentially activated plant hormone synthesis and signal transduction pathways of A. inebrians plants under different soil moisture availability.

The Plant Salicylic Acid Signalling Pathway Regulates the Infection of a Biotrophic Pathogen in Grasses Associated with an Epichloë Endophyte

The study of the contribution of the plant defence hormones, salicylic acid (SA) and jasmonic acid (JA), in the resistance against pathogens of plants associated with Epichloë fungal endophytes has been scanty. We hypothesised that Epichloë spp., capable of inducing host plant SA-dependent defences, would increase the levels of plant resistance against biotrophic pathogens. Plants of Achnatherum inebrians, with and without the fungal endophyte Epichloë gansuensis, were inoculated with the biotrophic fungal pathogen Blumeria graminis. We measured the status of plant defences (associated with SA and JA signalling pathways) and the levels of resistance to the pathogen. Plants associated with the endophyte showed less disease symptoms caused by the biotrophic pathogen than plants without the endophyte. In agreement with our hypothesis, the Epichloë endophyte increased the plant production of SA and enhanced the expression levels of plant genes of synthesis and response to the SA hormone. The elevated expression of SA-related genes coding for putative plant enzymes with anti-fungal activities promoted by the endophyte may explain the enhanced resistance to the pathogen. The present study highlights that interaction between the plant immune system and Epichloë fungal endophytes can contribute significantly to the resistance of endophyte-symbiotic plants against pathogens.

Effects of the Fungal Endophyte Epichloë festucae var. lolii on Growth and Physiological Responses of Perennial Ryegrass cv. Fairway to Combined Drought and Pathogen Stresses

Perennial ryegrass (Lolium perenne) is widely cultivated around the world for turf and forage. However, the plant is highly susceptible to disease and is sensitive to drought. The present study aims to determine the effect of the fungal endophyte Epichloë festucae var. lolii of perennial ryegrass on the combined stresses of drought and disease caused by Bipolaris sorokiniana in the greenhouse. In the experiment, plants infected (E+) or not infected (E-) with the fungal endophyte were inoculated with Bipolaris sorokiniana and put under different soil water regimes (30%, 50%, and 70%). The control treatment consisted of E+ and E- plants not inoculated with B. sorokiniana. Plant growth, phosphorus (P) uptake, photosynthetic parameters, and other physiological indices were evaluated two weeks after pathogen infection. The fungal endophyte in E+ plants increased P uptake, plant growth, and photosynthetic parameters but decreased the malondialdehyde concentration, proline content, and disease incidence of perennial ryegrass (p < 0.05). E+ plants had the lowest disease incidence at 70% soil water (p < 0.05). The study demonstrates that the fungal endophyte E. festucae var. lolii is beneficial for plant growth and stress tolerance in perennial ryegrass exposed to the combined stresses of drought and B. sorokiniana.

Epichloë Fungal Endophytes-From a Biological Curiosity in Wild Grasses to an Essential Component of Resilient High Performing Ryegrass and Fescue Pastures

The relationship between Epichloë endophytes found in a wide range of temperate grasses spans the continuum from antagonistic to mutualistic. The diversity of asexual mutualistic types can be characterised by the types of alkaloids they produce in planta. Some of these are responsible for detrimental health and welfare issues of ruminants when consumed, while others protect the host plant from insect pests and pathogens. In many temperate regions they are an essential component of high producing resilient tall fescue and ryegrass swards. This obligate mutualism between fungus and host is a seed-borne technology that has resulted in several commercial products being used with high uptake rates by end-user farmers, particularly in New Zealand and to a lesser extent Australia and USA. However, this has not happened by chance. It has been reliant on multi-disciplinary research teams undertaking excellent science to understand the taxonomic relationships of these endophytes, their life cycle, symbiosis regulation at both the cellular and molecular level, and the impact of secondary metabolites, including an understanding of their mammalian toxicity and bioactivity against insects and pathogens. Additionally, agronomic trials and seed biology studies of these microbes have all contributed to the delivery of robust and efficacious products. The supply chain from science, through seed companies and retailers to the end-user farmer needs to be well resourced providing convincing information on the efficacy and ensuring effective quality control to result in a strong uptake of these Epichloë endophyte technologies in pastoral agriculture.

Endophytic Fungi Activated Similar Defense Strategies of Achnatherum sibiricum Host to Different Trophic Types of Pathogens

It is well documented that Epichloë endophytes can enhance the resistance of grasses to herbivory. However, reports on resistance to pathogenic fungi are limited, and their conclusions are variable. In this study, we chose pathogenic fungi with different trophic types, namely, the biotrophic pathogen Erysiphales species and the necrotrophic pathogen Curvularia lunata, to test the effects of Epichloë on the pathogen resistance of Achnatherum sibiricum. The results showed that, compared to Erysiphales species, C. lunata caused a higher degree of damage and lower photochemical efficiency (Fv/Fm) in endophyte−free (E−) leaves. Endophytes significantly alleviated the damage caused by these two pathogens. The leaf damaged area and Fv/Fm of endophyte−infected (E+) leaves were similar between the two pathogen treatments, indicating that the beneficial effects of endophytes were more significant when hosts were exposed to C. lunata than when they were exposed to Erysiphales species. We found that A. sibiricum initiated jasmonic acid (JA)−related pathways to resist C. lunata but salicylic acid (SA)–related pathways to resist Erysiphales species. Endophytic fungi had no effect on the content of SA but increased the content of JA and total phenolic compounds, which suggest that endophyte infection might enhance the resistance of A. sibiricum to these two different trophic types of pathogens through similar pathways.

The fungal endophyte Epichloë gansuensis increases NaCl-tolerance in Achnatherum inebrians through enhancing the activity of plasma membrane H+-ATPase and glucose-6-phosphate dehydrogenase

Salt stress negatively affects plant growth, and the fungal endophyte Epichloëgansuensis increases the tolerance of its host grass species, Achnatherum inebrians, to abiotic stresses. In this work, we first evaluated the effects of E. gansuensis on glucose-6-phosphate dehydrogenase (G6PDH) and plasma membrane (PM) H⁺-ATPase activity of Achnatherum inebrians plants under varying NaCl concentrations. Our results showed that the presence of E. gansuensis increased G6PDH, PM H⁺-ATPase, superoxide dismutase and catalase activity to decrease O₂^•-, H₂O₂ and Na⁺ contents in A. inebrians under NaCl stress, resulting in enhanced salt tolerance. In addition, the PM NADPH oxidase activity and NADPH/NADP⁺ ratios were all lower in A. inebrians with E. ganusensis plants than A. inebrians plants without this endophyte under NaCl stress. In conclusion, E. gansuensis has a positive role in improving host grass yield under NaCl stress by enhancing the activity of G6PDH and PM H⁺-ATPase to decrease ROS content. This provides a new way for the selection of stress-resistant and high-quality forage varieties by the use of systemic fungal endophytes.

Role of Epichloë Endophytes in Defense Responses of Cool-Season Grasses to Pathogens: A Review

Various cool-season grasses are infected by Epichloë endophyte, and this symbiotic relationship is always of benefit to the host grass due to an increased resistance to abiotic and biotic stresses. Fungal diseases adversely affect the yield, quality, and economic benefits of rangelands, which affects the production of animal husbandry. Therefore, it is imperative to breed resistant cultivars and to better understand the role of fungal endophytes in order to protect grasses against pathogens. The present review introduces research regarding how these endophytes affect the growth of pathogens in vitro and how they change the resistance of host plants to plant diseases. From the perspective of physical defense, changes in physiological indexes, and secretion of chemical compounds, we summarize the potential mechanisms by which endophytes are able to enhance the disease resistance of a host grass. Through these, we aim to establish a solid theoretical foundation for plant disease control and disease resistance breeding by application of fungal endophytes. A broader understanding of fungal endophyte effects on hosts could create a new opportunity for managing or introducing fungal symbioses in both agronomic or non-agronomic ecosystems.

Knowing your neighbourhood-the effects of Epichloë endophytes on foliar fungal assemblages in perennial ryegrass in dependence of season and land-use intensity

Epichloë endophytes associated with cool-season grass species can protect their hosts from herbivory and can suppress mycorrhizal colonization of the hosts' roots. However, little is known about whether or not Epichloë endophyte infection can also change the foliar fungal assemblages of the host. We tested 52 grassland study sites along a land-use intensity gradient in three study regions over two seasons (spring vs. summer) to determine whether Epichloë infection of the host grass Lolium perenne changes the fungal community structure in leaves. Foliar fungal communities were assessed by Next Generation Sequencing of the ITS rRNA gene region. Fungal community structure was strongly affected by study region and season in our study, while land-use intensity and infection with Epichloë endophytes had no significant effects. We conclude that effects on non-systemic endophytes resulting from land use practices and Epichloë infection reported in other studies were masked by local and seasonal variability in this study's grassland sites.

Effect of Epichloë gansuensis Endophyte on the Nitrogen Metabolism, Nitrogen Use Efficiency, and Stoichiometry of Achnatherum inebrians under Nitrogen Limitation

The systemic fungal endophyte of the grass Achnatherum inebrians, Epichloë gansuensis, has important roles in enhancing resistance to biotic and abiotic stresses. In this work, we first evaluated the effects of E. gansuensis on nitrogen metabolism, nitrogen use efficiency, and stoichiometry of A. inebrians under varying nitrogen concentrations. The results demonstrated that E. gansuensis significantly improved the growth of A. inebrians under low nitrogen conditions. The fresh and dry weights, nitrogen reductase, nitrite reductase, and glutamine synthetase activity, NO₃^-, NH₄⁺, N, and P content, and also the total N accumulation, N utilization efficiency, and N uptake efficiency were all higher in leaves of A. inebrians with E. ganusensis (E+) plants than A. inebrians plants without this endophyte (E-) under low nitrogen availability. In conclusion, E. gansuensis has positive effects on improving the growth of A. inebrians under low-nitrogen conditions by modulating the enzymes of nitrogen metabolism and enhancing nitrogen use efficiency.

Do Endophytes Promote Growth of Host Plants Under Stress? A Meta-Analysis on Plant Stress Mitigation by Endophytes

Endophytes are microbial symbionts living inside plants and have been extensively researched in recent decades for their functions associated with plant responses to environmental stress. We conducted a meta-analysis of endophyte effects on host plants' growth and fitness in response to three abiotic stress factors: drought, nitrogen deficiency, and excessive salinity. Ninety-four endophyte strains and 42 host plant species from the literature were evaluated in the analysis. Endophytes increased biomass accumulation of host plants under all three stress conditions. The stress mitigation effects by endophytes were similar among different plant taxa or functional groups with few exceptions; eudicots and C₄ species gained more biomass than monocots and C₃ species with endophytes, respectively, under drought conditions. Our analysis supports the effectiveness of endophytes in mitigating drought, nitrogen deficiency, and salinity stress in a wide range of host species with little evidence of plant-endophyte specificity.

Season-Long Experimental Drought Alters Fungal Community Composition but Not Diversity in a Grassland Soil

Using terrestrial model ecosystems (TMEs), we investigated how reduced moisture conditions impact soil fungal communities from a temperate grassland over the course of an entire season. Starting at about 65% of the soil's maximum water holding capacity (WHC_max), TME soils were adjusted to three moisture levels for 15 weeks: 70% WHC_max, approximating starting conditions, 50% WHC_max, and 30% WHC_max, representing reduced moisture conditions. Diversity and abundances of soil fungi at the start and at the end of the experiment were characterized using Illumina meta-barcoding. Community diversity at the end of the experiment did not differ between experimental moisture levels and was comparable to diversity measures from the field. However, fungal communities did change compositionally in both abundances and presence/absence of species. Analyzing class-level and individual contributions of fungi to these changes revealed that only a minor portion reacted significantly, indicating that most compositional change was likely driven by many consistent small-scale shifts in presence/absences or abundances. Together, our results show that prolonged reduction in soil moisture conditions will trigger compositional changes in soil fungal communities but not necessarily change overall diversity. We highlight the cumulative contribution of minor but consistent changes among community members, as opposed to significant responses of individual species. We also detected a strong general experimental effect on soil fungi that are moved from the field to experimental TMEs, suggesting the importance of acclimatization effects in these communities under laboratory conditions.

Foliar microbiome transplants confer disease resistance in a critically-endangered plant

There has been very little effort to incorporate foliar microbiomes into plant conservation efforts even though foliar endophytes are critically important to the fitness and function of hosts. Many critically endangered plants that have been extirpated from the wild are dependent on regular fungicidal applications in greenhouses that cannot be maintained for remote out-planted populations, which quickly perish. These fungicides negatively impact potentially beneficial fungal symbionts, which may reduce plant defenses to pathogens once fungicide treatments are stopped. Using the host/parasite system of Phyllostegia kaalaensis and Neoerysiphe galeopsidis, we conducted experiments to test total foliar microbiome transplants from healthy wild relatives onto fungicide-dependent endangered plants in an attempt to mitigate disease and reduce dependency on fungicides. Plants were treated with total microbiome transplants or cultured subsets of this community and monitored for disease severity. High-throughput DNA screening of fungal ITS1 rDNA was used to track the leaf-associated fungal communities and evaluate the effectiveness of transplantation methods. Individuals receiving traditionally isolated fungal treatments showed no improvement, but those receiving applications of a simple leaf slurry containing an uncultured fungal community showed significant disease reduction, to which we partially attribute an increase in the mycoparasitic Pseudozyma aphidis. These results were replicated in two independent experimental rounds. Treated plants have since been moved to a native habitat and, as of this writing, remain disease-free. Our results demonstrate the effectiveness of a simple low-tech method for transferring beneficial microbes from healthy wild plants to greenhouse-raised plants with reduced symbiotic microbiota. This technique was effective at reducing disease, and in conferring increased survival to an out-planted population of critically endangered plants. It was not effective in a closely related plant. Plant conservation efforts should strive to include foliar microbes as part of comprehensive management plans.

Endophytic fungi and soil microbial community characteristics over different years of phytoremediation in a copper tailings dam of Shanxi, China

We conducted a survey of native grass species infected by endophytic fungi in a copper tailings dam over progressive years of phytoremediation. We investigated how endophytic fungi, soil microbial community structure and soil physiochemical properties and enzymatic activity varied in responses to heavy metal pollution over different stages of phytoremediation. endophyte infection frequency increased with years of phytoremediation. Rates of endophyte infection varied among different natural grass species in each sub-dam. Soil carbon content and soil enzymatic activity gradually increased through the years of phytoremediation. endophyte infection rates of Bothriochloa ischaemum and Festuca rubra were positively related to levels of cadmium (Cd) pollution levels, and fungal endophytes associated with Imperata cylindrical and Elymus dahuricus developed tolerance to lead (Pb). The structure and relative abundance of bacterial communities varied little over years of phytoremediation, but there was a pronounced variation in soil fungi types. Leotiomycetes were the dominant class of resident fungi during the initial phytoremediation period, but Pezizomycetes gradually became dominant as the phytoremediation period progressed. Fungal endophytes in native grasses as well as soil fungi and soil bacteria play different ecological roles during phytoremediation processes.

Advances in Research on Epichloë endophytes in Chinese Native Grasses

Epichloë fungal endophytes are broadly found in cool-season grasses. The symbiosis between these grasses and Epichloë may improve the abiotic and biotic resistance of the grass plant, but some Epichloë species produce alkaloids that are toxic for livestock. Therefore, it is important to understand the characteristics of the grass-Epichloë s symbiosis so that the beneficial aspects can be preserved and the toxic effects to livestock can be avoided. Since the 1990s, Chinese researchers have conducted a series of studies on grass-Epichloë symbiosis. In this review, we describe the current state of Epichloë endophyte research in Chinese native grasses. We found that more than 77 species of native grasses in China are associated with Epichloë endophytes. In addition, we review the effects of various Epichloë species on native grass responses to abiotic and biotic stress, phylogeny, and alkaloid production. We provide an overview of the study of Epichloë species on native grasses in China and directions for future research.