A fungal endophyte helps plants to tolerate root herbivory through changes in gibberellin and jasmonate signaling

Plant-Entomopathogenic Fungi Interaction: Recent Progress and Future Prospects on Endophytism-Mediated Growth Promotion and Biocontrol

Entomopathogenic fungi, often acknowledged primarily for their insecticidal properties, fulfill diverse roles within ecosystems. These roles encompass endophytism, antagonism against plant diseases, promotion of the growth of plants, and inhabitation of the rhizosphere, occurring both naturally and upon artificial inoculation, as substantiated by a growing body of contemporary research. Numerous studies have highlighted the beneficial aspects of endophytic colonization. This review aims to systematically organize information concerning the direct (nutrient acquisition and production of phytohormones) and indirect (resistance induction, antibiotic and secondary metabolite production, siderophore production, and mitigation of abiotic and biotic stresses) implications of endophytic colonization. Furthermore, a thorough discussion of these mechanisms is provided. Several challenges, including isolation complexities, classification of novel strains, and the impact of terrestrial location, vegetation type, and anthropogenic reluctance to use fungal entomopathogens, have been recognized as hurdles. However, recent advancements in biotechnology within microbial research hold promising solutions to many of these challenges. Ultimately, the current constraints delineate potential future avenues for leveraging endophytic fungal entomopathogens as dual microbial control agents.

Colonization of Piriformospora indica enhances rice resistance against the brown planthopper Nilaparvata lugens

BACKGROUND

Piriformospora indica is an endophytic fungus that can promote the growth and confer resistance against diverse stresses in host plants by root colonization. However, the effects of P. indica colonization on improving plant resistance to insect pests are still less explored. The brown planthopper (BPH) Nilaparvata lugens is a serious monophagous pest that causes extensive damage to rice plants. Here, we aimed to evaluate the effects of P. indica colonization on rice resistance against BPH.

RESULTS

The colonization of P. indica in rice roots resisted damage from BPH. Age-stage, two-sex life table analyses showed that feeding on P. indica-colonized rice plants affected BPH's female adult longevity, oviposition period, fecundity, population parameters and population size. BPH female adults feeding on P. indica-colonized plants excreted less honeydew. P. indica colonization remarkably increased the duration of np, N2, and N3 waveform, as well as the occurrences of N1 and N2, and decreased the duration of N4-b for BPH on rice plants. Meanwhile, the weight of BPH on the colonized plants was significantly lower than the control. In addition, the feeding and oviposition preferences of BPH to P. indica-colonized plants were reduced. qRT-RCR analyses revealed that P. indica colonization induced the expressions of jasmonic acid (JA)- and salicylic acid (SA)-related genes in rice plants.

CONCLUSION

P. indica colonization can reduce BPH performance on rice plants with potential inhibitory effects on population growth. Collectively, these results support the potential for endophytically colonized P. indica as an effective strategy to improve insect resistance of crops. © 2024 Society of Chemical Industry.

Nutrient and mycoremediation of a global menace 'arsenic': exploring the prospects of phosphorus and Serendipita indica-based mitigation strategies in rice and other crops

KEY MESSAGE

Serendipita indica induced metabolic reprogramming in colonized plants complements phosphorus-management in improving their tolerance to arsenic stress on multifaceted biological fronts. Restoration of the anthropic damage done to our environment is inextricably linked to devising strategies that are not only economically sound but are self-renewing and ecologically conscious. The dilemma of heavy metal (HM) dietary ingestion, especially arsenic (As), faced by humans and animals alike, necessitates the exploitation of such technologies and the cultivation of healthy and abundant crops. The remarkable symbiotic alliance between plants and 'mycorrhizas' has evolved across eons, benefiting growth/yield aspects as well as imparting abiotic/biotic stress tolerance. The intricate interdependence of Serendipita indica (S. indica) and rice plant reportedly reduce As accumulation, accentuating the interest of microbiologists, agriculturists, and ecotoxicological scientists apropos of the remediation mechanisms of As in the soil-AMF-rice system. Nutrient management, particularly of phosphorus (P), is also praised for mitigating As phytotoxicity by deterring the uptake of As molecules due to the rhizospheric cationic competition. Taking into consideration the reasonable prospects of success in minimizing As acquisition by rice plants, this review focuses on the physiological, metabolic, and transcriptional alterations underlying S. indica symbiosis, recuperation of As stress together with nutritional management of P by gathering case studies and presenting successful paradigms. Weaving together a volume of literature, we assess the chemical forms of As and related transport pathways, discuss As-P-rice interaction and the significance of fungi in As toxicity mitigation, predominantly the role of mycorrhiza, as well as survey of the multifaceted impacts of S. indica on plants. A potential strategy for simultaneous S. indica + P administration in paddy fields is proposed, followed by future research orientation to expand theoretic comprehension and encourage field-based implementation.

Plant-endophyte communication: Scaling from molecular mechanisms to ecological outcomes

Diverse communities of fungal endophytes reside in plant tissues, where they affect and are affected by plant physiology and ecology. For these intimate interactions to form and persist, endophytes and their host plants engage in intricate systems of communication. The conversation between fungal endophytes and plant hosts ultimately dictates endophyte community composition and function and has cascading effects on plant health and plant interactions. In this review, we synthesize our current knowledge on the mechanisms and strategies of communication used by endophytic fungi and their plant hosts. We discuss the molecular mechanisms of communication that lead to organ specificity of endophytic communities and distinguish endophytes, pathogens, and saprotrophs. We conclude by offering emerging perspectives on the relevance of plant-endophyte communication to microbial community ecology and plant health and function.

Endophytic fungi improved wheat resistance to Rhopalosiphum padi by decreasing its feeding efficiency and population fitness

The improvement of crop resistance to insect using endophytic fungi is an environmentally friendly and sustainable strategy for agricultural pest control. Clarifying the efficacy and mechanism of endophytic fungi in improving crop resistance to pest offers the opportunity for biological control. In this study, changes in the transcriptome and defense compounds of wheat inoculated with endophytic fungal strains (i.e., YC and BB) were evaluated, and the efficacy of endophytic fungi in improving wheat resistance to Rhopalosiphum padi was studied. The results showed that the numbers of upregulated differentially-expressed genes (DEGs) in wheat plants inoculated with endophytic fungal strains YC and BB were higher than those of the downregulated DEGs, irrespective of R. padi infestation. Defense-related metabolic pathways, such as plant hormone signal transduction and secondary metabolite biosynthesis pathways were significantly enriched. Endophytic fungal strains YC and BB significantly increased jasmonic acid, DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one), total flavone, and tannin contents in wheat plants (P < 0.05) but decreased salicylic acid content. Variations in the contents of defense compounds were significantly correlated with decreased feeding, development, and reproduction of R. padi fed on wheat plants inoculated with strains YC and BB (|r| = 0.68-0.91, P < 0.05). The results suggested that endophytic fungi significantly decreased the feeding efficiency and population fitness [YC: (-11.13%) - (-22.07%); BB: (-10.98%) - (-22.20%)] of R. padi by altering the phytohormone pathway and secondary metabolite biosynthesis in wheat plants. This study helps in understanding of the efficacy of endophytic fungi in improving wheat resistance to insect and will be conducive to integrated pest management.

Endophytic fungi: Unravelling plant-endophyte interaction and the multifaceted role of fungal endophytes in stress amelioration

Endophytic fungi colonize interior plant tissue and mostly form mutualistic associations with their host plant. Plant-endophyte interaction is a complex mechanism and is currently a focus of research to understand the underlying mechanism of endophyte asymptomatic colonization, the process of evading plant immune response, modulation of gene expression, and establishment of a balanced mutualistic relationship. Fungal endophytes rely on plant hosts for nutrients, shelter, and transmission and improve the host plant's tolerance against biotic stresses, including -herbivores, nematodes, bacterial, fungal, viral, nematode, and other phytopathogens. Endophytic fungi have been reported to improve plant health by reducing and eradicating the harmful effect of phytopathogens through competition for space or nutrients, mycoparasitism, and through direct or indirect defense systems by producing secondary metabolites as well as by induced systemic resistance (ISR). Additionally, for efficient crop improvement, practicing them would be a fruitful step for a sustainable approach. This review article summarizes the current research progress in plant-endophyte interaction and the fungal endophyte mechanism to overcome host defense responses, their subsequent colonization, and the establishment of a balanced mutualistic interaction with host plants. This review also highlighted the potential of fungal endophytes in the amelioration of biotic stress. We have also discussed the relevance of various bioactive compounds possessing antimicrobial potential against a variety of agricultural pathogens. Furthermore, endophyte-mediated ISR is also emphasized.

Structure and Ecological Function of Fungal Endophytes from Stems of Different Mulberry Cultivars

To explore the microbial community structure and ecological function of mulberry and their potential relationship with the resistance of mulberry, the community structure and function of endophytic fungi in 18 mulberry cultivars were analyzed and predicted by using high-throughput sequencing technology and the FUNGuild database. A total of 352 operational taxonomic units of fungi were observed at a 97% similarity level, representing six phyla of fungi, Fungi_unclassified, Ascomycota, Basidiomycota, Zygomycota, Rozellomycota, and Chytridiomycota. Fungi_unclassified was dominant, and Ascomycota was relatively dominant in all cultivars. At the genus level, Ascomycota_unclassified was dominant, and Ampelomyces was relatively dominant, with a richness in TAIWANCHANGGUOSANG 16.47-8975.69 times that in the other cultivars. Classified Ascomycota_unclassified was 4.75-296.65 times more common in NANYUANSIJI than in the other cultivars. Based on the FUNGuild analysis method, we successfully annotated six nutrient types, namely, pathotroph, pathotroph-saprotroph, pathotroph-saprotroph-symbiotroph, saprotroph, saprotroph-symbiotroph, and symbiotroph, among which saprophytic-symbiotic accounted for the largest proportion and was absolutely dominant in TWC. This research suggests that community composition differs among cultivars and that the diversity and richness of endophytic fungi in resistant cultivars are higher than those in susceptible cultivars. The ecological functions of cultivars with different resistances are quite different.

Colonization of Serendipita indica promotes resistance against Spodoptera exigua in onion (Allium cepa L.)

Plant-endophyte symbiosis influences plant defense and growth. Serendipita indica is a root endophyte that promotes growth and induces tolerance against biotic and abiotic stress in plants. In this study, we examined the effect of S. indica colonization on herbivore (Spodoptera exigua) resistance of onion (Allium cepa L.). We found that colonization of S. indica in the roots of onion significantly reduced the feeding damage of leaves by S. exigua larvae, and also resulted in a reduction in weight gain of the larvae when fed on S. indica plants. This enhanced resistance is a result of modulation of antioxidant and defense enzymes/genes in the host by S. indica mutualism. Specifically, the activities of enzymes such as Superoxide dismutase, peroxidase, polyphenol oxidase, phenylalanine ammonia-lyase, and H2O2 content were significantly higher in the early stages of S. exigua feeding in the S. indica colonized plants compared to the non-colonized counterparts. Similarly, defense genes also showed modulation in response to this tripartite interaction of onion -S. indica mutualism and S. exigua herbivory. The hierarchical cluster analysis and principal component analysis indicated a clear difference in the onion biochemical responses, which is due to the S. indica symbiosis. Our investigation demonstrates that onion-S. indica symbiosis significantly decreases chewing injury by efficiently modulating antioxidant and defense enzyme activities and gene expression in response to S. exigua herbivory. Therefore, S. indica can be used as a potential biocontrol agent for sustainable management of this important pest of Alliums.

Combatting insects mediated biotic stress through plant associated endophytic entomopathogenic fungi in horticultural crops

Horticultural production is a vital catalyst for economic growth, yet insect infestations reduce horticultural crop yield and quality. Pesticides and other pest control methods are used during planting to eliminate pests that cause direct and indirect losses. In such situations, endophytic entomo-pathogenic fungi (EEPF) can act as a potential tools for biological control. They protect plants by boosting growth, nutrition, morpho-physiology and salt or iron tolerance. Antixenosis, antibiosis and plant tolerance change insect performance and preferences. EEPF- plant colonisation slows herbivore development, food consumption, oviposition and larval survival. EEPF changes plant physio-chemical properties like volatile emission profile and secondary metabolite production to regulate insect pest defences. EEPF produces chitinases, laccases, amylases, and cellulases for plant defence. Recent studies focused on EEPF species' significance, isolation, identification and field application. Realizing their full potential is difficult due to insufficient mass production, storage stability and formulation. Genetic-molecular and bioinformatics can help to build EEPF-based biological control systems. Metagenomics helps study microbial EEPF taxonomy and function. Multi-omics and system biology can decode EEPF interactions with host plants and microorganisms. NGS (Next Generation Sequencing), comparative genomics, proteomics, transcriptomics, metabolomics, metatranscriptomics and microarrays are used to evaluate plant-EEPF relationships. IPM requires understanding the abiotic and biotic elements that influence plant-EEPF interaction and the physiological mechanisms of EEPF colonisation. Due to restricted research, there are hundreds of unexplored EEPFs, providing an urgent need to uncover and analyse them.

Characterizing rhizosphere microbial communities associated with tolerance to aboveground herbivory in wild and domesticated tomatoes

Root-associated microbial communities are well known for their ability to prime and augment plant defenses that reduce herbivore survival or alter behavior (i.e., resistance). In contrast, the role root microbes play in plant tolerance to herbivory, an evolutionarily sustainable alternative to resistance, is overlooked. In this study, we aimed to expand our limited understanding of what role rhizosphere microbial communities play in supporting tolerance to insect damage. Using domesticated tomatoes and their wild ancestors (Solanum spp.), we first documented how tobacco hornworm (Manduca sexta) herbivory impacted tomato fruit production in order to quantify plant tolerance. We then characterized the bacterial and fungal rhizosphere communities harbored by high and low tolerance plants. Wild tomatoes excelled at tolerating hornworm herbivory, experiencing no significant yield loss despite 50% leaf area removal. Their domesticated counterparts, on the other hand, suffered 26% yield losses under hornworm herbivory, indicating low tolerance. Ontogeny (i.e., mid- vs. late-season sampling) explained the most variation in rhizosphere community structure, with tomato line, tolerance, and domestication status also shaping rhizosphere communities. Fungal and bacterial community traits that associated with the high tolerance line include (1) high species richness, (2) relatively stable community composition under herbivory, and (3) the relative abundance of taxa belonging to Stenotrophomonas, Sphingobacterium, and Sphingomonas. Characterizing tolerance-associating microbiomes may open new avenues through which plant defenses are amended in pest management, such as plant breeding efforts that enhance crop recruitment of beneficial microbiomes.

The influence of endophytes on rice fitness under environmental stresses

KEY MESSAGE

Endophytes are crucial for the promotion of rice growth and stress tolerance and can be used to increase rice crop yield. Endophytes can thus be exploited in biotechnology and genetic engineering as eco-friendly and cost-effective means for the development of high-yielding and stress-tolerant rice plants. Rice (Oryza sativa) crop is continuously subjected to biotic and abiotic stresses, compromising growth and consequently yield. The situation is exacerbated by climate change impacting on ecosystems and biodiversity. Genetic engineering has been used to develop stress-tolerant rice, alongside physical and chemical methods to mitigate the effect of these stresses. However, the success of these strategies has been hindered by short-lived field success and public concern on adverse effects associated. The limited success in the field of stress-tolerant cultivars developed through breeding or transgenic approaches is due to the complex nature of stress tolerance as well as to the resistance breakdown caused by accelerated evolution of pathogens. It is therefore necessary to develop novel and acceptable strategies to enhance rice stress tolerance and durable resistance and consequently improve yield. In the last decade, plant growth promoting (PGP) microbes, especially endophytes, have drawn the attention of agricultural scientists worldwide, due to their ability to mitigate environmental stresses in crops, without causing adverse effects. Increasing evidence indicates that endophytes effectively confer fitness benefits also to rice under biotic and abiotic stress conditions. Endophyte-produced metabolites can control the expression of stress-responsive genes and improve the physiological performance and growth of rice plants. This review highlights the current evidence available for PGP microbe-promoted tolerance of rice to abiotic stresses such as salinity and drought and to biotic ones, with special emphasis on endophytes. Associated molecular mechanisms are illustrated, and prospects for sustainable rice production also in the light of the impending climate change, discussed.

Piriformospora indica recruits host-derived putrescine for growth promotion in plants

Growth promotion induced by the endosymbiont Piriformospora indica has been observed in various plants; however, except growth phytohormones, specific functional metabolites involved in P. indica-mediated growth promotion are unknown. Here, we used a gas chromatography-mass spectrometry-based untargeted metabolite analysis to identify tomato (Solanum lycopersicum) metabolites whose levels were altered during P. indica-mediated growth promotion. Metabolomic multivariate analysis revealed several primary metabolites with altered levels, with putrescine (Put) induced most significantly in roots during the interaction. Further, our results indicated that P. indica modulates the arginine decarboxylase (ADC)-mediated Put biosynthesis pathway via induction of SlADC1 in tomato. Piriformospora indica did not promote growth in Sladc1-(virus-induced gene silencing of SlADC1) lines of tomato and showed less colonization. Furthermore, using LC-MS/MS we showed that Put promoted growth by elevation of auxin (indole-3-acetic acid) and gibberellin (GA4 and GA7) levels in tomato. In Arabidopsis (Arabidopsis thaliana) adc knockout mutants, P. indica colonization also decreased and showed no plant growth promotion, and this response was rescued upon exogenous application of Put. Put is also important for hyphal growth of P. indica, indicating that it is co-adapted by both host and microbe. Taken together, we conclude that Put is an essential metabolite and its biosynthesis in plants is crucial for P. indica-mediated plant growth promotion and fungal growth.

Environmental stress determines the colonization and impact of an endophytic fungus on invasive knotweed

There is increasing evidence that microbes play a key role in some plant invasions. A diverse and widespread but little understood group of plant-associated microbes are the fungal root endophytes of the order Sebacinales. They are associated with exotic populations of invasive knotweed (Reynoutria ssp.) in Europe, but their effects on the invaders are unknown. We used the recently isolated Sebacinales root endophyte Serendipita herbamans to experimentally inoculate invasive knotweed and study root colonisation and effects on knotweed growth under different environmental conditions. We verified the inoculation success and fungal colonisation through immunofluorescence microscopy and qPCR. We found that S. herbamans strongly colonized invasive knotweed in low-nutrient and shade environments, but much less under drought or benign conditions. At low nutrients, the endophyte had a positive effect on plant growth, whereas the opposite was true under shaded conditions. Our study demonstrates that the root endophyte S. herbamans has the potential to colonize invasive knotweed fine roots and impact its growth, and it could thus also play a role in natural populations. Our results also show that effects of fungal endophytes on plants can be strongly environment-dependent, and may only be visible under stressful environmental conditions.

A Beneficial Plant-Associated Fungus Shifts the Balance toward Plant Growth over Resistance, Increasing Cucumber Tolerance to Root Herbivory

Plants allocate their limited resources toward different physiological processes, dynamically adjusting their resource allocation in response to environmental changes. How beneficial plant-associated microbes influence this allocation is a topic that continues to interest plant biologists. In this study, we examined the effect of a beneficial fungus, Phialemonium inflatum, on investment in growth and anti-herbivore resistance traits in cucumber plants (Cucumis sativus). We inoculated cucumber seeds with P. inflatum spores and measured several growth parameters, including germination rate, above and belowground biomass, and number of flowers. We also examined plant resistance to adult and larval striped cucumber beetles (Acalymma vitattum), and quantified levels of defense hormones in leaves and roots. Our results indicate that P. inflatum strongly enhances cucumber plant growth and reproductive potential. Although fungus treatment did not improve plant resistance to cucumber beetles, inoculated plants were more tolerant to root herbivory, experiencing less biomass reduction. Together, these findings document how a beneficial plant-associated fungus shifts plant investment in growth over herbivore resistance, highlighting the importance of microbes in mediating plant-herbivore interactions. These findings also have important implications for agricultural systems, where beneficial microbes are often introduced or managed to promote plant growth or enhance resistance.

Bioprospecting Desert Plants for Endophytic and Biostimulant Microbes: A Strategy for Enhancing Agricultural Production in a Hotter, Drier Future

Simple Summary

Endophytes are microbes that live inside plants without causing negative effects in their hosts. All land plants are known to have endophytes, and these endophytes have the capacity to be transferred between plants. Taking endophytes from desert plants, which grow in low-nutrient, high-stress environments, and transferring them to crop plants may alleviate some of the challenges being faced by the agricultural industry, such as increasing drought frequency and rising opposition to chemical use in agriculture. Studies have shown that desert endophytes have the capacity to increase nutrient uptake and increase plant resistance to drought and heat stress, salt stress, and pathogen attack. Currently, the agricultural industry focuses on using irrigation, chemical fertilizers, and chemical pesticides to solve such issues, which can be extremely damaging to the environment. While there is still a lot that is unknown about endophytes, particularly desert plant endophytes, current research provides evidence that desert plant endophytes could be an environmentally friendly alternative to the conventional solutions being applied today.

Abstract

Deserts are challenging places for plants to survive in due to low nutrient availability, drought and heat stress, water stress, and herbivory. Endophytes—microbes that colonize and infect plant tissues without causing apparent disease—may contribute to plant success in such harsh environments. Current knowledge of desert plant endophytes is limited, but studies performed so far reveal that they can improve host nutrient acquisition, increase host tolerance to abiotic stresses, and increase host resistance to biotic stresses. When considered in combination with their broad host range and high colonization rate, there is great potential for desert endophytes to be used in a commercial agricultural setting, especially as croplands face more frequent and severe droughts due to climate change and as the agricultural industry faces mounting pressure to break away from agrochemicals towards more environmentally friendly alternatives. Much is still unknown about desert endophytes, but future studies may prove fruitful for the discovery of new endophyte-based biofertilizers, biocontrol agents, and abiotic stress relievers of crops.

Piriformospora indica Primes Onion Response against Stemphylium Leaf Blight Disease

The root-endophytic fungus Piriformospora indica (=Serendipita indica) has been revealed for its growth-promoting effects and its capacity to induce resistance in a broad spectrum of host plants. However, the bioefficacy of this fungus had not yet been tested against any pathogen affecting onion (Allium cepa). In this study, the biocontrol potency of P. indica against onion leaf blight, an impacting disease caused by the necrotrophic fungal pathogen Stemphylium vesicarium, was evaluated. First, it was proved that colonisation of onion roots by P. indica was beneficial for plant growth, as it increased leaf development and root biomass. Most relevantly, P. indica was also effective in reducing Stemphylium leaf blight (SLB) severity, as assessed under greenhouse conditions and confirmed in field trials in two consecutive years. These investigations could also provide some insight into the biochemical and molecular changes that treatment with P. indica induces in the main pathways associated with host defence response. It was possible to highlight the protective effect of P. indica colonisation against peroxidative damage, and its role in signalling oxidative stress, by assessing changes in malondialdehyde and H2O2 content. It was also showed that treatment with P. indica contributes to modulate the enzymatic activity of superoxide dismutase, catalase, phenylalanine ammonia-lyase and peroxidase, in the course of infection. qPCR-based expression analysis of defence-related genes AcLOX1, AcLOX2, AcPAL1, AcGST, AcCHI, AcWRKY1, and AcWRKY70 provided further indications on P. indica ability to induce onion systemic response. Based on the evidence gathered, this study aims to propose P. indica application as a sustainable tool for improving SLB control, which might not only enhance onion growth performance but also activate defence signalling mechanisms more effectively, involving different pathways.

Jasmonate signaling restricts root soluble sugar accumulation and drives root-fungus symbiosis loss at flowering by antagonizing gibberellin biosynthesis

Jasmonate restricts accumulation of constitutive and fungus-induced root soluble sugars at flowering stage, and thus reduces root beneficial fungal colonization, but little is known about how these are achieved. To determine whether jasmonate-mediated depletion of soluble sugars is the result of direct phytohormonal cross-talk or indirect induced defensive secondary metabolism, we first profiled soluble sugar and tryptophan (Trp)-derived defensive secondary metabolites in the roots of wild-type and jasmonate signaling-impaired Arabidopsis thaliana at flowering upon a beneficial fungus Phomopsis liquidambaris inoculation. Next, jasmonate and gibberellin signaling were manipulated to determine the relationship between jasmonate and gibberellin, and to quantify the effects of these phytohormones on fungal colonization degree, soluble sugar accumulation, Trp-derived secondary metabolites production, and sugar source-sink transport and metabolism. Gibberellin complementation increased Ph. liquidambaris colonization and rescued jasmonate-dependent root soluble sugar depletion and phloem sugar transport and root invertase activity without influencing jasmonate-induced Trp-derived secondary metabolites production at flowering. Furthermore, jasmonate signaling antagonized gibberellin biosynthesis in Ph. liquidambaris-inoculated roots. Our results suggest a phytohormonal antagonism model that jasmonate signaling restricts root soluble sugar accumulation through antagonizing gibberellin biosynthesis rather than through promoting Trp-derived secondary metabolites production and thus drives beneficial fungal colonization decline at flowering.

Seed-borne, endospheric and rhizospheric core microbiota as predictors of plant functional traits across rice cultivars are dominated by deterministic processes

A host-plant and its associated microbiota depend on one another. However, the assembly process and the functioning of host-associated microbiota are poorly understood. Herein, rice was used as model plant to investigate the assemblage of bacterial microbiota, including those in the seed, root endosphere and rhizosphere. We also assessed the degree to which endosphere and rhizosphere communities were influenced by vertical transmission through seed and identified the core microbes that potentially associated with plant phenotypic properties. Plant microhabitat, rather than subspecies type, was the major driver shaping plant-associated bacterial microbiota. Deterministic processes were primarily responsible for community assembly in all microhabitats. The influence of vertical transmission from seed to root-associated bacterial communities appeared to be quite weak (endosphere) or even absent (rhizosphere). A core microbial community composed of 15 generalist species persisted across different microhabitats and represented key connectors in networks. Host-plant functional traits were linked to the relative abundance of these generalist core microbes and could be predicted from them using machine learning algorithms. Overall, bacterial microbiota is assembled by host-plant interactions in a deterministic-based manner. This study enhances our understanding of the driving mechanisms and associations of microbiota in various plant microhabitats and provides new perspectives to improve plant performance.

Piriformospora indica colonization increases the growth, development, and herbivory resistance of sweet potato (Ipomoea batatas L.)

Piriformospora indica symbiosis promoted the growth and photosynthesis, and simultaneously enhanced the resistance against insect herbivory by regulating sporamin-dependent defense in sweet potato. Piriformospora indica (P. indica), a versatile endophytic fungus, promotes the growth and confers resistance against multiple stresses by root colonization in plant hosts. In this study, the effects of P. indica colonization on the growth, physiological change, and herbivore resistance of leaf-vegetable sweet potato cultivar were investigated. P. indica symbiosis significantly improved the biomass in both above- and under-ground parts of sweet potato plants. In comparison with the non-colonized plants, the content of photosynthetic pigments and the efficiency of photosynthesis were increased in P. indica-colonized sweet potato plants. Further investigation showed that the activity of catalase was enhanced in both leaves and roots of sweet potato plants after colonization, but ascorbate peroxidase, peroxidase, and superoxide dismutase were not enhanced. Furthermore, the interaction between P. indica and sweet potato plants also showed the biological function in jasmonic acid (JA)-mediated defense. The plants colonized by P. indica had greatly increased JA accumulation and defense gene expressions, including IbNAC1, IbbHLH3, IbpreproHypSys, and sporamin, leading to elevated trypsin inhibitory activity, which was consistent with a reduced Spodoptera litura performance when larvae fed on the leaves of P. indica-colonized sweet potato plants. The root symbiosis of P. indica is helpful for the plant promoting growth and development and has a strong function as resistance inducers against herbivore attack in sweet potato cultivation by regulating sporamin-dependent defense.

The Fungal Endophyte Serendipita williamsii Does Not Affect Phosphorus Status but Carbon and Nitrogen Dynamics in Arbuscular Mycorrhizal Tomato Plants

Some members of the root endophytic Serendipitaceae were observed to frequently coexist with arbuscular mycorrhizal fungi (AMF), but their interactions and potential synergistic effects in plants have not yet been well elucidated. Here, we inoculated three-week-old tomato seedlings with Serendipita indica or Serendipita williamsii alone or in combination with the arbuscular mycorrhizal fungus Funneliformis mosseae and cultivated the plants in a greenhouse until the late vegetative stage. Our data show that the simultaneous presence of Serendipita spp. did not affect root colonization by AMF, proving the feasibility of their combination for future agronomic uses. The photosynthetic performance was enhanced in AM tomato plants, although growth remained unresponsive following single or dual inoculation with Serendipita spp. and AMF. With regard to nutrient status under dual inoculation, AMF-induced phosphorus increases remained unaffected, but nitrogen and carbon dynamics were highly altered. Specifically, the application of S. williamsii to mycorrhizal tomato plants significantly enhanced nitrogen concentration in the shoots, but this effect was also compensated with a carbon cost. Our findings indicate that S. williamsii performs differently from S. indica when co-inoculated with AMF, and this suggests an unknown mechanism that needs more detailed investigation.

The soil biotic community protects Rhododendron spp. across multiple clades from the oomycete Phytophthora cinnamomi at a cost to plant growth

The effects of whole soil biotic communities on plants is a result of positive and negative interactions from a complex suite of mutualists and pathogens. However, few experiments have evaluated the composite effects of whole soil biotic communities on plant growth and disease resistance. We conducted a factorial greenhouse experiment with 14 Rhododendron species grown with and without live conspecific soil biota and with and without the disease, Phytophthora cinnamomi. We tested the prediction that the presence of whole soil biotic communities influences survival in the presence of disease. We also explored functional trait correlations with disease susceptibility across the phylogeny. The presence of live soil biota led to higher survival in the presence of disease compared with sterilized soils, and the direction of this effect was consistent for seven species across four clades. The presence of live soil biota also significantly reduced plant growth rate and decreased shoot biomass, relative to plants grown in sterilized soil, indicating that live soil biota might influence plant allocation strategies. We found that Rhododendron species with higher Root Shoot Ratios were less susceptible to Phytophthora, suggesting that water relations influence disease susceptibility. Our findings that disease resistance and susceptibility occur independently across multiple clades and that whole soil biotic communities consistently enhance disease resistance across clades, suggest that soil biota may play an important role in disease resistance and can moderate disease-induced mortality.

A novel dark septate fungal endophyte positively affected blueberry growth and changed the expression of plant genes involved in phytohormone and flavonoid biosynthesis

Dark septate endophytes (DSEs) are one of the most studied groups of root fungal endophytes in recent years. However, the effects of DSE on host plant are still under debate, and the molecular mechanisms are poorly understood. In this study, we identified a DSE fungus of the genus Anteaglonium, named T010, from the wild blueberry. When inoculated into Vaccinium corymbosum L. plants, T010 could enhance root growth and promote shoot branching, leading to increased plant growth. By comparative transcriptome analysis, we obtained 1948 regulated differentially expressed genes (DEGs) from the V. corymbosum plants treated by T010. Further functional enrichment analysis identified a series of DEGs enriched in transcriptional regulation, material transport, phytohormone biosynthesis and flavonoid biosynthesis. Moreover, the comparative analysis of liquid chromatography-mass spectrometry verified that T010 treatment induced the changes in the contents of various phytohormones and flavonoids. This is the first report on the isolation of DSE fungi of the genus Anteaglonium from blueberry roots. Moreover, our results suggested that T010 colonization could result in a series of changes in cell metabolism, biosynthesis and signal pathways, thereby promoting plant growth. Particularly, the changes of phytohormone and flavonoid metabolism induced by T010 colonization might contribute to the promotion of blueberry growth. Our results will provide new insights into understanding of the interaction of DSE fungi and host plants, as well as the development and utilization of DSE preparations.

Calcium channel CNGC19 mediates basal defense signaling to regulate colonization by Piriformospora indica in Arabidopsis roots

The activation of calcium signaling is a crucial event for perceiving environmental stress. Colonization by Piriformospora indica, a growth-promoting root endosymbiont, activates cytosolic Ca2+ in Arabidopsis roots. In this study, we examined the role and functional relevance of calcium channels responsible for Ca2+ fluxes. Expression profiling revealed that CYCLIC NUCLEOTIDE GATED CHANNEL 19 (CNGC19) is an early-activated gene, induced by unidentified components in P. indica cell-wall extract. Functional analysis showed that loss-of-function of CNGC19 resulted in growth inhibition by P.indica, due to increased colonization and loss of controlled fungal growth. The cngc19 mutant showed reduced elevation of cytosolic Ca2+ in response to P. indica cell-wall extract in comparison to the wild-type. Microbe-associated molecular pattern-triggered immunity was compromised in the cngc19 lines, as evidenced by unaltered callose deposition, reduced cis-(+)-12-oxo-phytodienoic acid, jasmonate, and jasmonoyl isoleucine levels, and down-regulation of jasmonate and other defense-related genes, which contributed to a shift towards a pathogenic response. Loss-of-function of CNGC19 resulted in an inability to modulate indole glucosinolate content during P. indica colonization. CNGC19-mediated basal immunity was dependent on the AtPep receptor, PEPR. CNGC19 was also crucial for P. indica-mediated suppression of AtPep-induced immunity. Our results thus demonstrate that Arabidopsis CNGC19 is an important Ca2+ channel that maintains a robust innate immunity and is crucial for growth-promotion signaling upon colonization by P. indica.

The Endophytic Fungus Albifimbria verrucaria from Wild Grape as an Antagonist of Botrytis cinerea and Other Grape Pathogens

Gray mold, caused by Botrytis cinerea, is one of the most prevalent fungal diseases in table and wine grapes, affecting grape quality and yields. In this study, we isolated several endophytic fungi, including Alternaria alternata, Bipolaris cynodontis, Phoma sp., and Albifimbria verrucaria, from leaves of Amur grape (Vitis amurensis) cultivar Shuangyou and investigated their biocontrol activity against B. cinerea. In vitro dual assay showed that A. verrucaria isolate SYE-1 inhibited growth of B. cinerea. The isolate also had a wide range of biocontrol activity against Lasiodiplodia theobromae and Elsinoë ampelina. Mycelial growth and conidium germination of B. cinerea were significantly inhibited by metabolites of A. verrucaria in agar plates and culture extracts of A. verrucaria from liquid culture. The isolate produced a total chitinase activity of 0.4 U/ml after incubation for 10 days in Czapek's liquid medium. In addition, application of culture extracts of A. verrucaria prior to B. cinerea inoculation significantly reduced disease severity on grape leaves of the susceptible cultivar Red Globe. Taken together, our results indicate that A. verrucaria has potential as a biocontrol agent to control grape gray mold.

Host affinity of endophytic fungi and the potential for reciprocal interactions involving host secondary chemistry

PREMISE

Interactions between fungal endophytes and their host plants present useful systems for identifying important factors affecting assembly of host-associated microbiomes. Here we investigated the role of secondary chemistry in mediating host affinity of asymptomatic foliar endophytic fungi using Psychotria spp. and Theobroma cacao (cacao) as hosts.

METHODS

First, we surveyed endophytic communities in Psychotria species in a natural common garden using culture-based methods. Then we compared differences in endophytic community composition with differences in foliar secondary chemistry in the same host species, determined by liquid chromatography-tandem mass spectrometry. Finally, we tested how inoculation with live and heat-killed endophytes affected the cacao chemical profile.

RESULTS

Despite sharing a common environment and source pool for endophyte spores, different Psychotria host species harbored strikingly different endophytic communities that reflected intrinsic differences in their leaf chemical profiles. In T. cacao, inoculation with live and heat-killed endophytes produced distinct cacao chemical profiles not found in uninoculated plants or pure fungal cultures, suggesting that endophytes, like pathogens, induce changes in secondary chemical profiles of their host plant.

CONCLUSIONS

Collectively our results suggest at least two potential processes: (1) Plant secondary chemistry influences assembly and composition of fungal endophytic communities, and (2) host colonization by endophytes subsequently induces changes in the host chemical landscape. We propose a series of testable predictions based on the possibility that reciprocal chemical interactions are a general property of plant-endophyte interactions.

Catalase, glutathione, and protein phosphatase 2A-dependent organellar redox signalling regulate aphid fecundity under moderate and high irradiance

Redox processes regulate plant/insect responses, but the precise roles of environmental triggers and specific molecular components remain poorly defined. Aphid fecundity and plant responses were therefore measured in Arabidopsis thaliana mutants deficient in either catalase 2 (cat2), different protein phosphatase 2A (PP2A) subunits or glutathione (cad2, pad2, and clt1) under either moderate (250 μmol m^-2 s^-1 ) or high (800 μmol m^-2 s^-1 ) light. Aphid fecundity was decreased in pp2a-b'γ, cat2 and the cat2 pp2a-b'γ double mutants relative to the wild type under moderate irradiance. High light decreased aphid numbers in all genotypes except for cat2. Aphid fecundity was similar in the cat2 and glutathione-, phytoalexin-, and glucosinolate-deficient cat2cad2 double mutants under both irradiances. Aphid-induced increases in transcripts encoding the abscisic acid-related ARABIDOPSIS ZINC-FINGER PROTEIN 1 transcription factor were observed only under moderate light. Conversely, aphid induced increases in transcripts encoding the jasmonate-synthesis enzyme ALLENE OXIDE CYCLASE 3 was observed in all genotypes only under high light. Aphid-induced increases in REDOX RESPONSIVE TRANSCRIPTION FACTOR 1 mRNAs were observed in all genotypes except pp2a-b'ζ1-1 under both irradiances. Aphid fecundity is therefore regulated by cellular redox signalling that is mediated, at least in part, through PP2A-dependent mitochondria to nucleus signalling pathways.

The ecological role of bacterial seed endophytes associated with wild cabbage in the United Kingdom

Endophytic bacteria are known for their ability in promoting plant growth and defense against biotic and abiotic stress. However, very little is known about the microbial endophytes living in the spermosphere. Here, we isolated bacteria from the seeds of five different populations of wild cabbage (Brassica oleracea L) that grow within 15 km of each other along the Dorset coast in the UK. The seeds of each plant population contained a unique microbiome. Sequencing of the 16S rRNA genes revealed that these bacteria belong to three different phyla (Actinobacteria, Firmicutes, and Proteobacteria). Isolated endophytic bacteria were grown in monocultures or mixtures and the effects of bacterial volatile organic compounds (VOCs) on the growth and development on B. oleracea and on resistance against a insect herbivore was evaluated. Our results reveal that the VOCs emitted by the endophytic bacteria had a profound effect on plant development but only a minor effect on resistance against an herbivore of B. oleracea. Plants exposed to bacterial VOCs showed faster seed germination and seedling development. Furthermore, seed endophytic bacteria exhibited activity via volatiles against the plant pathogen F. culmorum. Hence, our results illustrate the ecological importance of the bacterial seed microbiome for host plant health and development.

Site-specific responses of foliar fungal microbiomes to nutrient addition and herbivory at different spatial scales

The plant microbiome can affect host function in many ways and characterizing the ecological factors that shape endophytic (microbes living inside host plant tissues) community diversity is a key step in understanding the impacts of environmental change on these communities. Phylogenetic relatedness among members of a community offers a way of quantifying phylogenetic diversity of a community and can provide insight into the ecological factors that shape endophyte microbiomes. We examined the effects of experimental nutrient addition and herbivory exclusion on the phylogenetic diversity of foliar fungal endophyte communities of the grass species Andropogon gerardii at four sites in the Great Plains of the central USA. Using amplicon sequencing, we characterized the effects of fertilization and herbivory on fungal community phylogenetic diversity at spatial scales that spanned within-host to between sites across the Great Plains. Despite increasing fungal diversity and richness, at larger spatial scales, fungal microbiomes were composed of taxa showing random phylogenetic associations. Phylogenetic diversity did not differ systematically when summed across increasing spatial scales from a few meters within plots to hundreds of kilometers among sites. We observed substantial shifts in composition across sites, demonstrating distinct but similarly diverse fungal communities were maintained within sites across the region. In contrast, at the scale of within leaves, fungal communities tended to be comprised of closely related taxa regardless of the environment, but there were no shifts in phylogenetic composition among communities. We also found that nutrient addition (fertilization) and herbivory have varying effects at different sites. These results suggest that the direction and magnitude of the outcomes of environmental modifications likely depend on the spatial scale considered, and can also be constrained by regional site differences in microbial diversity and composition.

Piriformospora indica-induced phytohormone changes and root colonization strategies are highly host-specific

Piriformospora indica, an endophytic fungus of Sebacinales, has a wide host range and promotes the performance of mono- and eudicot plants. Here, we compare the interaction of P. indica with the roots of seven host plants (Anthurium andraeanum, Arabidopsis thaliana, Brassica campestris, Lycopersicon esculentum, Oncidium orchid, Oryza sativa, and Zea mays). Microscopical analyses showed that the colonization time and the mode of hyphal invasion into the roots differ in the symbiotic interactions. Substantial differences between the species were also observed for the levels and accumulation of jasmonate (JA) and gibberellin (GA) and the transcript levels for genes involved in their syntheses. No obvious correlation could be detected between the endogenous JA and/or GA levels and the time point of root colonization in a given plant species. Our results suggest that root colonization strategies and changes in the two phytohormone levels are highly host-specific.

Endophyte Infection and Methyl Jasmonate Treatment Increased the Resistance of Achnatherum sibiricum to Insect Herbivores Independently

Alkaloids are usually thought to be responsible for protecting endophyte-infected (EI) grasses from their herbivores. For EI grasses that produce few alkaloids, can endophyte infection enhance their resistance to herbivores? Related studies are limited. In the Inner Mongolian steppe, Achnatherum sibiricum is highly infected by Epichloë endophytes, but produces few alkaloids. Locusts are the common insect herbivores of grasses. In this study, A. sibiricum was used as plant material. Methyl jasmonate (MJ, when applied exogenously, can induce responses similar to herbivore damage) treatment was performed. The effects of endophyte infection and MJ treatment on the resistance of A. sibiricum to Locusta migratoria were studied. We found that locusts preferred EF (endophyte-free) plants to EI plants in both choice and no-choice feeding experiments. Endophyte infection enhanced the resistance of A. sibiricum to locusts. Endophyte infection decreased soluble sugar concentrations, while it increased the total phenolic content and phenylalanine ammonia lyase (PAL) activity, which may contribute to the resistance of A. sibiricum to locusts. There was an interaction effect between MJ treatment and endophyte infection on the growth of the host. MJ treatment was a negative regulator of the plant growth-promoting effects of endophyte infection. There was no interaction effect between MJ treatment and endophyte infection on the defense characteristics of the host. In groups not exposed to locusts, MJ treatment and endophyte infection had a similar effect in decreasing the soluble sugar content, while increasing the total phenolic content and the PAL activity. In groups exposed to locusts, the effect of MJ treatment on the above characteristics disappeared, while the effect of endophyte infection became more obvious. All of these results suggest that even for endophytes producing few alkaloids, they could still increase the resistance of native grasses to insect herbivores. Furthermore, endophyte infection might mediate the defense responses of the host, independent of jasmonic acid (JA) pathways.

Auxin signalling of Arachis hypogaea activated by colonization of mutualistic fungus Phomopsis liquidambari enhances nodulation and N2 -fixation

Beneficial fungal and rhizobial symbioses share commonalities in phytohormones responses, especially in auxin signalling. Mutualistic fungus Phomopsis liquidambari effectively increases symbiotic efficiency of legume peanut (Arachis hypogaea L.) with another microsymbiont, bradyrhizobium, but the underlying mechanisms are not well understood. We quantified and manipulated the IAA accumulation in ternary P. liquidambari-peanut-bradyrhizobial interactions to uncover its role between distinct symbioses. We found that auxin signalling is both locally and systemically induced by the colonization of P. liquidambari with peanut and further confirmed by Arabidopsis harbouring auxin-responsive reporter, DR5:GUS, and that auxin action, including auxin transport, is required to maintain fungal symbiotic behaviours and beneficial traits of plant during the symbiosis. Complementation and action inhibition experiments reveal that auxin signalling is involved in P. liquidambari-mediated nodule development and N₂ -fixation enhancement and symbiotic gene activation. Further analyses showed that blocking of auxin action compromised the P. liquidambari-induced nodule phenotype and physiology changes, including vascular bundle development, symbiosome and bacteroids density, and malate concentrations, while induced the accumulation of starch granules in P. liquidambari-inoculated nodules. Collectively, our study demonstrated that auxin signalling activated by P. liquidambari symbiosis is recruited by peanut for bradyrhizobial symbiosis via symbiotic signalling pathway activation and nodule carbon metabolism enhancement.

Role of Phytohormones in Piriformospora indica-Induced Growth Promotion and Stress Tolerance in Plants: More Questions Than Answers

Phytohormones play vital roles in the growth and development of plants as well as in interactions of plants with microbes such as endophytic fungi. The endophytic root-colonizing fungus Piriformospora indica promotes plant growth and performance, increases resistance of colonized plants to pathogens, insects and abiotic stress. Here, we discuss the roles of the phytohormones (auxins, cytokinin, gibberellins, abscisic acid, ethylene, salicylic acid, jasmonates, and brassinosteroids) in the interaction of P. indica with higher plant species, and compare available data with those from other (beneficial) microorganisms interacting with roots. Crosstalks between different hormones in balancing the plant responses to microbial signals is an emerging topic in current research. Furthermore, phytohormones play crucial roles in systemic signal propagation as well as interplant communication. P. indica interferes with plant hormone synthesis and signaling to stimulate growth, flowering time, differentiation and local and systemic immune responses. Plants adjust their hormone levels in the roots in response to the microbes to control colonization and fungal propagation. The available information on the roles of phytohormones in beneficial root-microbe interactions opens new questions of how P. indica manipulates the plant hormone metabolism to promote the benefits for both partners in the symbiosis.

Fungal Endophytes: Beyond Herbivore Management

The incorporation of entomopathogenic fungi as biocontrol agents into Integrated Pest Management (IPM) programs without doubt, has been highly effective. The ability of these fungal pathogens such as Beauveria bassiana and Metarhizium anisopliae to exist as endophytes in plants and protect their colonized host plants against the primary herbivore pests has widely been reported. Aside this sole role of pest management that has been traditionally ascribed to fungal endophytes, recent findings provided evidence of other possible functions as plant yield promoter, soil nutrient distributor, abiotic stress and drought tolerance enhancer in plants. However, reports on these additional important effects of fungal endophytes on the colonized plants remain scanty. In this review, we discussed the various beneficial effects of endophytic fungi on the host plants and their primary herbivore pests; as well as some negative effects that are relatively unknown. We also highlighted the prospects of our findings in further increasing the acceptance of fungal endophytes as an integral part of pest management programs for optimized crop production.

Alternaria Brassicae Induces Systemic Jasmonate Responses in Arabidopsis Which Travel to Neighboring Plants via a Piriformsopora Indica Hyphal Network and Activate Abscisic Acid Responses

Stress information received by a particular local plant tissue is transferred to other tissues and neighboring plants, but how the information travels is not well understood. Application of Alternaria Brassicae spores to Arabidopsis leaves or roots stimulates local accumulation of jasmonic acid (JA), the expression of JA-responsive genes, as well as of NITRATE TRANSPORTER (NRT)2.5 and REDOX RESPONSIVE TRANSCRIPTION FACTOR1 (RRTF1). Infection information is systemically spread over the entire seedling and propagates radially from infected to non-infected leaves, axially from leaves to roots, and vice versa. The local and systemic NRT2.5 responses are reduced in the jar1 mutant, and the RRTF1 response in the rbohD mutant. Information about A. brassicae infection travels slowly to uninfected neighboring plants via a Piriformospora Indica hyphal network, where NRT2.5 and RRTF1 are up-regulated. The systemic A. brassicae-induced JA response in infected plants is converted to an abscisic acid (ABA) response in the neighboring plant where ABA and ABA-responsive genes are induced. We propose that the local threat information induced by A. brassicae infection is spread over the entire plant and transferred to neighboring plants via a P. indica hyphal network. The JA-specific response is converted to a general ABA-mediated stress response in the neighboring plant.

Seed and Root Endophytic Fungi in a Range Expanding and a Related Plant Species

Climate change is accelerating the spread of plants and their associated species to new ranges. The differences in range shift capacity of the various types of species may disrupt long-term co-evolved relationships especially those belowground, however, this may be less so for seed-borne endophytic microbes. We collected seeds and soil of the range-expanding Centaurea stoebe and the congeneric Centaurea jacea from three populations growing in Slovenia (native range of both Centaurea species) and the Netherlands (expanded range of C. stoebe, native range of C. jacea). We isolated and identified endophytic fungi directly from seeds, as well as from roots of the plants grown in Slovenian, Dutch or sterilized soil to compare fungal endophyte composition. Furthermore, we investigated whether C. stoebe hosts a reduced community composition of endophytes in the expanded range due to release from plant-species specific fungi while endophyte communities in C. jacea in both ranges are similar. We cultivated 46 unique and phylogenetically diverse endophytes. A majority of the seed endophytes resembled potential pathogens, while most root endophytes were not likely to be pathogenic. Only one endophyte was found in both roots and seeds, but was isolated from different plant species. Unexpectedly, seed endophyte diversity of southern C. stoebe populations was lower than of populations from the north, while the seed endophyte community composition of northern C. stoebe populations was significantly different southern C. stoebe as well as northern and southern C. jacea populations. Root endophyte diversity was considerably lower in C. stoebe than in C. jacea independent of plant and soil origin, but this difference disappeared when plants were grown in sterile soils. We conclude that the community composition of fungal endophytes not only differs between related plant species but also between populations of plants that expand their range compared to their native habitat. Our results suggest that fungal endophytes of two Centaurea species are not able to systemically infect plants. We highlight that endophytes remain poorly studied and further work should investigate the functional importance of endophytes.

Ecophylogeny of the endospheric root fungal microbiome of co-occurring Agrostis stolonifera

BACKGROUND

Within the root endosphere, fungi are known to be important for plant nutrition and resistance to stresses. However, description and understanding of the rules governing community assembly in the fungal fraction of the plant microbiome remains scarce.

METHODS

We used an innovative DNA- and RNA-based analysis of co-extracted nucleic acids to reveal the complexity of the fungal community colonizing the roots of an Agrostis stolonifera population. The normalized RNA/DNA ratio, designated the 'mean expression ratio', was used as a functional trait proxy. The link between this trait and phylogenetic relatedness was measured using the Blomberg's K statistic.

RESULTS

Fungal communities were highly diverse. Only ∼1.5% of the 635 OTUs detected were shared by all individuals, however these accounted for 33% of the sequence number. The endophytic fungal communities in plant roots exhibit phylogenetic clustering that can be explained by a plant host effect acting as environmental filter. The 'mean expression ratio' displayed significant but divergent phylogenetic signals between fungal phyla.

DISCUSSION

These results suggest that environmental filtering by the host plant favours the co-existence of related and similar OTUs within the Basidiomycota community assembly, whereas the Ascomycota and Glomeromycota communities seem to be impacted by competitive interactions which promote the co-existence of phylogenetically related but ecologically dissimilar OTUs.

Piriformospora indica Stimulates Root Metabolism of Arabidopsis thaliana

Piriformospora indica is a root-colonizing fungus, which interacts with a variety of plants including Arabidopsis thaliana. This interaction has been considered as mutualistic leading to growth promotion of the host. So far, only indolic glucosinolates and phytohormones have been identified as key players. In a comprehensive non-targeted metabolite profiling study, we analyzed Arabidopsis thaliana’s roots, root exudates, and leaves of inoculated and non-inoculated plants by ultra performance liquid chromatography/electrospray ionization quadrupole-time-of-flight mass spectrometry (UPLC/(ESI)-QTOFMS) and gas chromatography/electron ionization quadrupole mass spectrometry (GC/EI-QMS), and identified further biomarkers. Among them, the concentration of nucleosides, dipeptides, oligolignols, and glucosinolate degradation products was affected in the exudates. In the root profiles, nearly all metabolite levels increased upon co-cultivation, like carbohydrates, organic acids, amino acids, glucosinolates, oligolignols, and flavonoids. In the leaf profiles, we detected by far less significant changes. We only observed an increased concentration of organic acids, carbohydrates, ascorbate, glucosinolates and hydroxycinnamic acids, and a decreased concentration of nitrogen-rich amino acids in inoculated plants. These findings contribute to the understanding of symbiotic interactions between plant roots and fungi of the order of Sebacinales and are a valid source for follow-up mechanistic studies, because these symbioses are particular and clearly different from interactions of roots with mycorrhizal fungi or dark septate endophytes

Sebacinales - one thousand and one interactions with land plants

20 I 21 II 21 III 23 IV 29 V 33 VI 35 36 36 References 36 SUMMARY: Root endophytism and mycorrhizal associations are complex derived traits in fungi that shape plant physiology. Sebacinales (Agaricomycetes, Basidiomycota) display highly diverse interactions with plants. Although early-diverging Sebacinales lineages are root endophytes and/or have saprotrophic abilities, several more derived clades harbour obligate biotrophs forming mycorrhizal associations. Sebacinales thus display transitions from saprotrophy to endophytism and to mycorrhizal nutrition within one fungal order. This review discusses the genomic traits possibly associated with these transitions. We also show how molecular ecology revealed the hyperdiversity of Sebacinales and their evolutionary diversification into two sister families: Sebacinaceae encompasses mainly ectomycorrhizal and early-diverging saprotrophic species; the second family includes endophytes and lineages that repeatedly evolved ericoid, orchid and ectomycorrhizal abilities. We propose the name Serendipitaceae for this family and, within it, we transfer to the genus Serendipita the endophytic cultivable species Piriformospora indica and P. williamsii. Such cultivable Serendipitaceae species provide excellent models for root endophytism, especially because of available genomes, genetic tractability, and broad host plant range including important crop plants and the model plant Arabidopsis thaliana. We review insights gained with endophytic Serendipitaceae species into the molecular mechanisms of endophytism and of beneficial effects on host plants, including enhanced resistance to abiotic and pathogen stress.