Plant growth-promoting fungus, Trichoderma koningi suppresses isoflavonoid phytoalexin vestitol production for colonization on/in the roots of Lotus japonicus

Mechanisms for plant growth promotion activated by Trichoderma in natural and managed terrestrial ecosystems

Trichoderma spp. are free-living fungi present in virtually all terrestrial ecosystems. These soil fungi can stimulate plant growth and increase plant nutrient acquisition of macro- and micronutrients and water uptake. Generally, plant growth promotion by Trichoderma is a consequence of the activity of potent fungal signaling metabolites diffused in soil with hormone-like activity, including indolic compounds as indole-3-acetic acid (IAA) produced at concentrations ranging from 14 to 234 μg l-1, and volatile organic compounds such as sesquiterpene isoprenoids (C15), 6-pentyl-2H-pyran-2-one (6-PP) and ethylene (ET) produced at levels from 10 to 120 ng over a period of six days, which in turn, might impact plant endogenous signaling mechanisms orchestrated by plant hormones. Plant growth stimulation occurs without the need of physical contact between both organisms and/or during root colonization. When associated with plants Trichoderma may cause significant biochemical changes in plant content of carbohydrates, amino acids, organic acids and lipids, as detected in Arabidopsis thaliana, maize (Zea mays), tomato (Lycopersicon esculentum) and barley (Hordeum vulgare), which may improve the plant health status during the complete life cycle. Trichoderma-induced plant beneficial effects such as mechanisms of defense and growth are likely to be inherited to the next generations. Depending on the environmental conditions perceived by the fungus during its interaction with plants, Trichoderma can reprogram and/or activate molecular mechanisms commonly modulated by IAA, ET and abscisic acid (ABA) to induce an adaptative physiological response to abiotic stress, including drought, salinity, or environmental pollution. This review, provides a state of the art overview focused on the canonical mechanisms of these beneficial fungi involved in plant growth promotion traits under different environmental scenarios and shows new insights on Trichoderma metabolites from different chemical classes that can modulate specific plant growth aspects. Also, we suggest new research directions on Trichoderma spp. and their secondary metabolites with biological activity on plant growth.

Isoflavonoid metabolism in leguminous plants: an update and perspectives

Isoflavonoids constitute a well-investigated category of phenylpropanoid-derived specialized metabolites primarily found in leguminous plants. They play a crucial role in legume development and interactions with the environment. Isoflavonoids usually function as phytoalexins, acting against pathogenic microbes in nature. Additionally, they serve as signaling molecules in rhizobial symbiosis. Notably, owing to their molecular structure resembling human estrogen, they are recognized as phytoestrogens, imparting positive effects on human health. This review comprehensively outlines recent advancements in research pertaining to isoflavonoid biosynthesis, transcriptional regulation, transport, and physiological functions, with a particular emphasis on soybean plants. Additionally, we pose several questions to encourage exploration into novel contributors to isoflavonoid metabolism and their potential roles in plant-microbe interactions.

The effect of Trichoderma harzianum agents on physiological-biochemical characteristics of cucumber and the control effect against Fusarium wilt

At the seedling and adult plant phases, pot experiments were carried out to enhance the physiological-biochemical characteristics of cucumber, guarantee its high yield, and ensure its cultivation of quality. Trichoderma harzianum conidia agents at 104, 105, 106, and 107 cfu g-1 were applied in accordance with the application of Fusarium oxysporum powder at concentrations of 104 cfu/g on the protective enzyme activity, physiological and biochemical indices, seedling quality, resilience to Fusarium wilt, quality, and yield traits. Fusarium oxysporum powder at 104 cfu g-1 was used to treat CK1, while Fusarium oxysporum powder and T. harzianum conidia agents were not used to treat CK2. The results show that different T. harzianum agents improved the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), and peroxidase (POD) in cucumber seedlings, improved chlorophyll content, root activity, root-shoot ratio, and seedling strength index, and decreased malondialdehyde (MAD) content (P < 0.05). T3, a combination of 104 cfu g-1 Fusarium oxysporum powder and 106 cfu g-1 T. harzianum conidia agents, had the greatest promoting effect. The effects of different T. harzianum conidia agents and their application amounts on the control of cucumber Fusarium wilt were explored. T3 had the best promotion impact, and the control effect of cucumber Fusarium wilt at seedling stage and adult stage reached 83.98% and 70.08%, respectively. The quality index and yield formation of cucumber were also increased by several T. harzianum agents, with T3 having the strongest promotion effects. In comparison to CK1, the soluble sugar, Vc, soluble protein, and soluble solid contents of T3 cucumber fruit were 120.75%, 39.14%, 42.26%, and 11.64% higher (P < 0.05), respectively. In comparison to CK2, the soluble sugar, Vc, soluble protein, and soluble solid contents of T3 cucumber fruit were 66.06%, 24.28%, 36.15%, and 7.95% higher (P < 0.05), respectively. In comparison to CK1 and CK2, the yields of T3 cucumber were 50.19% and 35.86% higher, respectively. As a result, T. harzianum agents can enhance the physiological and biochemical traits of cucumber seedlings, raise the quality of cucumber seedlings, have a controlling impact on Fusarium wilt, and increase the yield and quality of cucumber fruit. The greatest effectiveness of T3 comes from its use. In this study, Trichoderma harzianum conidia agents demonstrated good impacts on cucumber yield formation and plant disease prevention, demonstrating their high potential as biocontrol agents.

Primary and Secondary Metabolites in Lotus japonicus

Lotus japonicus is a leguminous model plant used to gain insight into plant physiology, stress response, and especially symbiotic plant-microbe interactions, such as root nodule symbiosis or arbuscular mycorrhiza. Responses to changing environmental conditions, stress, microbes, or insect pests are generally accompanied by changes in primary and secondary metabolism to account for physiological needs or to produce defensive or signaling compounds. Here we provide an overview of the primary and secondary metabolites identified in L. japonicus to date. Identification of the metabolites is mainly based on mass spectral tags (MSTs) obtained by gas chromatography linked with tandem mass spectrometry (GC-MS/MS) or liquid chromatography-MS/MS (LC-MS/MS). These MSTs contain retention index and mass spectral information, which are compared to databases with MSTs of authentic standards. More than 600 metabolites are grouped into compound classes such as polyphenols, carbohydrates, organic acids and phosphates, lipids, amino acids, nitrogenous compounds, phytohormones, and additional defense compounds. Their physiological effects are briefly discussed, and the detection methods are explained. This review of the exisiting literature on L. japonicus metabolites provides a valuable basis for future metabolomics studies.

Colonization Ability of Bacillus subtilis NCD-2 in Different Crops and Its Effect on Rhizosphere Microorganisms

Bacillus subtilis strain NCD-2 is a promising biocontrol agent for soil-borne plant diseases and shows potential for promoting the growth of some crops. The purposes of this study were to analyze the colonization ability of strain NCD-2 in different crops and reveal the plant growth promotion mechanism of strain NCD-2 by rhizosphere microbiome analysis. qRT-PCR was used to determine the populations of strain NCD-2, and microbial communities’ structures were analyzed through amplicon sequencing after application of strain NCD-2. Results demonstrated that strain NCD-2 had a good growth promotion effect on tomato, eggplant and pepper, and it was the most abundant in eggplant rhizosphere soil. There were significantly differences in the types of beneficial microorganisms recruited for different crops after application of strain NCD-2. PICRUSt analysis showed that the relative abundances of functional genes for amino acid transport and metabolism, coenzyme transport and metabolism, lipid transport and metabolism, inorganic ion transport and metabolism, and defense mechanisms were enriched in the rhizospheres of pepper and eggplant more than in the rhizospheres of cotton, tomato and maize after application of strain NCD-2. In summary, the colonization ability of strain NCD-2 for five plants was different. There were differences in microbial communities’ structure in rhizosphere of different plants after application of strain NCD-2. Based on the results obtained in this study, it was concluded that the growth promoting ability of strain NCD-2 were correlated with its colonization quantity and the microbial species it recruited.

Genome insights into the plant growth-promoting bacterium Saccharibacillus brassicae ATSA2T

Endophytes can facilitate the improvement of plant growth and health in agriculturally important crops, yet their genomes and secondary metabolites remain largely unexplored. We previously isolated Saccharibacillus brassicae strain ATSA2^T from surface-sterilized seeds of kimchi cabbage and represented a novel species of the genus Saccharibacillus. In this study, we evaluated the plant growth-promoting (PGP) effect of strain ATSA2^T in kimchi cabbage, bok choy, and pepper plants grown in soils. We found a significant effect on the shoot and root biomass, and chlorophyll contents following strain ATSA2^T treatment. Strain ATSA2^T displayed PGP traits such as indole acetic acid (IAA, 62.9 μg/mL) and siderophore production, and phosphate solubilization activity. Furthermore, genome analysis of this strain suggested the presence of gene clusters involved in iron acquisition (fhuABD, afuABC, fbpABC, and fepCDG) and phosphate solubilization (pstABCHS, phoABHLU, and phnCDEP) and other phytohormone biosynthesis genes, including indole-3-acetic acid (trpABCDEFG), in the genome. Interestingly, the secondary metabolites cerecidin, carotenoid, siderophore (staphylobactin), and bacillaene underlying plant growth promotion were found in the whole genome via antiSMASH analysis. Overall, physiological testing and genome analysis data provide comprehensive insights into plant growth-promoting mechanisms, suggesting the relevance of strain ATSA2^T in agricultural biotechnology.

The Importance of Microorganisms for Sustainable Agriculture-A Review

In the face of climate change, progressive degradation of the environment, including agricultural land negatively affecting plant growth and development, endangers plant productivity. Seeking efficient and sustainable agricultural techniques to replace agricultural chemicals is one of the most important challenges nowadays. The use of plant growth-promoting microorganisms is among the most promising approaches; however, molecular mechanisms underneath plant-microbe interactions are still poorly understood. In this review, we summarized the knowledge on plant-microbe interactions, highlighting the role of microbial and plant proteins and metabolites in the formation of symbiotic relationships. This review covers rhizosphere and phyllosphere microbiomes, the role of root exudates in plant-microorganism interactions, the functioning of the plant's immune system during the plant-microorganism interactions. We also emphasized the possible role of the stringent response and the evolutionarily conserved mechanism during the established interaction between plants and microorganisms. As a case study, we discussed fungi belonging to the genus Trichoderma. Our review aims to summarize the existing knowledge about plant-microorganism interactions and to highlight molecular pathways that need further investigation.

Long-Term Organic–Inorganic Fertilization Regimes Alter Bacterial and Fungal Communities and Rice Yields in Paddy Soil

Microorganisms are the most abundant and diverse organisms in soils and have important effects on soil fertility. In this study, effects of the long-term fertilization treatments no fertilizer (CK), chemical fertilizer (nitrogen–phosphorus–potassium (NPK)), and organic–inorganic fertilizer (NPK and organic fertilizer (NPKM)) on rice yield and soil bacterial and fungal community diversity, structure, composition, and interaction networks were evaluated. Of the three treatments, the highest rice yield was in NPKM. Bacterial richness was significantly higher in NPKM than in NPK. Fertilization treatment significantly altered β diversity of communities, species composition of bacterial and fungal communities, and structure of soil microbial networks. The most complex bacterial and fungal interaction co-occurrence network with the highest average degree and numbers of edges and nodes was in NPKM. Relative abundance of the plant growth-promoting fungus Trichoderma increased significantly in NPKM compared with CK and NPK. The results of the study indicate that bacterial richness and microbial community member interactions (network complexity) might be suitable indicators of soil biological fertility. This research provides new insights on the effects of different fertilization regimes on responses of soil bacterial and fungal communities and their contributions to crop yield. New indicators such as bacterial richness and complexity of microbial interaction networks are also identified that can be used to evaluate soil biological fertility.

Complete Genome Sequences and Genome-Wide Characterization of Trichoderma Biocontrol Agents Provide New Insights into their Evolution and Variation in Genome Organization, Sexual Development, and Fungal-Plant Interactions

Trichoderma spp. represent one of the most important fungal genera to mankind and in natural environments. The genus harbors prolific producers of wood-decaying enzymes, biocontrol agents against plant pathogens, plant-growth-promoting biofertilizers, as well as model organisms for studying fungal-plant-plant pathogen interactions. Pursuing highly accurate, contiguous, and chromosome-level reference genomes has become a primary goal of fungal research communities. Here, we report the chromosome-level genomic sequences and whole-genome annotation data sets of four strains used as biocontrol agents or biofertilizers (Trichoderma virens Gv29-8, Trichoderma virens FT-333, Trichoderma asperellum FT-101, and Trichoderma atroviride P1). Our results provide comprehensive categorization, correct positioning, and evolutionary detail of both nuclear and mitochondrial genomes, including telomeres, AT-rich blocks, centromeres, transposons, mating-type loci, nuclear-encoded mitochondrial sequences, as well as many new secondary metabolic and carbohydrate-active enzyme gene clusters. We have also identified evolutionarily conserved core genes contributing to plant-fungal interactions, as well as variations potentially linked to key behavioral traits such as sex, genome defense, secondary metabolism, and mycoparasitism. The genomic resources we provide herein significantly extend our knowledge not only of this economically important fungal genus, but also fungal evolution and basic biology in general. IMPORTANCE Telomere-to-telomere and gapless reference genome assemblies are necessary to ensure that all genomic variants are studied and discovered, including centromeres, telomeres, AT-rich blocks, mating type loci, biosynthetic, and metabolic gene clusters. Here, we applied long-range sequencing technologies to determine the near-completed genome sequences of four widely used biocontrol agents or biofertilizers: Trichoderma virens Gv29-8 and FT-333, Trichoderma asperellum FT-101, and Trichoderma atroviride P1. Like those of three Trichoderma reesei wild isolates [QM6a, CBS999.97(MAT1-1) and CBS999.97(MAT1-2)] we reported previously, these four biocontrol agent genomes each contain seven nuclear chromosomes and a circular mitochondrial genome. Substantial intraspecies and intragenus diversities are also discovered, including single nucleotide polymorphisms, chromosome shuffling, as well as genomic relics derived from historical transposition events and repeat-induced point (RIP) mutations.

Bioprospecting of Rhizosphere-Resident Fungi: Their Role and Importance in Sustainable Agriculture

Rhizosphere-resident fungi that are helpful to plants are generally termed as 'plant growth promoting fungi' (PGPF). These fungi are one of the chief sources of the biotic inducers known to give their host plants numerous advantages, and they play a vital role in sustainable agriculture. Today's biggest challenge is to satisfy the rising demand for crop protection and crop yield without harming the natural ecosystem. Nowadays, PGPF has become an eco-friendly way to improve crop yield by enhancing seed germination, shoot and root growth, chlorophyll production, and fruit yield, etc., either directly or indirectly. The mode of action of these PGPF includes the solubilization and mineralization of the essential micro- and macronutrients needed by plants to regulate the balance for various plant processes. PGPF produce defense-related enzymes, defensive/volatile compounds, and phytohormones that control pathogenic microbes' growth, thereby assisting the plants in facing various biotic and abiotic stresses. Therefore, this review presents a holistic view of PGPF as efficient natural biofertilizers to improve crop plants' growth and resistance.

Harnessing the Rhizosphere of the Halophyte Grass Aeluropus littoralis for Halophilic Plant-Growth-Promoting Fungi and Evaluation of Their Biostimulant Activities

Hydroponic systems have gained interest and are increasingly used in hot and dry desert areas. Numbers of benefits are offered by hydroponic systems such as the ability to save water, enhance nutrients use efficiency, easy environmental control, and prevention of soil-borne diseases. However, the high consumption of chemical fertilizers for nutrient solution and the sensitivity of closed hydroponic systems to salinity are issues that need solutions. Thus, the main goal of our research activities is to isolate plant growth promoting fungi in order to develop sustainable hydroponic systems. We are working on isolating and testing the possibility to incorporate the cell-free filtrate (CFF) of plant growth promoting fungi (PGPF) in the composition of the nutrient solution. In this work, we isolated six strains of PGPF from the rhizosphere of the halophyte grass Aeluropus littoralis. Phylogenetic analyses of DNA sequences amplified by ITS1 and ITS4 primers identified the isolated fungi as: Byssochlamys spectabilis, Chaetomium globosum, Cephalotheca foveolata, Penicillium melinii, Alternaria tenuissima, and Nigrospora chinensis. The promoting of vigor in tobacco seedlings was used as criteria to evaluate the biostimulant activity of these fungi by adding either their mycelia (DE: direct effect) or their cell-free filtrates (CFF: indirect effect) to the plant-growth media. The best significant growth stimulation was obtained with plants treated by B. spectabilis. However, only the CFFs of Byssochlamys spectabilis (A5.1) and Penicillium melinii (A8) when added at a dilution factor of 1/50 to half-strength nutritive solution (0.5NS) resulted in significant improvement of all assessed growth parameters. Indeed, the A5.1CFF and A8CFF in 0.5NS induced a significant better increase in the biomass production when compared to NS or 0.5NS alone. All fungi produced indole acetic acid in the CFFs, which could be one of the key factors explaining their biostimulant activities. Furthermore, six genes involved in nitrogen-metabolism (NR1 and NRT1), auxin biosynthesis (Tryp1 and YUCCA6-like), and brassinosteroid biosynthesis (DET2 and DWF4) were shown to be induced in roots or leaves following treatment of plants with the all CFFs. This work opens up a prospect to study in deep the biostimulant activity of PGPFs and their applications to decrease the requirement of chemical fertilizers in the hydroponic growing systems.

Flavonoids and Isoflavonoids Biosynthesis in the Model Legume Lotus japonicus; Connections to Nitrogen Metabolism and Photorespiration

Phenylpropanoid metabolism represents an important metabolic pathway from which originates a wide number of secondary metabolites derived from phenylalanine or tyrosine, such as flavonoids and isoflavonoids, crucial molecules in plants implicated in a large number of biological processes. Therefore, various types of interconnection exist between different aspects of nitrogen metabolism and the biosynthesis of these compounds. For legumes, flavonoids and isoflavonoids are postulated to play pivotal roles in adaptation to their biological environments, both as defensive compounds (phytoalexins) and as chemical signals in symbiotic nitrogen fixation with rhizobia. In this paper, we summarize the recent progress made in the characterization of flavonoid and isoflavonoid biosynthetic pathways in the model legume Lotus japonicus (Regel) Larsen under different abiotic stress situations, such as drought, the impairment of photorespiration and UV-B irradiation. Emphasis is placed on results obtained using photorespiratory mutants deficient in glutamine synthetase. The results provide different types of evidence showing that an enhancement of isoflavonoid compared to standard flavonol metabolism frequently occurs in Lotus under abiotic stress conditions. The advance produced in the analysis of isoflavonoid regulatory proteins by the use of co-expression networks, particularly MYB transcription factors, is also described. The results obtained in Lotus japonicus plants can be also extrapolated to other cultivated legume species, such as soybean, of extraordinary agronomic importance with a high impact in feeding, oil production and human health.

Trichoderma: The "Secrets" of a Multitalented Biocontrol Agent

The plant-Trichoderma-pathogen triangle is a complicated web of numerous processes. Trichoderma spp. are avirulent opportunistic plant symbionts. In addition to being successful plant symbiotic organisms, Trichoderma spp. also behave as a low cost, effective and ecofriendly biocontrol agent. They can set themselves up in various patho-systems, have minimal impact on the soil equilibrium and do not impair useful organisms that contribute to the control of pathogens. This symbiotic association in plants leads to the acquisition of plant resistance to pathogens, improves developmental processes and yields and promotes absorption of nutrient and fertilizer use efficiency. Among other biocontrol mechanisms, antibiosis, competition and mycoparasitism are among the main features through which microorganisms, including Thrichoderma, react to the presence of other competitive pathogenic organisms, thereby preventing or obstructing their development. Stimulation of every process involves the biosynthesis of targeted metabolites like plant growth regulators, enzymes, siderophores, antibiotics, etc. This review summarizes the biological control activity exerted by Trichoderma spp. and sheds light on the recent progress in pinpointing the ecological significance of Trichoderma at the biochemical and molecular level in the rhizosphere as well as the benefits of symbiosis to the plant host in terms of physiological and biochemical mechanisms. From an applicative point of view, the evidence provided herein strongly supports the possibility to use Trichoderma as a safe, ecofriendly and effective biocontrol agent for different crop species.

TgSWO from Trichoderma guizhouense NJAU4742 promotes growth in cucumber plants by modifying the root morphology and the cell wall architecture

BACKGROUND

Colonization of Trichoderma spp. is essential for exerting their beneficial functions on the plant. However, the interactions between Trichoderma spp. and plant roots are still not completely understood. The aim of this study was to investigate how TgSWO affect Trichoderma guizhouense to establish themselves in the plant rhizosphere and promote plant growth. In this study, we deeply analyzed the molecular mechanism by which the functional characterization of the TgSWO by expressing different functional region deletion proteins (FRDP) of TgSWO.

RESULTS

Root scanning analysis results showed that TgSWO could dramatically increase root density and promote growth. In addition, we also found that TgSWO could expand root cell walls, subsequently increase root colonization. Moreover, knockout of TgSWO mutants (KO) or overexpression of TgSWO mutants (OE) produced greatly reduced or increased the number of cucumber root, respectively. To clarify the molecular mechanism of TgSWO in plant-growth-promotion, we analyzed the ability of different FRDP to expand the root cell wall. The root cell wall architecture were considerably altered when treated by ΔCBD protein (the TgSWO gene of lacking in the CBD domain was cloned and heterologously expressed), in correlation with the present YoaJ domain of TgSWO. In contrast, neither the expansion of cell walls nor the increase of roots was detectable in ΔYoaJ protein.

CONCLUSIONS

Our results emphasize the YoaJ domain is the most critical functional area of TgSWO during the alteration of cell wall architecture. Simultaneously, the results obtained in this study also indicate that TgSWO might play a plant-growth-promotion role in the Trichoderma-plant interactions by targeting the root cell wall.

Trichoderma as a Model to Study Effector-Like Molecules

Plants are capable of perceiving microorganisms by coordinating processes to establish different forms of plant–microbe relationships. Plant colonization is governed in fungal and bacterial systems by secreted effector molecules, suppressing plant defense responses and modulating plant physiology to promote either virulence or compatibility. Proteins, secondary metabolites, and small RNAs have been described as effector molecules that use different mechanisms to establish the interaction. Effector molecules have been studied in more detail due to their involvement in harmful interactions, leading to a negative impact on agriculture. Recently, research groups have started to study the effectors in symbiotic interactions. Interestingly, most symbiotic effectors are members of the same families present in phytopathogens. Nevertheless, the quantity and ratio of secreted effectors depends on the microorganism and the host, suggesting a complex mechanism of recognition between the plant and their associated microorganisms. Fungi belonging to Trichoderma genus interact with plants by inducing their defense system and promoting plant growth. Research suggests that some of these effects are associated with effector molecules that Trichoderma delivers during the association with the plant. In this review, we will focus on the main findings concerning the effector molecules reported in Trichoderma spp. and their role during the interaction with plants, mainly in the molecular dialogue that takes place between them.

Induction of isoflavonoid biosynthesis in Lotus japonicus after UV-B irradiation

Enhanced ultraviolet radiation (UV) is an important environmental factor that may cause reductions in the growth and productivity of plants. In the present work we studied the response to UV-B radiation in leaves of the model legume Lotus japonicus. After UV-B treatment, induction of phenyalanine-ammonia lyase gene expression and enzyme activity was detected. Among the ten genes encoding for PAL found in the L. japonicus genome, LjPAL1 was both the most expressed and the most induced. All the genes encoding for enzymes of the isoflavonoid pathway were also strongly induced; this was paralleled by a marked accumulation of vestitol and isoliquiritigenin. Moreover, accumulation of several other isoflavonoids was also detected. In vitro measurements of the free radical scavenging capacity of vestitol indicated that this compound can be an appropriate free radical scavenger, suggesting a possible role for this molecule in the response to abiotic stress. On the other hand, an increase of flavonol levels was not observed while the expression of the key enzymes for flavonol biosynthesis flavanone-3-hydroxylase and flavonol synthase was decreased. Taken together, these results indicate that L. japonicus follows a peculiar strategy in its response to UV radiation by accumulating isoflavonoids as an possible alternative to accumulation of flavonols as observed in other plant species.

Trichoderma as a Model to Study Effector-Like Molecules

Plants are capable of perceiving microorganisms by coordinating processes to establish different forms of plant-microbe relationships. Plant colonization is governed in fungal and bacterial systems by secreted effector molecules, suppressing plant defense responses and modulating plant physiology to promote either virulence or compatibility. Proteins, secondary metabolites, and small RNAs have been described as effector molecules that use different mechanisms to establish the interaction. Effector molecules have been studied in more detail due to their involvement in harmful interactions, leading to a negative impact on agriculture. Recently, research groups have started to study the effectors in symbiotic interactions. Interestingly, most symbiotic effectors are members of the same families present in phytopathogens. Nevertheless, the quantity and ratio of secreted effectors depends on the microorganism and the host, suggesting a complex mechanism of recognition between the plant and their associated microorganisms. Fungi belonging to Trichoderma genus interact with plants by inducing their defense system and promoting plant growth. Research suggests that some of these effects are associated with effector molecules that Trichoderma delivers during the association with the plant. In this review, we will focus on the main findings concerning the effector molecules reported in Trichoderma spp. and their role during the interaction with plants, mainly in the molecular dialogue that takes place between them.

Trichoderma harzianum diminished oxidative stress caused by 2,4- dichlorophenoxyacetic acid (2,4-D) in wheat, with insights from lipidomics

2,4-dichlorophenoxyacetic acid (2,4-D) is among the most commonly used herbicides applied for weed control during wheat cultivation. However, its application could affect wheat growth. The present study investigates the effect of the ascomycetous fungus Trichoderma harzianum on lipid peroxidation, phospholipids, signaling lipids and phospholipase D in the seedlings of wheat (Triticum aestivum L.) treated with 2,4-D (2.5 mg L^-1). In the group of 4-day-old seedlings exposed to the herbicide, increased lipid peroxidation and inhibition of growth were observed in shoots and roots. Moreover, elevated levels of oxylipins were noted. Among them, the amount of 13-HOTrE oxygenated from linolenic acid (18:3) increased the most significantly. Concurrently, in the seedlings inoculated with T. harzianum, growth was stimulated when the level of phosphatidylcholine (PC) increased. Moreover, in wheat seedlings treated with 2,4-D and T. harzianum, the level of lipid peroxidation was similar to that in the control and there was no increase observed in oxylipins and phospholipase D activity. T. harzianum might have partly alleviated the toxic effect of 2,4-D on wheat seedlings.

Trichoderma Biofertilizer Links to Altered Soil Chemistry, Altered Microbial Communities, and Improved Grassland Biomass

In grasslands, forage and livestock production results in soil nutrient deficits as grasslands typically receive no nutrient inputs, leading to a loss of grassland biomass. The application of mature compost has been shown to effectively increase grassland nutrient availability. However, research on fertilization regime influence and potential microbial ecological regulation mechanisms are rarely conducted in grassland soil. We conducted a two-year experiment in meadow steppe grasslands, focusing on above- and belowground consequences of organic or Trichoderma biofertilizer applications and potential soil microbial ecological mechanisms underlying soil chemistry and microbial community responses. Grassland biomass significantly (p = 0.019) increased following amendment with 9,000 kg ha⁻¹ of Trichoderma biofertilizer (composted cattle manure + inoculum) compared with other assessed organic or biofertilizer rates, except for BOF3000 (fertilized with 3,000 kg ha⁻¹ biofertilizer). This rate of Trichoderma biofertilizer treatment increased soil antifungal compounds that may suppress pathogenic fungi, potentially partially responsible for improved grassland biomass. Nonmetric multidimensional scaling (NMDS) revealed soil chemistry and fungal communities were all separated by different fertilization regime. Trichoderma biofertilizer (9,000 kg ha⁻¹) increased relative abundances of Archaeorhizomyces and Trichoderma while decreasing Ophiosphaerella. Trichoderma can improve grassland biomass, while Ophiosphaerella has the opposite effect as it may secrete metabolites causing grass necrosis. Correlations between soil properties and microbial genera showed plant-available phosphorus may influence grassland biomass by increasing Archaeorhizomyces and Trichoderma while reducing Ophiosphaerella. According to our structural equation modeling (SEM), Trichoderma abundance was the primary contributor to aboveground grassland biomass. Our results suggest Trichoderma biofertilizer could be an important tool for management of soils and ultimately grassland plant biomass.

Hydrolytic Amino Acids Employed as a Novel Organic Nitrogen Source for the Preparation of PGPF-Containing Bio-Organic Fertilizer for Plant Growth Promotion and Characterization of Substance Transformation during BOF Production

Opportunity costs seriously limit the large-scale production of bio-organic fertilizers (BOFs) both in China and internationally. This study addresses the utilization of amino acids resulting from the acidic hydrolysis of pig corpses as organic nitrogen sources to increase the density of TrichodermaharzianumT-E5 (a typical plant growth-promoting fungi, PGPF). This results in a novel, economical, highly efficient and environmentally friendly BOF product. Fluorescence excitation-emission matrix (EEM) spectroscopy combined with fluorescence regional integration (FRI) was employed to monitor compost maturity levels, while pot experiments were utilized to test the effects of this novel BOF on plant growth. An optimization experiment, based on response surface methodologies (RSMs), showed that a maximum T-E5 population (3.72 × 108 ITS copies g-1) was obtained from a mixture of 65.17% cattle manure compost (W/W), 19.33% maggot manure (W/W), 15.50% (V/W)hydrolytic amino acid solution and 4.69% (V/W) inoculum at 28.7°C after a 14 day secondary solid fermentation. Spectroscopy analysis revealed that the compost transformation process involved the degradation of protein-like substances and the formation of fulvic-like and humic-like substances. FRI parameters (PI, n, PII, n, PIII, n and PV, n) were used to characterize the degree of compost maturity. The BOF resulted in significantly higher increased chlorophyll content, shoot length, and shoot and root dry weights of three vegetables (cucumber, tomato and pepper) by 9.9%~22.4%, 22.9%~58.5%, 31.0%~84.9%, and 24.2%~34.1%, respectively. In summary, this study presents an operational means of increasing PGPF T-E5 populations in BOF to promote plant growth with a concomitant reduction in production cost. In addition, a BOF compost maturity assessment using fluorescence EEM spectroscopy and FRI ensured its safe field application.

Discriminative phytoalexin accumulation in Lotus japonicus against symbiotic and non-symbiotic microorganisms and related chemical signals

The phytoalexin response of Lotus japonicus seedlings to selected microbes and chemical signals was analyzed. The symbiotic rhizobium induced vestitol production weakly, while non-symbiotic rhizobia and potential pathogens led to increases in its accumulation. Whereas chitin-related molecules were ineffective, a flagellin-derived peptide not of symbiont origin induced phytoalexin production, indicating discriminative antibiotic production by the plant host.

Deciphering the hormonal signalling network behind the systemic resistance induced by Trichoderma harzianum in tomato

Root colonization by selected Trichoderma isolates can activate in the plant a systemic defense response that is effective against a broad-spectrum of plant pathogens. Diverse plant hormones play pivotal roles in the regulation of the defense signaling network that leads to the induction of systemic resistance triggered by beneficial organisms [induced systemic resistance (ISR)]. Among them, jasmonic acid (JA) and ethylene (ET) signaling pathways are generally essential for ISR. However, Trichoderma ISR (TISR) is believed to involve a wider variety of signaling routes, interconnected in a complex network of cross-communicating hormone pathways. Using tomato as a model, an integrative analysis of the main mechanisms involved in the systemic resistance induced by Trichoderma harzianum against the necrotrophic leaf pathogen Botrytis cinerea was performed. Root colonization by T. harzianum rendered the leaves more resistant to B. cinerea independently of major effects on plant nutrition. The analysis of disease development in shoots of tomato mutant lines impaired in the synthesis of the key defense-related hormones JA, ET, salicylic acid (SA), and abscisic acid (ABA), and the peptide prosystemin (PS) evidenced the requirement of intact JA, SA, and ABA signaling pathways for a functional TISR. Expression analysis of several hormone-related marker genes point to the role of priming for enhanced JA-dependent defense responses upon pathogen infection. Together, our results indicate that although TISR induced in tomato against necrotrophs is mainly based on boosted JA-dependent responses, the pathways regulated by the plant hormones SA- and ABA are also required for successful TISR development.

Analysis of volatile organic compounds emitted by plant growth-promoting fungus Phoma sp. GS8-3 for growth promotion effects on tobacco

We extracted volatile organic compounds (VOCs) emitted by a plant growth-promoting fungus (PGPF) Phoma sp. GS8-3 by gas chromatography and identified them by mass spectrometry. All of the identified compounds belonged to C4-C8 hydrocarbons. Volatiles varied in number and quantity by the culture period of the fungus (in days). 2-Methyl-propanol and 3-methyl-butanol formed the main components of the volatile blends for all the culture periods of fungus. Growth-promoting effects of the identified synthetic compounds were analyzed individually and in blends using tobacco plants. We found that the mixture of volatiles extracted from 3-day-old culture showed significant growth promotion in tobacco in vitro. The volatile blend showed better growth promotion at lower than higher concentrations. Our results confirm the potential role of volatile organic compounds in the mechanism of growth enhancement by GS8-3.

Stimulatory effects of arsenic-tolerant soil fungi on plant growth promotion and soil properties

Fifteen fungi were obtained from arsenic-contaminated agricultural fields in West Bengal, India and examined for their arsenic tolerance and removal ability in our previous study. Of these, the four best arsenic-remediating isolates were tested for plant growth promotion effects on rice and pea in the present study. A greenhouse-based pot experiment was conducted using soil inocula of individual fungi. The results indicated a significant (P<0.05) increase in plant growth and improvement of soil properties in inoculated soils compared to the control. A significant increase in plant growth was recorded in treated soils and varied from 16-293%. Soil chemical and enzymatic properties varied from 20-222% and 34-760%, respectively, in inoculated soil. Plants inoculated with inocula of Westerdykella and Trichoderma showed better stimulatory effects on plant growth and soil nutrient availability than Rhizopus and Lasiodiplodia. These fungi improved soil nutrient content and enhanced plant growth. These fungi may be used as bioinoculants for plant growth promotion and improved soil properties in arsenic-contaminated agricultural soils.

Trichoderma-plant-pathogen interactions: advances in genetics of biological control

Trichoderma spp. are widely used in agriculture as biofungicides. Induction of plant defense and mycoparasitism (killing of one fungus by another) are considered to be the most important mechanisms of Trichoderma-mediated biological control. Understanding these mechanisms at the molecular level would help in developing strains with superior biocontrol properties. In this article, we review our current understanding of the genetics of interactions of Trichoderma with plants and plant pathogens.

Pure culture of Metarhizium anisopliae LHL07 reprograms soybean to higher growth and mitigates salt stress

Little is known about the role of endophytic fungi against abiotic stresses and isoflavonoids (IF) contents of soybean. In current study, we investigated the role of fungal endophytes on the growth of soybean under salt stress conditions. Pure cultures of nine endophytic fungi were isolated from the roots of field-grown soybean plants, and their culture filtrates were screened on Waito-C and Dongjin-byeo rice cultivars; for identification of plant growth promoting fungal strains. It was observed that fungal isolate GMC-2B significantly promoted the growth of both Waito-C and Dongjin-byeo. GMC-2B was later identified as a new strain of Metarhizium anisopliae LHL07 on the basis of 18S rDNA sequences and phylogenetic analysis. Metarhizium anisopliae LHL07 inoculated soybean plants recorded significantly higher shoot length, shoot fresh and dry biomass, chlorophyll contents, transpiration rate, photosynthetic rate and leaf area; under sodium chloride induced salt stress as compared to non-inoculated control plants. An elevated proline and reduced superoxide dismutase and malondialdehyde contents in M. anisopliae LHL07 inoculated soybean plants demonstrated mitigation of salt induced oxidative stress. Furthermore, reduced abscisic acid and elevated jasmonic acid contents in soybean plants confirmed that lesser stress was convened to M. anisopliae inoculated-plants under salinity stress. We also assessed the role of M. anisopliae interaction on IF biosynthesis of soybean, and found significantly higher IF contents in M. anisopliae inoculated soybean plants. In conclusion, endophytic fungal interactions with soybean can be beneficial to improve soybean quality and quantity under salt affected agricultural systems.

Plant-beneficial effects of Trichoderma and of its genes

Trichoderma (teleomorph Hypocrea) is a fungal genus found in many ecosystems. Trichoderma spp. can reduce the severity of plant diseases by inhibiting plant pathogens in the soil through their highly potent antagonistic and mycoparasitic activity. Moreover, as revealed by research in recent decades, some Trichoderma strains can interact directly with roots, increasing plant growth potential, resistance to disease and tolerance to abiotic stresses. This mini-review summarizes the main findings concerning the Trichoderma-plant interaction, the molecular dialogue between the two organisms, and the dramatic changes induced by the beneficial fungus in the plant. Efforts to enhance plant resistance and tolerance to a broad range of stresses by expressing Trichoderma genes in the plant genome are also addressed.