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Soil water deficit seriously affects crop production, and soil arbuscular mycorrhizal fungi (AMF) enhance drought tolerance in crops by unclear mechanisms. Our study aimed to analyze changes in non-targeted metabolomics in roots of trifoliate orange (Poncirus trifoliata) seedlings under well-watered and soil drought after inoculation with Rhizophagus intraradices , with a focus on terpenoid profile. Root mycorrhizal fungal colonization varied from 70% under soil drought to 85% under soil well-watered, and shoot and root biomass was increased by AMF inoculation, independent of soil water regimes. A total of 643 secondary metabolites in roots were examined, and 210 and 105 differential metabolites were regulated by mycorrhizal fungi under normal water and drought stress, along with 88 and 17 metabolites being up-and down-regulated under drought conditions, respectively. KEGG annotation analysis of differential metabolites showed 38 and 36 metabolic pathways by mycorrhizal inoculation under normal water and drought stress conditions, respectively. Among them, 33 metabolic pathways for mycorrhization under drought stress included purine metabolism, pyrimidine metabolism, alanine, aspartate and glutamate metabolism, etc. We also identified 10 terpenoid substances, namely albiflorin, artemisinin (−)-camphor, capsanthin, β-caryophyllene, limonin, phytol, roseoside, sweroside, and α-terpineol. AMF colonization triggered the decline of almost all differential terpenoids, except for β-caryophyllene, which was up-regulated by mycorrhizas under drought, suggesting potential increase in volatile organic compounds to initiate plant defense responses. This study provided an overview of AMF-induced metabolites and metabolic pathways in plants under drought, focusing on the terpenoid profile. [ABSTRACT FROM AUTHOR]

Multiple functions of glomalin released by arbuscular mycorrhizal fungi are well-recognized, whereas the role of exogenous glomalins including easily extractable glomalin-related soil protein (EE-GRSP) and difficultly extractable glomalin-related soil protein (DE-GRSP) is unexplored for plant responses. Our study was carried out to assess the effects of exogenous EE-GRSP and DE-GRSP at varying strengths on plant growth and chlorophyll concentration of trifoliate orange (Poncirus trifoliata) seedlings, along with changes in root nutrient acquisition, auxin content, auxin-related enzyme and transporter protein gene expression, and element contents of purified GRSP. Sixteen weeks later, exogenous GRSP displayed differential effects on plant growth (height, stem diameter, leaf number, and biomass production): the increase by EE-GRSP and the decrease by DE-GRSP. The best positive effect on plant growth occurred at exogenous EE-GRSP at ½ strength. Similarly, the GRSP application also differently affected total chlorophyll content, root morphology (total length, surface area, and volume), and root N, P, and K content: positive effect by EE-GRSP and negative effect by DE-GRSP. Exogenous EE-GRSP accumulated more indoleacetic acid (IAA) in roots, which was associated with the upregulated expression of root auxin synthetic enzyme genes (PtTAA1, PtYUC3 , and PtYUC4) and auxin influx transporter protein genes (PtLAX1, PtLAX2 , and PtLAX3). On the other hand, exogenous DE-GRSP inhibited root IAA and indolebutyric acid (IBA) content, associated with the downregulated expression of root PtTAA1, PtLAX1 , and PtLAX3. Root IAA positively correlated with root PtTAA1, PtYUC3, PtYUC4, PtLAX1 , and PtLAX3 expression. Purified EE-GRSP and DE-GRSP showed similar element composition but varied in part element (C, O, P, Ca, Cu, Mn, Zn, Fe, and Mo) concentration. It concluded that exogenous GRSP triggered differential effects on growth response, and the effect was associated with the element content of pure GRSP and the change in auxins and root morphology. EE-GRSP displays a promise as a plant growth biostimulant in citriculture. [ABSTRACT FROM AUTHOR]

The role of arbuscular mycorrhizal fungi in sweet oranges is well known, but the function of their secondary metabolite, especially the easily extractable glomalin-related soil protein (EE-GRSP), an active fraction of glomalin, is still unclear. The proposed study aimed to analyze the field response of foliar application of exogenous EE-GRSP on treemycorrhizal development and fruit quality of two sweet orange (Citrus sinensis L. Osbeck) varieties viz., Lane Late Navel (LLN) and Rohde Red Valencia (RRV). Application of EE-GRSP significantly increased the root mycorrhizal colonization and soil mycorrhizal hyphal length in both the sweet orange varieties. The external quality of fruits (fruit weight, polar diameter, and equatorial diameter) also improved in response to foliar application of EE-GRSP in both sweet orange varieties. However, EE-GRSP treatment showed no change in fruit soluble solid content, while it increased the Vc content, solids-acid ratio, fructose, glucose, and sucrose content of sarcocarp in the two sweet oranges varieties. The LLN variety treated with EE-GRSP recorded significantly higher N, P, K, Fe, and Si content of sarcocarp as a mark of nutritional quality, while the RRV variety treated with EE-GRSP displayed a higher concentration of nutrients like Cu, Fe, Si, and Zn in the sarcocarp as compared with the corresponding non-treated control. To the best of our knowledge, this is the first report regarding the improvement in fruit quality of late-ripening sweet oranges (especially LLN) in response to foliar application of EE-GRSP as another potential biostimulant. [ABSTRACT FROM AUTHOR]

A feature of arbuscular mycorrhiza is enhanced drought tolerance of host plants, although it is unclear whether host H+-ATPase activity and gene expression are involved in the physiological process. The present study aimed to investigate the effects of an arbuscular mycorrhizal fungus (AMF), Funneliformis mosseae , on H+-ATPase activity, and gene expression of trifoliate orange (Poncirus trifoliata) seedlings subjected to well-watered (WW) and drought stress (DS), together with the changes in leaf gas exchange, root morphology, soil pH value, and ammonium content. Soil drought treatment dramatically increased H+-ATPase activity of leaf and root, and AMF inoculation further strengthened the increased effect. A plasma membrane (PM) H+-ATPase gene of trifoliate orange, PtAHA2 (MW239123), was cloned. The PtAHA2 expression was induced by mycorrhization in leaves and roots and also up-regulated by drought treatment in leaves of AMF-inoculated seedlings and in roots of AMF- and non-AMF-inoculated seedlings. And, the induced expression of PtAHA2 under mycorrhization was more prominent under DS than under WW. Mycorrhizal plants also showed greater photosynthetic rate, stomatal conductance, intercellular CO2 concentration, and transpiration rate and better root volume and diameter than non-mycorrhizal plants under DS. AMF inoculation significantly increased leaf and root ammonium content, especially under DS, whereas it dramatically reduced soil pH value. In addition, H+-ATPase activity was significantly positively correlated with ammonium contents in leaves and roots, and root H+-ATPase activity was significantly negatively correlated with soil pH value. Our results concluded that AMF stimulated H+-ATPase activity and PtAHA2 gene expression in response to DS, which resulted in great nutrient (e.g., ammonium) uptake and root growth, as well as low soil pH microenvironment. [ABSTRACT FROM AUTHOR]

Soil arbuscular mycorrhizal fungi (AMF) enhance the tolerance of plants against soil moisture deficit stress (SMDS), but the underlying mechanisms are still not fully understood. Polyamines (PAs) as low-molecular-weight, aliphatic polycations have strong roles in abiotic stress tolerance of plants. We aimed to investigate the effect of AMF (Funneliformis mosseae) inoculation on PAs, PA precursors, activities of PA synthases and degrading enzymes, and concentration of reactive oxygen species in the roots of trifoliate orange (Poncirus trifoliata) subjected to 15 days of SMDS. Leaf water potential and total chlorophyll levels were comparatively higher in AMF-inoculated than in non-AMF-treated plants exposed to SMDS. Mycorrhizal plants recorded a significantly higher concentration of precursors of PA synthesis such as L-ornithine, agmatine, and S -adenosyl methionine, besides higher putrescine and cadaverine and lower spermidine during the 15 days of SMDS. AMF colonization raised the PA synthase (arginine decarboxylase, ornithine decarboxylase, spermidine synthase, and spermine synthase) activities and PA-degrading enzymes (copper-containing diamine oxidase and FAD-containing polyamine oxidase) in response to SMDS. However, mycorrhizal plants showed a relatively lower degree of membrane lipid peroxidation, superoxide anion free radical, and hydrogen peroxide than non-mycorrhizal plants, whereas the difference between them increased linearly up to 15 days of SMDS. Our study concluded that AMF regulated PA homeostasis in roots of trifoliate orange to tolerate SMDS. [ABSTRACT FROM AUTHOR]

Glomalin-related soil protein (GRSP) is a specific glycoprotein secreted into the soil by hyphae and spores of arbuscular mycorrhizal fungi that have many potential functions. It is not clear whether exogenous GRSP has an effect on plant growth and soil properties or whether the effects are related to the type of GRSP used. In this study, trifoliate orange (Poncirus trifoliata L. Raf.) seedlings were used to analyze the effects of easily extractable GRSP (EE-GRSP) and difficultly extractable GRSP (DE-GRSP) at a quarter-, half-, and full-strength concentration on shoot and root biomass as well as soil properties The results showed that, at different strengths, exogenous EE-GRSR significantly increased shoot and root biomass compared to the control, which displayed the most significant effects from the half-strength EE-GRSP. In contrast, DE-GRSP, at various strengths, significantly reduced shoot and root biomass. Furthermore, the application of exogenous EE-GRSP stimulated soil water-stable aggregate (WSA) content at 2–4 mm and 0.5–1 mm sizes, while DE-GRSP strongly reduced WSA content at the 2–4 mm, 1–2 mm, 0.5–1 mm, and 0.25–0.5 mm sizes, consequently leading to an increase or decrease in the WSA stability, according to the mean weight diameter. However, exogenous EE-GRSP decreased soil pH and DE-GRSP increased it, which was related to WSA stability. Exogenous EE-GRSP almost significantly increased soil acidic, neutral, and alkaline phosphatase activity at different strengths, while exogenous DE-GRSP, also at different strengths, significantly inhibited soil acidic phosphatase activity. The application of both exogenous EE-GRSP and DE-GRSP increased the organic carbon content of the soil. This study concluded that exogenous GRSP exerted differential effects on plant biomass and soil properties, and EE-GRSP can be considered as a soil stimulant for use in citrus plants. To our knowledge, this is the first report on the negative effects of exogenous DE-GRSP on plant biomass and soil properties. [ABSTRACT FROM AUTHOR]

The development of the mining industry and the overuse of inorganic fertilizers have led to an excess of manganese (Mn) in the soil, thereby, contaminating the soil environment and people's health. On heavy metal-contaminated soils, the combined arbuscular mycorrhizal fungi (AMF)-phytoremediation technique becomes a hotspot because of its environmentally friendly, in situ remediation. AMF inoculation often leads to a decrease in host Mn acquisition, which provides a basis for its application in phytoremediation of contaminated soils. Moreover, the utilization value of native AMF is greater than that of exotic AMF, because native AMF can adapt better to Mn-contaminated soils. In addition to the fact that AMF enhance plant Mn tolerance responses such as regionalization, organic matter chelation, limiting uptake and efflux, and so on, AMF also develop plant-independent fungal pathways such as direct biosorption of Mn by mycorrhizal hyphae, fungal Mn transporter genes, and sequestration of Mn by mycorrhizal hyphae, glomalin, and arbuscule-containing root cortical cells, which together mitigate excessive Mn toxicity to plants. Clarifying AMF-plant interactions under Mn stress will provide support for utilizing AMF as a phytoremediation in Mn-contaminated soils. The review reveals in detail how AMF develop its own mechanisms for responding to excess Mn and how AMF enhance plant Mn tolerance, accompanied by perspectives for future research. [Display omitted] • AMF inoculation diversely affects host Mn levels, dominated by reduced Mn uptake. • Mn-contaminated soils reduce AMF diversity, along with Glomus as the dominant genus and native AMF more tolerant. • AMF enhances plant Mn tolerance such as regionalization and chelation. • AMF hyphae have direct biosorption and sequestration of Mn. • Fungal Mn transporters, glomalin, and arbuscule-contained cortical cells mitigate Mn. [ABSTRACT FROM AUTHOR]

Earthworms and arbuscular mycorrhizal fungi (AMF) are beneficial organisms in the soil and play an important role in improving soil fertility and plant growth. The objective of this study was to analyze the response of single versus dual inoculation of earthworms (Pheretima guillelmi) and AMF (Funneliformis mosseae) on mycorrhizal growth, root morphology, and rhizosphere properties of white clover (Trifolium repens). Addition of earthworms significantly increased the degree of root AMF colonization, while decreased hyphal length and spore number in the soil. Single or dual inoculation of F. mosseae and P. guillelmi significantly increased root traits (total length, area, volume, and average diameter), soil phosphatase activities (acid, neutral, and alkaline), easily extractable and total glomalin-related soil protein content, the percentage of soil water-stable aggregates at the size of 2–4 mm, 1–2 mm and 0.5–1 mm, aggregate stability, Bray-P, and soil organic carbon (SOC) contents. Among them, the dual inoculation further amplified the effect on glomalin production, phosphatase activity, and aggregate stability, but did not show a superposition effect on root improvement, Bray-P, and SOC. Our study, hence, suggested that AMF and earthworms have synergistic roles in elevating rhizosphere properties vis-à-vis agronomic responses of white clover. • Effects of earthworm-AMF (singly and in combination) on rhizosphere environment and crop response were studied. • Earthworms increased root AMF colonization, but reduced hyphae and spores in soils. • AMF or earthworms singly improved root traits, Bray-P, and soil organic carbon contents, but dual application of AMF and earthworms did not show a major effect than single application. • Single AMF or earthworms increased aggregation, phosphatase, GRSP, and dual addition amplified these responses. [ABSTRACT FROM AUTHOR]

• Endophytic fungi differentially affected Camellia oleifera 's growth, with S.i. and R.i. being more prominent. • S.i. and R.i. respectively triggered 65 and 163 differential metabolites, enriched in hormone biosynthesis. • Endophytic fungi had varying effects on endogenous auxin and cytokinin levels. • Leaf IBA and TZ positively correlated with aboveground biomass. • Root IAA, DZ, and TZ positively correlated with root biomass. Camellia oleifolia is an important oilseed woody plant that can be colonized by root-associated endophytic fungi, but the mechanism of how they promote growth improvement remains unclear. This study was to analyze the changes in biomass production, secondary metabolite profile, auxins, and cytokinins in C. oleifolia seedlings by four arbuscular mycorrhizal fungi (Diversispora versiformis, Rhizophagus intraradices, Funneliformis mosseae , and a mixture of the three above) and Serendipita indica. After 16 weeks of fungal inoculations, the root fungal colonization rate showed diverse changes, with S. indica (75 %) and R. intraradices (67 %) having relatively higher colonization rates. In addition, S. indica and R. intraradices significantly increased aboveground biomass, root biomass, and root surface area, whereas D. versiformis exhibited no significant effect. Non-targeted metabolomics of S. indica - and R. intraradices -inoculated roots detected a total of 802 metabolites, with 65 differential metabolites (33 up-regulated and 32 down-regulated) by S. indica and 163 differential metabolites (96 up-regulated and 67 down-regulated) by R. intraradices. The enriched metabolic pathways of these differential metabolites mainly included amino acid metabolism, secondary metabolites biosynthesis, and plant hormone biosynthesis in association with nine substances. The inoculation of endophytic fungi had varying effects on endogenous auxin and cytokinin levels, where leaf indole butyric acid and trans-zeatin levels were positively correlated with aboveground biomass, and root indole acetic acid, dihydrozeatin, and trans-zeatin levels were positively correlated with root biomass. It is concluded that root-associated endophytic fungi mediate the growth improvement by affecting auxins and cytokinins. [ABSTRACT FROM AUTHOR]

Medicinal plants are well known to have the advantages of high concentration of medicinal ingredients having clinical importance, curative value, small toxic and side effects. Important compounds viz., paclitaxel, camptothecin, and vincristine have been developed from medicinal plants as first-line of clinical drugs, leading to their consistently increasing demand globally. However, the destruction of natural environment due to excessive mining threatened such resources jeopardizing the successful growing of medicinal plants. A group of beneficial arbuscular mycorrhizal (AM) fungi is known to exist in the rhizosphere of medicinal plants, which can establish a reciprocal symbiosis with their roots, namely arbuscular mycorrhizas. These AM fungi are pivotal in the habitat adaptation of medicinal plants. Studies have demonstrated that AM fungi aided in growth promotion and nutrient absorption of medicinal plants, thereby, accelerating the accumulation of medicinal ingredients and aiding resistance against abiotic stresses such as drought, low temperature, and salinity. An AMlike fungus Piriformospora indica is known to be cultured in vitro without roots, later showed analogous effects of AM fungi on medicinal plants. These fungi provide new mechanistic pathways towards the artificial cultivation of medicinal plants loaded with ingredients in huge demand in international market. This review provides an overview of the diversity of AM fungi inhabiting the rhizosphere of medicinal plants, and analyzes the functioning of AM fungi and P. indica, coupled with future lines of research. [ABSTRACT FROM AUTHOR]

The present study aimed to evaluate the effect of an arbuscular mycorrhizal fungus (AMF), Clariodeoglomus etunicatum, on leaf food quality and relevant gene expression levels of tea (Camellia sinensis cv. 'Fuding Dabaicha') seedlings exposed to 0.5 µM P (P0.5) and 50 µM P (P50) levels. Twenty-four weeks later, the seedlings recorded higher root mycorrhizal fungal colonization in P50 than in P0.5. AMF-inoculated tea plants represented significantly higher leaf fructose and glucose contents and lower sucrose content than noninoculated plants, irrespective of substate P levels. AMF treatment also increased total amino acids content in P0.5 and P50, accompanied with higher expression of glutamate dehydrogenase (CsGDH) and lower expression of glutamine synthetase (CsGS) and glutamine oxoglutarate aminotransferase (CsGOGAT). The total flavonoid content was higher in mycorrhizal versus non-mycorrhizal plants under P0.5 and P50, together with induced expression of phenylalanine ammonia-lyase (CsPAL) and cinnamic acid 4-hydroxylase (CsC4H). Mycorrhizal fungal inoculation improved catechins content, which is due to the up-regulated expression of flavanone 3-hydroxylase ( CsF3H), flavonoid 3'-hydroxylase ( CsF3'H), dihydroflavonol 4-reductase ( CsDFR), leucoanthocyanidin reductase ( CsLAR), anthocyanidin reductase ( CsANR), and chalcone isomerase ( CsCHI) under P0.5. However, under P50, the gene involved in catechins synthesis was not affected or down-regulated by mycorrhization, implying a complex mechanism (e.g. nutrient improvement). AMF also inhibited the tea caffeine synthase 1 (CsTCS1) expression regardless of P levels. Therefore, the results of this study concluded that inoculation with C. etunicatum improves leaf food quality of tea exposed to P stress, but the improved mechanisms were different between P0.5 and P50. [ABSTRACT FROM AUTHOR]