Mycorrhizal Formation Research Articles

LbSakA-mediated phosphorylation of the scaffolding protein LbNoxR in the ectomycorrhizal basidiomycete Laccaria bicolor regulates NADPH oxidase activity, ROS accumulation and symbiosis development.

Ectomycorrhizal symbiosis, which involves mutually beneficial interactions between soil fungi and tree roots, is essential for promoting tree growth. To establish this symbiotic relationship, fungal symbionts must initiate and sustain mutualistic interactions with host plants while avoiding host defense responses. This study investigated the role of reactive oxygen species (ROS) generated by fungal NADPH oxidase (Nox) in the development of Laccaria bicolor/Populus tremula × alba symbiosis. Our findings revealed that L. bicolor LbNox expression was significantly higher in ectomycorrhizal roots than in free-living mycelia. RNAi was used to silence LbNox, which resulted in decreased ROS signaling, limited formation of the Hartig net, and a lower mycorrhizal formation rate. Using Y2H library screening, BiFC and Co-IP, we demonstrated an interaction between the mitogen-activated protein kinase LbSakA and LbNoxR. LbSakA-mediated phosphorylation of LbNoxR at T409, T477 and T480 positively modulates LbNox activity, ROS accumulation and upregulation of symbiosis-related genes involved in dampening host defense reactions. These results demonstrate that regulation of fungal ROS metabolism is critical for maintaining the mutualistic interaction between L. bicolor and P. tremula × alba. Our findings also highlight a novel and complex regulatory mechanism governing the development of symbiosis, involving both transcriptional and posttranslational regulation of gene networks.

Effects of fungicide treatments on mycorrhizal communities and carbon acquisition in themixotrophicPyrola japonica (Ericaceae).

Pyrola japonica, a member of the family Ericaceae, is a mixotroph that grows on forest floors and obtains carbon (C) from both its photosynthesis and its mycorrhizal fungi. Its mycorrhizal community is dominated by Russulaceae. However, the mechanism of its C acquisition and its flexibility are not well understood. Our aim was to assess the impact of disturbance of the mycorrhizal fungal communities on C acquisition by P. japonica. We repeatedly applied a fungicide (Benomyl) to soils around P. japonica plants in a broad-leaved forest of central Japan, in order to disturb fungal associates near roots. After fungicide treatment, P. japonica roots were collected and subjected to barcoding by next-generation sequencing, focusing on the ITS2 region. The rate of mycorrhizal formation and α-diversity did not significantly change upon fungicide treatments. Irrespective of the treatments, Russulaceae represented more than 80% of the taxa. Leaves and seeds of the plants were analysed for 13C stable isotope ratios that reflect fungal C gain. Leaf and seed δ13C values with the fungicide treatment were significantly lower than those with the other treatments. Thus the fungicide did not affect mycorrhizal communities in the roots, but disturbed mycorrhizal fungal pathways via extraradical hyphae, and resulted in a more photosynthetic behaviour of P. japonica for leaves and seeds.

Metagenomic Analyses of Viruses in the Orchid Mycorrhizal Interaction Using Improved Assemble Tools.

In nature, mycorrhizal association with soil-borne fungi is indispensable for orchid species. Compatible mycorrhizal fungi form endo-mycorrhizal structures in orchid cells, and the fungal structures are digested in orchid cells to be supplied to orchids as nutrition. Because orchid seeds lack the reserves for germination, they keep receiving nutrition through mycorrhizal formation from seed germination until nonphotosynthetic young seedlings develop leaves and become photoautotrophic. Seeds of all orchids germinate with the help of their own fungal partners, and therefore, specific partnership has been acquired in a long evolutionary history between orchids and fungi. Assuming that horizontal transmission of viruses may occur in such a close relationship, we are focusing on viruses that infect orchids and their mycorrhizal fungi. We prepared aseptically germinated orchid plants (i.e., fungi-free plants) together with pure-cultured fungal isolates and conducted transcriptome analyses (RNA-seq) by next-generation sequencing (NGS) approach. To reconstruct virus-related sequences that would have been present in the RNA sample of interest, de novo assembly process is required using short read sequences obtained from RNA-seq. In the previous version of our protocol (see Viral Metagenomics, first edition 2018), virus searches were conducted using contig sets constructed by a single assembler, but this time we devised a method to construct more reliable contigs using multiple assemblers and again reinvestigated that viruses could be detected. Because the virus detection efficiency and number of detected virus species clearly differed depending on the assembly pipeline and the number of the input data, multiple methods should be used to identify viral infection, if possible.

Effects of wildfire disturbance on forest soil microbes and colonization of ericoid mycorrhizal fungi in northern China

Wildfires affect forest succession and restoration by changing the community structure of soil microorganisms. Mycorrhizal formation is essential for plant growth and development. However, the driving mechanism of their natural succession after wildfire is still unclear. In this study, we examined the community structure of soil bacteria and fungi along a time series of natural recovery after wildfires in the Greater Khingan Range of China (2020 fires, 2017 fires, 2012 fires, 2004 fires, 1991 fires, and unburned). By exploring the effects of wildfire on plant traits, fruit nutrition, colonization of mycorrhizal fungi and its influencing mechanism. The results show that natural succession after wildfires significantly changed the community composition of bacteria and fungi, with β diversity having a greater impact but less impact on the α diversity of microorganisms. Wildfires significantly changed plant traits and fruit nutrient content. The changes in colonization rate and customization intensity of mycorrhizal fungi were caused by increased MDA content and soluble sugar content and increased MADS-box gene and DREB1 gene expression in lingonberry (Vaccinium vitis-idaea L.). Our results showed that the soil bacterial and fungal communities in the boreal forest ecosystem changed significantly during wildfire recovery and changed the colonization rate of lingonberry mycorrhizal fungi. This study provides a theoretical basis for the restoration of forest ecosystems after wildfires.

Responses of Bacterial Community Structure, Diversity, and Chemical Properties in the Rhizosphere Soil on Fruiting-Body Formation of Suillus luteus.

Mycorrhiza helper bacteria (MHB) play an important role in driving mycorrhizal formation. There are few reports on the relationship between bacteria and fruiting growths. Taking mycorrhizal rhizosphere soil from sporocarps of the S. luteus and non-mycorrhizal rhizosphere soil of the host plant (Larix gmelinii), we measured the bacterial community structure and diversity and chemical properties to clarify the effect of bacteria on fruiting-body formation. The bacterial diversity was significantly higher in mycorrhizal rhizosphere soil (p < 0.05) than that in non-mycorrhizal rhizosphere soil. The relative abundance of Burkholderia, Bradyrhizobium, Pseudomonas, and Rhizobium was significantly higher (p < 0.05) in mycorrhizal rhizosphere soil than in non-mycorrhizal rhizosphere soil. The soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), total potassium (TK), ammonium nitrogen (AN), available phosphorus (AP), available potassium (AK), and the activity of catalase, urease, and phosphatase in mycorrhizal rhizosphere soil were significantly higher (p < 0.05) than those in non-mycorrhizal rhizosphere soil. A redundancy analysis (RDA) showed that dominant bacteria are closely related to soil enzyme activity and physicochemical properties (p < 0.05). The boletus recruits a large number of bacteria around the plant roots that speed up nutrient transformation and increase the soil nutrient content, providing an important guarantee for mycelium culture and fruiting-body formation. These findings provide ideas for the nutritional supply of boletus sporocarps and lay the theoretical foundation for the efficient artificial cultivation of boletus.

A Eucalyptus Pht1 Family Gene EgPT8 Is Essential for Arbuscule Elongation of Rhizophagus irregularis.

The majority of vascular flowering plants can establish arbuscular mycorrhizal (AM) symbiosis with AM fungi. These associations contribute to plant health and plant growth against various environmental stresses. In the mutualistic endosymbiosis, the AM fungi deliver phosphate (Pi) to the host root through highly branched hyphae called arbuscules. The molecular mechanisms of Pi transfer from AM fungi to the plant have been determined, which are dominated by AM-specific Pi transporters belonging to the PHOSPHATE TRANSPORTER 1 (Pht1) family within the subfamily I. However, it is unknown whether Pht1 family proteins are involved in other regulations in AM symbiosis. Here, we report that the expression of EgPT8 is specifically activated by AM fungus Rhizophagus irregularis and is localized in root cortical cells containing arbuscules. Interestingly, knockdown of EgPT8 function does not affect the Eucalyptus grandis growth, total phosphorous (P) concentration, and arbuscule formation; however, the size of mature arbuscules was significantly suppressed in the RNAi-EgPT8 lines. Heterogeneous expression of EgPT4, EgPT5, and EgPT8 in the Medicago truncatula mutant mtpt4-2 indicates that EgPT4 and EgPT5 can fully complement the defects of mutant mtpt4-2 in mycorrhizal Pi uptake and arbuscule formation, while EgPT8 cannot complement the defective AM phenotype of the mtpt4-2 mutant. Based on our results, we propose that the AM fungi-specific subfamily I transporter EgPT8 has novel functions and is essential to arbuscule elongation. IMPORTANCE Arbuscular mycorrhizal (AM) formation in host root cortical cells is initiated by exchanges of diffusible molecules, among which Pi uptake is known as the important feature of AM fungi on symbiosis functioning. Over the last two decades, it has been repeatedly proven that most vascular plants harbor two or more AM-specific Pht1 proteins; however, there is no direct evidence regarding the potential link among these Pi transporters at the symbiotic interface. This work revealed a novel function of a structurally conserved protein involved in lateral arbuscule development. In total, we confirmed that three AM-specific Pht1 family proteins are nonredundant in Eucalyptus grandis and that EgPT8 is responsible for fungal arbuscule elongation of Rhizophagus irregularis.

Identification of upregulated genes in Tricholoma matsutake mycorrhiza.

Many plant roots associate with fungi to form mycorrhizae; tree roots especially associate with ectomycorrhizal fungi, such as Tricholoma species. Tricholoma matsutake is an economically important fungus in Asian countries and usually inhabits forests primarily composed of Pinus densiflora (Japanese red pine). In this study, to understand the mycorrhizal association between T. matsutake and P. densiflora, genes specifically expressed in mycorrhiza compared with those expressed in mycelia and fruiting bodies were identified by RNA-seq. This revealed that genes for chromatin, proteasomes, signal transduction, pheromones, cell surface receptors, cytoskeleton, RNA processing and transporters from T. matsutake were highly expressed in mycorrhiza. It also identified 35 mycorrhiza-induced small secreted proteins (MiSSPs) that were highly expressed in mycorrhiza. Meanwhile, genes for proteases, defence-related proteins, cell-wall degradation, signal transduction, pinene synthesis, plant hormones and transporters from P. densiflora were highly expressed in mycorrhiza. These genes may be involved in mycorrhizal formation and maintenance. A MiSSP, 1460819, was highly expressed in mycorrhiza, and this expression was maintained for 24 months. These results provide insight into the mycorrhizal association between T. matsutake and P. densiflora.

Development of an organomineral fertiliser formulation that improves tomato growth and sustains arbuscular mycorrhizal colonisation

Achieving sustainable agricultural development requires the efficient use of nutrient resources for crop production. Recovering nutrients from animal manures may play a key role in achieving this. Animal manures typically have low nutrient concentrations, and in ratios that are often not ideal for balanced crop nutrition.Here, combinations of organic and inorganic phosphorus (P) were formulated as granular products (organomineral fertilisers) with granule size suitable for transport and spreading. The fertilisers were produced by granulating powdered chicken litter with MAP and urea powders making the following formulations: 0:4, 1:3, 2:2, 3:1, 4:0. The kinetics of NH4+-N and P release from the fertilisers, and the effects on tomato growth and nutrition, as well as arbuscular mycorrhizal formation in roots following fertiliser application, were determined.Cumulative NH4+-N release ceased within 12 h, and was lower in the formulations with higher proportions of chicken litter. The cumulative P released reached approximately 80% of total P in all formulations, and the time to obtain maximum P dissolution was 19 days in the formulation that contained only chicken litter. The organomineral fertilisers increased tomato shoot growth by 15–28% compared to the chicken litter only, MAP only and MAP/urea formulations. Reasonable levels of mycorrhizal colonisation of tomato roots was achieved with the organomineral fertilisers.The results demonstrated that optimum plant growth does not depend solely on immediately available P, and that timing of nutrient supply to match plant demand is important. The combination of chicken litter with MAP sustained nutrient supply and improved plant growth. Taken together, organomineral fertiliser formulations are potential alternatives to inorganic P fertilisers that can improve crop growth and nutrition, while provide a sustainable use for animal production wastes.

Mycorrhizal formation of light-coniferous species of urbanized ecosystems

Mycorrhiza formation plays a key role in the adaptation of light-coniferous species of urbanized territories, since the fungal symbiont acts as a barrier against technogenic impact. The article presents the study of mycorrhiza formation of Pinus sylvestris and Larix sukaczewii in urbanized ecosystems of the Strelitamak industrial center, Republic of Bashkortostan. The material was sampled in 2009 and 2016 at 8 sample plots. Anatomical and morphological structures of trees roots absorbing parts were analysed, micropreparations of cross sections were made. Mycorrhiza formation under the influence of technogenic pollution is not suppressed, the development of the fungal component of mycorrhiza increases. Pine mycorrhizal associations were found to be more sensitive to industrial pollution than larch mycorrhiza. The variety of fungus sheath of light coniferous species changes according to a single scheme. The plant makes for the unfavorable ecological conditions by a higher level of mycorrhiza formation development.

Biodiversity and mycorrhizal formation of medicinal plants in the fallow areas of the Botanical garden

Biodiversity and mycorrhizal formation of medicinal plants in the fallow areas of the Botanical garden

Ecophysiology, quality, and mycorrhizal dependency in Musa spp. (cv. Grand naine) seedlings

Abstract The use of alternative technologies involving biological processes, with economic and ecological gains, is desirable for both the expansion of Musa spp. farming and the renovation of areas with low yields. Arbuscular mycorrhizal fungi (AMF) can stimulate plant growth, especially by increasing the absorption of phosphorus (P) and other nutrients. This study analyzes the influence of AMF on the growth and physiology of micropropagated Musaspp. plants submitted to doses of P. The experimental design was randomized blocks, in a 5 x 5 factorial arrangement, in which the factors were inoculation with AMF (Glomus clarum, Gigaspora margarita, , Gigaspora albida,Clareoideoglomus etunicatum, and the control without AMF) and five doses of P (0, 50, 100, 200, and 400 mg kg-1), with four replicates. The application of P doses increased growth in micropropagated Musaspp. seedlings, regardless of mycorrhizal inoculation. The highest rates of mycorrhizal colonization occurred at the lowest P doses, and the dose of 50 mg kg-1 P provided better conditions for mycorrhizal formation in all AMF species under study. The symbioses with AMF, as well as the use of P, increased photosynthesis rate, thus favoring the growth, development, and quality of Musa spp. seedlings. Species G. clarum, C. etunicatum, and G. margarita were the most promising for plant growth.

Changes in soil microbial communities from exposed rocks to arboreal rhizosphere during vegetation succession in a karst mountainous ecosystem

ABSTRACT To provide information that can support natural vegetation restoration in karst areas, we investigated the change rules of soil microbial communities during vegetation succession from bare rock to arboreal forest using high-throughput sequencing. The results showed that vegetation succession did not cause significant changes in alpha diversity of soil microbial communities. The main bacterial phyla were Proteobacteria, Actinobacteria, and Acidobacteria during vegetation succession. There was a shift from Ascomycota to Basidiomycota during succession, and the relative abundance of Basidiomycota in arboreal rhizosphere soil was the highest; this promoted mycorrhizal formation with the trees and mineral nutrient absorption by the host. Most of the symbiotic networks between soil microorganisms showed cooperative relationships. We propose that the dominant microbes contributed to the biological weathering of limestone and soil evolution under vascular plants. Furthermore, the findings of this study can help improve soil properties by providing insight into how to adjust microbial composition.

マツタケ菌根形成のためのアカマツの根系操作（I）表土の掻き取りと被覆による根の誘導方法の検討

マツタケ菌根形成のためのアカマツの根系操作（I）表土の掻き取りと被覆による根の誘導方法の検討

Molecular signal communication during arbuscular mycorrhizal formation induces significant transcriptional reprogramming of wheat (Triticum aestivum) roots.

Arbuscular mycorrhizal (AM) symbiosis begins with molecular signal communication (MSC) between AM fungi and the roots of the host plant. We aimed to test the hypothesis that the transcriptional profiles of wheat roots can be changed significantly by AM symbiotic signals, without direct contact. Non-mycorrhizal (NM) and MSC treatments involved burying filter membrane bags containing sterilized and un-sterilized inoculum of the AM fungus Rhizophagus irregularis, respectively. The bags physically separated roots and AM structures but allowed molecular signals to pass through. Extracted RNA from wheat roots was sequenced by high-throughput sequencing. Shoot total nitrogen and phosphorus content of wheat plants was decreased by the MSC treatment. A total of 2360 differentially expressed genes (DEGs), including 1888 up-regulated DEGs and 472 down-regulated DEGs, were found dominantly distributed on chromosomes 2A, 2B, 2D, 3B, 5B and 5D. The expression of 59 and 121 genes was greatly up- and down-regulated, respectively. Only a portion of DEGs could be enriched into known terms during gene ontology analysis, and were mostly annotated to 'catalytic activity', 'protein metabolic process' and 'membrane' in the molecular function, biological process and cellular component ontology categories, respectively. More than 120 genes that may be involved in key processes during AM symbiosis development were regulated at the pre-physical contact stages. The transcriptional profiles of wheat roots can be changed dramatically by MSC. Much of the information provided by our study is of great importance for understanding the mechanisms underlying the development of AM symbiosis.

Identification and expression analysis of the arbuscular mycorrhiza-inducible Rieske non-heme oxygenase Ptc52 gene from tomato

Arbuscular mycorrhizal (AM) formation enhances plant growth and fitness through improved uptake of water and mineral nutrients in exchange for carbon compounds to the AM fungus. The fungal structure for the reciprocal exchange of nutrients in the symbiosis is the arbuscule, and defence genes expressed in cells containing arbuscules could play a role in the control of hyphal spread and arbuscule formation in the root. We characterized and analyzed the Ptc52 gene from tomato (SlPtc52), a member of the gene family of non-heme oxygenases, whose function has been related to the lethal leaf spot 1 (Lls1) lesion mimic phenotype in plants which is sometimes associated with enhanced disease resistance. Sequence analysis of the SlPTC52 protein revealed conserved typical motifs from non-heme oxygenases, including a Rieske [2Fe-2S] motif, a mononuclear non-heme iron-binding motif and a C-terminal CxxC motif. The level of transcript accumulation was low in stem, flower and green fruits, and high in leaves. Although SlPtc52 expression was perceptible at low levels in roots, its expression increased concomitantly with AM fungus root colonization. Tomato non-mycorrhizal hairy roots expressing the GUS protein under the control of promoter SlPtc52 exhibited GUS activity in the endodermis, the apical meristem of the root tip and in the lateral root primordium. AM fungal colonization also resulted in intensive GUS activity that clearly corresponds to cortical cells containing arbuscules. SlPtc52 gene silencing led to a delay in root colonization and a decrease in arbuscular abundance, suggesting that SlPTC52 plays a regulatory role during AM symbiosis.

Contributions of indigenous arbuscular mycorrhizal fungi to growth of retama monosperma and acacia gummifera under water stress (case study: essaouira sand dunes forest)

ABSTRACTTwo leguminous plant species: Retama monosperma and Acacia gummifera were selected for water deficit tolerance test for future use in reforestation programs of the Atlantic sand dunes forest of Essaouira region. Mycorrhizal fungal colonization was used to help plants amend the water deficit. To assess R. monosperma and A. gummifera response to water stress and the effectiveness of mycorrhizal formation alleviating it, two categories for each plant species were made, one inoculated with mycorrhizal fungi and the other not, were submitted to a hydric deficit treatment of four levels for 6 months. This treatment impact on the plants was assessed by comparing root/shoot dry weight ratios, levels of nitrogen and phosphorus, and by measuring mycorrhizal colonization frequencies and intensities. Results showed that these parameters were significantly affected by water deficit. The presence of the mycorrhizal fungi had significantly enhanced plants phosphorus uptake by 72–124% for Acacia gummifera and 87–161% for Retama monosperma. Nitrogen uptake was increased by 134–388% for Retama monosperma and 510–901% for Acacia gummifera. The colonization frequencies changed significantly only for the treatment extreme level and stayed between 80%-90% for the other levels. The mycorrhization intensities showed significant lessening between each treatment level decreasing from 35% to 10%.

Analysis of symbiotic microbial status of Atlantic sand dunes forest and its effects on Acacia gummifera and Retama monosperma (Fabaceae) to be used in reforestation

Atlantic forest natural soil flora was tested on two leguminous pioneer species Acacia gummifera and Retama monosperma to be used in rehabilitation programs of the coastal sand dunes forest of the Essaouira region. The rhizospheric soil of two endemic plant species: R. monosperma and Juniperus phoenicea was sampled and split into two categories, one from native rhizospheric soil, the other of the sterilized rhizospheric soil. Investigation was focused on mycorrhizal formations, but other forms of beneficial symbiosis such as rhizobia and viable soil microflora were also studied. Growth and nutrition variables assessed included lengths of roots and shoots, number of branches, ratio of root to shoot dry mass and water, nitrogen and phosphorus levels. Results showed important mycorrhizal associations in roots of both plants, presence of nodules and abundance of viable soil microflora. J. phoenicea had a 100% frequency of mycorrhizal formation and an intensity of 80% compared to a frequency of 80% and intensity of 54% for R. monosperma. Nodules had the same density of CFU regardless of the origin. Abundance of viable microflora in rhisospheric soil of R. monosperma, J. phoenicea and the control differed significantly. Among the studied variables for A. gummifera and R. monosperma, nitrogen and phosphorus uptakes significantly wit the use of the nonsterilized rhizospheric soil. Both species doubled their phosphorus uptake when colonized by mycorrhizal species, R. monosperma doubled its nitrogen uptake and A. gummifera increased it by seven times compared with the control. No significant difference was noted for the other variables.

Metagenomic Analyses of the Viruses Detected in Mycorrhizal Fungi and Their Host Orchid.

In nature, mycorrhizal association with soilborne fungi is indispensable for orchid families. Fungal structures from compatible endo-mycorrhizal fungi in orchid cells are digested in cells to be supplied to orchids as nutrition. Because orchid seeds lack the reserves for germination, they keep receiving nutrition through mycorrhizal formation from seed germination until shoots develop (leaves) and become photoautotrophic. Seeds of all orchid species surely geminate with the help of their own fungal partners, and this specific partnership has been acquired for a long evolutional history between orchids and fungi.We have studied the interactions between orchids and mycorrhizal fungi and recently conducted transcriptome analyses (RNAseq) by a next-generation sequencing (NGS) approach. It is possible that orchid RNA isolated form naturally grown plants is contaminated with RNAs derived from mycorrhizal fungi in the orchid cells. To avoid such contamination, we here prepared aseptically germinated orchid plants (i.e., fungus-free plants) together with a pure-cultured fungal isolate and field-growing orchid samples. In the cDNA library prepared from orchid and fungal tissues, we found that partitivirus-like sequences were common in an orchid and its mycorrhizal fungus. These partitivirus-like sequences were closely related by a phylogenetic analysis, suggesting that transmission of an ancestor virus between the two organisms occurred through the specific relation of the orchid and its associated fungus.

Does mycorrhizal colonisation vary between maize and sunflower under limitations to radiation source or carbohydrate sink?

The aim of this work was to analyse and compare indigenous arbuscular mycorrhizal colonisation (AMC) in relation to growth and total soluble carbohydrates (TSC) in two major, physiologically contrasting crop species: maize (Zea mays L.) and sunflower (Helianthus annuus L.). In order to promote contrasting TSC concentrations, we modified the radiation source by shading and the carbohydrate sink by manipulating reproductive sinks at different phenological stages during the grain-filling period in two field experiments. We assessed plant dry matter, TSC in stems, and root AMC from flowering until final harvest. AMC during the grain-filling period decreased in maize and increased in sunflower. A sink limitation increased AMC in maize, and reduced it in sunflower. A source limitation decreased AMC in both species, especially in sunflower. AMC was positively related to TSC in maize, but negatively in sunflower. The relationship was affected by shading in sunflower, but not in maize. In both species, a different linear model described the relationship between AMC and TSC in plants submitted to the removal of the reproductive organs. The results highlight the role of carbohydrates in mediating mycorrhizal formation, and show for the first time the opposite AMC–TSC relationships in maize and sunflower.

Nitric Oxide Accelerates Mycorrhizal Effects on Plant Growth and Root Development of Trifoliate Orange

Arbuscular mycorrhizal fungi (AMF) actively colonize plant roots and thus enhance plant growth through different mechanisms. In the present study, trifoliate orange (Poncirus trifoliata) seedlings inoculated with Diversispora versiformis were subjected to 0 and 0.2 mmol/L sodium nitroprusside (SNP, a nitric oxide donor) treatments. After eight weeks, exogenous SNP considerably increased root mycorrhizal colonization by 25%, showing a positive stimulating effect of NO on mycorrhizal formation. Mycorrhizal inoculation significantly increased plant growth performance (height, stem diameter, leaf number and shoot and root dry weight) and root traits (length, projected area, surface area, volume and number of 2nd and 3rd order lateral roots) than non-mycorrhizal treatment and NO (exogenous SNP treatment) heavily strengthened the mycorrhizal effects. Moreover, NO and mycorrhization induced more fine root (0-0.5 cm) formation. There was an opposite changed trend in root sucrose and leaf and root glucose contents by SNP in AMF versus non-AMF seedlings. All these results implied that NO plays important roles in mycorrhizal formation and development and also accelerates mycorrhizal effects on plant growth and root development of trifoliate orange.