Arbuscular Mycorrhizal Symbiosis Research Articles

The soybean sugar transporter GmSWEET6 participates in sucrose transport towards fungi during arbuscular mycorrhizal symbiosis.

In arbuscular mycorrhizal (AM) symbiosis, sugars in root cortical cells could be exported as glucose or sucrose into peri-arbuscular space for use by AM fungi. However, no sugar transporter has been identified to be involved in sucrose export. An AM-inducible SWEET transporter, GmSWEET6, was functionally characterised in soybean, and its role in AM symbiosis was investigated via transgenic plants. The expression of GmSWEET6 was enhanced by inoculation with the cooperative fungal strain in both leaves and roots. Heterologous expression in a yeast mutant showed that GmSWEET6 mainly transported sucrose. Transgenic plants overexpressing GmSWEET6 increased sucrose concentration in root exudates. Overexpression or knockdown of GmSWEET6 decreased plant dry weight, P content, and sugar concentrations in non-mycorrhizal plants, which were partly recovered in mycorrhizal plants. Intriguingly, overexpression of GmSWEET6 increased root P content and decreased the percentage of degraded arbuscules, while knockdown of GmSWEET6 increased root sugar concentrations in RNAi2 plants and the percentage of degraded arbuscules in RNAi1 plants compared with wild-type plants when inoculated with AM fungi. These results in combination with subcellular localisation of GmSWEET6 to peri-arbuscular membranes strongly suggest that GmSWEET6 is required for AM symbiosis by mediating sucrose efflux towards fungi.

Comparative proteomic analysis identifies proteins associated with arbuscular mycorrhizal symbiosis in Poncirus trifoliata

Comparative proteomic analysis identifies proteins associated with arbuscular mycorrhizal symbiosis in Poncirus trifoliata

A journey into the world of small RNAs in the arbuscular mycorrhizal symbiosis.

Arbuscular mycorrhizal (AM) symbiosis is a mutualistic interaction between fungi and most land plants that is underpinned by a bidirectional exchange of nutrients. AM development is a tightly regulated process that encompasses molecular communication for reciprocal recognition, fungal accommodation in root tissues and activation of symbiotic function. As such, a complex network of transcriptional regulation and molecular signaling underlies the cellular and metabolic reprogramming of host cells upon AM fungal colonization. In addition to transcription factors, small RNAs (sRNAs) are emerging as important regulators embedded in the gene network that orchestrates AM development. In addition to controlling cell-autonomous processes, plant sRNAs also function as mobile signals capable of moving to different organs and even to different plants or organisms that interact with plants. AM fungi also produce sRNAs; however, their function in the AM symbiosis remains largely unknown. Here, we discuss the contribution of host sRNAs in the development of AM symbiosis by considering their role in the transcriptional reprogramming of AM fungal colonized cells. We also describe the characteristics of AM fungal-derived sRNAs and emerging evidence for the bidirectional transfer of functional sRNAs between the two partners to mutually modulate gene expression and control the symbiosis.

Integrated transcriptomics and metabolomics reveal specific phenolic and flavonoid accumulation in licorice (Glycyrrhiza uralensis Fisch.) induced by arbuscular mycorrhiza symbiosis under drought stress

Arbuscular mycorrhizal (AM) symbiosis can strengthen plant defense against abiotic stress, such as drought, through multiple mechanisms; however, the specialized chemical defenses induced by AM symbiosis are largely unknown. In a pot experiment, licorice (Glycyrrhiza uralensis Fisch.) inoculated with and without arbuscular mycorrhizal fungus Rhizophagus irregularis Schenck & Smith were grown under well-watered or water deficit conditions. Transcriptomic and metabolomic analyses were combined to investigate licorice root specialized metabolism induced by AM symbiosis under drought stress. Results showed that mycorrhizal plants had few dead leaves, less biomass reduction, and less differentially expressed genes and metabolite features in response to drought compared with nonmycorrhizal plants. Transcriptomic and metabolomic data revealed that mycorrhizal roots generally accumulated lignin regardless of the water regime; however, the expression of genes involved in lignin biosynthesis was significantly downregulated by drought stress in mycorrhizal plants. By contrast, AM inoculation significantly decreased specialized metabolites accumulation, including phenolics and flavonoids under well-watered conditions, whereas these decreases turned to be nonsignificant under drought stress. Moreover, these specific phenolics and flavonoids showed significant drought-induced accumulation pattern in mycorrhizal roots. These results highlight that accumulation of specific root phenolics and flavonoids may support the drought tolerance of mycorrhizal plants.

Mycorrhizal fungi-mediated uptake of tree-derived nutrients by crops – the role of tree-maintained versus crop-associated fungal mycelia

Arbuscular mycorrhizal (AM) fungi translocate nutrients within agroforestry systems but the role of common mycorrhizal fungal networks (CMNs) is unclear. We compared AM fungi-mediated nutrient transfer from mango versus faidherbia trees to maize plants to understand how to foster the AM symbiosis for enhanced agroecosystem sustainability. In mesocosms we applied 15N and 33P tracers via tree stem injection or root-free soil labeling compartments to test tree-to-maize versus soil-to-maize nutrient transfer via AM fungi. Maize plants grew in large in-growth cores with intact versus broken mycelia. Soil-to-maize transfer was assessed with and without trees to compare nutrient transfer via tree-maintained AM fungi i.e. CMNs versus maize-associated AM fungi. Tracer application via stem injection neither corroborated nor falsified our hypothesis of tree-to-maize nitrogen and phosphorus transfer. Soil-to-maize nutrient transfer occurred but was not enhanced by the presence of mango or faidherbia trees. Competition with maize plants for nitrogen but not phosphorus was greater with mango than faidherbia trees. Results from our experimental set-up provide neither evidence nor disproval for CMNs between two-year-old trees and ten-week-old maize plants. In the absence of trees and tree-maintained AM fungal mycelia maize plants developed their own AM fungal mycelia that mediated uptake of nutrients from beyond the maize plants’ rooting zones.

Water conditions and arbuscular mycorrhizal symbiosis affect the phytoremediation of petroleum-contaminated soil by Phragmites australis

Phytoremediation of petroleum-contaminated soils using the synergistic functions of plants and rhizosphere microorganisms is a promising technology. However, successfully applying this approach presents challenges under certain conditions (submerged environments). This study analyzed the potential role of Phragmites australis in symbiosis with arbuscular mycorrhizal (AM) fungi during petroleum remediation at two water levels. AM inoculation promoted P. australis aboveground growth under non-flooded conditions, whereas flooding significantly increased P. australis biomass. The highest total petroleum hydrocarbon (TPH) degradation efficiency was observed in non-flooded soils, whereas submergence severely inhibited TPHs dissipation. Plants with AM inoculation treatments substantially enhanced the removal of TPHs under flooded conditions. TPH removal was positively correlated with dehydrogenase activity but negatively correlated with easily extracted glomalin-related soil proteins. Moreover, different petroleum-hydrocarbon-decaying candidates contributed to TPH removal in these two cultured soils. These findings provide valuable information for the remediation of future TPH-contaminated soils, especially applied in intermittently submerged environments.

The mycoparasite Pythium oligandrum induces legume pathogen resistance and shapes rhizosphere microbiota without impacting mutualistic interactions.

Pythium oligandrum is a soil-borne oomycete associated with rhizosphere and root tissues. Its ability to enhance plant growth, stimulate plant immunity and parasitize fungal and oomycete preys has led to the development of agricultural biocontrol products. Meanwhile, the effect of P. oligandrum on mutualistic interactions and more generally on root microbial communities has not been investigated. Here, we developed a biological system comprising P. oligandrum interacting with two legume plants, Medicago truncatula and Pisum sativum. P. oligandrum activity was investigated at the transcriptomics level through an RNAseq approach, metabolomics and finally metagenomics to investigate the impact of P. oligandrum on root microbiota. We found that P. oligandrum promotes plant growth in these two species and protects them against infection by the oomycete Aphanomyces euteiches, a devastating legume root pathogen. In addition, P. oligandrum up-regulated more than 1000 genes in M. truncatula roots including genes involved in plant defense and notably in the biosynthesis of antimicrobial compounds and validated the enhanced production of M. truncatula phytoalexins, medicarpin and formononetin. Despite this activation of plant immunity, we found that root colonization by P. oligandrum did not impaired symbiotic interactions, promoting the formation of large and multilobed symbiotic nodules with Ensifer meliloti and did not negatively affect the formation of arbuscular mycorrhizal symbiosis. Finally, metagenomic analyses showed the oomycete modifies the composition of fungal and bacterial communities. Together, our results provide novel insights regarding the involvement of P. oligandrum in the functioning of plant root microbiota.

Are Histidine Kinases of Arbuscular Mycorrhizal Fungi Involved in the Response to Ethylene and Cytokinins?

Signals are exchanged at all stages of the arbuscular mycorrhizal (AM) symbiosis between fungi and their host plants. Root-exuded strigolactones are well-known early symbiotic cues, but the role of other phytohormones as interkingdom signals has seldom been investigated. Here we focus on ethylene and cytokinins, for which candidate receptors have been identified in the genome of the AM fungus Rhizophagus irregularis. Ethylene is known from the literature to affect asymbiotic development of AM fungi, and in the present study, we found that three cytokinin forms could stimulate spore germination in R. irregularis. Heterologous complementation of a Saccharomyces cerevisiae mutant strain with the candidate ethylene receptor RiHHK6 suggested that this protein can sense and transduce an ethylene signal. Accordingly, its N-terminal domain expressed in Pichia pastoris displayed saturable binding to radiolabeled ethylene. Thus, RiHHK6 displays the expected characteristics of an ethylene receptor. In contrast, the candidate cytokinin receptor RiHHK7 did not complement the S. cerevisiae mutant strain or Medicago truncatula cytokinin receptor mutants and seemed unable to bind cytokinins, suggesting that another receptor is involved in the perception of these phytohormones. Taken together, our results support the hypothesis that AM fungi respond to a range of phytohormones and that these compounds bear multiple functions in the rhizosphere beyond their known roles as internal plant developmental regulators. Our analysis of two phytohormone receptor candidates also sheds new light on the possible perception mechanisms in AM fungi. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Autoactivation of mycorrhizal symbiosis signaling through gibberellin deactivation in orchid seed germination.

Orchids parasitically depend on external nutrients from mycorrhizal fungi for seed germination. Previous findings suggest that orchids utilize a genetic system of mutualistic arbuscular mycorrhizal (AM) symbiosis, in which the plant hormone gibberellin (GA) negatively affects fungal colonization and development, to establish parasitic symbiosis. Although GA generally promotes seed germination in photosynthetic plants, previous studies have reported low sensitivity of GA in seed germination of mycoheterotrophic orchids where mycorrhizal symbiosis occurs concurrently. To elucidate the connecting mechanisms of orchid seed germination and mycorrhizal symbiosis at the molecular level, we investigated the effect of GA on a hyacinth orchid (Bletilla striata) seed germination and mycorrhizal symbiosis using asymbiotic and symbiotic germination methods. Additionally, we compared the transcriptome profiles between asymbiotically and symbiotically germinated seeds. Exogenous GA negatively affected seed germination and fungal colonization, and endogenous bioactive GA was actively converted to the inactive form during seed germination. Transcriptome analysis showed that B. striata shared many of the induced genes between asymbiotically and symbiotically germinated seeds, including GA metabolism- and signaling-related genes and AM-specific marker homologs. Our study suggests that orchids have evolved in a manner that they do not use bioactive GA as a positive regulator of seed germination and instead autoactivate the mycorrhizal symbiosis pathway through GA inactivation to accept the fungal partner immediately during seed germination.

Arbuscular-Mycorrhizal Symbiosis in Medicago Regulated by the Transcription Factor MtbHLHm1;1 and the Ammonium Facilitator Protein MtAMF1;3.

Root systems of most land plants are colonised by arbuscular mycorrhiza fungi. The symbiosis supports nutrient acquisition strategies predominantly associated with plant access to inorganic phosphate. The nutrient acquisition is enhanced through an extensive network of external fungal hyphae that extends out into the soil, together with the development of fungal structures forming specialised interfaces with root cortical cells. Orthologs of the bHLHm1;1 transcription factor, previously described in soybean nodules (GmbHLHm1) and linked to the ammonium facilitator protein GmAMF1;3, have been identified in Medicago (Medicago truncatula) roots colonised by AM fungi. Expression studies indicate that transcripts of both genes are also present in arbuscular containing root cortical cells and that the MtbHLHm1;1 shows affinity to the promoter of MtAMF1;3. Both genes are induced by AM colonisation. Loss of Mtbhlhm1;1 expression disrupts AM arbuscule abundance and the expression of the ammonium transporter MtAMF1;3. Disruption of Mtamf1;3 expression reduces both AM colonisation and arbuscule development. The respective activities of MtbHLHm1;1 and MtAMF1;3 highlight the conservation of putative ammonium regulators supporting both the rhizobial and AM fungal symbiosis in legumes.

Soil compaction effects on arbuscular mycorrhizal symbiosis in wheat depend on host plant variety

Background and aimsSupporting arbuscular mycorrhizal (AM) nutrient acquisition in crops may reduce the need for fertilizer inputs, leading to more cost effective and sustainable crop production. In wheat, AM fungal responsiveness and benefits of symbiosis vary among varieties. This study explored the role of soil compaction in this variation.MethodsWe examined in a field experiment how soil compaction affects AM fungal colonization and biomass in five spring wheat varieties, and how these varieties differ in their AM-mediated phosphorus (P) uptake. We also studied soil properties, and AM fungal community composition in roots and soil.ResultsSoil compaction increased AM fungal colonization in the variety Alderon, characterized by root traits that indicate inefficient P uptake. Wheat P concentration and P:N ratio in Alderon and Diskett increased with increased root AM fungal colonization and biomass. In Diskett, which is the most cultivated spring wheat variety in Sweden and has intermediate root traits, total P content per m2 also increased with root AM fungal colonization and biomass.ConclusionsSome wheat varieties, potentially those characterized by P inefficient root traits, such as Alderon, may depend more on AM-mediated P uptake in compacted than in non-compacted soil. Increased P uptake with increased AM fungal colonization in Diskett suggests that efficient root and AM-mediated nutrient uptake can occur simultaneously in a modern variety. Breeding varieties that use roots and AM symbiosis as complementary strategies for nutrient uptake could improve nutrient uptake efficiency and help farmers achieve stable yields in varying conditions.

Identification of microRNAs involved in ectomycorrhizal formation in Populus tomentosa.

The majority of woody plants are able to form ectomycorrhizal (ECM) symbioses with fungi. During symbiotic development, plants undergo a complex re-programming process involving a series of physiological and morphological changes. MicroRNAs (miRNAs) are important components of the regulatory network underlying symbiotic development. To elucidate the mechanisms of miRNAs and miRNA-mediated mRNA cleavage during symbiotic development, we conducted high-throughput sequencing of small RNAs and degradome tags from roots of Populus tomentosa inoculated with Cenococcum geophilum. This process led to the annotation of 51 differentially expressed miRNAs between non-mycorrhizal and mycorrhizal roots of P. tomentosa, including 13 novel miRNAs. Increased or decreased accumulation of several novel and conserved miRNAs in ECM roots, including miR162, miR164, miR319, miR396, miR397, miR398, novel-miR44 and novel-miR47, suggests essential roles for these miRNAs in ECM formation. The degradome analysis identified root transcripts as miRNA-mediated mRNA cleavage targets, which was confirmed using real-time quantitative PCR. Several of the identified miRNAs and corresponding targets are involved in arbuscular mycorrhizal symbioses. In summary, increased or decreased accumulation of specific miRNAs and miRNA-mediated cleavage of symbiosis-related genes indicate that miRNAs play important roles in the regulatory network underlying symbiotic development.

Formation of arbuscular mycorrhizal symbiosis and its effect on the possibility of infection by parasitic plants

Aim. The purpose of the work is to analyze the data available in the literature on the mechanisms of formation of mycorrhizal symbiosis, in particular, the participation of strigolactones in this process and the influence of mycorrhizal symbiosis on the possibility of plant infection by parasitic plants. Results. The article provides a brief overview of the formation of arbuscular mycorrhizal symbiosis and the role of strigolactones in this process. Evidence is provided that strigolactones secreted by roots into the rhizosphere are signal molecules for AM fungi, as they stimulate their metabolism and induce spore germination, growth and branching of hyphae of AM fungi. In turn, AM fungi release signaling molecules that initiate processes related to the formation of symbiosis in plants. Conclusions. Data available in the literature indicate that strigolactones play an important role in the formation of mycorrhizal symbiosis. Mycorrhizal plants are often less susceptible to infection by parasitic plants, which may depend on the species of both the host plant and the AM fungus. The formation of mycorrhizal symbiosis can be a factor that weakens the infection by parasitic plants, the study of this issue can be important for increasing the effectiveness of the fight against parasitic plants.

Role of Arbuscular Mycorrhizal Fungi in Regulating Growth, Enhancing Productivity, and Potentially Influencing Ecosystems under Abiotic and Biotic Stresses.

Arbuscular mycorrhizal fungi (AMF) form symbiotic relationships with the roots of nearly all land-dwelling plants, increasing growth and productivity, especially during abiotic stress. AMF improves plant development by improving nutrient acquisition, such as phosphorus, water, and mineral uptake. AMF improves plant tolerance and resilience to abiotic stressors such as drought, salt, and heavy metal toxicity. These benefits come from the arbuscular mycorrhizal interface, which lets fungal and plant partners exchange nutrients, signalling molecules, and protective chemical compounds. Plants' antioxidant defence systems, osmotic adjustment, and hormone regulation are also affected by AMF infestation. These responses promote plant performance, photosynthetic efficiency, and biomass production in abiotic stress conditions. As a result of its positive effects on soil structure, nutrient cycling, and carbon sequestration, AMF contributes to the maintenance of resilient ecosystems. The effects of AMFs on plant growth and ecological stability are species- and environment-specific. AMF's growth-regulating, productivity-enhancing role in abiotic stress alleviation under abiotic stress is reviewed. More research is needed to understand the molecular mechanisms that drive AMF-plant interactions and their responses to abiotic stresses. AMF triggers plants' morphological, physiological, and molecular responses to abiotic stress. Water and nutrient acquisition, plant development, and abiotic stress tolerance are improved by arbuscular mycorrhizal symbiosis. In plants, AMF colonization modulates antioxidant defense mechanisms, osmotic adjustment, and hormonal regulation. These responses promote plant performance, photosynthetic efficiency, and biomass production in abiotic stress circumstances. AMF-mediated effects are also enhanced by essential oils (EOs), superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), hydrogen peroxide (H2O2), malondialdehyde (MDA), and phosphorus (P). Understanding how AMF increases plant adaptation and reduces abiotic stress will help sustain agriculture, ecosystem management, and climate change mitigation. Arbuscular mycorrhizal fungi (AMF) have gained prominence in agriculture due to their multifaceted roles in promoting plant health and productivity. This review delves into how AMF influences plant growth and nutrient absorption, especially under challenging environmental conditions. We further explore the extent to which AMF bolsters plant resilience and growth during stress.

Adaptive response of flavonoids in Robinia pseudoacacia L. affected by the contamination of cadmium and elevated CO2 to arbuscular mycorrhizal symbiosis

As a key component in non-enzyme resistance system, flavonoids play a crucial role in the plant growth and defenses, which are significantly affected by biotic and abiotic factors such as fungi, bacteria, viruses, heavy metals, and atmospheric CO2. Arbuscular mycorrhizal fungi (AMF) play an important role in enhancing plant tolerance to adverse environments, which can significantly affect the synthesis of flavonoids by forming mycorrhizal symbionts with plant roots. However, few studies explored the combined effects of AMF, elevated CO2, and heavy metals on flavonoids in plants. Here, we investigated the adaptive response of flavonoids accumulation in Robinia pseudoacacia L. seedlings affected by the contamination of cadmium (Cd) and elevated CO2 to arbuscular mycorrhizal symbiosis. The results showed that G. mosseae decreased (p < 0.05) Cd content in leaves by 62.2% under elevated CO2. Moreover, G. mosseae colonization led to significant decreases in robinin, quercetin, kaempferol and acacetin by 17.4%, 11.1%, 15.5% and 23.1% under elevated CO2 + Cd, respectively. Additionally, G. mosseae down-regulated (p < 0.05) expression levels of phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS) genes under elevated CO2 + Cd, and CHS and uridine diphosphate flavonoid glucosyltransferase (UFGT) activities decreased (p < 0.05). Quercetin, kaempferol and acacetin showed positive (p < 0.05) correlation with PAL and CHS genes expression and PAL, CHS, and UFGT activities. Cadmium, C/N ratio, carotenoids, leaf biomass, total chlorophyll, P, and starch in leaves and G. mosseae colonization rate in roots influenced (p < 0.05) flavonoids content. Overall, G. mosseae reduced flavonoids synthesis by down-regulating gene expression levels and activities of key enzymes under elevated CO2 + Cd. The results improved our understanding of the regulation of AMF on non-enzymatic resistance of plants grown in heavy metal-contaminated soils under increasing atmospheric CO2 scenarios.

Comparative RNA sequencing-based transcriptome profiling of ten grapevine rootstocks: shared and specific sets of genes respond to mycorrhizal symbiosis.

Arbuscular mycorrhizal symbiosis improves water and nutrient uptake by plants and provides them other ecosystem services. Grapevine is one of the major crops in the world. Vitis vinifera scions generally are grafted onto a variety of rootstocks that confer different levels of resistance against different pests, tolerance to environmental stress, and influence the physiology of the scions. Arbuscular mycorrhizal fungi are involved in the root architecture and in the immune response to soil-borne pathogens. However, the fine-tuned regulation and the transcriptomic plasticity of rootstocks in response to mycorrhization are still unknown. We compared the responses of 10 different grapevine rootstocks to arbuscular mycorrhizal symbiosis (AMS) formed with Rhizophagus irregularis DAOM197198 using RNA sequencing-based transcriptome profiling. We have highlighted a few shared regulation mechanisms, but also specific rootstock responses to R. irregularis colonization. A set of 353 genes was regulated by AMS in all ten rootstocks. We also compared the expression level of this set of genes to more than 2000 transcriptome profiles from various grapevine varieties and tissues to identify a class of transcripts related to mycorrhizal associations in these 10 rootstocks. Then, we compared the response of the 351 genes upregulated by mycorrhiza in grapevine to their Medicago truncatula homologs in response to mycorrhizal colonization based on available transcriptomic studies. More than 97% of the 351M. truncatula-homologous grapevine genes were expressed in at least one mycorrhizal transcriptomic study, and 64% in every single RNAseq dataset. At the intra-specific level, we described, for the first time, shared and specific grapevine rootstock genes in response to R. irregularis symbiosis. At the inter-specific level, we defined a shared subset of mycorrhiza-responsive genes.

Non-targeted metabolomics analysis reveals the mechanism of arbuscular mycorrhizal symbiosis regulating the cold-resistance of Elymus nutans.

Elymus nutans is a perennial grass of the Gramineae family. Due to its cold-resistance and nutrition deficiency tolerance, it has been applied to the ecological restoration of degraded alpine grassland on the Qinghai-Tibet Plateau. As an important symbiotic microorganism, arbuscular mycorrhizal fungi (AMF) have been proven to have great potential in promoting the growth and stress resistance of Gramineae grasses. However, the response mechanism of the AMF needs to be clarified. Therefore, in this study, Rhizophagus irregularis was used to explore the mechanism regulating cold resistance of E. nutans. Based on pot experiments and metabolomics, the effects of R. irregularis were investigated on the activities of antioxidant enzyme and metabolites in the roots of E. nutans under cold stress (15/10°C, 16/8 h, day/night). The results showed that lipids and lipid molecules are the highest proportion of metabolites, accounting for 14.26% of the total metabolites. The inoculation with R. irregularis had no significant effects on the activities of antioxidant enzyme in the roots of E. nutans at room temperature. However, it can significantly change the levels of some lipids and other metabolites in the roots. Under cold stress, the antioxidant enzyme activities and the levels of some metabolites in the roots of E. nutans were significantly changed. Meanwhile, most of these metabolites were enriched in the pathways related to plant metabolism. According to the correlation analysis, the activities of antioxidant enzyme were closely related to the levels of some metabolites, such as flavonoids and lipids. In conclusion, AMF may regulate the cold-resistance of Gramineae grasses by affecting plant metabolism, antioxidant enzyme activities and antioxidant-related metabolites like flavonoids and lipids. These results can provide some basis for studying the molecular mechanism of AMF regulating stress resistance of Gramineae grasses.

Comprehensive regulatory networks for tomato organ development based on the genome and RNAome of MicroTom tomato.

MicroTom has a short growth cycle and high transformation efficiency, and is a prospective model plant for studying organ development, metabolism, and plant-microbe interactions. Here, with a newly assembled reference genome for this tomato cultivar and abundant RNA-seq data derived from tissues of different organs/developmental stages/treatments, we constructed multiple gene co-expression networks, which will provide valuable clues for the identification of important genes involved in diverse regulatory pathways during plant growth, e.g. arbuscular mycorrhizal symbiosis and fruit development. Additionally, non-coding RNAs, including miRNAs, lncRNAs, and circRNAs were also identified, together with their potential targets. Interacting networks between different types of non-coding RNAs (miRNA-lncRNA), and non-coding RNAs and genes (miRNA-mRNA and lncRNA-mRNA) were constructed as well. Our results and data will provide valuable information for the study of organ differentiation and development of this important fruit. Lastly, we established a database (http://eplant.njau.edu.cn/microTomBase/) with genomic and transcriptomic data, as well as details of gene co-expression and interacting networks on MicroTom, and this database should be of great value to those who want to adopt MicroTom as a model plant for research.

A snapshot of the transcriptome of Medicago truncatula (Fabales: Fabaceae) shoots and roots in response to an arbuscular mycorrhizal fungus and the pea aphid (Acyrthosiphon pisum) (Hemiptera: Aphididae).

Plants simultaneously interact with belowground symbionts such as arbuscular mycorrhizal (AM) fungi and aboveground antagonists such as aphids. Generally, plants gain access to valuable resources including nutrients and water through the AM symbiosis and are more resistant to pests. Nevertheless, aphids' performance improves on mycorrhizal plants, and it remains unclear whether a more nutritious food source and/or attenuated defenses are the contributing factors. This study examined the shoot and root transcriptome of barrel medic (Medicago truncatula Gaertn.) plants highly colonized by the AM fungus Rhizophagus irregularis (Blaszk., Wubet, Renker, and Buscot) C. Walker and A. Schüßler (Glomerales: Glomeraceae) and exposed to 7 days of mixed age pea aphid (Acyrthosiphon pisum (Harris)) herbivory. The RNA-seq samples chosen for this study showed that aphids were heavier when fed mycorrhizal plants compared to nonmycorrhizal plants. We hypothesized that (i) insect-related plant defense pathways will be downregulated in shoots of mycorrhizal plants with aphids compared to nonmycorrhizal plants with aphids; (ii) pathways involved in nutrient acquisition, carbohydrate-related and amino acid transport will be upregulated in shoots of mycorrhizal plants with aphids compared to nonmycorrhizal plants with aphids; and (iii) roots of mycorrhizal plants with aphids will exhibit mycorrhiza-induced resistance. The transcriptome data revealed that the gene repertoire related to defenses, nutrient transport, and carbohydrates differs between nonmycorrhizal and mycorrhizal plants with aphids, which could explain the weight gain in aphids. We also identified novel candidate genes that are differentially expressed in nonmycorrhizal plants with aphids, thus setting the stage for future functional studies.

The alleviation mechanisms of cadmium toxicity in Broussonetia papyrifera by arbuscular mycorrhizal symbiosis varied with different levels of cadmium stress

The alleviation of cadmium (Cd) toxicity in Broussonetia papyrifera by arbuscular mycorrhizal (AM) fungi are still not completely elucidated. This study investigated the effects of Rhizophagus irregularis on physiological and biochemical characteristics, and molecular regulation in B. papyrifera under different levels of Cd (0, 30, 90 and 270 mg kg-1 Cd) stress. Results showed that (1) AM symbiosis improved the growth and photosynthesis, enhanced ROS levels as stress signaling and maintained ROS balance under low and medium Cd stress. (2) AM symbiosis regulated AsA-GSH cycle to mitigate ROS overproduction under high Cd stress. (3) AM fungus can chelate more Cd under high Cd stress, increasing soil pH and GRSP content. (4) AM plants can fix or chelate more Cd by P in leaves and reserve more P in stems under high Cd stress. (5) AM symbioses increased root net Cd2+ influx and uptake under medium Cd stress but inhibited under high Cd stress, with upregulation of genes related heavy metals (HMs) transport under medium Cd stress and inhibited the transcription of genes related HMs transport under high Cd stress. Therefore, the alleviation mechanisms of Cd toxicity in B. papyrifera by R. irregularis symbiosis depends on the levels of Cd stress.