Abstract Arbuscular Mycorrhizal Fungi Research Articles

Effects of arbuscular mycorrhizal fungi on carbon assimilation and ecological stoichiometry of maize under combined abiotic stresses

Abstract Arbuscular mycorrhizal fungi (AMF) enhance plant tolerance to abiotic stresses like salinity and improve crop yield. However, their effects are variable, and the underlying cause of such variation remains largely unknown. This study aimed to assess how drought modified the effect of AMF on plant resistance to high calcium-saline stress. A pot experiment was performed to examine how AMF inoculation affects the growth, photosynthetic activity, nutrient uptake and carbon (C), nitrogen (N) and phosphorus (P) stoichiometric ratio (C:N:P) of maize under high calcium stress and contrasting water conditions. The results showed that high calcium stress significantly reduced mycorrhizal colonization, biomass accumulation, C assimilation rate and C:N stoichiometric ratio in plant tissues. Besides, the adverse effects of calcium stress on photosynthesis were exacerbated under drought. AMF inoculation profoundly alleviated such reductions under drought and saline stress. However, it barely affected maize performance when subjected to calcium stress under well-watered conditions. Moreover, watering changed AMF impact on nutrient allocation in plant tissues. Under well-watered conditions, AMF stimulated P accumulation in roots and plant growth, but did not induce leaf P accumulation proportional to C and N, resulting in increased leaf C:P and N:P ratios under high calcium stress. In contrast, AMF decreased N content and the N:P ratio in leaves under drought. Overall, AMF inoculation improved maize resistance to calcium-salt stress through enhanced photosynthesis and modulation of nutrient stoichiometry, particularly under water deficit conditions. These results highlighted the regulatory role of AMF in carbon assimilation and nutrient homeostasis under compound stresses, and provide significant guidance on the improvement of crop yield in saline and arid regions.

Fungal symbiont diversity drives growth of Holcus lanatus depending on soil nutrient availability

Abstract Arbuscular mycorrhizal (AM) fungi frequently colonise plant roots and can affect plant morphology and physiology through their contribution to plant nutrition. However, the functional role of AM fungi in the presence of other microbial symbionts, including widespread Mucoromycotina ‘fine root endophytes’ (MFRE) fungi, remains largely unknown. While both AM fungi and MFRE transfer nutrients, including nitrogen, from inorganic and organic sources to host plants, their combined effects on co‐colonised plants have only been investigated in liverworts. Here, we compare the morphology and physiology of the grass Holcus lanatus grown with an AM fungal community versus a more diverse symbiotic fungal community containing both AM fungi and MFRE. Holcus lanatus plants were grown in the presence of either a diverse MFRE+AM fungi soil inoculum or a multi‐species AM fungal inoculum. Plant traits associated with growth were quantified, along with fungal transfer of 15N tracer to plants from a variety of sources (ammonium chloride, alanine, glycine and algal necromass). Holcus lanatus grown with the AM fungal community had greater root and shoot growth during early development and prior to the addition of 15N‐labelled sources, compared with plants grown with the more diverse symbiotic fungal community. When nitrogen sources were made available to the fungal symbionts in the pot microcosms, plants growing with the MFRE+AM fungi soil inoculum had a faster growth rate than plants growing with the AM fungal community. At harvest, H. lanatus grown with the AM fungal community had a larger biomass, and there were no differences in 15N tracer assimilation in plants across the two fungal community treatments. Our results demonstrate that the diversity of fungal inocula in conjunction with soil nutrient availability determine the benefits derived by plants from diverse fungal symbionts. Our research contributes to understanding host plant outcomes in diverse multi‐symbiont scenarios. Read the free Plain Language Summary for this article on the Journal blog.

OsSYMRK Plays an Essential Role in AM Symbiosis in Rice (Oryza sativa).

Arbuscular mycorrhizal (AM) fungi establish mutualistic symbiosis with a wide range of terrestrial plants, including rice. However, the mechanisms underlying the initiation of AM symbiosis are yet to be elucidated, particularly in nonleguminous plants. We previously demonstrated that chitin elicitor receptor kinase 1 (OsCERK1), a lysin motif receptor-like kinase essential for chitin-triggered immunity, also plays a key role in AM symbiosis in rice. However, the mechanisms underlying the regulation of switching between immunity and symbiosis by OsCERK1 are yet to be fully elucidated. SYMBIOSIS RECEPTOR-LIKE KINASE (SYMRK)/DOES NOT MAKE INFECTIONS 2 (DMI2) is a leucine-rich repeat receptor-like kinase associated with both root nodule symbiosis and AM symbiosis in legumes. The homolog of SYMRK in rice, OsSYMRK, has a shorter form than that in legumes because OsSYMRK lacks a malectin-like domain (MLD). The MLD reportedly contributes to symbiosis in Lotus japonicus; however, the contribution of OsSYMRK to AM symbiosis in rice remains unclear. Phylogenetic analyses indicated that the MLD of SYMRK/DMI2 is widely conserved even in mosses and ferns but absent in commelinids, including rice. To understand the function of OsSYMRK, we produced an Ossymrk knockout mutant using genome editing technology. AM colonization was mostly abolished in Ossymrk with a more severe phenotype than Oscerk1. Ca2+ spiking against chitin tetramer was also diminished in Ossymrk. In contrast, comparable defense responses against chitin heptamer to the wild type were observed in Ossymrk. Bimolecular fluorescence complementation studies demonstrating an interaction between OsSYMRK and OsCERK1 indicate that OsSYMRK may play an important role in switching from immunity to symbiosis through the interaction with OsCERK1 in rice.

Mycorrhizal fungi alter root exudation to cultivate a beneficial microbiome for plant growth

Abstract Arbuscular mycorrhizal (AM) fungi traditionally form symbioses with most plant species. Although AM fungi have critical effects on microbial communities, the pathways showing how AM fungi shape rhizosphere bacterial communities and their functions are rarely explored. Here, through three systematic experiments, AM fungi–bacteria interactions were first investigated in the rhizosphere of Lotus japonicus, then the interactions were confirmed by a second experiment with wild‐type and a mycorrhiza‐defective mutant ljcbx of L. japonicus. The mechanisms were presented by adding core bacteria and AM fungi to the plant rhizosphere in the third experiment. We found that AM fungi–bacteria interactions enhanced host plant growth and identified a core bacterial group that uniquely enhanced host plant growth. Adding core bacteria and AM fungi promoted host growth and nutrient acquisition compared to adding AM fungi or core bacteria independently. Allelopathic substances secreted by AM fungal colonizing host roots to recruit the rhizosphere bacteria were detected by the multi‐omics joint analysis, showing that arachidonic acid was the main allelopathic substance that affected AM fungi–bacteria interactions. Our findings provide direct evidence that mycorrhizal infection simulated root exudation, such as arachidonic acid, recruited a beneficial microbiome to the host rhizosphere, increasing plant growth and soil nutrient turnover. Read the free Plain Language Summary for this article on the Journal blog.

Defense responses of arbuscular mycorrhizal fungus-colonized poplar seedlings against gypsy moth larvae: a multiomics study

Arbuscular mycorrhizal (AM) fungi may help protect plants against herbivores; however, their use for the pest control of woody plants requires further study. Here, we investigated the effect of Glomus mosseae colonization on the interactions between gypsy moth larvae and Populus alba × P. berolinensis seedlings and deciphered the regulatory mechanisms underlying the mycorrhizal-induced resistance in the leaves of mycorrhizal poplar using RNA-seq and nontargeted metabolomics. The resistance assay showed that AM fungus inoculation protected poplar seedlings against gypsy moth larvae, as evidenced by the decreased larval growth and reduced larval survival. A transcriptome analysis revealed that differentially expressed genes (DEGs) were involved in jasmonic acid biosynthesis (lipoxygenase, hydroperoxide dehydratase, and allene oxide cyclase) and signal transduction (jasmonate-ZIM domain and transcription factor MYC2) and identified the genes that were upregulated in mycorrhizal seedlings. Except for chalcone synthase and anthocyanidin synthase, which were downregulated in mycorrhizal seedlings, all DEGs related to flavonoid biosynthesis were upregulated, including 4-coumarate-CoA ligase, chalcone isomerase, flavanone 3-hydroxylase, flavonol synthase, and leucoanthocyanidin reductase. The metabolome analysis showed that several metabolites with insecticidal properties, including coumarin, stachydrine, artocarpin, norizalpinin, abietic acid, 6-formylumbelliferone, and vanillic acid, were significantly accumulated in the mycorrhizal seedlings. These findings suggest the potential of mycorrhiza-induced resistance for use in pest management of woody plants and demonstrate that the priming of JA-dependent responses in poplar seedlings contributes to mycorrhiza-induced resistance to insect pests.

The mycorrhizal-induced growth promotion and insect resistance reduction in Populus alba × P. berolinensis seedlings: a multi-omics study.

Arbuscular mycorrhizal (AM) fungi are an alternative to chemical insecticides or fertilizers, and there is an urgent need to extend the application of AM fungi to woody plants. This study aims to investigate the growth and resistance against the gypsy moth larvae (Lymantria dispar) in Glomus intraradices-colonized Populus alba × P. berolinensis seedlings, and to unravel the transcriptome and metabolome phenotypes recruited by AM fungus colonization that affect plant growth and insect resistance. Our results showed a positive mycorrhizal growth response, i.e., growth and biomass of mycorrhizal seedlings were enhanced. However, AM fungus inoculation reduced the resistance of poplar to gypsy moth larvae, as evidenced by the decreased carbon/nitrogen ratio in leaves, as well as the increased larval growth and shortened larval developmental duration. Transcriptome analysis revealed that in both auxin and gibberellin signaling transductions, all nodes were responsive to AM symbiosis and most differentially expressed genes belonging to effectors were up-regulated in mycorrhizal seedlings. Furthermore, the two key enzymes (4-coumarate-CoA ligase and trans-cinnamate 4-monooxygenase) involved in the synthesis of p-Coumaroyl-CoA, an initial metabolite in flavonoid biosynthesis and the first rate-limiting enzyme (chalcone synthase) in flavonoid biosynthesis, were down-regulated at the transcriptional level. Consistent with the transcriptome results, metabolome analysis found that the amounts of all differentially accumulated flavonoid compounds (e.g., catechin and quercetin) identified in mycorrhizal seedlings were decreased. Taken together, these findings highlight the diverse outcomes of AM fungi-host plant-insect interaction and reveal the regulatory network of the positive mycorrhizal growth response and mycorrhizal-induced reduction of insect resistance in poplar.

Mycorrhizal growth and phosphorus responses of tropical soybean (Glycine max L.) cultivars differ with arbuscular mycorrhizal fungi isolates and phosphorus application rates in a derived-savanna zone of Nigeria

Arbuscular mycorrhizal fungi (AMF) form symbiosis with most crops and provide a sustainable approach to promote crop productivity in phosphorus (P) deficient soils. There is scarcity of information on mycorrhizal growth and P responses in relation to different AMF isolates, P rates and soybean cultivars in Nigeria. Thus, field experiments were conducted for two consecutive years (2017 − 2018) to explore the impacts of different AMF isolates (Funneliformis mosseae, Rhizophagus intraradices and Claroideoglomus etunicatum) and P application rates (0, 20 and 40 kg P2O5 ha−1) on plant growth, mycorrhizal responses, nodulation, P nutrition and grain yield of two soybean cultivars (TGx 1448-2E and TGX 1440-1E). The results showed that mycorrhizal inoculation significantly enhanced root colonization, shoot biomass, nodulation, P uptake, P use efficiency and grain yield of the soybean cultivars compared to control. Inoculation of R. intraradices and F. mosseae consistently favored mycorrhizal responses compared to C. etunicatum. Application of high P rate (40 kg ha−1) negatively affected root colonization, mycorrhizal growth and P responses in inoculated plants. Both cultivars showed similar mycorrhizal responses. Mycorrhizal growth and P responses were significantly enhanced with inoculation of R. intraradices or F. mosseae and P rate of 20 kg ha−1, which resulted in increased P uptake, shoot biomass and grain yield in both cropping years . The findings indicated that inoculation of R. intraradices or F. mosseae with moderate P rate (20 kg ha−1) is optimal to promote plant growth, P nutrition and grain yield of tropical soybean for sustainable cultivation in Nigeria.

Arbuscular Mycorrhizal Colonization in Five Tropical Forest Tree Legumes of Chittagong University Campus in Bangladesh

Arbuscular mycorrhizal (AM) colonization in five tropical forest tree legumes (Gliricidia sepium, Dalbergia sissoo, Indigofera tysmanii, Delonix regia and Samanea saman) was investigated in Chittagong University (CU) campus. The results of the present study clearly suggests that, Vesicular AM fungi (VAM) are common in all the studied forest tree species, and that the studied forest tree species differ in their rates of AM formation. The intensity of colonization is maximum (98%) in I. tysmonii followed by D. sissoo (95%), D. regia (63%), S. saman (59%) and G. sepium (52%). Coiled structures of hyphae were recorded in D. regia. Arbuscule formation was recorded in D. sissooand in I. tysmonii. Mycorrhizal spores were found in rhizosphere soils of all the sites. Glomus, Acaulospora, Entrophospora and Gigaspora spores were identified in all the hosts. Forest plants differ in their rates of AM formation. Edhapic conditions like moisture content, soil pH also influence the extent of root colonization.Keyword: Mycorrhizae, Legume, Colonization, Edhapic condition, Rhizosphere, Underground networking.

Improvement of Provitamin A in Maize Varieties Using Arbuscular Mycorrhizal Fungus, Glomus clarum

Arbuscular mycorrhizal fungus (AMF, Glomus clarum) has been used widely as a bio-amendment and bio-control agent in several biotechnological studies. In this study, biofortification of maize with provitamin A using AMF was investigated. Five maize varieties (V1 = white drought-resistant maize, V2= yellow provitamin A maize, V3= white drought-tolerant maize, V4= yellow striga-resistant maize and V5= white striga-resistant maize) were evaluated in a screen house experiment laid out in a completely randomized design with three treatments: T1 = maize + AMF before planting, T2 = maize + AMF, inoculated two weeks after planting and T3 (control) = maize only, and four replications. The result showed that AMF significantly (p<0.05, p = 0.0029) increased the provitamin A level of the maize varieties. White drought-tolerant maize (V3) had the highest provitamin A content (581.57 µg) after harvest, while the least (288.33 µg) was found in white drought-resistant maize (V1). Also, the effect of the treatments on the growth traits (plant height, leaf length, number of leaves per plant) of the maize varieties was highly significant. Therefore, AMF could be considered in breeding maize with high provitamin A content and improved morphological characters.

Arbuscular mycorrhizal fungi species differentially regulate plant growth, phosphorus uptake and stress tolerance of soybean in lead contaminated soil

Arbuscular mycorrhizal fungi (AMF) symbiosis can enhance plant growth in unfavorable conditions. However, functional variations among different AMF species for their ability to enhance phosphorus (P) uptake and soybean tolerance in lead (Pb) contaminated soil have rarely been examined. The present study therefore aimed to compare the growth, P uptake and Pb tolerance of soybean plants colonized by different AMF and to test the relationship between P uptake efficiency and Pb uptake in Pb contaminated soil. Soybean inoculated with three different AMF, Funneliformis mosseae, Claroideoglomus etunicatum, and Rhizophagus intraradices and control was grown under three Pb addition levels (0, 100 and 300 mg kg−1) in a pot experiment. The results showed that AMF inoculation significantly promoted the plant growth, P uptake and Pb accumulation in the roots, with less translocation of Pb from roots to the shoots compared to non-inoculated plants. Soybean plants inoculated with R. intraradices were more tolerant to Pb toxicity compared with other two AMF species in terms of higher root colonization, biomass, P uptake and seed yield. Significant linear correlations were observed between biomass, P uptake and Pb uptake of the plant. The findings in this study are essential in using AMF to promote soybean growth and P uptake in heavy metal-contaminated soils. Moreover, symbiotic P uptake and retention of Pb in roots of plants could serve as important criteria for screening of efficient AMF species or isolates for plant growth, P nutrition and metal tolerance in heavy metal contaminated soils.

Is AMF inoculation an alternative to maximize the in vitro antibacterial activity of Libidibia ferrea extracts?

Arbuscular mycorrhizal fungi (AMF) are known to provide plant species with several benefits, such as an increased production of bioactive compounds. However, it is yet to be defined whether extracts of mycorrhizal plants are more efficient in vitro antibacterial actions when compared to non-mycorrhizal plants. We tested the hypothesis of whether or not, methanolic extracts of Libidibia ferrea fruits, from plants established in the field and inoculated with AMF, have higher antibacterial action when inoculated with Acaulospora longula, Claroideoglomus etunicatum or Gigaspora albida. In addition, native L. ferrea fruits collected from the Caatinga area were also tested. The extracts of L. ferrea fruits inoculated with A. longula had higher in vitro antibacterial action in relation to the extracts of fruits from non-inoculated plants (p <0.05) thus characterizing the first record of different antibacterial actions of plant extracts due to inoculation with AMF. The extracts of L. ferrea fruits inoculated with A. longula were more efficient in inhibiting growth of Gram-negative bacteria. The zone diameters of inhibition ranged from 2.48 % to 7.56 % larger than the zones of the non-inoculated L. ferrea fruit extracts. The inoculation of L. ferrea with AMF may represent an alternative way of producing fruits with different antibacterial activity.

Arbuscular Mycorrhizae: Under-Tapped Potential Benefits and Perspective on Africa

Arbuscular Mycorrhizal Fungi (AMF) is attracting global attention as organic fertilizers and alternatives to chemical fertilizers in crop management practices. Mycorrhizae technology application in Africa is still juvenile compared to other continents in small-to-large scale agriculture and commerce. The sustainable use of AMF technology in in resolving bioremediation, bio-restorations and conservation challenges is currently limited by the paucity of their inocula production. Their natural versatility encourages a research trajectory toward their cultivation and exploitation of their potential benefits in improving food, bioeconomic securities and product development. This review focuses on the natural dynamics and potentials of AMF beyond agriculture to biotechnologically oriented product development of industrial, environmental and food relevancies.

Effects of Arbuscular Mycorrhizal Fungi on Root Growth and Architecture of Tulip Gesneriana

Arbuscular mycorrhizal fungi(AMF) can promote the absorption of soil water and mineral nutrients, improve photosynthesis, and make host attain higher quality finally by establishing symbiotic relationship between AMF and host root. To improve Tulip gesneriana quality have practical meaning under no bad affect to cultivation soil, in the light of its economical and ecological values. However, some AMF may be diverse from others, the concrete function of AMF on commercial tulip varieties need to explore. Therefore, three different sets of arbuscular mycorrhizal fungi were inoculated into tulip rhizosphere soil, which were set as 4(Diversispora versiformis), 7(Diversispora spurca) and 1 + 3 + 4 (Rhizophagus intraradias + Funneliformis mosseae + Diversispora versiformis), respectively. The results showed that the activity of most of the measured indices increased, the average root diameter and sucrose content decreased in those three mycorrhizal treatments. Our research provide some theoretical basis for the application of AMF on T.gesneriana ecological cultivation in future.

Nodulation and biological nitrogen fixation in soybean (Glycine max L.) as influenced by phosphorus fertilization and arbuscular mycorrhizal inoculation

Abstract Arbuscular mycorrhizal fungi (AMF) can be used to promote the productivity of legumes on phosphorus- (P) deficient soils. The present study investigates the inoculation effects of three AMF species (Funneliformis mosseae, Rhizophagus intraradices, and Claroideoglomus etunicatum) and the control (uninoculated) on nitrogen fixation efficiency and growth performance of tropical soybean cultivar (TGx1448-2E) under varying P fertilizer rates (0, 20, and 40 kg P2O5 ha−1) in a derived savannah of Nigeria. The results showed that shoot and root dry matter, number of nodules, relative ureide abundance (RUA), nitrogen derived from atmosphere (Ndfa), total N fixed, shoot P uptake, grain, and biomass yield significantly increased with AMF inoculation, with better performance observed in plants inoculated with Rhizophagus intraradices and Funneliformis mosseae compared to Claroideoglomus etunicatum. Similarly, the soybean growth variables, P uptake, and nitrogen fixation activities increased with increasing P application rates. Conversely, AMF root colonization significantly reduced with increasing P rate. Interaction of AMF inoculation and P rates significantly influenced soybean growth and nitrogen fixation. R. intraradices inoculation with 20 kg P2O5 ha−1 resulted in the highest amount of RUA, Ndfa, N fixed, and grain yield. It could be concluded from this study that R. intraradices with moderate P rate could be used to enhance nodulation, nitrogen fixation, and soybean yield in P-deficient soils.

Low indigenous AM fungal activity would be a necessary but not sufficient condition for effective utilization of exogenous AM fungal inoculum to forage corn

ABSTRACT Arbuscular mycorrhizal (AM) fungi is expected to be utilized in low input agriculture for their function to supply nutrients and water to host plants. AM fungal inoculum has been provided, but it has been known that their effect is context dependent. To clarify the factors that determine the effect of AM fungal inoculation to forage corn, a pot experiment was conducted using different indigenous AM fungal infection potential that evaluated with a modified infection unit method. Because we hypothesized that low indigenous AM fungal infection potential would be required to obtain significant inoculation effect, we prepared soils with different indigenous AM fungal infection potential by mixing sterile and non-sterile soils with different ratio. AM fungal colonization of non-inoculated series were increased with increase of indigenous AM fungal infection potential. Inoculation effect to increase of AM fungal colonization to corn root was generally larger in soils with low indigenous AM fungal infection potential and with low phosphorus (P) level, however, the effect was not very prominent in the soil with moderate P levels. Plant growth and plant P uptake showed similar trend with AM fungal colonization, i.e., enhanced P uptake and increase in plant dry matter were obtained when change in AM fungal colonization was larger. Therefore, low indigenous AM fungal infection potential would be required but not a sufficient condition to obtain AM fungal inoculation effect to forage corn.

Effects of elevated carbon dioxide on arbuscular mycorrhizal fungi activities and soil microbial properties in soybean (Glycine max L. Merrill) rhizosphere

Arbuscular mycorrhizal fungi (AMF) help in promoting plant growth and mediating key belowground processes, however, AMF responses to the continuous increase in the atmospheric carbon dioxide (CO2) is yet elusive. This has led to considerable interest in the impacts elevated CO2 on AMF and belowground processes in recent years. The present study investigated the effect of elevated CO2 on AMF sporulation and root colonization and soil microbial properties in the rhizosphere of soybean. The pot experiment consisted of two levels of CO2 (ambient; 350 ppm and elevated; 550 ppm) and three soybean cultivars (TGx 1440-1E, TGx 1448-2F and TGx 1480-2F) conducted in open top chambers, laid out in randomized complete block design, replicated thrice. The results showed that elevated CO2 increased the AMF spore density and root colonization of the soybean cultivars. Elevated CO2 increased the microbial biomass carbon (34.2–45.4%), microbial biomass nitrogen (44.6–54.9%), soil nitrogen (30.3–50.6%), available phosphorus (20.8–45.7%) in the rhizosphere of the soybean cultivars compared to the ambient CO2 . These could have resulted in increased plant biomass, pod number, 100-seed weight and seed yield under elevated CO2 . From the results of this study, increased atmospheric CO2 regulates AMF activities, microbial properties and improve soybean performance. Thus, this study may help to a better understanding of the responses of AMF and belowground process with increasing atmospheric CO2.

Mycorrhizal colonization in bread wheat varieties differing in their response to phosphorus

Arbuscular mycorrhizal fungi (AMF) play an important role in phosphorus (P) nutrition of plants. Varietal differences in AMF infection occur but there is limited information on the importance of these differences to P efficiency in wheat. This work was conducted to determine whether variation in AMF infection could help explain genetic differences in responses to P. Ten wheat varieties that vary in their grain yield response to P were compared at different rates of P in two controlled environment experiments. Plant samples were also collected from a field experiment with two P rates. Significant genetic variation was observed for AMF colonization in all experiments, but these differences were not consistently related to the yield responsiveness to P among the ten varieties. Two varieties, Carazinho and RAC875 that have a low yield response to P, had consistently high root colonization while a P-responsive variety, Wyalkatchem, had low root colonization. Adding P fertilizer reduced AMF colonization and at high P rates negative associations between AMF colonization and seedling growth and P uptake were observed among the varieties. Among some varieties, their grain yield response to P and P efficiency were consistent with their AMF colonization. However, the negative effect of mycorrhizal infection on seedling growth at high soil P suggests AMF colonization may only be a suitable trait for improved P efficiency in farming systems where available P is consistently low.

Dioxins/furans disturb the life cycle of the arbuscular mycorrhizal fungus, Rhizophagus irregularis and chicory root elongation grown under axenic conditions

Arbuscular mycorrhizal fungi (AMF)-assisted phytoremediation is a promising technology for sustainable removal of hazardous pollutants like dioxins/furans (PCDD/F) from the soil. However, little is known on AMF development in the presence of the persistent organic pollutants, PCDD/F. Thus, the present work aims at investigating the impact of increasing PCDD/F concentrations on the development of both partners of the symbiosis: the AMF, Rhizophagus irregularis and the chicory roots, Cichorium intybus L. grown under axenic conditions. Our results show that even R. irregularis spore germination is not affected by PCDD/F, it occurred mainly in linear way. However, root colonization, extra-radical hyphal elongation and sporulation are reduced by 40, 30, and 75%, respectively, at the highest PCDD/F concentration. In addition, while non-mycorrhizal root growth (length and dry weight) decreased at the highest PCDD/F concentration, no negative effect was observed on the dry weight of mycorrhizal roots. In conclusion, our findings show that although high PCDD/F concentrations disturb the main stages of R. irregularis development, the AMF remains able to fulfill its life cycle in the presence of PCDD/F. Moreover, the mycorrhizal inoculation protects the host plant against PCDD/F phytotoxicity. AMF could thus represent an interesting amendment option to assist phytoremediation of PCDD/F contaminated soils.

New MiSeq based strategy exposed plant-preferential arbuscular mycorrhizal fungal communities in arid soils of Mexico

Arbuscular mycorrhizal fungi (AMF) are obligate symbionts of c. 80% of land plants, having enormous ecological and economic impact, as they often improve crop plant nutrition and yield. DNA-based identification with molecular markers is used to analyze AM fungal communities in the field, but reaching species level taxonomic resolution remains challenging. Thus, currently there is no consensus on how to analyze high-throughput sequences and assign them into species. Here, a new sequencing strategy combined with taxonomic affiliations implemented with an evolutionary placement algorithm (EPA) was established. It is based on sequencing a c. 450 bp region of the large subunit (LSU) ribosomal rRNA gene with the MiSeq-Illumina platform. The method is suitable for the discrimination of closely related AMF species and was used to study host-AMF preferences in roots of Pequin pepper, soybean and orange at one location in the arid northeast of Mexico. Twenty AM fungal species from 13 genera were detected. Phylogenetic affiliation of reads to species revealed crop preferential associations. In Pequin pepper roots, several Rhizophagus species represented most of the community, Rhizophagus clarus being the most abundant. The soybean AM fungal community was dominated by Rhizophagus irregularis and Funneliformis mosseae and that of orange by several species of Dominikia, some of them only found in this crop. Unraveling the AMF-plant preferences of important crops by an affordable and robust sequencing method, combined with phylotaxonomic AMF species resolution, is an important tool to obtain taxonomic units that are meaningful in both biological and ecological studies.

Coexistence of genetically different Rhizophagus irregularis isolates induces genes involved in a putative fungal mating response

Arbuscular mycorrhizal fungi (AMF) are of great ecological importance because of their effects on plant growth. Closely related genotypes of the same AMF species coexist in plant roots. However, almost nothing is known about the molecular interactions occurring during such coexistence. We compared in planta AMF gene transcription in single and coinoculation treatments with two genetically different isolates of Rhizophagus irregularis in symbiosis independently on three genetically different cassava genotypes. Remarkably few genes were specifically upregulated when the two fungi coexisted. Strikingly, almost all of the genes with an identifiable putative function were known to be involved in mating in other fungal species. Several genes were consistent across host plant genotypes but more upregulated genes involved in putative mating were observed in host genotype (COL2215) compared with the two other host genotypes. The AMF genes that we observed to be specifically upregulated during coexistence were either involved in the mating pheromone response, in meiosis, sexual sporulation or were homologs of MAT-locus genes known in other fungal species. We did not observe the upregulation of the expected homeodomain genes contained in a putative AMF MAT-locus, but observed upregulation of HMG-box genes similar to those known to be involved in mating in Mucoromycotina species. Finally, we demonstrated that coexistence between the two fungal genotypes in the coinoculation treatments explained the number of putative mating response genes activated in the different plant host genotypes. This study demonstrates experimentally the activation of genes involved in a putative mating response and represents an important step towards the understanding of coexistence and sexual reproduction in these important plant symbionts.