AM Root Research Articles

Combination of Silicate-Based Soil Conditioners with Plant Growth-Promoting Microorganisms to Improve Drought Stress Resilience in Potato.

Due to shallow root systems, potato is a particularly drought-sensitive crop. To counteract these limitations, the application of plant growth-promoting microorganisms (PGPMs) is discussed as a strategy to improve nutrient acquisition and biotic and abiotic stress resilience. However, initial root colonization by PGPMs, in particular, can be affected by stress factors that negatively impact root growth and activity or the survival of PGPMs in the rhizosphere. In this study, perspectives for the use of commercial silicate-based soil conditioners (SCs) supposed to improve soil water retention were investigated. The SC products were based on combinations with lignocellulose polysaccharides (Sanoplant® = SP) or polyacrylate (Geohumus® = GH). It was hypothesized that SC applications would support beneficial plant-inoculant interactions (arbuscular mycorrhiza, AM: Rhizophagus irregularis MUCL41833, and Pseudomonas brassicacearum 3Re2-7) on a silty loam soil-sand mixture under water-deficit conditions (6-12 weeks at 15-20% substrate water-holding capacity, WHC). Although no significant SC effects on WHC and total plant biomass were detectable, the SC-inoculant combinations increased the proportion of leaf biomass not affected by drought stress symptoms (chlorosis, necrosis) by 66% (SP) and 91% (GH). Accordingly, osmotic adjustment (proline, glycine betaine accumulation) and ROS detoxification (ascorbate peroxidase, total antioxidants) were increased. This was associated with elevated levels of phytohormones involved in stress adaptations (abscisic, jasmonic, salicylic acids, IAA) and reduced ROS (H2O2) accumulation in the leaf tissue. In contrast to GH, the SP treatments additionally stimulated AM root colonization. Finally, the SP-inoculant combination significantly increased tuber biomass (82%) under well-watered conditions, and a similar trend was observed under drought stress, reaching 81% of the well-watered control. The P status was sufficient for all treatments, and no treatment differences were observed for stress-protective nutrients, such as Zn, Mn, or Si. By contrast, GH treatments had negative effects on tuber biomass, associated with excess accumulation of Mn and Fe in the leaf tissue close to toxicity levels. The findings suggest that inoculation with the PGPMs in combination with SC products (SP) can promote physiological stress adaptations and AM colonization to improve potato tuber yield, independent of effects on soil water retention. However, this does not apply to SC products in general.

Influence of Rhizobium Co-inoculated with Arbuscular Mycorrhiza and Phosphate Solubilizing Bacteria on the Growth of Peanut Tainan 9 variety

The study of rhizobium co-inoculated with arbuscular mycorrhiza and phosphate solubilizing bacteria on peanut growth in pot experiment was laid out on completely randomized design (CRD). The experiment consisted of 5 treatments; 1) control (without microorganism), 2) rhizobium (R: Rhizobium sp.),3) R + arbuscular mycorrhiza (R+AM),4) R + Phosphate Solubilizing bacteria (R+PSB: Rhizobium sp. + Bacillus sp.) and 5) R+AM+PSB with 4 replications. The results showed that co-inoculated of microorganisms (R+AM+PSB) provided the highest root length, and the highest fresh weight and dry weight of shoot and root. The treatment of R+AM showed the peak of nodules number (115 nodules/plant), nodules fresh weight and dry weight (0.65 and 0.16 g/plant). R+AM+PSB treatment increased the percentage of AM root length colonized at 26.64%. However, total nitrogen content in peanut shoot was highest in R+PSB. The concentrations of phosphorus and potassium in peanut shoot and root parts were not significant among treatments. Co-inoculate of R and PSB produced the highest nitrogen fixation at 87.73 mg N/plant.

OsEXO70L2 is required for large lateral root formation and arbuscular mycorrhiza establishment in rice

As a major subunit of the exocyst complex, members of the EXO70 family have mainly been shown to play roles in cell polarity and morphogenesis in Arabidopsis, but their roles in plant endosymbiosis, such as with arbuscular mycorrhizal fungi (AMF), have rarely been reported. Here, using knockout and overexpression lines, we show that OsEXO70L2, which encodes a divergent EXO70 protein in rice, controls the number of primary roots and is essential for large lateral root formation. Furthermore, the OsEXO70L2 mutant sr1 displayed rare internal AMF hyphae and no arbuscules. We also found that AMF sporulation can occur in roots despite low colonization and that AMF colonization and sporulation are modulated by photoperiod and co-culture with clover. Finally, genes related to auxin homeostasis were found to be affected in the OsEXO70L2 knockout or overexpression lines, suggesting that auxin is at least partly responsible for the phenotypes. This study provides new perspectives on the role of the exocyst complex during root development and AM in rice.

The Effects of Local Weed Species on Arbuscular Mycorrhizal Fungal Communities in an Organic Winter Wheat (Triticum durum L.) Field in Lebanon.

We examined the potential effects of weed species on the arbuscular mycorrhizal fungi (AMF) in an organic winter wheat (Triticum durum) field in Lebanon. In this agroecosystem, the field and its surroundings were covered with spontaneous vegetation corresponding to local weeds. The coexistence between wheat and weeds did not modify AM fungal community diversity and colonization in T. durum but changed their composition. We evidenced 22 operational taxonomic units (OTUs) specifically shared between wheat associated with weeds (Tdw) and weeds, regardless of their localization and 12 OTUs with an abundance of variation between wheat without neighboring weeds (Td) and Tdw. The number of AM propagules and total C and N contents were higher in soil covered with wheat associated with weeds (TdWsoil) vs. wheat without neighboring weeds (Tdsoil). In greenhouse experiments, the shoot biomass and root mycorrhizal intensity of Medicago sativa, used as a trap plant, were higher using TdWsoil vs. Tdsoil as the inoculum. Positive correlations were observed between soil AM propagule numbers and M. sativa shoot biomass, on the one hand and M. sativa mycorrhizal intensity, on the other hand. Weeds seemed to exert significant effects on root AM fungal composition in T. durum and these effects may contribute to enhanced AMF development in the field.

In-Vivo Antivenom Effect of Annona senegalensis (Pers) Against Biological Activities of Naja nigricollis (Hallowell) Envenomation

Snake bites are a common, serious medical issue often neglected in developing countries. This study aims to investigate the effectiveness of methanolic extract from the root bark of Annona senegalensis in neutralizing the biological activities of Naja nigricollis envenomation in vivo. The methanolic extract was fractionated using a liquid-liquid fractionating method. The inhibition of venom-induced edematogenic and hemorrhagic effects was evaluated in albino rats using a pre-incubation protocol. The aqueous-methanol fraction (AM) of A. senegalensis AM root methanolic extract significantly inhibited the hemorrhagic and edema-inducing activities of the venom. The methanolic extract derived from the root bark of A. senegalensis has exhibited promising potential as an effective anti-snake venom agent.

Plant growth-promoting rhizobacteria’s (PGPR) effects on Medicago sativa growth, arbuscular mycorrhizal colonisation, and soil enzyme activities

ABSTRACT Plant growth-promoting rhizobacteria (PGPR) can ameliorate soil fertility and boost crop yields. This paper reports a study of the effect of PGPR inoculation on Medicago sativa plants. Sixteen indigenous PGPR were isolated and screened for PGP traits. Their influence was assessed on the growth of M. sativa plants, root colonisation by arbuscular mycorrhizal fungi (AMF), and soil enzyme activities (SEA). The bacterial isolates showed interesting PGP traits. They increased the plant’s shoot and root dry weights, AM colonisation, and SEA. Two bacteria assigned to Pseudomonas koreensis and Alcaligenes faecalis were selected as effective inoculants for M. sativa plants. These PGPR may represent suitable candidates as bio-enhancers and biofertilizers in sustainable agricultural systems.

The effect of inoculation with Rhizophagus irregularis on the expression level of phosphate transporter genes in the roots of Medicago lupulina under conditions of low phosphorus level in the substrate

The dynamics of expression of some genes responsible for phosphorus transport (PT1, PT2, PT4, ATP1) at different developmental stages of Medicago lupulina in roots inoculated and uninoculated with AM fungus were analyzed. The levels of MtPT1 and MtPT2 transcripts were decreased under condition of AM symbiosis development. For the first time it is in M. lupulina AM roots that MlATP1 expression has been analyzed. The dynamics of AM-specific MlPT4 and MlATP1 expression depended on developmental stage of the host plant. The key changes in gene expression were observed at the stemming stage of M. lupulina plants.

Greater chemical signaling in root exudates enhances soil mutualistic associations in invasive plants compared to natives.

Invasive plants can change soil properties resulting in improved growth. Although invaders are known to alter soil chemistry, it remains unclear if chemicals secreted by roots facilitate invasive plant-soil mutualisms. With up to 19 confamilial pairs of invasive and native plants, and most of which were congeners, we explored the root exudate-induced changes in plant-arbuscular mycorrhizal (AM) fungal mutualisms. We found that, relative to natives, invaders had greater AM colonization, greater biomass and their root exudates contained higher concentrations of two common chemical signals - quercetin and strigolactones - which are known to stimulate AM fungal growth and root colonization. An exudate exchange experiment showed that root exudates from invaders increased AM colonization more than exudates from natives. However, application of activated carbon led to greater reduction in AM colonization and plant biomass for invaders than natives, suggesting stronger effects of chemical signals in root exudates from invaders. We show that nonnative plants promote interactions with soil mutualists via enhancing root exudate chemicals, which could have important implications for invasion success.

Degradation of soil arbuscular mycorrhizal fungal diversity and functionality accompanied by the aggravation of pepper Phytophthora blight in a facility shed in Southwest China

AbstractArbuscular mycorrhizal (AM) fungi play a vital role in plant's resistance against soil‐borne pathogens including Phytophthora capsici, which causes the devastating Phytophthora blight and threatens pepper (Capsicum annuum L.) cultivation worldwide. In order to understand the interaction of indigenous AM fungal community and P. capsici during the aggravation of Phytophthora blight, a survey was performed in a facility shed in Southwest China. The blight severity of pepper plants was evaluated based on a 0–5 scale (L0–L5), and the corresponding root AM fungal colonization, and the abundance and community composition of AM fungi as well as the population of P. capsici in root‐adjacent soil, were all investigated. Along with the rise of disease severity, increased soil P. capsici population was shown. In contrast, there were significant decreases in root colonization rate and the diversity indices rather than the abundance of soil AM fungi. The root colonization rate and the diversity indices of AM fungi all showed significant negative correlations with soil P. capsici population. Compared to plants with lower disease severities (L0–L2), higher severities (L3–L5) significantly modified soil AM fungal community composition, mainly through replacing the beneficial Glomus phylotypes by Paraglomus ones. Overall, the results disclosed the dynamic competition between indigenous AM fungi and P. capsici behind the onset of pepper Phytophthora blight, which highlights the importance of establishing soil suppressiveness on the control of soil‐borne diseases.

Herbal root extracts in Ben-Cha-Moon-Yai remedy attenuated pain-like behaviors and inflammation through the opioid and prostaglandin systems

Ethnopharmacological relevanceBen-Cha-Moon-Yai (BMY) remedy used in Thai traditional medicine as an anti-inflammatory, analgesic, and antipyretic agent compromises five herbal root extracts of equal weights: Aegle marmelos (L.) Corrêa (AM), Oroxylum indicum (L.) Kurz (OI), Dimocarpus longan Lour. (DL), Dolichandrone serrulata (Wall. ex DC.) Seem. (DS), and Walsura trichostemon Miq. (WT). Aim of the studyTo assess the anti-nociceptive and anti-inflammatory effects of the root extracts of all five species of BMY in experimental animal (mouse) models to ensure the rational use of herbal products in Thai traditional medicine. Materials and methodsRoot extracts prepared by ethanol and water extraction were used for the biological assays in animal models at five dose levels: 25, 50,100,200 & 400 mg/kg. The anti-nociceptive activity was evaluated based on hot-plate latency, duration of paw licking induced by formalin, and abdominal writhing induced by acetic acid. Carrageenan- and prostaglandin-induced paw oedema models were used to determine the anti-inflammatory activity. ResultsThe oral administration of AM, DS and WT root extracts displayed significant analgesic effects in the hot-plate test, both phases (early and late) of formalin test and acetic-acid induced writhing test at different dose levels. OI and DL only produced significant analgesia in the late phase of the formalin test and writhing test. The pretreatment of animals with the non-selective opioid receptor antagonist naloxone, reverse AM, DS and WT induced-antinociceptive activity. In both carrageenan and prostaglandin-induced paw oedema tests, all five herbal plant root extracts significantly reduced paw oedema at 3 h or more at different dose levels. Rotarod test results showed no effects of five herbal plant root extracts on the balance and the motor coordination at the highest dose level evaluated (400 mg/kg). ConclusionThe root extracts of AM, DS, and WT possess both central and peripheral anti-nociceptive properties, while OI and DL possess only peripheral analgesic properties. All five root extracts own anti-inflammatory properties, which might be due to their activity on the prostaglandin system. Altogether these findings ensure the rational use of BMY remedy in Thai traditional medicine.

Impacts of Urbanization Undermine Nestedness of the Plant-Arbuscular Mycorrhizal Fungal Network.

Cities are prone to ecological problems, yet the impacts of rapid global urbanization on the feedback between above- and belowground subsystems remain largely unknown. We sampled the roots of 8 common herbaceous plants within the Fifth Ring (urban areas) and in Jiufeng National Forest Park (rural areas) in Beijing (China) to assess the impacts of urbanization on the network of plant-arbuscular mycorrhizal (AM) fungal associations. Using Illumina MiSeq sequencing, 81 AM fungal OTUs were identified in 78 herb root samples. The Shannon, Simpson, and Pielou indices of root AM fungi in urban areas were significantly higher than those in rural areas. In this study, a significantly nested mycorrhizal association network was observed in rural areas (NODF = 64.68), whereas a non-nested pattern was observed in urban areas (NODF = 55.50). The competition index C-score (0.0769) of AM fungi in urban areas was slightly lower than that in rural areas (0.1431), and the species specialization (d’) of 8 host plants and fungal dissimilarity among 8 host plants in urban areas were significantly lower than those in rural areas. Convergent associations among hosts may be an important factor influencing this non-nested pattern of the plant-AM fungi network in urban areas. Generalists, rather than specialists, were enhanced during the establishment of mycorrhizal associations in urban areas. Our results suggest that reduced selectivity of host plants, and generalist promotion and specialist reduction of AM fungi during urbanization may contribute to the non-nested network of plant-AM fungal associations.

Nodule-associated bacteria alter the mutualism between arbuscular mycorrhizal fungi and N2 fixing bacteria

Legumes can interact simultaneously with multiple microbial partners in symbiosis, including arbuscular mycorrhizal fungi (AMF), N2-fixing bacteria, and nodule-associated bacteria. However, our understanding of their functional diversity and interactions remains limited. The objective of this study was to evaluate individual and combined effects of these three symbioses on the abundance and function of the symbionts, including the growth, nitrogen content, nodulation and root traits of Mimosa scabrella (Bracatinga), a common leguminous tree in South America. We grew seedlings in a growth chamber for 90 days using sterile soil inoculated with all combinations of AMF, N2 fixing and nodule-associated bacteria. We found that the tripartite symbiosis formed by host, AMF and N2 fixing bacteria increased shoot biomass 3.7x and N content 5.2x relative to non-inoculated controls. This response was 71% greater than the sum of the respective individual treatments, confirming for the first time in M. scabrella a synergistic effect of such dual inoculation. In contrast, the presence of nodule-associated bacteria in a tetrapartite symbiosis resulted in a 57.7% reduction in the number of nodules in any treatment where N2 fixing bacteria were present. Concurrently, total AM root colonization decreased by approximately 50% in the tetrapartite compared to the tripartite symbiosis. We conclude that the tripartite symbiosis formed by M. scabrella, N2 fixing bacteria, and AMF can act synergistically in promoting plant biomass and N2 fixation. However, nodule-associated bacteria can act “opportunistically”, causing a detrimental effect on the tripartite mutualism. Our findings highlight the functional complexity of multipartite symbioses and how interactions among partners can determine biological processes and outcomes.

Controlled Assays for Phenotyping the Effects of Strigolactone-Like Molecules on Arbuscular Mycorrhiza Development.

Arbuscular mycorrhiza is an ancient symbiosis between most land plants and fungi of the Glomeromycotina, in which the fungi provide mineral nutrients to the plant in exchange for photosynthetically fixed organic carbon. Strigolactones are important signals promoting this symbiosis, as they are exuded by plant roots into the rhizosphere to stimulate activity of the fungi. In addition, the plant karrikin signaling pathway is required for root colonization. Understanding the molecular mechanisms underpinning root colonization by AM fungi, requires the use of plant mutants as well as treatments with different environmental conditions or signaling compounds in standardized cocultivation systems to allow for reproducible root colonization phenotypes. Here we describe how we set up and quantify arbuscular mycorrhiza in the model plants Lotus japonicus and Brachypodium distachyon under controlled conditions. We illustrate a setup for open pot culture as well as for closed plant tissue culture (PTC) containers, for plant-fungal cocultivation in sterile conditions. Furthermore, we explain how to harvest, store, stain, and image AM roots for phenotyping and quantification of different AM structures.

Aquaporins and cation transporters are differentially regulated by two arbuscular mycorrhizal fungi strains in lettuce cultivars growing under salinity conditions

The aim was to identify the effects of AM symbiosis on the expression patterns of genes associated with K+ and Na+ compartmentalization and translocation and on K+/Na+ homeostasis in some lettuce (Lactuca sativa) cultivars as well as the effects of the relative abundance of plant AQPs on plant water status. Two AM fungi species (Funneliformis mosseae and Claroideoglomus lamellosum) isolated from the hyper-arid Atacama Desert (northern Chile) were inoculated to two lettuce cultivars (Grand Rapids and Lollo Bionda), and watered with 0 and 60 mM NaCl. At 60 days of plant growth, the AM symbiotic development, biomass production, nutrient content (Pi, Na+, K+), physiological parameters, gene expressions of ion channels and transporters (NHX and HKT1), and aquaporins proteins abundance (phosphorylated and non-phosphorylated) were evaluated. Salinity increased the AM root colonization by both inocula. AM lettuce plants showed an improved growth, increased relative water content and improved of K/Na ratio in root. In Grand Rapids cultivar, the high efficiency of photosystem II was higher than Lollo Bionda cultivar; on the contrary, stomatal conductance was higher in Lollo Bionda. Nevertheless, both parameters were increased by AM colonization. In the same way, LsaHKT1;1, LsaHKT1;6, LsaNHX2, LsaNHX4, LsaNHX6 and LsaNHX8 genes and aquaporins PIP2 were up-regulated differentially by both AM fungi. The improved plant growth was closely related to a higher water status due to increased PIP2 abundance, as well as to the upregulation of LsaNHX gene expression, which concomitantly improved plant nutrition and K+/Na+ homeostasis maintenance.

Fly Ash and Compost Amendments and Mycorrhizal Inoculation Enhanced the Survival and Growth of Delonix regia in Cu-Ni Mine Tailings

Delonix regia, an ornamental tree that can tolerate an elevated level of heavy metals, was evaluated for phytoremediation potential in mine tailings with fly ash, compost, and mycorrhiza. A two-factorial experiment was conducted under screen house conditions using mine tailings from Bamangwato Concessions Limited (BCL) Cu-Ni mine. The treatments are mine tailing (MT) without mycorrhiza (MT – AM), MT with mycorrhiza (MT + AM), MT with 10% fly ash (FA) without mycorrhiza (MT + FA – AM), mine tailings with 10% FA with mycorrhiza (MT + FA + AM), MT with 10% compost (CP) without mycorrhiza (MT + CP – AM), and MT with 10% CP with mycorrhiza (MT + CP + AM). After 40 wk, results showed an interaction effect of amendments and mycorrhiza wherein compost and FA enhanced the survival, AM root colonization, plant height, and dry matter yield of D. regia seedlings. Mycorrhiza further enhanced these growth parameters, especially in pure mine tailings. The As, Cu, Mn, Ni, Pb, and Zn concentration in plant tissues were reduced substantially by FA and compost amendments. Mycorrhiza also reduced the As, Cu, Ni, Pb, and Zn in pure mine tailings but enhanced the concentration of these metals in the presence of FA and compost. These results could be attributed to the decrease of heavy metal availability and increase of nutrients due to FA and compost while mycorrhiza decreased the translocation of heavy metals regardless of the presence of FA and compost. Overall, results indicated that the survival and growth of D. regia in BCL Cu-Ni mine tailings could be enhanced by the combined application of fly ash, compost, and mycorrhiza.

Effect of agronomic treatments on arbuscular mycorrhizal fungi under nursery conditions of Warangal

Influence of different agronomic practices on root nodulation, AM colonization and growth of forest tree species was studied in two agroforestry tree species Acacia nilotica and Albizia lebbeck. Neem cake and Farmyard manure and sewage water were analyzed for their effect on A. nilotica and A.lebbeck. These treatments along with different AM fungi were also analyzed. Farmyard manure was found to be effective with Glomus fasiculatum in A. nilotica and Neem cake was given best results in A.l ebbeck with Glomus fasiculatum.

Biodiversity of arbuscular mycorrhizal fungi associated with selected medicinal plants of Hamirpur district of Himachal Pradesh, India

The present investigation was focused on exploration of biodiversity of Arbuscular mycorrhizal fungi (AMF) associated with different medicinal plants. Twenty-two medicinal plants belonging to 14 families were analyzed for AMF colonization. The plant roots and their respective rhizosphereic soil samples were collected from different localities of hamirpur district, himachal pardesh for AMF analysis and spore assessment per 50gm of soil sample of soil. The results revealed that number of AM spores in the rhizosphere of plant was not related to percent of AM root colonization. Highest per cent of root colonization was reported in Ricinus communis (86.5±4.68 %) and Achyranthes aspera lacks colonization. Highest number of AM spore was found in rhizosperic soil sample of Mimosa pudica (177.4±4.306) and least number of spores in Datura stramonium (47.53±2.76). Fourty three AM species belonging to five genera i.e. Glomus, Acaulospora, Gigaspora, Entrophospora and Sclerocystis were isolated during investigation. Maximum AM spore diversity was observed in Mentha viridis followed by Catharanthus roseus and least diversity related to Datura stramonium. The study confirmed that diversity of AM fungi varies with plant to plant.

Contalactone, a contaminant formed during chemical synthesis of the strigolactone reference GR24 is also a strigolactone mimic

Strigolactone (SL) plant hormones control plant architecture and are key players in both symbiotic and parasitic interactions. GR24, a synthetic SL analog, is the worldwide reference compound used in all bioassays for investigating the role of SLs in plant development and in rhizospheric interactions. In 2012, the first characterization of the SL receptor reported the detection of an unknown compound after incubation of GR24 samples with the SL receptor. We reveal here the origin of this compound (P270), which comes from a by-product formed during GR24 chemical synthesis. We present the identification of this by-product, named contalactone. A proposed chemical pathway for its formation is provided as well as an evaluation of its bioactivity on pea, Arabidopsis, root parasitic plant seeds and AM fungi, characterizing it as a SL mimic. Quality of GR24 samples can be easily checked by carrying out microscale hydrolysis in a basic aqueous medium to easily detect P270 as indicator of the presence of the contalactone impurity. In all cases, before being used for bioassays, GR24 must be careful purified by preparative HPLC.

Metabolic responses to arbuscular mycorrhizal fungi are shifted in roots of contrasting soybean genotypes.

Modern breeding programs have reduced genetic variability and might have caused a reduction in plant colonization by arbuscular mycorrhizal fungi (AM). In our previous studies, mycorrhizal colonization was affected in improved soybean genotypes, mainly arbuscule formation. Despite substantial knowledge of the symbiosis-related changes of the transcriptome and proteome, only sparse clues regarding metabolite alterations are available. Here, we evaluated metabolite changes between improved (I-1) and unimproved (UI-4) soybean genotypes and also compare their metabolic responses after AM root colonization. Soybean genotypes inoculated or not with AM were grown in a chamber under controlled light and temperature conditions. At 20days after inoculation, we evaluated soluble metabolites of each genotype and treatment measured by GC-MS. In this analysis, when comparing non-AM roots between genotypes, I-1 had a lower amount of 31 and higher amount of only 4 metabolites than the UI-4 genotype. When comparing AM roots, I-1 had a lower amount of 36 and higher amount of 4 metabolites than UI-4 (different to those found altered in non-AM treated plants). Lastly, comparing the AM vs non-AM treatments, I-1 had increased levels of three and reduced levels of 24 metabolites, while UI-4 only had levels of 12 metabolites reduced by the effect of mycorrhizas. We found the major changes in sugars, polyols, amino acids, and carboxylic acids. In a targeted analysis, we found lower levels of isoflavonoids and alpha-tocopherol and higher levels of malondialdehyde in the I-1 genotype that can affect soybean-AM symbiosis. Our studies have the potential to support improving soybean with a greater capacity to be colonized and responsive to AM interaction.

LACK OF SYMBIONT ACCOMMODATION controls intracellular symbiont accommodation in root nodule and arbuscular mycorrhizal symbiosis in Lotus japonicus.

Nitrogen-fixing rhizobia and arbuscular mycorrhizal fungi (AMF) form symbioses with plant roots and these are established by precise regulation of symbiont accommodation within host plant cells. In model legumes such as Lotus japonicus and Medicago truncatula, rhizobia enter into roots through an intracellular invasion system that depends on the formation of a root-hair infection thread (IT). While IT-mediated intracellular rhizobia invasion is thought to be the most evolutionarily derived invasion system, some studies have indicated that a basal intercellular invasion system can replace it when some nodulation-related factors are genetically modified. In addition, intracellular rhizobia accommodation is suggested to have a similar mechanism as AMF accommodation. Nevertheless, our understanding of the underlying genetic mechanisms is incomplete. Here we identify a L. japonicus nodulation-deficient mutant, with a mutation in the LACK OF SYMBIONT ACCOMMODATION (LAN) gene, in which root-hair IT formation is strongly reduced, but intercellular rhizobial invasion eventually results in functional nodule formation. LjLAN encodes a protein that is homologous to Arabidopsis MEDIATOR 2/29/32 possibly acting as a subunit of a Mediator complex, a multiprotein complex required for gene transcription. We also show that LjLAN acts in parallel with a signaling pathway including LjCYCLOPS. In addition, the lan mutation drastically reduces the colonization levels of AMF. Taken together, our data provide a new factor that has a common role in symbiont accommodation process during root nodule and AM symbiosis.