The mycorrhiza-specific ammonium transporter ZmAMT3;1 mediates mycorrhiza-dependent nitrogen uptake in maize roots.

Most plant species can form symbioses with arbuscular mycorrhizal fungi (AMFs), which may enhance the host plant's acquisition of soil nutrients. In contrast to phosphorus nutrition, the molecular mechanism of mycorrhizal nitrogen (N) uptake remains largely unknown, and its physiological relevance is unclear. Here, we identified a gene encoding an AMF-inducible ammonium transporter, ZmAMT3;1, in maize (Zea mays) roots. ZmAMT3;1 was specifically expressed in arbuscule-containing cortical cells and the encoded protein was localized at the peri-arbuscular membrane. Functional analysis in yeast and Xenopus oocytes indicated that ZmAMT3;1 mediated high-affinity ammonium transport, with the substrate NH4+ being accessed, but likely translocating uncharged NH3. Phosphorylation of ZmAMT3;1 at the C-terminus suppressed transport activity. Using ZmAMT3;1-RNAi transgenic maize lines grown in compartmented pot experiments, we demonstrated that substantial quantities of N were transferred from AMF to plants, and 68%-74% of this capacity was conferred by ZmAMT3;1. Under field conditions, the ZmAMT3;1-dependent mycorrhizal N pathway contributed >30% of postsilking N uptake. Furthermore, AMFs downregulated ZmAMT1;1a and ZmAMT1;3 protein abundance and transport activities expressed in the root epidermis, suggesting a trade-off between mycorrhizal and direct root N-uptake pathways. Taken together, our results provide a comprehensive understanding of mycorrhiza-dependent N uptake in maize and present a promising approach to improve N-acquisition efficiency via plant-microbe interactions.

Hyphosphere interactions between Rhizophagus irregularis and Rahnella aquatilis promote carbon-phosphorus exchange at the peri-arbuscular space in Medicago truncatula.

Arbuscular mycorrhizal (AM) fungi form a continuum between roots and soil. One end of this continuum is comprised of the highly intimate plant-fungus interface with intracellular organelles for nutrient exchange, while on the other end the fungus interacts with bacteria to compensate for the AM fungus' inability to take up organic nutrients from soil. How both interfaces communicate in this highly complex tripartite mutualism is widely unknown. Here, the effects of phosphate-solubilizing bacteria (PSB) Rahnella aquatilis dwelling at the surface of the extraradical hyphae of Rhizophagus irregularis was analysed based on the expression of genes involved in C-P exchange at the peri-arbuscular space (PAS) in Medicago truncatula. The interaction between AM fungus and PSB resulted in an increase in uptake and transport of Pi along the extraradical hyphae and its transfer from AM fungus to plant. In return, this was remunerated by a transfer of C from plant to AM fungus, improving the C-P exchange at the PAS. These results demonstrated that a microorganism (i.e., a PSB) developing at the hyphosphere interface can affect the C-P exchange at the PAS between plant and AM fungus, suggesting a fine-tuned communication operated between three organisms via two distantly connected interfaces.

Concepts and consequences of the hyphosphere core microbiome for arbuscular mycorrhizal fungal fitness and function.

Arbuscular mycorrhizal (AM) fungi-associated hyphosphere microbiomes can be considered as the second genome of the mycorrhizal phosphorus uptake pathway. Their composition can be thought of as a stably recurring component of a holobiont, defined by the hyphosphere core microbiome, which is thought to benefit AM fungal fitness. Here, we review evidence indicating the existence of the hyphosphere core microbiome, highlight its functions linked to those functions lacking in AM fungi, and further explore the mechanisms by which different core members ensure their stable coexistence. We conclude that deciphering and utilizing the hyphosphere core microbiome provides an entry point for understanding the complex interactions among plants, AM fungi, and bacteria.

Arbuscular mycorrhizal fungi enhance plant phosphorus uptake through stimulating hyphosphere soil microbiome functional profiles for phosphorus turnover.

The extraradical hyphae of arbuscular mycorrhizal (AM) fungi are colonized by different bacteria in natural and agricultural systems, but the mechanisms by which AM fungi interact with the hyphosphere soil microbiome and influence soil organic phosphorus (P) mobilization remain unclear. We grew Medicago in two-compartment microcosms, inoculated with Rhizophagus irregularis, or not, in the root compartment and set up P treatments (without P, with P addition as KH2 PO4 or nonsoluble phytate) in the hyphal compartment. We studied the processes of soil P turnover and characterized the microbiome functional profiles for P turnover in the hyphosphere soil by metagenomic sequencing. Compared with the bulk soil, the hyphosphere soil of R. irregularis was inhabited by a specific bacterial community and their functional profiles for P turnover was stimulated. At the species level, the shift in hyphosphere soil microbiome was characterized by the recruitment of the genome bin2.39 harbouring both gcd and phoD genes and genome bin2.97 harbouring the phoD gene, which synergistically drove nonsoluble phytate mobilization in the hyphosphere soil. Our results suggest that AM fungi recruits a specific hyphosphere soil microbiome and stimulated their functional profiles for P turnover to enhance utilization of phytate.

A core microbiome in the hyphosphere of arbuscular mycorrhizal fungi has functional significance in organic phosphorus mineralization.

The mycorrhizal pathway is an important phosphorus (P) uptake pathway for more than two-thirds of land plants. The arbuscular mycorrhizal (AM) fungi-associated hyphosphere microbiome has been considered as the second genome of mycorrhizal P uptake pathway and functionality in mobilizing soil organic P (Po). However, whether there is a core microbiome in the hyphosphere and how this is implicated in mining soil Po are less understood. We established on-site field trials located in humid, semiarid, and arid zones and a microcosm experiment in a glasshouse with specific AM fungi and varying soil types to answer the above questions. The hyphosphere microbiome of AM fungi enhanced soil phosphatase activity and promoted Po mineralization in all sites. Although the assemblage of hyphosphere microbiomes identified in three climate zones was mediated by environmental factors, we detected a core set in three sites and the subsequent microcosm experiment. The core members were co-enriched in the hyphosphere and dominated by Alphaproteobacteria, Actinobacteria, and Gammaproteobacteria. Moreover, these core bacterial members aggregate into stable guilds that contributed to phosphatase activity. The core hyphosphere microbiome is taxonomically conserved and provides functions, with respect to the mineralization of Po, that AM fungi lack.

A Cryptosporidium PI(4)K inhibitor is a drug candidate for cryptosporidiosis.

Diarrhoeal disease is responsible for 8.6% of global child mortality. Recent epidemiological studies found the protozoan parasite Cryptosporidium to be a leading cause of paediatric diarrhoea, with particularly grave impact on infants and immunocompromised individuals. There is neither a vaccine nor an effective treatment. Here we establish a drug discovery process built on scalable phenotypic assays and mouse models that take advantage of transgenic parasites. Screening a library of compounds with anti-parasitic activity, we identify pyrazolopyridines as inhibitors of Cryptosporidium parvum and Cryptosporidium hominis. Oral treatment with the pyrazolopyridine KDU731 results in a potent reduction in intestinal infection of immunocompromised mice. Treatment also leads to rapid resolution of diarrhoea and dehydration in neonatal calves, a clinical model of cryptosporidiosis that closely resembles human infection. Our results suggest that the Cryptosporidium lipid kinase PI(4)K (phosphatidylinositol-4-OH kinase) is a target for pyrazolopyridines and that KDU731 warrants further preclinical evaluation as a drug candidate for the treatment of cryptosporidiosis.

Arbuscular mycorrhizal fungi enhance mineralisation of organic phosphorus by carrying bacteria along their extraradical hyphae.

Arbuscular mycorrhizal (AM) fungi gain access to nutrient patches outside the rhizosphere by producing an extensive network of fine hyphae. Here, we focused on establishing the mechanism by which AM fungal hyphae reach discrete organic patches with a cohort of functional bacteria transported in a biofilm on their surface. We investigated the mechanisms and impact of the translocation of phosphate solubilising bacteria (PSB) along AM fungal hyphae in bespoke microcosms. An in vitro culture experiment was also conducted to determine the direct impact of hyphal exudates of AM fungi upon the growth of PSB. The extraradical hyphae of AM fungi can transport PSB to organic phosphorus (P) patches and enhance organic P mineralisation both under in vitro culture and soil conditions. Bacteria move in a thick water film formed around fungal hyphae. However, the bacteria cannot be transferred to the organic P patch without an energy source in the form of hyphal exudates. Our results could be harnessed to better manage plant-microbe interactions and improve the ability of biological inocula involving AM fungi and bacteria to enhance the sustainability of agricultural crops in P limited conditions.

Prospective Intention-Based Lifestyle Contracts: mHealth Technology and Responsibility in Healthcare.

As the rising costs of lifestyle-related diseases place increasing strain on public healthcare systems, the individual's role in disease may be proposed as a healthcare rationing criterion. Literature thus far has largely focused on retrospective responsibility in healthcare. The concept of prospective responsibility, in the form of a lifestyle contract, warrants further investigation. The responsibilisation in healthcare debate also needs to take into account innovative developments in mobile health technology, such as wearable biometric devices and mobile apps, which may change how we hold others accountable for their lifestyles. Little is known about public attitudes towards lifestyle contracts and the use of mobile health technology to hold people responsible in the context of healthcare. This paper has two components. Firstly, it details empirical findings from a survey of 81 members of the United Kingdom general public on public attitudes towards individual responsibility and rationing healthcare, prospective and retrospective responsibility, and the acceptability of lifestyle contracts in the context of mobile health technology. Secondly, we draw on the empirical findings and propose a model of prospective intention-based lifestyle contracts, which is both more aligned with public intuitions and less ethically objectionable than more traditional, retrospective models of responsibility in healthcare.

Phosphorus forms affect the hyphosphere bacterial community involved in soil organic phosphorus turnover.

Interactions between bacteria and arbuscular mycorrhizal (AM) fungi play a significant role in mediating organic phosphorus (P) transformations and turnover in soil. The bacterial community in soil is largely responsible for mobilization of the soil organic P pool, and the released P is taken up by extraradical AM hyphae, which mediate its use for plant growth. However, the functional microbiome involved in organic P mineralization in the hyphosphere remains poorly understood. The aim of this study was to determine how AM hyphae-associated bacterial communities related to P turnover in the hyphosphere of leek (Allium porrum) respond to different forms of soil P. Using a compartmented microcosm, leek was grown with the AM fungus Funneliformis mosseae, and the extraradical mycelium of F. mosseae was allowed to grow into a separate hyphal compartment containing either no added P, or P as KH2PO4 or phytin. High-throughput sequencing showed that the alkaline phosphatase (ALP)-harboring bacterial community associated with the AM hyphae was dominated by Sinorhizobium, Bradyrhizobium, Pseudomonas, and Ralstonia and was significantly changed in response to different P treatments, with Pseudomonas showing higher relative abundance in organic P treatments than in control and inorganic P treatments. Pseudomonas was also the major genus harboring the ß-propeller phytase (BPP) gene in the hyphosphere, but the BPP-harboring community structure was not affected by the presence of different P forms. These results demonstrate the profound differences in ALP- and BPP-harboring bacterial communities in the hyphosphere at bacterial genus level, providing new insights to link bacteria and biogeochemical P cycling driven in association with mycorrhizal hyphae.

The arbuscular mycorrhizal fungus Rhizophagus irregularis MUCL 43194 induces the gene expression of citrate synthase in the tricarboxylic acid cycle of the phosphate-solubilizing bacterium Rahnella aquatilis HX2.

An increasing number of studies have demonstrated that arbuscular mycorrhizal fungi can cooperate with other soil microorganisms, e.g., bacteria, which develop near or on the surface of the extraradical hyphae where they perform multiple functions. However, the mechanisms involved in this privileged relationship are still poorly known. In the present study, we investigated how the arbuscular mycorrhizal fungus Rhizophagus irregularis MUCL 43194 influences the three pace-making enzymes (i.e., citrate synthase, isocitrate dehydrogenase, and α-oxoglutarate dehydrogenase) of the tricarboxylic acid (TCA) cycle in the phosphate-solubilizing bacterium Rahnella aquatilis HX2. The study was conducted under strict in vitro culture conditions and analysis made at the transcriptional level. Results showed that R. irregularis induced the expression of the gene-encoding citrate synthase (gltA), the pace-making enzyme involved in the first step of the TCA cycle, in R. aquatilis at all time points of observation (i.e., 1, 6, 12, 24, 48, and 72 h). The expression of the gene-encoding isocitrate dehydrogenase (icd) significantly decreased at 6, 12, 24, 48, and 72 h and the expression of the gene-encoding α-oxoglutarate dehydrogenase E1 component (kgdhc) significantly increased at 1, 6, and 48 h. The above results suggested that R. irregularis may influence the level of adenosine triphosphate production in R. aquatilis and thus the metabolism of the bacterium by stimulating the expression of gltA involved in the TCA cycle. Our results suggest a fine-tuned dialog between R. irregularis MUCL 43194 and R. aquatilis HX2 and emphasize the complexity of the interactions that might take place at the hyphal surface of arbuscular mycorrhizal fungi hosting communities of microbes.

Maize varieties can strengthen positive plant-soil feedback through beneficial arbuscular mycorrhizal fungal mutualists.

Plant-soil feedback (PSF) describes the process whereby plant species modify the soil environment, which subsequently impacts the growth of the same or another plant species. Our aim was to explore PSF by two maize varieties (a landrace and a hybrid variety) and three arbuscular mycorrhizal fungi (AMF) species (Funneliformis mosseae, Claroideoglomus etunicatum, Gigaspora margarita, and the mixture). We carried out a pot experiment with a conditioning and a feedback phase to determine PSF with different species of AMF and with a non-mycorrhizal control. Sterilized soil was conditioned separately by each variety, with or without AMF; in the feedback phase, each soil community was used to grow each in its "home" soil and in the "away" soil. Plant performance was assessed as shoot biomass, phosphorus (P) concentration and P content, and fungal performance was assessed as mycorrhizal colonization and hyphal length density. Both maize varieties were differentially influenced by AMF in the conditioning phase. In the feedback phase, PSF was generally negative for non-mycorrhizal plants or when plants were colonized by G. margarita, whereas PSF was positive in the other three AMF treatments. When plants were grown on home soil, hyphal length density was larger than on away soil. We conclude that different maize varieties can strengthen positive plant-soil feedback for themselves through beneficial mutualists for themselves, but not across the maize varieties.

Arbuscular mycorrhizal fungi stimulate organic phosphate mobilization associated with changing bacterial community structure under field conditions.

The extraradical hyphae of arbuscular mycorrhizal fungi (AMF) harbour and interact with a microbial community performing multiple functions. However, how the AMF-microbiome interaction influences the phosphorus (P) acquisition efficiency of the mycorrhizal pathway is unclear. Here we investigated whether AMF and their hyphal microbiome play a role in promoting organic phosphorus (P) mineralizing under field conditions. We developed an AMF hyphae in-growth core system for the field using PVC tubes sealed with membrane with different size of pores (30 or 0.45 µm) to allow or deny AMF hyphae access to a patch of organic P in root-free soil. AMF and their hyphae associated microbiome played a role in enhancing soil organic P mineralization in situ in the field, which was shown to be a function of the change in bacteria community on the hyphae surface. The bacterial communities attached to the AMF hyphae surface were significantly different from those in the bulk soil. Importantly, AMF hyphae recruited bacteria that produced alkaline phosphatase and provided a function that was absent from the hyphae. These results demonstrate the importance of understanding trophic interactions to be able to gain insight into the functional controls of nutrient cycles in the rhizosphere.

Simultaneously maximizing root/mycorrhizal growth and phosphorus uptake by cotton plants by optimizing water and phosphorus management.

BACKGROUND: There are two plant phosphorus (P)-uptake pathways, namely the direct P uptake by roots and the indirect P uptake through arbuscular mycorrhizal fungi (AMF). Maximizing the efficiency of root and AMF processes associated with P acquisition by adjusting soil conditions is important for simultaneously ensuring high yields and the efficient use of available P. RESULTS: A root box experiment was conducted in 2015 and 2016. The aim was to investigate the effects of different P and soil water conditions on root/mycorrhizal growth and P uptake by cotton plants. Hyphal growth was induced in well-watered soil, but decreased with increasing P concentrations. Additionally, P fertilizers regulated root length only under well-watered conditions, with the longest roots observed in response to 0.2 g P2O5 kg- 1. In contrast, root elongation was essentially unaffected by P fertilizers under drought conditions. And soil water in general had more significant effects on root and hyphal growth than phosphorus levels. In well-watered soil, the application of P significantly increased the cotton plant P uptake, but there were no differences between the effects of 0.2 and 1 g P2O5 kg- 1. So optimizing phosphorus inputs and soil water can increase cotton growth and phosphorus uptake by maximizing the efficiency of phosphorus acquisition by roots/mycorrhizae. CONCLUSIONS: Soil water and P contents of 19-24% and 20-25 mg kg- 1, respectively, simultaneously maximized root/mycorrhizal growth and P uptake by cotton plants.

Carbon and phosphorus exchange may enable cooperation between an arbuscular mycorrhizal fungus and a phosphate-solubilizing bacterium.

Arbuscular mycorrhizal fungi (AMF) transfer plant photosynthate underground which can stimulate soil microbial growth. In this study, we examined whether there was a potential link between carbon (C) release from an AMF and phosphorus (P) availability via a phosphate-solubilizing bacterium (PSB). We investigated the outcome of the interaction between the AMF and the PSB by conducting a microcosm and two Petri plate experiments. An in vitro culture experiment was also conducted to determine the direct impact of AMF hyphal exudates on growth of the PSB. The AMF released substantial C to the environment, triggering PSB growth and activity. In return, the PSB enhanced mineralization of organic P, increasing P availability for the AMF. When soil available P was low, the PSB competed with the AMF for P, and its activity was not stimulated by the fungus. When additional P was added to increase soil available P, the PSB enhanced AMF hyphal growth, and PSB activity was also stimulated by the fungus. Our results suggest that an AMF and a free-living PSB interacted to the benefit of each other by providing the C or P that the other microorganism required, but these interactions depended upon background P availability.

In situ stable isotope probing of phosphate-solubilizing bacteria in the hyphosphere.

This study used a [(13)C]DNA stable isotope probing (SIP) technique to elucidate a direct pathway for the translocation of (13)C-labeled photoassimilate from maize plants to extraradical mycelium-associated phosphate-solubilizing bacteria (PSB) that mediate the mineralization and turnover of soil organic phosphorus (P) in the hyphosphere. Inoculation with PSB alone did not provide any benefit to maize plants but utilized the added phytate-P to their own advantage, while inoculation with Rhizophagus irregularis alone significantly promoted shoot biomass and P content compared with the control. However, compared with both sole inoculation treatments, combined inoculation with PSB and R. irregularis in the hyphosphere enhanced organic P mineralization and increased microbial biomass P in the soil. There was no extra benefit to plant P uptake but the hyphal growth of R. irregularis was reduced, suggesting that PSB benefited from the arbuscular mycorrhizal (AM) fungal mycelium and competed for soil P with the fungus. The combination of T-RFLP (terminal restriction fragment length polymorphism) analysis with a clone library revealed that one of the bacteria that actively assimilated carbon derived from pulse-labeled maize plants was Pseudomonas alcaligenes (Pseudomonadaceae) that was initially inoculated into the hyphosphere soil. These results provide the first in situ demonstration of the pathway underlying the carbon flux from plants to the AM mycelium-associated PSB, and the PSB assimilated the photosynthates exuded by the fungus and promoted mineralization and turnover of organic P in the soil.

Sea buckthorn (Hippophae rhamnoides L.) oil protects against chronic stress-induced inhibitory function of natural killer cells in rats.

Chronic stress can suppress natural killer (NK) cell activity; this may also be related to the effect of stress on the neuroendocrine-immune network. Sea buckthorn (SBT) (Hippophae rhamnoides L.) is a thorny nitrogen fixing deciduous shrub, native to both Europe and Asia. It has been used as a medicinal plant in Tibetan and Mongolian traditional medicines. SBT has multifarious medical properties, including anti-fatigue as well as immunoregulatory effects. This study reports the effects of SBT oil with regard to the cytotoxicity and quantity of NK cells in the blood of a chronic-stress rat model, in addition to its mechanisms on the neuroendocrine-immune network. These results show that SBT oil, given by gavage to rats with chronic stress, could increase the following: body weight, NK cell quantities, and cytotoxicity, as well as the expression of perforin and granzyme B. The results also show that SBT oil in rats with chronic stress could suppress cortisol, ACTH, IL-1ß and TNF-α levels, in addition to increasing 5-HT and IFN-γ serum levels. This leads to suggest that SBT oil, in rats with chronic stress, can increase NK cell cytotoxicity by upregulating the expression of perforin and granzyme B, thus causing associated effects of SBT oil on the neuroendocrine-immune network.

Increasing phosphorus concentration in the extraradical hyphae of Rhizophagus irregularis DAOM 197198 leads to a concomitant increase in metal minerals.

Plants associated with arbuscular mycorrhizal fungi (AMF) acquire phosphorus via roots and extraradical hyphae. How soil P level affects P accumulation within hyphae and how P in hyphae influences the accumulation of metal minerals remains little explored. A bi-compartmented in vitro cultivation system separating a root compartment (RC), containing a Ri T-DNA transformed carrot root associated to the AMF Rhizophagus irregularis DAOM 197198, from a hyphal compartment (HC), containing only the extraradical hyphae, was used. The HC contained a liquid growth medium (i.e., the modified Strullu-Romand medium containing P in the form of KH2PO4) without (0 µM) or adjusted to 35, 100, and 700 µM of KH2PO4. The accumulation of P and metal minerals (Ca, Mg, K, Na, Fe, Cu, Mn) within extraradical hyphae and AMF-colonized roots, and the expression of the phosphate transporter gene GintPT were assessed. The expression of GintPT in the extraradical hyphae did not differ in absence of KH2PO4 or in presence of 35 and 100 µM KH2PO4 in the HC but was markedly reduced in presence of 700 µM KH2PO4. Hyphal P concentration was significantly lowest in absence of KH2PO4, intermediate at 35 and 100 µM KH2PO4 and significantly highest in presence of 700 µM KH2PO4 in the HC. The concentrations of K, Mg, and Na were positively associated with the concentration of P in the extraradical hyphae developing in the HC. Similarly, P concentration in extraradical hyphae in the HC was related to P concentration in the growth medium and influenced the concentration of K, Mg, and Na. The accumulation of the metal mineral K, Mg, and Na in the extraradical hyphae developing in the HC was possibly related to their function in neutralizing the negative charges of PolyP accumulated in the hyphae.

Schizophrenia and papillary thyroid carcinoma in an adolescent female with 22q11.2 deletion syndrome.

22q11.2 deletion syndrome is a condition with complex multisystem involvement, and many clinicians will encounter patients living with the condition. 22q11.2 deletion syndrome is known to significantly increase the risk of psychosis, and there is some emerging evidence that 22q11.2 deletion syndrome may be associated with an increased risk of malignancy. We report on a case of an adolescent female who had a delayed diagnosis of 22q11.2 deletion syndrome after she developed severe psychosis at an early age. She was subsequently diagnosed in late adolescence with papillary thyroid carcinoma. This case contributes to the limited body of evidence regarding the treatment of psychosis secondary to 22q11.2 deletion syndrome and the potential increased risk of malignancy associated with the genetic condition.

Arbuscular mycorrhizal fungi and Streptomyces: brothers in arms to shape the structure and function of the hyphosphere microbiome in the early stage of interaction.

BACKGROUND: Fungi and bacteria coexist in a wide variety of environments, and their interactions are now recognized as the norm in most agroecosystems. These microbial communities harbor keystone taxa, which facilitate connectivity between fungal and bacterial communities, influencing their composition and functions. The roots of most plants are associated with arbuscular mycorrhizal (AM) fungi, which develop dense networks of hyphae in the soil. The surface of these hyphae (called the hyphosphere) is the region where multiple interactions with microbial communities can occur, e.g., exchanging or responding to each other's metabolites. However, the presence and importance of keystone taxa in the AM fungal hyphosphere remain largely unknown. RESULTS: Here, we used in vitro and pot cultivation systems of AM fungi to investigate whether certain keystone bacteria were able to shape the microbial communities growing in the hyphosphere and potentially improved the fitness of the AM fungal host. Based on various AM fungi, soil leachates, and synthetic microbial communities, we found that under organic phosphorus (P) conditions, AM fungi could selectively recruit bacteria that enhanced their P nutrition and competed with less P-mobilizing bacteria. Specifically, we observed a privileged interaction between the isolate Streptomyces sp. D1 and AM fungi of the genus Rhizophagus, where (1) the carbon compounds exuded by the fungus were acquired by the bacterium which could mineralize organic P and (2) the in vitro culturable bacterial community residing on the surface of hyphae was in part regulated by Streptomyces sp. D1, primarily by inhibiting the bacteria with weak P-mineralizing ability, thereby enhancing AM fungi to acquire P. CONCLUSIONS: This work highlights the multi-functionality of the keystone bacteria Streptomyces sp. D1 in fungal-bacteria and bacterial-bacterial interactions at the hyphal surface of AM fungi. Video Abstract.

Cross-kingdom nutrient exchange in the plant-arbuscular mycorrhizal fungus-bacterium continuum.

The association between plants and arbuscular mycorrhizal fungi (AMF) affects plant performance and ecosystem functioning. Recent studies have identified AMF-associated bacteria as cooperative partners that participate in AMF-plant symbiosis: specific endobacteria live inside AMF, and hyphospheric bacteria colonize the soil that surrounds the extraradical hyphae. In this Review, we describe the concept of a plant-AMF-bacterium continuum, summarize current advances and provide perspectives on soil microbiology. First, we review the top-down carbon flow and the bottom-up mineral flow (especially phosphorus and nitrogen) in this continuum, as well as how AMF-bacteria interactions influence the biogeochemical cycling of nutrients (for example, carbon, phosphorus and nitrogen). Second, we discuss how AMF interact with hyphospheric bacteria or endobacteria to regulate nutrient exchange between plants and AMF, and the possible molecular mechanisms that underpin this continuum. Finally, we explore future prospects for studies on the hyphosphere to facilitate the utilization of AMF and hyphospheric bacteria in sustainable agriculture.