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

Functional Characterization of Ammonium Transporter LjAMT2;4 During Lotus japonicus Symbiosis with Rhizobia and Arbuscular Mycorrhizal Fungi

Arbuscular mycorrhizal fungi (AMF) and rhizobia are important symbiotic microorganisms in soil, which can symbiose with legumes to form mycorrhizal symbionts and nodules, respectively. Once a stable symbiotic relationship is established, these microorganisms have been found to enhance nitrogen absorption by legumes. Although plants can directly utilize ammonium through ammonium transporters (AMTs), there is limited research on the role of the AMT gene family in promoting ammonium transport in symbiotic relationships. Lotus japonicus, a common host of arbuscular mycorrhizal fungi and rhizobia, serves as a model legume plant. In this study, we examined the characteristics of the ammonium transporter LjAMT2;4 in L. japonicus and found that LjAMT2;4 is localized to the plasma membrane and is predominantly expressed in roots. The promoter region of LjAMT2;4 contains cis-acting elements induced by arbuscular mycorrhizal fungi and rhizomes, and the expression of LjAMT2;4 was induced by AM fungi and rhizobia. However, there was no significant difference in the mycorrhizal colonization rate of ljamt2;4 compared to the wild type, while the absence of LjAMT2;4 significantly increased the number of root nodules under nitrogen-starved conditions, enhancing nitrogen fixation and alleviating nitrogen stress in extremely nitrogen-starved environments, ultimately promoting plant growth. These findings suggest that manipulating the genes involved in symbiotic nitrogen fixation, such as LjAMT2;4, could offer new strategies for sustainable agricultural production. Given that AM and rhizobia symbiosis are critical for crop growth, our findings may inform strategies to improve agricultural management.

Glutamine synthetase GhGLN1.5 regulates arbuscular mycorrhizal symbiosis and Verticillium wilt resistance in cotton by modulating inorganic nitrogen assimilation

Arbuscular mycorrhizal (AM) fungi play a crucial role in the nitrogen uptake and Verticillium wilt resistance of cotton. The absorbed inorganic nitrogen is converted into organic nitrogen through nitrogen assimilation mediated by glutamine synthetase (GS). However, the role of GS in AM symbiosis and Verticillium wilt resistance remains unclear. We identified an AM fungus-induced GS gene, GhGLN1.5, which participated in AM symbiosis. Both in vivo and in vitro analyses demonstrated that GhGLN1.5 exhibits catalytic activity of GS. The knockdown of GhGLN1.5 resulted in a reduction of AM colonization, nitrogen uptake capacity, and AM symbiosis-dependent resistance to Verticillium wilt. Heterologous expression of GhGLN1.5 enhanced AM symbiosis, increased GS activity, and promoted plant growth. The knockout of GhGLN1.5 in cotton inhibited AM symbiosis. Furthermore, we identified an AM fungus-induced ethylene response factor gene GhWRI3 through yeast one-hybrid library screening and found that GhWRI3 activates the expression of GhGLN1.5 via AW-box element. These findings provide valuable insights into the molecular mechanisms of GhGLN1.5 expression in AM symbiosis, nitrogen assimilation, and Verticillium wilt resistance in cotton, suggesting potential strategies for regulating AM symbiosis in cotton through the WRI3-GLN1.5 module.

Symbiotic synergy: How Arbuscular Mycorrhizal Fungi enhance nutrient uptake, stress tolerance, and soil health through molecular mechanisms and hormonal regulation

Arbuscular Mycorrhizal (AM) symbiosis is integral to sustainable agriculture and enhances plant resilience to abiotic and biotic stressors. Through their symbiotic association with plant roots, AM improves nutrient and water uptake, activates antioxidant defenses, and facilitates hormonal regulation, contributing to improved plant health and productivity. Plants release strigolactones, which trigger AM spore germination and hyphal branching, a process regulated by genes, such as D27, CCD7, CCD8, and MAX1. AM recognition by plants is mediated by receptor-like kinases (RLKs) and LysM domains, leading to the formation of arbuscules that optimize nutrient exchange. Hormonal regulation plays a pivotal role in this symbiosis; cytokinins enhance AM colonization, auxins support arbuscule formation, and brassinosteroids regulate root growth. Other hormones, such as salicylic acid, gibberellins, ethylene, jasmonic acid, and abscisic acid, also influence AM colonization and stress responses, further bolstering plant resilience. In addition to plant health, AM enhances soil health by improving microbial diversity, soil structure, nutrient cycling, and carbon sequestration. This symbiosis supports soil pH regulation and pathogen suppression, offering a sustainable alternative to chemical fertilizers and improving soil fertility. To maximize AM 's potential of AM in agriculture, future research should focus on refining inoculation strategies, enhancing compatibility with different crops, and assessing the long-term ecological and economic benefits. Optimizing AM applications is critical for improving agricultural resilience, food security, and sustainable farming practices.

The interaction of nutrient uptake with biotic and abiotic stresses in plants

Plants depend heavily on efficient nutrient uptake and utilization for optimal growth and development. However, plants are constantly subjected to a diverse array of biotic stresses, such as pathogen infections, insect pests, and herbivory, as well as abiotic stress like drought, salinity, extreme temperatures, and nutrient imbalances. These stresses significantly impact the plant's ability to take up nutrient and use it efficiency. Understanding how plants maintain nutrient uptake and use efficiency under biotic and abiotic stress conditions is crucial for improving crop resilience and sustainability. This review explores the recent advancements in elucidating the mechanisms underlying nutrient uptake and utilization efficiency in plants under such stress conditions. Our aim is to offer a comprehensive perspective that can guide the breeding of stress-tolerant and nutrition-efficient crop varieties, ultimately contributing to the advancement of sustainable agriculture.

Genetic and molecular mechanisms underlying nitrogen use efficiency in maize

Nitrogen (N) is vital for crop growth and yield, impacting food quality. However, excessive use of N fertilizers leads to high agricultural costs and environmental challenges. This review offers a thorough synthesis of the genetic and molecular regulation of N uptake, assimilation, and remobilization in maize, emphasizing the role of key genes and metabolic pathways in enhancing N use efficiency (NUE). We summarize the genetic regulators of N transports for nitrate (NO3-) and ammonium (NH4+) that contribute to efficient N uptake and transportation. We further discuss the molecular mechanisms by which root system development adapts to N distribution and how N influences root system development and growth. Given the advancements in high-throughput microbiome studies, we delve into the impact of rhizosphere microorganisms on NUE and the complex plant-microbe interactions that regulate maize NUE. Additionally, we conclude with intricate regulatory mechanisms of N assimilation and remobilization in maize, involving key enzymes, transcription factors, and amino acid transporters. We also scrutinize the known N signaling perception and transduction mechanisms in maize. This review underscores the challenges in improving maize NUE and advocates for an integrative research approach that leverages genetic diversity and synthetic biology, paving the way for sustainable agriculture.

ZmL75 is required for colonization by arbuscular mycorrhizal fungi and for saline-alkali tolerance in maize

Saline-alkali soil severely reduces the productivity of crops, including maize (Zea mays). Although several genes associated with saline-alkali tolerance have been identified in maize, the underlying regulatory mechanism remains elusive. Here, we report a direct link between colonization by arbuscular mycorrhizal fungi (AMF) and saline-alkali tolerance in maize. We identify s75, a natural maize mutant that cannot survive under moderate saline-alkali soil conditions or establish AM symbioses. The saline-alkali hypersensitive phenotype of s75 is caused by a 1340-bp deletion in Zm00001d033915, designated as ZmL75. This gene encodes a glycerol-3-phosphate acyltransferase localized in the endoplasmic reticulum, and is responsible for AMF colonization. ZmL75 expression levels in roots correspond with the root length colonization (RLC) rate during early vegetative development. Notably, the s75 mutant line shows a complete loss of AMF colonization, along with alterations in the diversity and structure of its root fungal microbiota. Conversely, overexpression of ZmL75 increases the RLC rate and enhances tolerance to saline-alkali soil conditions. These results suggest that ZmL75 is required for symbiosis with AMF, which directly improves saline-alkali tolerance. Our findings provide insights into maize-AMF interactions and offer a potential strategy for maize improvement.

OsNLP3 and OsPHR2 orchestrate direct and mycorrhizal pathways for nitrate uptake by regulating NAR2.1-NRT2s complexes in rice

Nitrogen (N) is the most important essential nutrient required by plants. Most land plants have evolved two N uptake pathways, a direct root pathway and a symbiotic pathway, via association with arbuscular mycorrhizal (AM) fungi. However, the interaction between the two pathways is ambiguous. Here, we report that OsNAR2.1-OsNRT2s, the nitrate (NO3-) transporter complexes with crucial roles in direct NO3- uptake, are also recruited for symbiotic NO3- uptake. OsNAR2.1 and OsNRT2.1/2.2 are coregulated by NIN-like protein 3 (OsNLP3), a key regulator in NO3- signaling, and OsPHR2, a major regulator of phosphate starvation responses. More importantly, AM symbiosis induces expression of OsNAR2.1-OsNRT2s, OsNLP3, and OsSPX4, encoding an intracellular Pi sensor, in arbuscular-containing cells, but weakens their expression in the epidermis. OsNAR2.1 and OsNLP3 can activate both mycorrhizal NO3- uptake and mycorrhization efficiency. Overall, we demonstrate that OsNLP3 and OsPHR2 orchestrate the direct and mycorrhizal NO3- uptake pathways by regulating the NAR2.1-NRT2s complexes in rice.

The Mechanism of Ammonia-Assimilating Bacteria Promoting the Growth of Oyster Mushrooms (Pleurotus ostreatus)

Oyster mushrooms (Pleurotus ostreatus) are one of the most commonly grown edible mushrooms using compost, which contains high concentrations of ammonia. In this study, inoculation of the oyster mushroom culture substrate with ammonia-assimilating bacterium Enterobacter sp. B12, either before or after composting, reduced the ammonia nitrogen content, increased the total nitrogen content of the compost, and enhanced the mushroom yield. Co-cultivation with P. ostreatus mycelia on potato dextrose agar (PDA) plates containing 200 mM NH4+, B12 reduced reactive oxygen species (ROS) accumulation in the mycelia and downregulated the expression of the ROS-generating enzymes NADPH oxidase A (NOXA) and the stress hormone ethylene synthase 1-aminocyclopropane-1-carboxylate oxidase (ACO). It also downregulated the expression of the ammonia-assimilating related genes in the mycelia, such as glutamate dehydrogenase (GDH), glutamate synthase (GOGAT), glutamine synthetase (GS), ammonia transporter protein (AMT), and amino acid transporter protein (AAT), while upregulating its own ammonia-assimilation genes. These findings suggest that the mechanism by which B12 promoted oyster mushroom growth was that B12 assimilated ammonia, alleviated ammonia stress, mitigated ROS accumulation in the mycelia, and supplied ammonia and amino acids to the mycelia. To our knowledge, ammonia-assimilating bacteria are a novel type of mushroom growth promoter (MGP).

Ammonia-Assimilating Bacteria Promote Wheat (Triticum aestivum) Growth and Nitrogen Utilization

Nitrogen fertilizers in agriculture often suffer losses. Ammonia-assimilating bacteria can immobilize ammonia and reduce these losses, but they have not been used in agriculture. This study identified an ammonia-assimilating strain, Enterobacter sp. B12, which assimilated ammonia via the glutamate dehydrogenase (GDH) pathway at low levels (5 mM) and the glutamine synthetase (GS)-glutamine-2-oxoglutarate aminotransferase (GOGAT) pathway at high levels (10 mM). Inoculating wheat with B12 increased seedling dry weight, nitrogen accumulation, rhizosphere soil nitrogen content, and root enzyme activities, including GDH, superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), under both conditions. However, root GS, GOGAT enzyme activities, and ammonia assimilation-related gene expressions were lower than the controls. The results suggest that the ammonia-assimilating bacterium promotes wheat growth, nitrogen accumulation, and soil nitrogen immobilization by establishing an ammonia and amino acid exchange with roots and enhancing root antioxidant capacity, making it a potential plant growth-promoting rhizobacteria (PGPR).

Arbuscular mycorrhizal fungi mediate soil N dynamics, mitigating N2O emissions and N-leaching while promoting crop N uptake in green manure systems

Arbuscular mycorrhizal fungi (AMF), as symbionts of the plant root system, play a pivotal ecological role in soil nutrient dynamics. However, the mechanisms by which AMF mediates nitrogen (N) transformation at the soil-crop interface, particularly under green manure management, remain insufficiently understood. This study investigates these mechanisms through a long-term field experiment, employing four green manure management practices during the flowering stage of common vetch: tillage with total green manure incorporation (TG), no-tillage with total green manure mulching (NTG), aboveground biomass removal with root incorporation (T), and aboveground biomass removal with no-tillage (NT), alongside a conventional tillage control without green manure (CT). Results indicate that NTG notably enhanced AMF abundance and dominant species, attributed largely to increases in soil available N, microbial biomass carbon (MBC), and soil pH. AMF colonization rates in maize roots peaked at 69.7 % under NTG. Additionally, soil mineral N was 17.7 % higher under NTG than TG, with aggregate N concentration increasing by 72.4 %. A strong positive correlation emerged between aggregate N and AMF colonization rates. NTG also significantly elevated nos Z gene abundance and nitrous oxide (N2O) reductase activity while lowering the (nir K +nir S) / nos Z ratio. Optimized root architecture under NTG was similarly correlated with AMF colonization, supporting N retention and uptake. Structural equation modeling further confirmed that aggregate N and root structure were primary contributors to reduced N leaching, while root architecture enhanced maize N uptake and N2O reductase activity. The increase in nos Z and N2O reductase reductase significantly reduced N2O emissions. In summary, no-tillage with green manure mulching effectively mitigated N loss and improved crop N uptake by enhancing AMF abundance and colonization.

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.

Independent and differential effects of arbuscular mycorrhizal fungal composition and plant pathogens on plant traits and nitrogen uptake

Arbuscular mycorrhizal fungi (AMF), as microbial mutualists, interact with various microbial taxa, including pathogens, and significantly shape the ecology and evolution of their host species. However, how AMF and pathogens jointly or independently affect plant traits and nitrogen uptake remains unclear. Here, we conducted a factorial experiment with three AMF treatments (AMF-free-control, Funneliformis mosseae, and a mixture of AMF species of F. mosseae and C. etunicatum), four plant-pathogen pairs, each under two pathogen treatments (one pathogen and a pathogen-free control). After 65 days of growth, we measured AMF colonization, pathogen infection, plant functional traits and ammonium and nitrate uptake. Our findings reveal that AMF and pathogens independently influence plant traits and nitrogen uptake, with no observed interactions between them. Specifically, colonization by F. mosseae or a mixed AMF species reduced nitrate uptake and plant height, without affecting root traits or ammonium uptake. In contrast, pathogen infection enhanced acquisitive root traits, such as increased specific root length and area but did not impact shoot traits or nitrogen uptake. These results broaden our understanding of the tripartite interactions among plants, AMF and pathogens, offering insights into how plant-microbial relationships influence plant health, growth and nitrogen cycling.

Cenococcum geophilum impedes cadmium toxicity in Pinus massoniana by modulating nitrogen metabolism

Nitrogen (N) is of great significance to the absorption, distribution and detoxification of cadmium (Cd). Ectomycorrhizal fungi (EMF) are able to affect the key processes of plant N uptake to resist Cd stress, while the mechanism is still unclear. Therefore, we explored potential strategies of Cenococcum geophilum (C. geophilum) symbiosis to alleviate Cd stress in Pinus massoniana (P. massoniana) from the perspective of plant N metabolism and soil N transformation. The results showed that inoculation of C. geophilum significantly increased the activities of NR, NiR and GS in the shoots and roots of P. massoniana, thereby promoting the assimilation of NO3- and NH4+ into amino acids. Moreover, C. geophilum promoted soil urease and protease activities, but decreased soil NH4+ content, indicating that C. geophilum might increase plant uptake of soil inorganic N. qRT-PCR results showed that C3 symbiosis significantly up-regulated the expression of genes encoding functions involved in NH4+ uptake (AMT3;1), NO3- uptake (NRT2.1, NRT2.4, NRT2.9), as well as Cd resistance (ABCC1 and ABCC2), meanwhile down-regulated the expression of NRT7.3, Cd transporter genes (HMA2 and NRAMP3) in the roots of P. massoniana seedlings. These results demonstrated that C. geophilum was able to alleviate Cd stress by increasing the absorption and assimilation of inorganic N in plants and inhibiting the transport of Cd from roots to shoots, which provided new insights into how EMF improved host resistance to abiotic stress.

Root physiological and soil microbial mechanisms underlying responses to nitrogen deficiency and compensation in Indica and Japonica rice

Compensatory effects are common biological phenomena in nature. In this study, we investigated the changes in root nitrogen uptake, root morphological and physiological responses, and changes in the rhizosphere soil microbial communities of indica and japonica rice during a nitrogen deficiency-sensitive period and an effective compensation period with double the nitrogen supply. We conducted a bucket experiment using Suxiu 867 (a japonica rice variety) and Yangxian You 918 (an indica rice variety). Treatments included CK (constant distribution of nitrogen fertilizer at each growth stage, represented by CK867 and CK918) and NDC (nitrogen deficiency in the tillering stage, double nitrogen application in the ear differentiation stage to compensate, represented by NDC867 and NDC918) variations. Both varieties presented the highest δ15N and 15N abundances and Ndff (refers to the proportion of nitrogen in a plant's body that comes directly from the fertilizer applied.) in rice under the NDC treatment. Metagenomic sequencing of rhizospheric soil showed that the dominant bacterial groups at the phylum level among each treatment were Actinobacteria, Proteobacteria, Chloroflexi, Acidobacteria, Gemmatimonadetes, and Nitrospirae. The rhizosphere of indica rice was more enriched with the microbial communities involved in nitrogen metabolism, which contributed to higher nitrogen utilization efficiency. A correlation-based network was constructed and provides insights into the formation of nitrogen deficiency compensation effects and contributes to the enhancement of nitrogen uptake and utilization efficiency in rice production.

Plasma membrane H+-ATPases in mineral nutrition and crop improvement

Plasma membrane H+-ATPases (PMAs) pump H+ out of the cytoplasm by consuming ATP to generate a membrane potential and proton motive force for the transmembrane transport of nutrients into and out of plant cells. PMAs are involved in nutrient acquisition by regulating root growth, nutrient uptake, and translocation, as well as the establishment of symbiosis with arbuscular mycorrhizas. Under nutrient stresses, PMAs are activated to pump more H+ and promote organic anion excretion, thus improving nutrient availability in the rhizosphere. Herein we review recent progress in the physiological functions and the underlying molecular mechanisms of PMAs in the efficient acquisition and utilization of various nutrients in plants. We also discuss perspectives for the application of PMAs in improving crop production and quality.

Functionality of arbuscular mycorrhizal fungi varies across different growth stages of maize under drought conditions

Physio-biochemical regulations governing crop growth period are pivotal for drought adaptation. Yet, the extent to which functionality of arbuscular mycorrhizal fungi (AM fungi) varies across different stages of maize growth under drought conditions remains uncertain. Therefore, periodic functionality of two different AM fungi i.e., Rhizophagus irregularis SUN16 and Glomus monosporum WUM11 were assessed at jointing, silking, and pre-harvest stages of maize subjected to different soil moisture gradients i.e., well-watered (80% SMC (soil moisture contents)), moderate drought (60% SMC), and severe drought (40% SMC). The study found that AM fungi significantly (p < 0.05) affected various morpho-physiological and biochemical parameters at different growth stages of maize under drought. As the plants matured, AM fungi enhanced root colonization, glomalin contents, and microbial biomass, leading to increased nutrient uptake and antioxidant activity. This boosted AM fungal activity ultimately improved photosynthetic efficiency, evident in increased photosynthetic pigments and photosynthesis. Notably, R. irregularis and G. monosporum improved water use efficiency and mycorrhizal dependency at critical growth stages like silking and pre-harvest, indicating their potential for drought resilience to stabilize yield. The principal component analysis highlighted distinct plant responses to drought across growth stages and AM fungi, emphasizing the importance of early-stage sensitivity. These findings underscore the potential of incorporating AM fungi into agricultural management practices to enhance physiological and biochemical responses, ultimately improving drought tolerance and yield in dryland maize cultivation.

Effects of nitrogen forms on Cd uptake and tolerance in wheat seedlings

Hydroponic experiment was conducted to explore the effects of two nitrogen (N) levels with five nitrate nitrogen (NO3--N) and ammonium nitrogen (NH4+-N) ratios on the growth status and Cd migration patterns of wheat seedlings under Cd5 and Cd30 level. Results showed that higher Cd were detrimental to the growth, absorption of K and Ca, expression of genes mediating NO3--N and NH4+-N transport, which also increased the content of malondialdehyde (MDA) and hydrogen peroxide (H2O2) in shoots and roots of wheat seedlings. Higher N treatment alleviated the inhibitory effects of Cd stress on the biomass, root development, photosynthesis and increased the tolerance index of wheat seedlings. The ratio of NO3--N and NH4+-N was the main factor driving Cd accumulation in wheat seedlings, the combined application of NH4+-N and NO3--N was more conducive for the growth, nitrogen assimilation and Cd tolerance to the Cd stressed wheat seedlings. Increased NO3--N application rates significantly up-regulated the expression levels of TaNPF2.12, TaNRT2.2, increased NH4+-N application rates significantly up-regulated the expression levels of TaAMT1.1. The high proportion of NO3--N promoted the absorption of K, Ca and Cd in the shoots and roots of wheat seedlings, while NH4+-N was the opposite. Under low Cd conditions, the NO3--N to NH4+-N ratio of 1:1 was more conducive to the growth of wheat seedlings, under high Cd stress, the optimal of NO3--N to NH4+-N was 1:2 for inhibiting the accumulation of Cd in wheat seedlings. The results indicated that increasing NH4+-N ratio appropriately could inhibit wheat Cd uptake by increasing NH4+, K+ and Ca2+ for K and Ca channels, and promote wheat growth by promoting N assimilation process.

Arbuscular mycorrhizal symbiosis modulates nitrogen uptake and assimilation to enhance drought tolerance of Populus cathayana

This study aims to investigate effects of arbuscular mycorrhizal fungi (AMF) inoculation on nitrogen (N) uptake and assimilation in Populus cathayana under drought stress (DS). Herein, we measured photosynthetic performance, antioxidant enzyme system, N level and N assimilation enzymes, proteins content and distribution, transcripts of genes associated with N uptake or transport in P. cathayana with AMF (AM) or without AMF (NM) under soil water limitation and adequate irrigation. Compared with NM-DS P. cathayana, the growth, gas exchange properties, antioxidant enzyme activities, total N content and the proportion of water-soluble and membrane-bound proteins in AM-DS P. cathayana were increased. Meanwhile, nitrate reductase (NR) activity, NO3- and NO2- concentrations in AM-DS P. cathayana were reduced, while NH4+ concentration, glutamine synthetase (GS) and glutamate synthetase (GOGAT) activities were elevated, indicating that AM symbiosis reduces NO3- assimilation while promoting NH4+ assimilation. Furthermore, the transcriptional levels of NH4+ transporter genes (PcAMT1-4 and PcAMT2-1) and NO3- transporter genes (PcNRT2-1 and PcNRT3-1) in AM-DS P. cathayana roots were significantly down-regulated, as well as NH4+ transporter genes (PcAMT1-6 and PcAMT4-3) in leaves. In AM P. cathayana roots, DS significantly up-regulated the transcriptional levels of RiCPSI and RiURE, the key N transport regulatory genes in AMF compared with adequate irrigation. These results indicated that AM N transport pathway play an essential role on N uptake and utilization in AM P. cathayana to cope with DS. Therefore, this research offers a novel perspective on how AM symbiosis enhances plant resilience to drought at aspect of N acquisition and assimilation.

Microbe-dependent and independent nitrogen and phosphate acquisition and regulation in plants

Nitrogen (N) and phosphorus (P) are the most important macronutrients required for plant growth and development. To cope with the limited and uneven distribution of N and P in complicated soil environments, plants have evolved intricate molecular strategies to improve nutrient acquisition that involve adaptive root development, production of root exudates, and the assistance of microbes. Recently, great advances have been made in understanding the regulation of N and P uptake and utilization and how plants balance the direct uptake of nutrients from the soil with the nutrient acquisition from beneficial microbes such as arbuscular mycorrhiza. Here, we summarize the major advances in these areas and highlight plant responses to changes in nutrient availability in the external environment through local and systemic signals.

Diversified molecular adaptations of inorganic nitrogen assimilation and signaling machineries in plants

Plants evolved sophisticated machineries to monitor levels of external nitrogen supply, respond to nitrogen demand from different tissues and integrate this information for coordinating its assimilation. Although roles of inorganic nitrogen in orchestrating developments have been studied in model plants and crops, systematic understanding of the origin and evolution of its assimilation and signaling machineries remains largely unknown. We expanded taxon samplings of algae and early-diverging land plants, covering all main lineages of Archaeplastida, and reconstructed the evolutionary history of core components involved in inorganic nitrogen assimilation and signaling. Most components associated with inorganic nitrogen assimilation were derived from the ancestral Archaeplastida. Improvements of assimilation machineries by gene duplications and horizontal gene transfers were evident during plant terrestrialization. Clusterization of genes encoding nitrate assimilation proteins might be an adaptive strategy for algae to cope with changeable nitrate availability in different habitats. Green plants evolved complex nitrate signaling machinery that was stepwise improved by domains shuffling and regulation co-option. Our study highlights innovations in inorganic nitrogen assimilation and signaling machineries, ranging from molecular modifications of proteins to genomic rearrangements, which shaped developmental and metabolic adaptations of plants to changeable nutrient availability in environments.

Phosphorus/nitrogen sensing and signaling in diverse root-fungus symbioses

Establishing mutualistic relationships between plants and fungi is crucial for overcoming nutrient deficiencies in plants. This review highlights the intricate nutrient sensing and uptake mechanisms used by plants in response to phosphate and nitrogen starvation, as well as their interactions with plant immunity. The coordination of transport systems in both host plants and fungal partners ensures efficient nutrient uptake and assimilation, contributing to the long-term maintenance of these mutualistic associations. It is also essential to understand the distinct responses of fungal partners to external nutrient levels and forms, as they significantly impact the outcomes of symbiotic interactions. Our review also highlights the importance of evolutionarily younger and newly discovered root-fungus associations, such as endophytic associations, which offer potential benefits for improving plant nutrition. Mechanistic insights into the complex dynamics of phosphorus and nitrogen sensing within diverse root-fungus associations can facilitate the identification of molecular targets for engineering symbiotic systems and developing plant phenotypes with enhanced nutrient use efficiency. Ultimately, this knowledge can inform tailored fertilizer management practices to optimize plant nutrition.

The role of arbuscular mycorrhizal symbiosis in plant abiotic stress

Arbuscular mycorrhizal fungi (AMF) can penetrate plant root cortical cells, establish a symbiosis with most land plant species, and form branched structures (known as arbuscules) for nutrient exchange. Plants have evolved a complete plant-AMF symbiosis system to sustain their growth and development under various types of abiotic stress. Here, we highlight recent studies of AM symbiosis and the regulation of symbiosis process. The roles of mycorrhizal symbiosis and host plant interactions in enhancing drought resistance, increasing mineral nutrient uptake, regulating hormone synthesis, improving salt resistance, and alleviating heavy metal stress were also discussed. Overall, studies of AM symbiosis and a variety of abiotic stresses will aid applications of AMF in sustainable agriculture and can improve plant production and environmental safety.

The arbuscular mycorrhizal fungus Rhizophagus irregularis uses the copper exporting ATPase RiCRD1 as a major strategy for copper detoxification

Arbuscular mycorrhizal (AM) fungi establish a mutualistic symbiosis with most land plants. AM fungi regulate plant copper (Cu) acquisition both in Cu deficient and polluted soils. Here, we report characterization of RiCRD1, a Rhizophagus irregularis gene putatively encoding a Cu transporting ATPase. Based on its sequence analysis, RiCRD1 was identified as a plasma membrane Cu + efflux protein of the P1B1-ATPase subfamily. As revealed by heterologous complementation assays in yeast, RiCRD1 encodes a functional protein capable of conferring increased tolerance against Cu. In the extraradical mycelium, RiCRD1 expression was highly up-regulated in response to high concentrations of Cu in the medium. Comparison of the expression patterns of different players of metal tolerance in R. irregularis under high Cu levels suggests that this fungus could mainly use a metal efflux based-strategy to cope with Cu toxicity. RiCRD1 was also expressed in the intraradical fungal structures and, more specifically, in the arbuscules, which suggests a role for RiCRD1 in Cu release from the fungus to the symbiotic interface. Overall, our results show that RiCRD1 encodes a protein which could have a pivotal dual role in Cu homeostasis in R. irregularis, playing a role in Cu detoxification in the extraradical mycelium and in Cu transfer to the apoplast of the symbiotic interface in the arbuscules.

Molecular and Systems Biology Approaches for Harnessing the Symbiotic Interaction in Mycorrhizal Symbiosis for Grain and Oil Crop Cultivation

Mycorrhizal symbiosis, the mutually beneficial association between plants and fungi, has gained significant attention in recent years due to its widespread significance in agricultural productivity. Specifically, arbuscular mycorrhizal fungi (AMF) provide a range of benefits to grain and oil crops, including improved nutrient uptake, growth, and resistance to (a)biotic stressors. Harnessing this symbiotic interaction using molecular and systems biology approaches presents promising opportunities for sustainable and economically-viable agricultural practices. Research in this area aims to identify and manipulate specific genes and pathways involved in the symbiotic interaction, leading to improved cereal and oilseed crop yields and nutrient acquisition. This review provides an overview of the research frontier on utilizing molecular and systems biology approaches for harnessing the symbiotic interaction in mycorrhizal symbiosis for grain and oil crop cultivation. Moreover, we address the mechanistic insights and molecular determinants underpinning this exchange. We conclude with an overview of current efforts to harness mycorrhizal diversity to improve cereal and oilseed health through systems biology.

Nutrient-dependent cross-kingdom interactions in the hyphosphere of an arbuscular mycorrhizal fungus

Introduction

The hyphosphere of arbuscular mycorrhizal (AM) fungi is teeming with microbial life. Yet, the influence of nutrient availability or nutrient forms on the hyphosphere microbiomes is still poorly understood.

Methods

Here, we examined how the microbial community (prokaryotic, fungal, protistan) was affected by the presence of the AM fungus Rhizophagus irregularis in the rhizosphere and the root-free zone, and how different nitrogen (N) and phosphorus (P) supplements into the root-free compartment influenced the communities.

Results

The presence of AM fungus greatly affected microbial communities both in the rhizosphere and the root-free zone, with prokaryotic communities being affected the most. Protists were the only group of microbes whose richness and diversity were significantly reduced by the presence of the AM fungus. Our results showed that the type of nutrients AM fungi encounter in localized patches modulate the structure of hyphosphere microbial communities. In contrast we did not observe any effects of the AM fungus on (non-mycorrhizal) fungal community composition. Compared to the non-mycorrhizal control, the root-free zone with the AM fungus (i.e., the AM fungal hyphosphere) was enriched with Alphaproteobacteria, some micropredatory and copiotroph bacterial taxa (e.g., Xanthomonadaceae and Bacteroidota), and the poorly characterized and not yet cultured Acidobacteriota subgroup GP17, especially when phytate was added. Ammonia-oxidizing Nitrosomonas and nitrite-oxidizing Nitrospira were significantly suppressed in the presence of the AM fungus in the root-free compartment, especially upon addition of inorganic N. Co-occurrence network analyses revealed that microbial communities in the root-free compartment were complex and interconnected with more keystone species when AM fungus was present, especially when the root-free compartment was amended with phytate.

Conclusion

Our study showed that the form of nutrients is an important driver of prokaryotic and eukaryotic community assembly in the AM fungal hyphosphere, despite the assumed presence of a stable and specific AM fungal hyphoplane microbiome. Predictable responses of specific microbial taxa will open the possibility of using them as co-inoculants with AM fungi, e.g., to improve crop performance.

Identification and functional characterization of the sugarcane (Saccharum spp.) AMT2-type ammonium transporter ScAMT3;3 revealed a presumed role in shoot ammonium remobilization

Sugarcane (Saccharum spp.) is an important crop for sugar and bioethanol production worldwide. To maintain and increase sugarcane yields in marginal areas, the use of nitrogen (N) fertilizers is essential, but N overuse may result in the leaching of reactive N to the natural environment. Despite the importance of N in sugarcane production, little is known about the molecular mechanisms involved in N homeostasis in this crop, particularly regarding ammonium (NH4 +), the sugarcane's preferred source of N. Here, using a sugarcane bacterial artificial chromosome (BAC) library and a series of in silico analyses, we identified an AMMONIUM TRANSPORTER (AMT) from the AMT2 subfamily, sugarcane AMMONIUM TRANSPORTER 3;3 (ScAMT3;3), which is constitutively and highly expressed in young and mature leaves. To characterize its biochemical function, we ectopically expressed ScAMT3;3 in heterologous systems (Saccharomyces cerevisiae and Arabidopsis thaliana). The complementation of triple mep mutant yeast demonstrated that ScAMT3;3 is functional for NH3/H+ cotransport at high availability of NH4 + and under physiological pH conditions. The ectopic expression of ScAMT3;3 in the Arabidopsis quadruple AMT knockout mutant restored the transport capacity of 15N-NH4 + in roots and plant growth under specific N availability conditions, confirming the role of ScAMT3;3 in NH4 + transport in planta. Our results indicate that ScAMT3;3 belongs to the low-affinity transport system (Km 270.9 µM; Vmax 209.3 µmol g-1 root DW h-1). We were able to infer that ScAMT3;3 plays a presumed role in NH4 + source-sink remobilization in the shoots via phloem loading. These findings help to shed light on the functionality of a novel AMT2-type protein and provide bases for future research focusing on the improvement of sugarcane yield and N use efficiency.

Mycorrhizal status and host genotype interact to shape plant nutrition in field grown maize (Zea mays ssp. mays)

Arbuscular mycorrhizal fungi (AMF) establish symbioses with the major cereal crops, providing plants with increased access to nutrients while enhancing their tolerance to toxic heavy metals. However, not all plant varieties benefit equally from this association. In this study, we used quantitative trait loci (QTL) mapping to evaluate the combined effect of host genotypic variation (G) and AMF across 141 genotypes on the concentration of 20 mineral elements in the leaves and grain of field grown maize (Zea mays spp. mays). Our mapping design included selective incorporation of a castor AMF-incompatibility mutation, allowing estimation of AMF, QTL and QTLxAMF effects by comparison of mycorrhizal and non-mycorrhizal plants. Overall, AMF compatibility was associated with higher concentrations of boron (B), copper (Cu), molybdenum (Mo), phosphorus (P), selenium (Se) and zinc (Zn) and lower concentrations of arsenic (As), iron (Fe), magnesium (Mg), manganese (Mn), potassium (K) and strontium (Sr). In addition to effects on individual elements, pairwise correlation matrices for element concentration differed between mycorrhizal and non-mycorrhizal plants. We mapped 22 element QTLs, including 18 associated with QTLxAMF effects that indicate plant genotype-specific differences in the impact of AMF on the host ionome. Although there is considerable interest in AMF as biofertilizers, it remains challenging to estimate the impact of AMF in the field. Our design illustrates an effective approach for field evaluation of AMF effects. Furthermore, we demonstrate the capacity of the ionome to reveal host genotype-specific variation in the impact of AMF on plant nutrition.

Root phenotypes for improved nitrogen capture

Background

Suboptimal nitrogen availability is a primary constraint for crop production in low-input agroecosystems, while nitrogen fertilization is a primary contributor to the energy, economic, and environmental costs of crop production in high-input agroecosystems. In this article we consider avenues to develop crops with improved nitrogen capture and reduced requirement for nitrogen fertilizer.

Scope

Intraspecific variation for an array of root phenotypes has been associated with improved nitrogen capture in cereal crops, including architectural phenotypes that colocalize root foraging with nitrogen availability in the soil; anatomical phenotypes that reduce the metabolic costs of soil exploration, improve penetration of hard soil, and exploit the rhizosphere; subcellular phenotypes that reduce the nitrogen requirement of plant tissue; molecular phenotypes exhibiting optimized nitrate uptake kinetics; and rhizosphere phenotypes that optimize associations with the rhizosphere microbiome. For each of these topics we provide examples of root phenotypes which merit attention as potential selection targets for crop improvement. Several cross-cutting issues are addressed including the importance of soil hydrology and impedance, phenotypic plasticity, integrated phenotypes, in silico modeling, and breeding strategies using high throughput phenotyping for co-optimization of multiple phenes.

Conclusions

Substantial phenotypic variation exists in crop germplasm for an array of root phenotypes that improve nitrogen capture. Although this topic merits greater research attention than it currently receives, we have adequate understanding and tools to develop crops with improved nitrogen capture. Root phenotypes are underutilized yet attractive breeding targets for the development of the nitrogen efficient crops urgently needed in global agriculture.

Arbuscular mycorrhizal fungi-induced tolerance to chromium stress in plants

Chromium (Cr) is one of the toxic elements that harms all forms of life, including plants. Industrial discharges and mining largely contribute to Cr release into the soil environment. Excessive Cr pollution in arable land significantly reduces the yield and quality of important agricultural crops. Therefore, remediation of polluted soil is imperative not only for agricultural sustainability but also for food safety. Arbuscular mycorrhizal fungi (AMF) are widespread soil-borne endophytic fungi that form mutualistic relationships with the vast majority of land plants. In mycorrhizal symbiosis, AMF are largely dependent on the host plant-supplied carbohydrates and lipids, in return, AMF aid the host plants in acquiring water and mineral nutrients, especially phosphorus, nitrogen and sulfur from distant soils, and this distinguishing feature of the two-way exchange of resources is a functional requirement for such mutualism and ecosystem services. In addition to supplying nutrients and water to plants, the AMF symbiosis enhances plant resilience to biotic and abiotic stresses including Cr stress. Studies have revealed vital physiological and molecular mechanisms by which AMF alleviate Cr phytotoxicity and aid plants in nutrient acquisition under Cr stress. Notably, plant Cr tolerance is enhanced by both the direct effects of AMF on Cr stabilization and transformation, and the indirect effects of AMF symbiosis on plant nutrient uptake and physiological regulation. In this article, we summarized the research progress on AMF and associated mechanisms of Cr tolerance in plants. In addition, we reviewed the present understanding of AMF-assisted Cr remediation. Since AMF symbiosis can enhance plant resilience to Cr pollution, AMF may have promising prospects in agricultural production, bioremediation, and ecological restoration in Cr-polluted soils.

Analysis of the AMT gene family in chili pepper and the effects of arbuscular mycorrhizal colonization on the expression patterns of CaAMT2 genes

BACKGROUND

Ammonium (NH₄⁺) is a key nitrogen source supporting plant growth and development. Proteins in the ammonium transporter (AMT) family mediate the movement of NH₄⁺ across the cell membrane. Although several studies have examined AMT genes in various plant species, few studies of the AMT gene family have been conducted in chili pepper.

RESULTS

Here, a total of eight AMT genes were identified in chili pepper, and their exon/intron structures, phylogenetic relationships, and expression patterns in response to arbuscular mycorrhizal (AM) colonization were explored. Synteny analyses among chili pepper, tomato, eggplant, soybean, and Medicago revealed that the CaAMT2;1, CaAMT2.4, and CaAMT3;1 have undergone an expansion prior to the divergence of Solanaceae and Leguminosae. The expression of six AMT2 genes was either up-regulated or down-regulated in response to AM colonization. The expression of CaAMT2;1/2;2/2;3 and SlAMT2;1/2;2/2;3 was significantly up-regulated in AM fungi-inoculated roots. A 1,112-bp CaAMT2;1 promoter fragment and a 1,400-bp CaAMT2;2 promoter fragment drove the expression of the β-glucuronidase gene in the cortex of AM roots. Evaluation of AM colonization under different NH₄⁺ concentrations revealed that a sufficient, but not excessive, supply of NH₄⁺ promotes the growth of chili pepper and the colonization of AM. Furthermore, we demonstrated that CaAMT2;2 overexpression could mediate NH₄⁺ uptake in tomato plants.

CONCLUSION

In sum, our results provide new insights into the evolutionary relationships and functional divergence of chili pepper AMT genes. We also identified putative AMT genes expressed in AM symbiotic roots.

Genome-Wide Identification and Characterization of Ammonium Transporter (AMT) Genes in Rapeseed (Brassica napus L.)

Ammonium transporters (AMTs) are plasma membrane proteins mediating ammonium uptake and transport. As such, AMTs play vital roles in ammonium acquisition and mobilization, plant growth and development, and stress and pathogen defense responses. Identification of favorable AMT genotypes is a prime target for crop improvement. However, to date, systematic identification and expression analysis of AMT gene family members has not yet been reported for rapeseed (Brassica napus L.). In this study, 20 AMT genes were identified in a comprehensive search of the B. napus genome, 14 members of AMT1 and 6 members of AMT2. Tissue expression analyses revealed that the 14 AMT genes were primarily expressed in vegetative organs, suggesting that different BnaAMT genes might function in specific tissues at the different development stages. Meanwhile, qRT-PCR analysis found that several BnaAMTs strongly respond to the exogenous N conditions, implying the functional roles of AMT genes in ammonium absorption in rapeseed. Moreover, the rapeseed AMT genes were found to be differentially regulated by N, P, and K deficiency, indicating that crosstalk might exist in response to different stresses. Additionally, the subcellular localization of several BnaAMT proteins was confirmed in Arabidopsis protoplasts, and their functions were studied in detail by heterologous expression in yeast. In summary, our studies revealed the potential roles of BnaAMT genes in N acquisition or transportation and abiotic stress response and could provide valuable resources for revealing the functionality of AMTs in rapeseed.

Proteomics as a tool to decipher plant responses in arbuscular mycorrhizal interactions: a meta-analysis

The beneficial symbiosis between plants and arbuscular mycorrhizal (AM) fungi leads to a deep reprogramming of plant metabolism, involving the regulation of several molecular mechanisms, many of which are poorly characterized. In this regard, proteomics is a powerful tool to explore changes related to plant-microbe interactions. This study provides a comprehensive proteomic meta-analysis conducted on AM-modulated proteins at local (roots) and systemic (shoots/leaves) level. The analysis was implemented by an in-depth study of root membrane-associated proteins and by a comparison with a transcriptome meta-analysis. A total of 4262 differentially abundant proteins were retrieved and, to identify the most relevant AM-regulated processes, a range of bioinformatic studies were conducted, including functional enrichment and protein-protein interaction network analysis. In addition to several protein transporters which are present in higher amounts in AM plants, and which are expected due to the well-known enhancement of AM-induced mineral uptake, our analysis revealed some novel traits. We detected a massive systemic reprogramming of translation with a central role played by the ribosomal translational apparatus. On one hand, these new protein-synthesis efforts well support the root cellular re-organization required by the fungal penetration, and on the other they have a systemic impact on primary metabolism.

A transcriptional activator from Rhizophagus irregularis regulates phosphate uptake and homeostasis in AM symbiosis during phosphorous starvation

Introduction

Phosphorus (P) is one of the most important nutrient elements for plant growth and development. Under P starvation, arbuscular mycorrhizal (AM) fungi can promote phosphate (Pi) uptake and homeostasis within host plants. However, the underlying mechanisms by which AM fungal symbiont regulates the AM symbiotic Pi acquisition from soil under P starvation are largely unknown. Here, we identify a HLH domain containing transcription factor RiPho4 from Rhizophagus irregularis.

Methods

To investigate the biological functions of the RiPho4, we combined the subcellular localization and Yeast One-Hybrid (Y1H) experiments in yeasts with gene expression and virus-induced gene silencing approach during AM symbiosis.

Results

The approach during AM symbiosis. The results indicated that RiPho4 encodes a conserved transcription factor among different fungi and is induced during the in planta phase. The transcription of RiPho4 is significantly up-regulated by P starvation. The subcellular localization analysis revealed that RiPho4 is located in the nuclei of yeast cells during P starvation. Moreover, knock-down of RiPho4 inhibits the arbuscule development and mycorrhizal Pi uptake under low Pi conditions. Importantly, RiPho4 can positively regulate the downstream components of the phosphate (PHO) pathway in R. irregularis.

Discussion

In summary, these new findings reveal that RiPho4 acts as a transcriptional activator in AM fungus to maintain arbuscule development and regulate Pi uptake and homeostasis in the AM symbiosis during Pi starvation.

The RNAome landscape of tomato during arbuscular mycorrhizal symbiosis reveals an evolving RNA layer symbiotic regulatory network

Arbuscular mycorrhizal symbiosis (AMS) is an ancient plant-fungus relationship that is widely distributed in terrestrial plants. The formation of symbiotic structures and bidirectional nutrient exchange requires the regulation of numerous genes. However, the landscape of RNAome during plant AMS involving different types of regulatory RNA is poorly understood. In this study, a combinatorial strategy utilizing multiple sequencing approaches was used to decipher the landscape of RNAome in tomato, an emerging AMS model. The annotation of the tomato genome was improved by a multiple-platform sequencing strategy. A total of 3,174 protein-coding genes were upregulated during AMS, 42% of which were alternatively spliced. Comparative-transcriptome analysis revealed that genes from 24 orthogroups were consistently induced by AMS in eight phylogenetically distant angiosperms. Seven additional orthogroups were specifically induced by AMS in all surveyed dicot AMS host plants. However, these orthogroups were absent or not induced in monocots and/or non-AMS hosts, suggesting a continuously evolving AMS-responsive network in addition to a conserved core regulatory module. Additionally, we detected 587 lncRNAs, ten miRNAs, and 146 circRNAs that responded to AMS, which were incorporated to establish a tomato AMS-responsive, competing RNA-responsive endogenous RNA (ceRNA) network. Finally, a tomato symbiotic transcriptome database (TSTD, https://efg.nju.edu.cn/TSTD) was constructed to serve as a resource for deep deciphering of the AMS regulatory network. These results help elucidate the reconfiguration of the tomato RNAome during AMS and suggest a sophisticated and evolving RNA layer responsive network during AMS processes.

Genome-wide identification, expression profiling, and functional analysis of ammonium transporter 2 (AMT2) gene family in cassava (Manihot esculenta crantz)

Background: Nitrogen (N), absorbed primarily as ammonium (NH₄ ⁺) from soil by plant, is a necessary macronutrient in plant growth and development. Ammonium transporter (AMT) plays a vital role in the absorption and transport of ammonium (NH₄ ⁺). Cassava (Manihot esculenta Crantz) has a strong adaptability to nitrogen deprivation. However, little is known about the functions of ammonium transporter AMT2 in cassava. Methods: The cassava AMT2-type genes were identified and their characteristics were analyzed using bioinformatic techniques. The spatial expression patterns were analyzed based on the public RNA-seq data and their expression profiles under low ammonium treatment were studied using Real-time quantitative PCR (RT-qPCR) method. The cassava AMT2 genes were transformed into yeast mutant strain TM31019b by PEG/LiAc method to investigate their functions. Results: Seven AMT2-type genes (MeAMT2.1-2.7) were identified in cassava and they were distributed on 6 chromosomes and included two segmental duplication events (MeAMT2.2/MeAMT2.4 and MeAMT2.3/MeAMT2.5). Based on their amino acid sequences, seven MeAMT2 were further divided into four subgroups, and each subgroup contained similar motif constitution and protein structure. Synteny analysis showed that two and four MeAMT2 genes in cassava were collinear with those in the Arabidopsis and soybean genomes, respectively. Sixteen types of cis-elements were identified in the MeAMT2 promoters, and they were related to light-, hormone-, stress-, and plant growth and development-responsive elements, respectively. Most of the MeAMT2 genes displayed tissue-specific expression patterns according to the RNA-seq data, of them, three MeAMT2 (MeAMT2.3, MeAMT2.5, and MeATM2.6) expressions were up-regulated under ammonium deficiency. Complementation experiments showed that yeast mutant strain TM31019b transformed with MeAMT2.3, MeAMT2.5, or MeATM2.6 grew better than untransgenic yeast cells under ammonium deficiency, suggesting that MeAMT2.3, MeAMT2.5, and MeATM2.6 might be the main contributors in response to ammonium deficiency in cassava. Conclusion: This study provides a basis for further study of nitrogen efficient utilization in cassava.

Aboveground herbivory does not affect mycorrhiza-dependent nitrogen acquisition from soil but inhibits mycorrhizal network-mediated nitrogen interplant transfer in maize

Arbuscular mycorrhizal fungi (AMF) are considered biofertilizers for sustainable agriculture due to their ability to facilitate plant uptake of important mineral elements, such as nitrogen (N). However, plant mycorrhiza-dependent N uptake and interplant transfer may be highly context-dependent, and whether it is affected by aboveground herbivory remains largely unknown. Here, we used ¹⁵N labeling and tracking to examine the effect of aboveground insect herbivory by Spodoptera frugiperda on mycorrhiza-dependent N uptake in maize (Zea mays L.). To minimize consumption differences and ¹⁵N loss due to insect chewing, insect herbivory was simulated by mechanical wounding and oral secretion of S. frugiperda larvae. Inoculation with Rhizophagus irregularis (Rir) significantly improved maize growth, and N/P uptake. The ¹⁵N labeling experiment showed that maize plants absorbed N from soils via the extraradical mycelium of mycorrhizal fungi and from neighboring plants transferred by common mycorrhizal networks (CMNs). Simulated aboveground leaf herbivory did not affect mycorrhiza-mediated N acquisition from soil. However, CMN-mediated N transfer from neighboring plants was blocked by leaf simulated herbivory. Our findings suggest that aboveground herbivory inhibits CMN-mediated N transfer between plants but does not affect N acquisition from soil solutions via extraradical mycorrhizal mycelium.