Arbuscular mycorrhizal symbiosis enhances the drought tolerance of Populus cathayana by modulating glutamate and lysine metabolism

Arbuscular mycorrhizal symbiosis (AMS) is a ubiquitous mutualistic interaction between many terrestrial plants and fungi, with lipids playing a pivotal role in nutrient exchange. However, few genetic regulators of AMS have been functionally validated in tomato. To investigate candidate genes, we employed CRISPR-Cas9 and VIGS to generate knockout and knockdown lines. A comprehensive suite of molecular biology techniques, including yeast-1/2-hybridization, BiFC, ChIP-qPCR, and RNA-sequencing, was used to elucidate the regulatory roles of SlWRI5a, SlHY5, and SlFatM in fatty acid (FA) biosynthesis and AMS in tomato. FA composition was analyzed using gas chromatography. In this study, we validated SlWRI5a and SlFatM as key regulators of 16-carbon FA biosynthesis during AMS in tomato and demonstrated physical interactions between SlWRI5a and SlHY5. SlHY5 expression was induced by AMS and promoted root FA biosynthesis. Finally, we demonstrated that SlWRI5a and SlHY5 can co-regulate SlFatM-mediated FA accumulation, thereby influencing AMF colonization efficiency in tomato. Our findings reveal the SlWRI5a/SlHY5-SlFatM regulatory module, offering new insights into lipid-mediated AMS in tomato. This work also highlights a novel role for HY5 during fungal symbiosis, underscoring its broader significance in plant-microbe interactions.

Recent evidence shows that arbuscular mycorrhizal (AM) symbiosis, as defined by the presence of arbuscules, is established by two distinct fungal groups, with the distinctive 'fine root endophyte' morphotype formed by fungi from the subphylum Mucoromycotina rather than the sub-phylum Glomeromycotina. While FRE forming fungi are globally distributed, there is currently no understanding of the genomic basis for their symbiosis or how this symbiosis compares to that of other mycorrhizal symbionts. We used culture-independent metagenome sequencing to assemble and characterise the metagenome-assembled genome (MAG) of a putative arbuscule forming fine root endophyte, which we show belonged to the family Planticonsortiaceae within the order Densosporales. The MAG shares key traits with Glomeromycotina fungi, which indicate obligate biotrophy, including the absence of fatty acid and thiamine biosynthesis pathways, limited enzymatic abilities to degrade plant cell walls, and a high abundance of calcium transporters. In contrast to Glomeromycotina fungi, it exhibits a higher capacity for degradation of microbial cell walls, a complete cellulose degradation pathway, low abundances of copper, nitrate and ammonium transporters, and a complete pathway for vitamin B6 biosynthesis. These differences, particularly those typically associated with saprotrophic functions, highlight the potential for contrasting interactions between Mucoromycotina and Glomeromycotina fungi with their host plant and the environment. In turn, this could support niche differentiation in resource acquisition and complementary ecological functions.

Translating the nitrogen-fixing ability of legume-rhizobia symbiosis to other crops has long been a dream for molecular biologists. Over the past two decades, several crucial genes involved in the pathway have been identified, that prevails as an intricate network governing root nodule symbiosis (RNS). RNS signaling employs the common symbiotic signaling pathway required for Arbuscular Mycorrhizal (AM) symbiosis (plant-fungal symbiosis) that is widely known in several crop plants. Therefore, understanding the similarities and divergence between the two signaling pathways has always been a hotspot for research. The major adjuvants in the RNS pathway are the Nod Factor Receptors (NFRs - that perceive Nod Factors released by rhizobia), and a Nodule-INception protein (NIN - a transcription factor that activates cortical cell division), which direct the pathway from AMS towards RNS. Therefore, understanding the structure and the signaling mechanism(s) of NFRs and NIN is crucial for the success of translational approaches. In this article, we will be highlighting the most recent discoveries pertaining to the functionality of NFRs, which have taken us a few steps closer towards receptor engineering into non-nodulating plants.

Summary statementUnderstanding how plants orchestrate nutrient exchange within arbuscular mycorrhizal symbiosis is critical for sustainable agriculture. Here, we discuss the RAM1‐WRI transcriptional complex as a central hub governing this process, likely have conserved for 450 million years.

Cell division and specification are crucial for plant development and coping with diverse environmental cues. Most land plants rely on symbiosis with arbuscular mycorrhizal (AM) fungi to cope with soil nutrient limitations by forming arbuscules in root inner cortex cells. What determines the AM susceptibility of these inner cortex cells is currently unknown. Here we show that DELLA transcriptional regulators control the number of inner cortex cells with an AM-susceptible identity at the root stem cell niche of Medicago truncatula in a dose-dependent manner. Genetic analyses suggest that this activity converges with the well-known mobile SHORT-ROOT transcription factor regulating ground tissue development. Furthermore, we show that MtDELLA1 protein moves from the stele/endodermis to the cortex in the mature part of the root to facilitate arbuscule formation. We propose that the formation of a root inner cortex cell identity controlled by mobile DELLA and SHORT-ROOT is a fundamental basis for AM symbiosis.

This study reveals lipid-related metabolic rewiring in tomato roots during arbuscular mycorrhizal symbiosis, identifying potential candidate lipids for fungal carbon transfer and signaling. Arbuscular mycorrhizal (AM) symbiosis induces substantial metabolic rearrangement in host plants to facilitate nutrient exchange and symbiotic efficiency. While previous metabolomic studies have characterized metabolite shifts in AM symbiosis, the lipid-related metabolic rewiring underlying nutrient exchange in host plant roots remains poorly resolved. Here, we investigated the metabolic response in tomato roots colonized by AM fungi. A total of 219 differentially accumulated metabolites (DAMs) were identified by the ultra-high-performance liquid chromatography-tandem mass spectrometry analysis, with lipids and lipid-like molecules representing the predominant classes. The most significantly upregulated metabolite was 2-(14,15-epoxyeicosatrienoyl) glycerol, a 2-monoacylglycerols (2-MAGs) mapped to arachidonic acid metabolism. This compound represents a C20-based epoxy fatty acid-derived 2-MAG, distinct from the C16:0 2-MAG induced by AM symbiosis in legumes, thereby implying the possibility of transferring diverse lipid substrates from different host plants to AM fungi. Concurrently, enhanced accumulation of dihomo-γ-linolenic acid (DGLA) and arachidonic acid (ARA) in AM fungi colonized roots underscored alterations of arachidonic acid metabolism and unsaturated fatty acid pathway. Gene set enrichment analysis based on the transcriptome data revealed significant transition of the glycerophospholipid metabolism pathway, primarily driven by multiple lysophosphatidylcholine (LPC) species that showed significant upregulation. Integrated transcriptomic and metabolomic analysis identified 31 overlapping KEGG pathways, emphasizing the importance of lipid and amino acid metabolism. In summary, our integrated analysis demonstrates that lipid-related metabolic reprogramming, represented by the induction of 2-MAGs and LPCs, is a feature of AM symbiosis that enables cross-kingdom nutrient exchange and host metabolic adaptation.

Arbuscular mycorrhizal (AM) symbiosis is an ancient association that played a key role in the adaptation of plants to terrestrial environments. Originating over 400 million years ago at the dawn of land plants, this interaction depends on a core set of conserved genes that enable hosts to establish and maintain symbiotic relationships with AM fungi. The AM symbiotic program includes distinct genetic components for each stage of development, from signal perception to nutrient exchange. While AM-host plants have retained key genes dedicated to symbiosis, non-host lineages have independently lost these genes multiple times over evolutionary history. Recent studies in the liverwort Marchantia paleacea demonstrate that core mechanisms underlying AM symbiosis are conserved from bryophytes to angiosperms. Comparative genomic studies continue to uncover how symbiosis-specific genes are integrated with broadly conserved cellular machinery to sustain this interaction. Understanding these deeply conserved genetic modules is essential for uncovering the evolutionary foundations of plant-microbe associations and for harnessing their potential in sustainable agriculture.

Arbuscular mycorrhizal symbiosis (AMS) is a ubiquitous and ancient interaction between plant root systems and fungi of the Glomeromycotina subphylum. The resulting relationship is mutually beneficial and deeply intimate where the fungus intracellularly colonises root cortex cells to receive organic carbon and deliver minerals and water to the plant. Fungal colonisation of plant roots and cells is extremely dynamic and asynchronous across the root system. Symbiosis development must therefore result from spatio-temporally fine-tuned molecular control mechanisms of plant and fungus. Although the plant genetic program underpinning AMS has been extensively studied, little is known about its dynamic regulation across root cell layers and developmental stages of the association. Thus, many questions remain outstanding: how do different cell-types transcriptionally respond to AMS, how are distinct cell-type specific regulatory states coordinated, and what are the transcriptional activities in the fungus associated with discrete stages of root colonisation? The advent of single cell-based techniques now enables the high-resolution analysis to address these questions. In this review, we recapitulate the current knowledge on the spatio-temporal control of AMS, we evaluate the relevance of existing spatial datasets to AMS research and provide new perspectives for future study.

Symbiosis with arbuscular mycorrhizal (AM) fungi is a crucial strategy for plant adaptation to low phosphorus (P) stress. However, the mechanisms underlying how phosphate (Pi) signaling regulators participate in AM colonization remain largely unknown in soybean (Glycine max). In this study, the expression of GmSPX5, one member of the SPX (SYG1/Pho81/XPR1) family, was induced by AM fungal inoculation in soybean roots. Furthermore, the expression of GmSPX5 seems to overlap with AM infection structures through analyzing GUS activity of transgenic soybean plants harboring ProGmSPX5:GUS. Four transgenic lines with GmSPX5 overexpression (OX8 and OX12) and suppression (Ri9 and Ri11) were subsequently used to examine the functions of GmSPX5 on AM symbiosis and Pi acquisition. Despite no difference between Ri and wild-type (WT), the overexpression of GmSPX5 significantly increased AM colonization as reflected by 8.4% in OX8 and 8.7% in OX12, respectively. Consistently, the dry weight and total P content of OX8 and OX12 were higher than WT. Furthermore, a total of 3483 genes were found to exhibit differential expression patterns in roots between OX12 and WT, including genes related to linolenic acid metabolism and flavonoid metabolism. Meanwhile, the composition of the bacterial community in the roots of OX12 was distinct from that in WT through β-diversity analysis. Particularly, an ASV19 (Sphingomonadales) was enriched in OX12 roots, which was positively related to total P content and AM fungi colonization. Taken together, these results highlight that GmSPX5 can regulate AM symbiosis, as well as Pi acquisition in soybean. Our findings advance the understanding of SPX functions in plant-microbe interaction.

Potassium uptake function of LbKT1 and LbSKOR from Lycium barbarum and their influence on the arbuscular mycorrhizal symbiosis.

Trade-offs between arbuscular mycorrhizal symbiosis and root hairs in phosphorus source utilization are determined by functional divergence of the rhizosphere bacterial microbiome in barley

Bidirectional interference between nanoplastics and arsenic in arbuscular mycorrhizal symbiosis: Reciprocal modulation of uptake, transformation and translocation.

Most terrestrial plants establish symbiotic relationships with microorganisms to acquire nutrients and simultaneously restrict pathogen infection. In rice, the receptor-like kinase OsARK1 is essential for the colonization and development of arbuscular mycorrhizal (AM) fungi. However, whether OsARK1 participates in plant–pathogen interactions remain unknown. Here, we demonstrate that OsARK1 is involved in the transcriptional reprogramming of immune defense-related genes prior to and following AM colonization. Mutation of OsARK1 resulted in increased susceptibility to Magnaporthe oryzae (blast fungus) and Xanthomonas oryzae (bacterial blight). Transcriptomic profiling during blast infection demonstrated OsARK1 coordinates early immune responses; particularly, the upregulation of genes encoding lectin receptor-like kinases (LecRLKs), nucleotide-binding leucine-rich repeat (NLR) immune receptors and secondary metabolism-related genes was significantly impaired in Osark1 mutant. Collectively, OsARK1 acts as a positive regulator of rice immunity against pathogens while fine-tuning defense suppression during beneficial AM symbiosis.

SummaryMost land plants form the ancient arbuscular mycorrhizal (AM) symbiosis, while carnivory is a younger trait that evolved in several angiosperm orders. The two biotic interactions similarly help plants acquire mineral nutrients, raising the question of whether they can coexist. However, the mycorrhizal status of carnivorous plants has long remained speculative.We surveyed the occurrence of AM‐associated genes across carnivorous plant lineages, performed AM fungal inoculation assays, and microscopically evaluated the patterns of colonization.We found convergent losses of the AM trait either coincident with or predating the emergence of carnivory. Exceptionally, the carnivorous plant Roridula gorgonias retains symbiosis‐related genes and forms arbuscules. The youngest carnivorous lineage, Brocchinia reducta, showed signatures of the early stages of AM trait loss. An AM‐associated CHITINASE gene encodes a digestive enzyme in the carnivorous plant Cephalotus, suggesting gene co‐option.We uncovered a mutually exclusive trend of AM symbiosis and carnivory, with only rare instances of coexistence. These findings illuminate the largely unexplored processes by which plant nutritional strategies evolve and supplant one another over time.

Arbuscular mycorrhizal fungi (AMF) are increasingly recognized for their potential to remediate per- and polyfluoroalkyl substances (PFASs) in constructed wetlands (CWs), but their mechanisms in affecting PFAS removal remain unclear. This study aims to elucidate AMF's impacts on PFAS removal and their role in mitigating the environmental risks posed by residual PFASs in the effluent. The results indicated that the primary removal pathways of PFASs in CWs were substrate adsorption and microbial degradation, while plant uptake contributed minimally (0.2-0.3%). AMF enhanced host plant absorption and translocation of PFASs, thereby increasing PFAS accumulation in plant tissues. Additionally, AMF promoted the enrichment of key microbes (e.g., Chloroflexi and Proteobacteria), which stabilized and enhanced the activity of the rhizosphere microbial network, facilitating PFAS biotransformation and degradation. Through the reinforcement of microbial degradation, substrate adsorption, and plant uptake pathways, AMF symbiosis significantly enhanced PFAS removal, increasing efficiency by 10.5-13.3% compared to treatments without AMF. Notably, long-chain (C > 7) PFASs pose higher ecological risks compared to short-chain (C ≤ 7) PFASs. AMF effectively reduced the ecological risks associated with residual PFASs and their metabolites in the effluent. The results highlight AMF's potential to improve PFAS removal in CWs and offer valuable insights for developing sustainable, high-efficiency pollution control strategies.

The regulation of cellular protein homeostasis involves the ubiquitin-proteasome system (UPS) by selectively targeting misfolded or end-of-life proteins. The involvement of the UPS in biotic stresses has been studied mainly in plant-pathogen interactions and poorly in plant-mutualistic interactions. Here, we studied through proteomic approaches (western blot, pull-down of polyubiquinated proteins and nano-LC-MS-MS analysis), the involvement of the UPS during the establishment of the mutualistic interaction between the arbuscular mycorrhizal fungus Rhizophagus irregularis DAOM197198 and the roots of Medicago truncatula, as well as in the established symbiosis. Roots of M. truncatula seedlings were harvested 0h, 3h, 6h, 9h, 12h, 24h and 15days post-inoculation. We characterized a short-time and a-long-time response of the root ubiquitinome. Some proteins as such as flotilins or involved in the translational machinery were less-ubiquitinated, suggesting the facilitation of the de novo synthesis of proteins required to the establishment of arbuscular mycorrhizal symbiosis. In contrast, other proteins as transporters involved in plant nutrition through the direct pathway (i.e., MtPT5) and some enzymes involved in the lipid biosynthesis pathways were more-ubiquitinated, highlighting their putative degradation. In addition, Cdc48 protein accumulates in roots from 9 to 24h post-inoculation, suggesting a role of Cdc48 in the transitory immune response during plant-fungal interactions. The activity of the UPS is consequently central in the establishment and functioning of arbuscular mycorrhizal symbiosis by modulating protein ubiquitination.

Arbuscular mycorrhizal networks-A climate-smart blueprint for agriculture.

BackgroundChanges in plant growth and root traits in wheat (Triticum aestivum L.) vary depending on the level of phosphorus (P) supply. Two important strategies for P acquisition in wheat are the release of carboxylates into the rhizosphere and the presence of arbuscular mycorrhizal fungi (AMF). However, the relationship between root exudates and P concentration in the shoot and root, as well as the role of AMF in this process, is not yet fully understood. This study was conducted utilizing three P supply rates (0, 50, and 200 mg P kg−1 soil) in conjunction with AMF inoculation. We examined the effects of AMF on amount of rhizosphere carboxylates and plant P uptake for nine P contrasting wheat genotypes.ResultsAMF decreased carboxylates, root biomass, root P content of wheat, and AMF reduced wheat root P allocation of wheat under all P levels. Notably, at 50 mg kg−1 P level, the shoot P concentration of AMF-inoculated wheat exceeded that of other P levels, having a positive mycorrhizal responsiveness in all wheat genotypes. Furthermore, analysis revealed that wheat root morphology and acid phosphatase activity significantly influenced mycorrhizal growth responsiveness, while root carboxylates played a significant role in mycorrhizal P responsiveness.ConclusionsThe P acquisition of wheat was found to be contingent upon the interplay of root morphology, AMF, and carboxylate levels, with AMF and carboxylate playing a more crucial role in enhancing P absorption. Consequently, the current research provides important insights for nutrient management in wheat agricultural cultivation.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12870-025-07023-6.

Abstract Arbuscular mycorrhizal (AM) fungi improve water and nutrient acquisition of most land plants. Additionally, they can help plants to alleviate abiotic stresses, such as salinity which causes a major threat for many crop species. Potassium (K+) plays a major role in plant tolerance to salinity, and we recently demonstrated, by using rubidium (Rb+) as a proxy, that AM fungi can directly transfer K+ to their host plant. Here, we first investigated the impact of K+ availability on soybean root development upon salinity. Then, using two-compartment systems, we also inoculated soybean plants with the AM fungus Rhizophagus irregularis, grew them in various K+ and sodium (Na+) regimes, and used Rb+ to track K+ movements. Root development parameters, biomass, colonization rate, and nutrient concentrations were assessed in AM and non-mycorrhizal plants. Our results show that soybean root development was significantly affected by NaCl treatments, rather than K+ availability. Additionally, although the AM symbiosis was drastically reduced by high salinity, it improved K+ concentrations and prevented Na+ accumulation in inoculated plants, mainly under limiting K+ conditions. Rb+ transport was observed only when the plants were in demand for K+, but was inhibited by high salinity. Finally, we also show that the addition of NaCl slightly influences the availability of K+ and Rb+. This report shows the combined impact of K+ availability and AM symbiosis on soybean tolerance to salinity and discusses the limitations of using Rb+ as a proxy for K+ upon increasing salinity conditions.