RESUMEN
The mutualistic arbuscular mycorrhizal (AM) symbiosis arose in land plants more than 450 million years ago and is still widely found in all major land plant lineages. Despite its broad taxonomic distribution, little is known about the molecular components underpinning symbiosis outside of flowering plants. The ARBUSCULAR RECEPTOR-LIKE KINASE (ARK) is required for sustaining AM symbiosis in distantly related angiosperms. Here, we demonstrate that ARK has an equivalent role in symbiosis maintenance in the bryophyte Marchantia paleacea and is part of a broad AM genetic program conserved among land plants. In addition, our comparative transcriptome analysis identified evolutionarily conserved expression patterns for several genes in the core symbiotic program required for presymbiotic signaling, intracellular colonization, and nutrient exchange. This study provides insights into the molecular pathways that consistently associate with AM symbiosis across land plants and identifies an ancestral role for ARK in governing symbiotic balance.
Asunto(s)
Embryophyta , Regulación de la Expresión Génica de las Plantas , Micorrizas , Proteínas de Plantas , Simbiosis , Simbiosis/genética , Micorrizas/fisiología , Micorrizas/genética , Embryophyta/genética , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Marchantia/genética , Marchantia/microbiología , FilogeniaRESUMEN
The apocarotenoid strigolactones (SLs) facilitate pre-symbiotic communication between arbuscular mycorrhizal (AM) fungi and plants. Related blumenol-C-glucosides (blumenols), have also been associated with symbiosis, but the cues that are involved in the regulation of blumenol accumulation during AM symbiosis remain unclear. In rice, our analyses demonstrated a strict correlation between foliar blumenol abundance and intraradical fungal colonisation. More specifically, rice mutants affected at distinct stages of the interaction revealed that fungal cortex invasion was required for foliar blumenol accumulation. Plant phosphate status and D14L hormone signalling had no effect, contrasting their known role in induction of SLs. This a proportion of the SL biosynthetic enzymes, D27 and D17, are equally required for blumenol production. These results importantly clarify that, while there is a partially shared biosynthetic pathway between SL and blumenols, the dedicated induction of the related apocarotenoids occurs in response to cues acting at distinct stages during the root colonisation process. However, we reveal that neither SLs nor blumenols are essential for fungal invasion of rice roots.
Asunto(s)
Lactonas , Micorrizas , Oryza , Simbiosis , Micorrizas/fisiología , Oryza/microbiología , Oryza/metabolismo , Oryza/genética , Oryza/fisiología , Lactonas/metabolismo , Raíces de Plantas/microbiología , Raíces de Plantas/metabolismo , Reguladores del Crecimiento de las Plantas/metabolismo , Glucósidos/metabolismo , Regulación de la Expresión Génica de las PlantasRESUMEN
Arbuscular mycorrhizal (AM) symbiosis, the nutritional partnership between AM fungi and most plant species, is globally ubiquitous and of great ecological and agricultural importance. Studying the processes of AM symbiosis is confounded by its highly spatiotemporally dynamic nature. While microscopy methods exist to probe the spatial side of this plant-fungal interaction, the temporal side remains more challenging, as reliable deep-tissue time-lapse imaging requires both symbiotic partners to remain undisturbed over prolonged time periods. Here, we introduce the AMSlide: a noninvasive, high-resolution, live-imaging system optimised for AM symbiosis research. We demonstrate the AMSlide's applications in confocal microscopy of mycorrhizal roots, from whole colonisation zones to subcellular structures, over timeframes from minutes to weeks. The AMSlide's versatility for different microscope set-ups, imaging techniques, and plant and fungal species is also outlined. It is hoped that the AMSlide will be applied in future research to fill in the temporal blanks in our understanding of AM symbiosis, as well as broader root and rhizosphere processes.
RESUMEN
The root systems of most plant species are aided by the soil-foraging capacities of symbiotic arbuscular mycorrhizal (AM) fungi of the Glomeromycotina subphylum. Despite recent advances in our knowledge of the ecology and molecular biology of this mutualistic symbiosis, our understanding of the AM fungi genome biology is just emerging. Presented here is a close to T2T genome assembly of the model AM fungus Rhizophagus irregularis DAOM197198, achieved through Nanopore long-read DNA sequencing and Hi-C data. This haploid genome assembly of R. irregularis, alongside short- and long-read RNA-Sequencing data, was used to produce a comprehensive annotation catalog of gene models, repetitive elements, small RNA loci, and DNA cytosine methylome. A phylostratigraphic gene age inference framework revealed that the birth of genes associated with nutrient transporter activity and transmembrane ion transport systems predates the emergence of Glomeromycotina. While nutrient cycling in AM fungi relies on genes that existed in ancestor lineages, a burst of Glomeromycotina-restricted genetic innovation is also detected. Analysis of the chromosomal distribution of genetic and epigenetic features highlights evolutionarily young genomic regions that produce abundant small RNAs, suggesting active RNA-based monitoring of genetic sequences surrounding recently evolved genes. This chromosome-scale view of the genome of an AM fungus genome reveals previously unexplored sources of genomic novelty in an organism evolving under an obligate symbiotic life cycle.
Asunto(s)
Glomeromycota , Micorrizas , Simbiosis/genética , Micorrizas/genética , Genómica , Glomeromycota/genética , ARNRESUMEN
Many plants associate with arbuscular mycorrhizal fungi for nutrient acquisition, while legumes also associate with nitrogen-fixing rhizobial bacteria. Both associations rely on symbiosis signaling and here we show that cereals can perceive lipochitooligosaccharides (LCOs) for activation of symbiosis signaling, surprisingly including Nod factors produced by nitrogen-fixing bacteria. However, legumes show stringent perception of specifically decorated LCOs, that is absent in cereals. LCO perception in plants is activated by nutrient starvation, through transcriptional regulation of Nodulation Signaling Pathway (NSP)1 and NSP2. These transcription factors induce expression of an LCO receptor and act through the control of strigolactone biosynthesis and the karrikin-like receptor DWARF14-LIKE. We conclude that LCO production and perception is coordinately regulated by nutrient starvation to promote engagement with mycorrhizal fungi. Our work has implications for the use of both mycorrhizal and rhizobial associations for sustainable productivity in cereals.
Asunto(s)
Medicago truncatula , Micorrizas , Rhizobium , Medicago truncatula/microbiología , Regulación de la Expresión Génica de las Plantas , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Micorrizas/fisiología , Simbiosis , Rhizobium/metabolismo , NutrientesRESUMEN
Root systems regulate their branching patterns in response to environmental stimuli. Lateral root development in both monocotyledons and dicotyledons is enhanced in response to inoculation with arbuscular mycorrhizal (AM) fungi, which has been interpreted as a developmental response to specific, symbiosis-activating chitinaceous signals. Here, we report that generic instead of symbiosis-specific, chitin-derived molecules trigger lateral root formation. We demonstrate that this developmental response requires the well-known microbe-associated molecular pattern (MAMP) receptor, Chitin Elicitor Receptor Kinase 1 (CERK1), in rice, Medicago truncatula, and Lotus japonicus, as well as the non-host of AM fungi, Arabidopsis thaliana, lending further support for a broadly conserved signal transduction mechanism across angiosperms. Using rice mutants impaired in strigolactone biosynthesis and signaling, we show that strigolactone signaling is necessary to regulate this developmental response. Rice CERK1 operates together with either Chitin Elicitor Binding Protein (CEBiP) or Nod Factor Receptor 5 (NFR5) in immunity and symbiosis signaling, respectively; for the lateral root response, however, all three LysM receptors are required. Our work, therefore, reveals an overlooked but a conserved role of LysM receptors integrating MAMP perception with developmental responses in plants, an ability that might influence the interaction between roots and the rhizosphere biota.
Asunto(s)
Arabidopsis , Magnoliopsida , Micorrizas , Oryza , Micorrizas/fisiología , Lactonas/metabolismo , Simbiosis/fisiología , Oryza/metabolismo , Quitina/metabolismo , Arabidopsis/genética , Arabidopsis/metabolismo , Raíces de Plantas/metabolismo , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismoRESUMEN
The arbuscular mycorrhizal (AM) symbiosis is characterized by the reciprocal exchange of nutrients. AM fungi are oleaginous microorganisms that obtain essential fatty acids from host plants. A lipid biosynthesis and delivery pathway has been proposed to operate in inner root cortex cells hosting arbuscules, a cell type challenging to access microscopically. Despite the central role lipids play in the association, lipid distribution patterns during arbuscule development are currently unknown. We developed a simple co-staining method employing fluorophore-conjugated Wheat Germ Agglutinin (WGA) and a lipophilic blue fluorochrome, Ac-201, for the simultaneous imaging of arbuscules and lipids distributed within arbuscule-containing cells in high resolution. We observed lipid distribution patterns in wild-type root infection zones in a variety of plant species. In addition, we applied this methodology to mutants of the Lotus japonicus GRAS transcription factor RAM1 and the Oryza sativa half-size ABC transporter STR1, both proposed to be impaired in the symbiotic lipid biosynthesis-delivery pathway. We found that lipids accumulated in cortical cells hosting stunted arbuscules in Ljram1 and Osstr1, and observed lipids in the arbuscule body of Osstr1, suggesting that in the corresponding plant species, RAM1 and STR1 may not be essential for symbiotic lipid biosynthesis and transfer from arbuscule-containing cells, respectively. The versatility of this methodology has the potential to help elucidate key questions on the complex lipid dynamics fostering AM symbioses.
Asunto(s)
Micorrizas , Transportadoras de Casetes de Unión a ATP/metabolismo , Colorantes Fluorescentes , Regulación de la Expresión Génica de las Plantas , Lípidos , Micorrizas/metabolismo , Proteínas de Plantas/metabolismo , Raíces de Plantas/metabolismo , Simbiosis , Factores de Transcripción/metabolismo , Aglutininas del Germen de Trigo/metabolismoRESUMEN
Despite the vast abundance and global importance of plant and microbial species, the large majority go unnoticed and unappreciated by humans, contributing to pressing issues including the neglect of study and research of these organisms, the lack of interest and support for their protection and conservation, low microbial and botanical literacy in society, and a growing disconnect between people and nature. The invisibility of many of these organisms is a key factor in their oversight by society, but also points to a solution: sharing the wealth of visual data produced during scientific research with a broader audience. Here, we discuss how the invisible can be visualised for a public audience, and the benefits it can bring. SUMMARY: Whether too small, slow or concealed, the majority of species on Earth go unseen by humans. One such rather unobservable group of organisms are the arbuscular mycorrhizal (AM) fungi, who form beneficial symbioses with plants. AM symbiosis is ubiquitous and vitally important globally in ecosystem functioning, but partly as a consequence of its invisibility, it receives disproportionally little attention and appreciation. Yet AM fungi, and other unseen organisms, need not remain overlooked: from decades of scientific research there exists a goldmine of visual data, which if shared effectively we believe can alleviate the issues of low awareness. Here, we use examples from our experience of public engagement with AM symbiosis as well as evidence from the literature to outline the diverse ways in which invisible organisms can be visualised for a broad audience. We highlight outcomes and knock-on consequences of this visualisation, ranging from improved human mental health to environmental protection, making the case for researchers to share their images more widely for the benefit of plants (and fungi and other overlooked organisms), people and planet.
RESUMEN
Arbuscular mycorrhizal (AM) fungi form mutualistic relationships with most land plant species. AM fungi have long been considered as ancient asexuals. Long-term clonal evolution would be remarkable for a eukaryotic lineage and suggests the importance of alternative mechanisms to promote genetic variability facilitating adaptation. Here, we assessed the potential of transposable elements for generating such genomic diversity. The dynamic expression of TEs during Rhizophagus irregularis spore development suggests ongoing TE activity. We find Mutator-like elements located near genes belonging to highly expanded gene families. Whole-genome epigenomic profiling of R. irregularis provides direct evidence of DNA methylation and small RNA production occurring at TE loci. Our results support a model in which TE activity shapes the genome, while DNA methylation and small RNA-mediated silencing keep their overproliferation in check. We propose that a well-controlled TE activity directly contributes to genome evolution in AM fungi.
RESUMEN
Receptor-like kinases (RLKs) are key cell signaling components. The rice ARBUSCULAR RECEPTOR-LIKE KINASE 1 (OsARK1) regulates the arbuscular mycorrhizal (AM) association postarbuscule development and belongs to an undefined subfamily of RLKs. Our phylogenetic analysis revealed that ARK1 has an ancient paralogue in spermatophytes, ARK2 Single ark2 and ark1/ark2 double mutants in rice showed a nonredundant AM symbiotic function for OsARK2 Global transcriptomics identified a set of genes coregulated by the two RLKs, suggesting that OsARK1 and OsARK2 orchestrate symbiosis in a common pathway. ARK lineage proteins harbor a newly identified SPARK domain in their extracellular regions, which underwent parallel losses in ARK1 and ARK2 in monocots. This protein domain has ancient origins in streptophyte algae and defines additional overlooked groups of putative cell surface receptors.
Asunto(s)
Micorrizas/metabolismo , Oryza/enzimología , Filogenia , Proteínas Tirosina Quinasas Receptoras/metabolismo , Secuencia de Aminoácidos , Dominios Proteicos , Proteínas Tirosina Quinasas Receptoras/químicaRESUMEN
The evolutionarily ancient α/ß hydrolase DWARF14-LIKE (D14L) is indispensable for the perception of beneficial arbuscular mycorrhizal (AM) fungi in the rhizosphere, and for a range of developmental processes. Variants of D14L recognise natural strigolactones and the smoke constituent karrikin, both classified as butenolides, and additional unknown ligand(s), critical for symbiosis and development. Recent advances in the understanding of downstream effects of D14L signalling include biochemical evidence for the degradation of the repressor SMAX1. Indeed, genetic removal of rice SMAX1 leads to the de-repression of symbiosis programmes and to the simultaneous increase in strigolactone production. As strigolactones are key to attraction of the fungus in the rhizosphere, the D14L signalling pathway appears to coordinate fungal stimulation and root symbiotic competency. Here, we discuss the possible integrative roles of D14L signalling in conditioning plants for AM symbiosis.
Asunto(s)
Micorrizas , Oryza , Raíces de Plantas/genética , Transducción de Señal , SimbiosisRESUMEN
Arbuscular mycorrhizal fungi (AMF) are ubiquitous in cultivated soils, forming symbiotic relationships with the roots of major crop species. Studies in controlled conditions have demonstrated the potential of AMF to enhance the growth of host plants. However, it is difficult to estimate the actual benefit in the field, not least because of the lack of suitable AMF-free controls. Here we implement a novel strategy using the selective incorporation of AMF-resistance into a genetic mapping population to evaluate maize response to AMF. We found AMF to account for about one-third of the grain production in a medium input field, as well as to affect the relative performance of different plant genotypes. Characterization of the genetic architecture of the host response indicated a trade-off between mycorrhizal dependence and benefit. We identified several QTL linked to host benefit, supporting the feasibility of breeding crops to maximize profit from symbiosis with AMF.
Asunto(s)
Micorrizas/fisiología , Proteínas de Plantas/metabolismo , Zea mays/metabolismo , Zea mays/microbiología , Regulación de la Expresión Génica de las Plantas , Proteínas de Plantas/genética , Raíces de Plantas/microbiología , Suelo , SimbiosisRESUMEN
Most plants associate with beneficial arbuscular mycorrhizal (AM) fungi that facilitate soil nutrient acquisition. Prior to contact, partner recognition triggers reciprocal genetic remodelling to enable colonisation. The plant Dwarf14-Like (D14L) receptor conditions pre-symbiotic perception of AM fungi, and also detects the smoke constituent karrikin. D14L-dependent signalling mechanisms, underpinning AM symbiosis are unknown. Here, we present the identification of a negative regulator from rice, which operates downstream of the D14L receptor, corresponding to the homologue of the Arabidopsis thaliana Suppressor of MAX2-1 (AtSMAX1) that functions in karrikin signalling. We demonstrate that rice SMAX1 is a suppressor of AM symbiosis, negatively regulating fungal colonisation and transcription of crucial signalling components and conserved symbiosis genes. Similarly, rice SMAX1 negatively controls strigolactone biosynthesis, demonstrating an unexpected crosstalk between the strigolactone and karrikin signalling pathways. We conclude that removal of SMAX1, resulting from D14L signalling activation, de-represses essential symbiotic programmes and increases strigolactone hormone production.
Asunto(s)
Proteínas de Arabidopsis/fisiología , Péptidos y Proteínas de Señalización Intracelular/fisiología , Micorrizas/fisiología , Oryza/microbiología , Proteínas de Plantas/fisiología , Simbiosis , Arabidopsis/genética , Arabidopsis/microbiología , Proteínas de Arabidopsis/genética , Furanos/metabolismo , Regulación de la Expresión Génica de las Plantas , Germinación , Compuestos Heterocíclicos con 3 Anillos/metabolismo , Homocigoto , Péptidos y Proteínas de Señalización Intracelular/genética , Lactonas/metabolismo , Familia de Multigenes , Oryza/genética , Filogenia , Proteínas de Plantas/genética , Raíces de Plantas/microbiología , Piranos/metabolismo , RNA-Seq , Transducción de SeñalRESUMEN
Plant receptor-like kinases (RLKs) control the initiation, development, and maintenance of symbioses with beneficial mycorrhizal fungi and nitrogen-fixing bacteria. Carbohydrate perception activates symbiosis signaling via Lysin-motif RLKs and subsequently the common symbiosis signaling pathway. As the receptors activated are often also immune receptors in multiple species, exactly how carbohydrate identities avoid immune activation and drive symbiotic outcome is still not fully understood. This may involve the coincident detection of additional signaling molecules that provide specificity. Because of the metabolic costs of supporting symbionts, the level of symbiosis development is fine-tuned by a range of local and mobile signals that are activated by various RLKs. Beyond early, precontact symbiotic signaling, signal exchanges ensue throughout infection, nutrient exchange, and turnover of symbiosis. Here, we review the latest understanding of plant symbiosis signaling from the perspective of RLK-mediated pathways.
Asunto(s)
Proteínas Quinasas/metabolismo , Receptores de Superficie Celular/metabolismo , Simbiosis , Ligandos , Péptidos/metabolismo , Transducción de SeñalRESUMEN
Phosphorous is important for life but often limiting for plants. The symbiotic pathway of phosphate uptake via arbuscular mycorrhizal fungi (AMF) is evolutionarily ancient and today occurs in natural and agricultural ecosystems alike. Plants capable of this symbiosis can obtain up to all of the phosphate from symbiotic fungi, and this offers potential means to develop crops less dependent on unsustainable P fertilizers. Here, we review the mechanisms and insights gleaned from the fine-tuned signal exchanges that orchestrate the intimate mutualistic symbiosis between plants and AMF. As the currency of trade, nutrients have signaling functions beyond being the nutritional goal of mutualism. We propose that such signaling roles and metabolic reprogramming may represent commitments for a mutualistic symbiosis that act across the stages of symbiosis development.
Asunto(s)
Micorrizas/metabolismo , Fosfatos/metabolismo , Plantas/microbiología , Simbiosis , Micorrizas/fisiologíaRESUMEN
During establishment of arbuscular mycorrhizal symbioses, fungal hyphae invade root cells producing transient tree-like structures, the arbuscules, where exchange of photosynthates for soil minerals occurs. Arbuscule formation and collapse lead to rapid production and degradation of plant and fungal membranes, their spatiotemporal dynamics directly influencing nutrient exchange. We determined the ultra-structural details of both membrane surfaces and the interstitial apoplastic matrix by transmission electron microscopy tomography during growth and senescence of Rhizophagus irregularis arbuscules in rice. Invasive growth of arbuscular hyphae was associated with abundant fungal membrane tubules (memtubs) and plant peri-arbuscular membrane evaginations. Similarly, the phylogenetically distant arbuscular mycorrhizal fungus, Gigaspora rosea, and the fungal maize pathogen, Ustilago maydis, developed memtubs while invading host cells, revealing structural commonalities independent of the mutualistic or parasitic outcome of the interaction. Additionally, extracellular vesicles formed continuously in the peri-arbuscular interface from arbuscule biogenesis to senescence, suggesting an involvement in inter-organismic signal and nutrient exchange throughout the arbuscule lifespan.
Asunto(s)
Membrana Celular/ultraestructura , Vesículas Extracelulares/metabolismo , Micorrizas/fisiología , Oryza/microbiología , Células Vegetales/microbiología , Membrana Celular/microbiología , Tomografía con Microscopio Electrónico , Glomeromycota/fisiología , Hifa/fisiología , Micorrizas/citología , Oryza/citología , Oryza/genética , Hojas de la Planta/citología , Hojas de la Planta/microbiología , Hojas de la Planta/ultraestructura , Raíces de Plantas/citología , Raíces de Plantas/microbiología , Raíces de Plantas/ultraestructura , Plantas Modificadas Genéticamente , Simbiosis , Ustilago/patogenicidad , Zea mays/microbiologíaRESUMEN
In terrestrial ecosystems most plant species live in mutualistic symbioses with nutrient-delivering arbuscular mycorrhizal (AM) fungi. Establishment of AM symbioses includes transient, intracellular formation of fungal feeding structures, the arbuscules. A plant-derived peri-arbuscular membrane (PAM) surrounds the arbuscules, mediating reciprocal nutrient exchange. Signaling at the PAM must be well coordinated to achieve this dynamic cellular intimacy. Here, we identify the PAM-specific Arbuscular Receptor-like Kinase 1 (ARK1) from maize and rice to condition sustained AM symbiosis. Mutation of rice ARK1 causes a significant reduction in vesicles, the fungal storage structures, and a concomitant reduction in overall root colonization by the AM fungus Rhizophagus irregularis. Arbuscules, although less frequent in the ark1 mutant, are morphologically normal. Co-cultivation with wild-type plants restores vesicle and spore formation, suggesting ARK1 function is required for the completion of the fungal life-cycle, thereby defining a functional stage, post arbuscule development.