Growing evidence has highlighted the essential role of plant hormones, notably, cytokinins (CKs), in nitrogen-fixing symbiosis, both at early and late nodulation stages1,2. Despite numerous studies showing the central role of CK in nodulation, the importance of CK transport in the symbiosis is unknown. Here, we show the role of ABCG56, a full-size ATP-binding cassette (ABC) transporter in the early stages of the nodulation. MtABCG56 is expressed in roots and nodules and its messenger RNA levels increase upon treatment with symbiotic bacteria, isolated Nod factor and CKs, accumulating within the epidermis and root cortex. MtABCG56 exports bioactive CKs in an ATP-dependent manner over the plasma membrane and its disruption results in an impairment of nodulation. Our data indicate that ABCG-mediated cytokinin transport is important for proper establishment of N-fixing nodules.
- MeSH
- ABC transportér, podrodina G genetika metabolismus MeSH
- biologický transport MeSH
- cytokininy metabolismus MeSH
- fixace dusíku MeSH
- Medicago truncatula genetika mikrobiologie MeSH
- regulátory růstu rostlin metabolismus MeSH
- Rhizobium fyziologie MeSH
- rostlinné proteiny genetika metabolismus MeSH
- symbióza genetika MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- ABC transportér, podrodina G MeSH
- cytokininy MeSH
- regulátory růstu rostlin MeSH
- rostlinné proteiny MeSH
Research efforts directed to elucidation of mechanisms behind trading of resources between the partners in the arbuscular mycorrhizal (AM) symbiosis have seen a considerable progress in the recent years. Yet, despite of the recent developments, some key questions still remain unanswered. For example, it is well established that the strictly biotrophic AM fungus releases phosphorus to- and receives carbon molecules from the plant symbiont, but the particular genes, and their products, responsible for facilitating this exchange, are still not fully described, nor are the principles and pathways of their regulation. Here, we made a de novo quest for genes involved in carbon transfer from the plant to the fungus using genome-wide gene expression array targeting whole root and whole shoot gene expression profiles of mycorrhizal and non-mycorrhizal Medicago truncatula plants grown in a glasshouse. Using physiological intervention of heavy shading (90% incoming light removed) and the correlation of expression levels of MtPT4, the mycorrhiza-inducible phosphate transporter operating at the symbiotic interface between the root cortical cells and the AM fungus, and our candidate genes, we demonstrate that several novel genes may be involved in resource tradings in the AM symbiosis established by M. truncatula. These include glucose-6-phosphate/phosphate translocator, polyol/monosaccharide transporter, DUR3-like, nucleotide-diphospho-sugar transferase or a putative membrane transporter. Besides, we also examined the expression of other M. truncatula phosphate transporters (MtPT1-3, MtPT5-6) to gain further insights in the balance between the "direct" and the "mycorrhizal" phosphate uptake pathways upon colonization of roots by the AM fungus, as affected by short-term carbon/energy deprivation. In addition, the role of the novel candidate genes in plant cell metabolism is discussed based on available literature.
- MeSH
- fosfor metabolismus MeSH
- Medicago truncatula genetika metabolismus mikrobiologie MeSH
- metabolické sítě a dráhy MeSH
- mykorhiza genetika fyziologie MeSH
- regulace genové exprese u rostlin MeSH
- rostlinné proteiny genetika MeSH
- sekvenování exomu MeSH
- stanovení celkové genové exprese MeSH
- symbióza MeSH
- uhlík metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- fosfor MeSH
- rostlinné proteiny MeSH
- uhlík MeSH
During arbuscular mycorrhizal symbiosis, colonization of the root is modulated in response to the physiological status of the plant, with regulation occurring locally and systemically. Here, we identify differentially expressed genes encoding CLAVATA3/ESR-related (CLE) peptides that negatively regulate colonization levels by modulating root strigolactone content. CLE function requires a receptor-like kinase, SUNN; thus, a CLE-SUNN-strigolactone feedback loop is one avenue through which the plant modulates colonization levels.
- MeSH
- Glomeromycota fyziologie MeSH
- kořeny rostlin metabolismus mikrobiologie MeSH
- laktony metabolismus MeSH
- Medicago truncatula metabolismus mikrobiologie MeSH
- mykorhiza fyziologie MeSH
- rostlinné geny * MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
- Názvy látek
- laktony MeSH
The relationship between mycorrhiza functioning and composition of arbuscular mycorrhizal (AM) fungal communities is an important but experimentally still rather little explored topic. The main aim of this study was thus to link magnitude of plant benefits from AM symbiosis in different abiotic contexts with quantitative changes in AM fungal community composition. A synthetic AM fungal community inoculated to the model host plant Medicago truncatula was exposed to four different abiotic contexts, namely drought, elevated phosphorus availability, and shading, as compared to standard cultivation conditions, for two cultivation cycles. Growth and phosphorus uptake of the host plants was evaluated along with the quantitative composition of the synthetic AM fungal community. Abiotic context consistently influenced mycorrhiza functioning in terms of plant benefits, and the effects were clearly linked to the P requirement of non-inoculated control plants. In contrast, the abiotic context only had a small and transient effect on the quantitative AM fungal community composition. Our findings suggest no relationship between the degree of mutualism in AM symbiosis and the relative abundances of AM fungal species in communities in our simplified model system. The observed progressive dominance of one AM fungal species indicates an important role of different growth rates of AM fungal species for the establishment of AM fungal communities in simplified systems such as agroecosystems.
- Klíčová slova
- Community, Medicago truncatula, Mycorrhizal functioning, Phosphorus, Pre-conditioning, qPCR,
- MeSH
- fosfor analýza MeSH
- Medicago truncatula mikrobiologie MeSH
- mykobiom * MeSH
- mykorhiza fyziologie MeSH
- období sucha MeSH
- sluneční záření MeSH
- symbióza * MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- fosfor MeSH
Arbuscular mycorrhizas (AM) are the most common symbiotic associations between a plant's root compartment and fungi. They provide nutritional benefit (mostly inorganic phosphate [Pi]), leading to improved growth, and nonnutritional benefits, including defense responses to environmental cues throughout the host plant, which, in return, delivers carbohydrates to the symbiont. However, how transcriptional and metabolic changes occurring in leaves of AM plants differ from those induced by Pi fertilization is poorly understood. We investigated systemic changes in the leaves of mycorrhized Medicago truncatula in conditions with no improved Pi status and compared them with those induced by high-Pi treatment in nonmycorrhized plants. Microarray-based genome-wide profiling indicated up-regulation by mycorrhization of genes involved in flavonoid, terpenoid, jasmonic acid (JA), and abscisic acid (ABA) biosynthesis as well as enhanced expression of MYC2, the master regulator of JA-dependent responses. Accordingly, total anthocyanins and flavonoids increased, and most flavonoid species were enriched in AM leaves. Both the AM and Pi treatments corepressed iron homeostasis genes, resulting in lower levels of available iron in leaves. In addition, higher levels of cytokinins were found in leaves of AM- and Pi-treated plants, whereas the level of ABA was increased specifically in AM leaves. Foliar treatment of nonmycorrhized plants with either ABA or JA induced the up-regulation of MYC2, but only JA also induced the up-regulation of flavonoid and terpenoid biosynthetic genes. Based on these results, we propose that mycorrhization and Pi fertilization share cytokinin-mediated improved shoot growth, whereas enhanced ABA biosynthesis and JA-regulated flavonoid and terpenoid biosynthesis in leaves are specific to mycorrhization.
- MeSH
- cyklopentany metabolismus MeSH
- flavonoidy metabolismus MeSH
- fosfáty metabolismus MeSH
- Glomeromycota fyziologie MeSH
- kyselina abscisová metabolismus MeSH
- listy rostlin genetika mikrobiologie fyziologie MeSH
- Medicago truncatula genetika mikrobiologie fyziologie MeSH
- mykorhiza fyziologie MeSH
- oxylipiny metabolismus MeSH
- regulace genové exprese u rostlin MeSH
- regulátory růstu rostlin metabolismus MeSH
- rostlinné proteiny genetika metabolismus MeSH
- sekundární metabolismus * MeSH
- symbióza MeSH
- terpeny metabolismus MeSH
- upregulace MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- cyklopentany MeSH
- flavonoidy MeSH
- fosfáty MeSH
- jasmonic acid MeSH Prohlížeč
- kyselina abscisová MeSH
- oxylipiny MeSH
- regulátory růstu rostlin MeSH
- rostlinné proteiny MeSH
- terpeny MeSH
Root colonization by arbuscular mycorrhizal fungi (AMF) can be quantified by different approaches. We compared two approaches that enable discrimination of specific AMF taxa and are therefore emerging as alternative to most commonly performed microscopic quantification of AMF in roots: quantitative real-time PCR (qPCR) using markers in nuclear ribosomal DNA (nrDNA) and mitochondrial ribosomal DNA (mtDNA). In a greenhouse experiment, Medicago truncatula was inoculated with four isolates belonging to different AMF species (Rhizophagus irregularis, Claroideoglomus claroideum, Gigaspora margarita and Funneliformis mosseae). The AMF were quantified in the root samples by qPCR targeted to both markers, microscopy and contents of AMF-specific phospholipid fatty acids (PLFA). Copy numbers of nrDNA and mtDNA were closely related within all isolates; however, the slopes and intercepts of the linear relationships significantly differed among the isolates. Across all isolates, a large proportion of variance in nrDNA copy numbers was explained by root colonization intensity or contents of AMF-specific PLFA, while variance in mtDNA copy numbers was mainly explained by differences among AMF isolates. We propose that the encountered inter-isolate differences in the ratios of mtDNA and nrDNA copy numbers reflect different physiological states of the isolates. Our results suggest that nrDNA is a more suitable marker region than mtDNA for the quantification of multiple AMF taxa as its copy numbers are better related to fungal biomass across taxa than are copy numbers of mtDNA.
- Klíčová slova
- Arbuscular mycorrhizal fungi, Isolate discrimination, Microsymbiont screening, Mitochondrial DNA, Molecular genetic quantification, Nuclear ribosomal DNA, PLFA, Real-time PCR,
- MeSH
- buněčné jádro genetika MeSH
- DNA fungální genetika MeSH
- Glomeromycota genetika MeSH
- kořeny rostlin mikrobiologie MeSH
- kvantitativní polymerázová řetězová reakce * MeSH
- Medicago truncatula mikrobiologie MeSH
- mitochondriální DNA genetika MeSH
- mykorhiza genetika MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- DNA fungální MeSH
- mitochondriální DNA MeSH
Quantification of carbon (C) fluxes in mycorrhizal plants is one of the important yet little explored tasks of mycorrhizal physiology and ecology. 13CO2 pulse-chase labelling experiments are increasingly being used to track the fate of C in these plant-microbial symbioses. Nevertheless, continuous monitoring of both the below- and aboveground CO2 emissions remains a challenge, although it is necessary to establish the full C budget of mycorrhizal plants. Here, a novel CO2 collection system is presented which allows assessment of gaseous CO2 emissions (including isotopic composition of their C) from both belowground and shoot compartments. This system then is used to quantify the allocation of recently fixed C in mycorrhizal versus nonmycorrhizal Medicago truncatula plants with comparable biomass and mineral nutrition. Using this system, we confirmed substantially greater belowground C drain in mycorrhizal versus nonmycorrhizal plants, with the belowground CO2 emissions showing large variation because of fluctuating environmental conditions in the glasshouse. Based on the assembled 13C budget, the C allocation to the mycorrhizal fungus was between 2.3% (increased 13C allocation to mycorrhizal substrate) and 2.9% (reduction of 13C allocation to mycorrhizal shoots) of the plant gross photosynthetic production. Although the C allocation to shoot respiration (measured during one night only) did not differ between the mycorrhizal and nonmycorrhizal plants under our experimental conditions, it presented a substantial part (∼10%) of the plant C budget, comparable to the amount of CO2 released belowground. These results advocate quantification of both above- and belowground CO2 emissions in future studies.
- Klíčová slova
- 13C isotope labelling, Belowground carbon (C) allocation, Glomeromycota, Medicago truncatula, Rhizophagus irregularis, Shade,
- MeSH
- fotosyntéza fyziologie MeSH
- Glomeromycota fyziologie MeSH
- kořeny rostlin metabolismus MeSH
- Medicago truncatula metabolismus mikrobiologie MeSH
- mykorhiza metabolismus MeSH
- oxid uhličitý chemie metabolismus MeSH
- uhlík metabolismus MeSH
- výhonky rostlin metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- oxid uhličitý MeSH
- uhlík MeSH
Monitoring populations of arbuscular mycorrhizal fungi (AMF) in roots is a pre-requisite for improving our understanding of AMF ecology and functioning of the symbiosis in natural conditions. Among other approaches, quantification of fungal DNA in plant tissues by quantitative real-time PCR is one of the advanced techniques with a great potential to process large numbers of samples and to deliver truly quantitative information. Its application potential would greatly increase if the samples could be preserved by drying, but little is currently known about the feasibility and reliability of fungal DNA quantification from dry plant material. We addressed this question by comparing quantification results based on dry root material to those obtained from deep-frozen roots of Medicago truncatula colonized with Rhizophagus sp. The fungal DNA was well conserved in the dry root samples with overall fungal DNA levels in the extracts comparable with those determined in extracts of frozen roots. There was, however, no correlation between the quantitative data sets obtained from the two types of material, and data from dry roots were more variable. Based on these results, we recommend dry material for qualitative screenings but advocate using frozen root materials if precise quantification of fungal DNA is required.
- MeSH
- DNA fungální genetika izolace a purifikace MeSH
- kořeny rostlin chemie růst a vývoj mikrobiologie MeSH
- Medicago truncatula chemie růst a vývoj mikrobiologie MeSH
- mykorhiza chemie genetika MeSH
- ochrana biologická MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- DNA fungální MeSH
Medicago truncatula represents a model plant species for understanding legume-bacteria interactions. M. truncatula roots form a specific root-nodule symbiosis with the nitrogen-fixing bacterium Sinorhizobium meliloti. Symbiotic nitrogen fixation generates high iron (Fe) demands for bacterial nitrogenase holoenzyme and plant leghemoglobin proteins. Leguminous plants acquire Fe via "Strategy I," which includes mechanisms such as rhizosphere acidification and enhanced ferric reductase activity. In the present work, we analyzed the effect of S. meliloti volatile organic compounds (VOCs) on the Fe-uptake mechanisms of M. truncatula seedlings under Fe-deficient and Fe-rich conditions. Axenic cultures showed that both plant and bacterium modified VOC synthesis in the presence of the respective symbiotic partner. Importantly, in both Fe-rich and -deficient experiments, bacterial VOCs increased the generation of plant biomass, rhizosphere acidification, ferric reductase activity, and chlorophyll content in plants. On the basis of our results, we propose that M. truncatula perceives its symbiont through VOC emissions, and in response, increases Fe-uptake mechanisms to facilitate symbiosis.
- MeSH
- biomasa MeSH
- chlorofyl analýza MeSH
- FMN-reduktasa metabolismus MeSH
- koncentrace vodíkových iontů MeSH
- kořenové hlízky rostlin mikrobiologie MeSH
- Medicago truncatula chemie růst a vývoj metabolismus mikrobiologie MeSH
- půda chemie MeSH
- Sinorhizobium meliloti metabolismus MeSH
- těkavé organické sloučeniny metabolismus MeSH
- železo metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- chlorofyl MeSH
- ferric citrate iron reductase MeSH Prohlížeč
- FMN-reduktasa MeSH
- půda MeSH
- těkavé organické sloučeniny MeSH
- železo MeSH
