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At least 19 recordsLinked to original sources

PubMed2006

Symbioses of methanotrophs and deep-sea mussels (Mytilidae: Bathymodiolinae).

The symbioses between invertebrates and chemosynthetic bacteria allow both host and symbiont to colonize and thrive in otherwise inhospitable deep-sea habitats. Given the global distribution of the bathymodioline symbioses, this association is an excellent model for evaluating co-speciation and evolution of symbioses. Thus far, the methanotroph and chemoautotroph endosymbionts of mussels are tightly clustered within two independent clades of gamma Proteobacteria, respectively. Further physiological and genomic studies will elucidate the ecological and evolutionary roles that these bacterial clades play in the symbiosis and chemosynthetic community. Due to the overall abundance of the methanotrophic symbioses at hydrothermal vents and hydrocarbon seeps, they likely play a significant, but as of yet unquantified, role in the biogeochemical cycling of methane. With this in mind, the search for methanotrophic symbioses should not be restricted to these known deep-sea habitats, but rather should be expanded to include methane-rich coastal marine and freshwater environments inhabited by methanotrophs and bivalves. Our current understanding of the bathymodioline symbioses provides a strong foundation for future explorations into the origin, ecology, and evolution of methanotroph symbioses, which are now becoming possible through a combination of classical and advanced molecular techniques.

Animals↗

PubMed1999

Pathways of inorganic nitrogen assimilation in chemoautotrophic bacteria-marine invertebrate symbioses: expression of host and symbiont glutamine synthetase

Symbioses between chemoautotrophic bacteria and marine invertebrates living at deep-sea hydrothermal vents and other sulfide-rich environments function autotrophically by oxidizing hydrogen sulfide as an energy source and fixing carbon dioxide into organic compounds. For chemoautotrophy to support growth, these symbioses must be capable of inorganic nitrogen assimilation, a process that is not well understood in these or other aquatic symbioses. Pathways of inorganic nitrogen assimilation were investigated in several of these symbioses: the vent tubeworms Riftia pachyptila and Tevnia jerichonana, the vent bivalves Calyptogena magnifica and Bathymodiolus thermophilus, and the coastal bivalve Solemya velum. Nitrate reductase activity was detected in R. pachyptila, T. jerichonana and B. thermophilus, but not in C. magnifica and S. velum. This is evidence for nitrate utilization, either assimilation or respiration, by some vent species and is consistent with the high levels of nitrate availability at vents. The ammonia assimilation enzymes glutamine synthetase (GS) and glutamate dehydrogenase (GDH) were detected in all symbioses tested, indicating that ammonia resulting from nitrate reduction or from environmental uptake can be incorporated into amino acids. A complicating factor is that GS and GDH are potentially of both host and symbiont origin, making it unclear which partner is involved in assimilation. GS, which is considered to be the primary ammonia-assimilating enzyme of autotrophs, was investigated further. Using a combination of molecular and biochemical approaches, host and symbiont GS were distinguished in the intact association. On the basis of Southern hybridizations, immunoreactivity, subunit size and thermal stability, symbiont GS was found to be a prokaryote GS. Host GS was distinct from prokaryote GS. The activities of host and symbiont GS were separated by anion-exchange chromatography and quantified. Virtually all activity in symbiont-containing tissue was due to symbiont GS in R. pachyptila, C. magnifica and B. thermophilus. In contrast, no symbiont GS activity was detected in the gill of S. velum, the predominant activity in this species appearing to be host GS. These findings suggest that ammonia is primarily assimilated by the symbionts in vent symbioses, whereas in S. velum ammonia is first assimilated by the host. The relationship between varying patterns of GS expression and host-symbiont nutritional exchange is discussed.

Journal Article↗

PubMed1985

Correlations between characteristics of some free-living Chlorella sp. and their ability to form stable symbioses with Hydra viridis.

Aposymbiotic polyps of Hydra viridis were infected with 17 strains of in vitro cultured Chlorella sp. Larvae of Artemia fed with the chlorellae were used as an infecting vector. Of the 17 strains, seven formed stable symbioses and one formed a transient infection that disappeared within several weeks. Chlorellae of the nine other strains were cleared out of the infected hydra within 2-3 days. There was a distinct correlation between the ability of the chlorellae to form stable symbioses and their ability to adapt and grow in media enriched with 0.5% proteose peptone. Only strains that grew in the latter medium formed symbioses with the hydra. The symbioses formed with the different strains of chlorellae differed from one another. Hydra infected with some strains greened completely while those infected with other strains greened only partially. The degree of infection varied also within each population, and there were differences in the distribution of the various chlorellae along the stalk and inside the digestive cells of the hydra. Growth rates of the infected hydra were all less that those of aposymbiotic hydra or of hydra hosting native zoochlorellae. We conclude that adaptability to a nutrient-rich environment inside the perialgal vacuole of the digestive cell and a sufficient growth rate therein are crucial to the ability of chlorellae to form stable symbioses with H. viridis. In time, co-adaptation of hydra and chlorellae would restore the normal growth rate of the former and bring about regularity to the form and extent of infection by the latter.

Cells, Cultured↗

PubMed1998

Rhizobium mongolense sp. nov. is one of three rhizobial genotypes identified which nodulate and form nitrogen-fixing symbioses with Medicago ruthenica [(L.) Ledebour].

Medicago ruthenica [(L.) Ledebour] is native to inner Mongolia where rhizosphere samples were collected for the isolation of 106 rhizobial cultures. Besides nodulating the original trap host, the isolates formed nitrogen-fixing symbioses with Phaseolus vulgaris. Only half of the isolates nodulated alfalfa (Medicago sativa), but these did not form nitrogen-fixing symbioses. Rhizobium tropici also formed nitrogen-fixing symbioses with Medicago ruthenica. A total of 56 distinctive multilocus electrophoretic types (ETs) were identified among 94 of the 106 isolates which were analysed for variation in electrophoretic mobility of 12 enzyme loci. One isolate (USDA 1920) possessed a unique ET, while the ETs of the other isolates formed two weakly divergent subgroups approximately equal in size. It was concluded from small subunit rRNA gene sequences of eight isolates of Medicago ruthenica that they belonged to the genus Rhizobium and not to the genus Sinorhizobium which is more commonly associated with Medicago. Genomic similarity, determined from DNA hybridization analysis, between USDA 1920 and the strain representing the remaining isolates (USDA 1844) was lower than 20%. Based upon these observations it was concluded that at least three genomic species of rhizobia form nitrogen-fixing symbioses with Medicago ruthenica. One of these genomic species is R. tropici, another is represented by the single isolate USDA 1920 and the name Rhizobium mongolense is proposed for the third genomic species represented by USDA 1844.

Alleles↗

PubMed2006

Tracing nonlegume orthologs of legume genes required for nodulation and arbuscular mycorrhizal symbioses.

Most land plants can form a root symbiosis with arbuscular mycorrhizal (AM) fungi for assimilation of inorganic phosphate from the soil. In contrast, the nitrogen-fixing root nodule symbiosis is almost completely restricted to the legumes. The finding that the two symbioses share common signaling components in legumes suggests that the evolutionarily younger nitrogen-fixing symbiosis has recruited functions from the more ancient AM symbiosis. The recent advances in cloning of the genes required for nodulation and AM symbioses from the two model legumes, Medicago truncatula and Lotus japonicus, provide a unique opportunity to address biological questions pertaining to the evolution of root symbioses in plants. Here, we report that nearly all cloned legume genes required for nodulation and AM symbioses have their putative orthologs in nonlegumes. The orthologous relationship can be clearly defined on the basis of both sequence similarity and microsyntenic relationship. The results presented here serve as a prelude to the comparative analysis of orthologous gene function between legumes and nonlegumes and facilitate our understanding of how gene functions and signaling pathways have evolved to generate species- or family-specific phenotypes.

DNA, Complementary↗

PubMed2006

Mutualism and parasitism: the yin and yang of plant symbioses.

Plants are solar-powered sugar factories that feed a multitude of other organisms. Many of these organisms associate directly with host plants to gain access to the plant's photosynthates. Such symbioses encompass a wide collection of styles ranging from mutualistic to commensal and parasitic. Among these, the mutualistic arbuscular mycorrhizal (AM) symbiosis is one of the evolutionarily oldest symbioses of plants, relying on the formation of an intimate relationship between fungi of the Glomeromycota and roots of the majority of vascular flowering plants. In this symbiosis, the fungus intracellularly colonizes living root cells, implying the existence of an extreme form of compatibility. Interestingly, molecular events that happen in the plant in response to mycorrhizal colonization also occur in other beneficial and, as recently shown, even antagonistic plant symbioses. Thus, basic 'compatibility modules' appear to be partially conserved between mutualism and parasitism.

Mycorrhizae↗

PubMed2003

Comparison of nodule induction in legume and actinorhizal symbioses: the induction of actinorhizal nodules does not involve ENOD40.

Two types of root nodule symbioses are known for higher plants, legume and actinorhizal symbioses. In legume symbioses, bacterial signal factors induce the expression of ENOD40 genes. We isolated an ENOD40 promoter from an actinorhizal plant, Casuarina glauca, and compared its expression pattern in a legume (Lotus japonicus) and an actinorhizal plant (Allocasuarina verticillata) with that of an ENOD40 promoter from the legume soybean (GmENOD40-2). In the actinorhizal Allocasuarina sp., CgENOD40-GUS and GmENOD40-2-GUS showed similar expression patterns in both vegetative and symbiotic development, and neither promoter was active during nodule induction. The nonsymbiotic expression pattern of CgENOD40-GUS in the legume genus Lotus resembled the nonsymbiotic expression patterns of legume ENOD40 genes; however, in contrast to GmENOD40-2-GUS, CgENOD40-GUS was not active during nodule induction. The fact that only legume, not actinorhizal, ENOD40 genes are induced during legume nodule induction can be linked to the phloem unloading mechanisms established in the zones of nodule induction in the roots of both types of host plants.

Base Sequence↗

PubMed2004

A reconciliation analysis of host switching in plant-fungal symbioses.

Plant-fungal symbioses include many familiar antagonistic and mutualistic associations and some model cases of coevolution. The relationship between coevolution at the different evolutionary scales has remained an open question. Widespread host specificity and documented host switches offer conflicting indications of what to expect from comparisons of plant and fungal phylogenies. This study sought to establish the role of plant phylogeny in determining fungal phylogeny and the relative contributions of codivergence and host switching by comparing tree topologies for 15 plant-fungal symbioses. Second it attempted to characterize the relationship between phylogenetic congruence and switching. Trees were estimated from published sequences and reconciliation analysis was applied in the form of cophylogeny mapping using "jungles". This provided an exhaustive account of all possible switches capable of reconciling two associated phylogenies. A continuum of cophylogenetic dynamics was identified, ranging from mostly codivergence (e.g., Exobasidium) to mostly switching, (e.g., Erysiphe). Surprisingly, congruent solutions do not necessarily have fewer switches when using cophylogeny mapping, but a significant negative relationship between congruence and the distance of switches proved to be a useful indicator. According to reconciliation analysis, the contribution of host phylogeny varies widely across plant-fungal symbioses, making host specificity and coadaptation poor indicators of macroevolutionary trends because they are necessary, but not sufficient, conditions.

Computational Biology↗

PubMed2004

Symbioses of grasses with seedborne fungal endophytes.

Grasses (family Poaceae) and fungi of the family Clavicipitaceae have a long history of symbiosis ranging in a continuum from mutualisms to antagonisms. This continuum is particularly evident among symbioses involving the fungal genus Epichloe (asexual forms = Neotyphodium spp.). In the more mutualistic symbiota, the epichloe endophytes are vertically transmitted via host seeds, and in the more antagonistic symbiota they spread contagiously and suppress host seed set. The endophytes gain shelter, nutrition, and dissemination via host propagules, and can contribute an array of host fitness enhancements including protection against insect and vertebrate herbivores and root nematodes, enhancements of drought tolerance and nutrient status, and improved growth particularly of the root. In some systems, such as the tall fescue N. coenophialum symbioses, the plant may depend on the endophyte under many natural conditions. Recent advances in endophyte molecular biology promise to shed light on the mechanisms of the symbioses and host benefits.

Animals↗

PubMed2001

Anaerobic sulfur metabolism in thiotrophic symbioses.

Hydrogen sulfide is generally accepted to be the energy source for the establishment of sulfur-oxidizing symbiotic communities. Here, we show that sulfur-storing symbioses not only consume but also produce large amounts of hydrogen sulfide. The prerequisite for this process appears to be the absence of oxygen. Anaerobic sulfide production is widespread among different thiotrophic symbioses from vent and non-vent sites (Riftia pachyptila, Calyptogena magnifica, Bathymodiolus thermophilus, Lucinoma aequizonata and Calyptogena elongata). The extent of H2S generation correlates positively with the amount of elemental sulfur stored in the symbiont-bearing tissues of the hosts. Sulfide production starts a few hours after anoxia sets in, with H2S initially accumulating in the circulatory system before it is excreted into the surrounding environment. We propose that not sulfate but the elemental sulfur deposited in the symbionts serves as a terminal electron acceptor during anoxia and is reduced to sulfide. In anoxia-tolerant symbioses such as L. aequizonata, anaerobic sulfur respiration may be important for producing maintenance energy to help the species survive several months without oxygen. The increased levels of cysteine in the gills of L. aequizonata may be caused by a lack of reoxidation due to the absence of oxygen.

Anaerobiosis↗

PubMed1999

Molecular phylogenies of plants and Frankia support multiple origins of actinorhizal symbioses.

Molecular phylogenetic trees were reconstructed from nucleotide sequences of nifH and 16S rDNA for Frankia and of rbcL for actinorhizal plants. Comparison of Frankia phylogenetic trees reconstructed using nifH and 16S rDNA sequences indicated that subgroupings of both trees correspond with each other in terms of plant origins of Frankia strains. The results suggested that 16S rDNAs can be utilized for coevolution analysis of actinorhizal symbioses. Frankia and plant phylogenetic trees reconstructed using 16S rDNA and rbcL sequences were compared. The comparison by tree matching and likelihood ratio tests indicated that although branching orders of both trees do not strictly correspond with each other, subgroupings of Frankia and their host plants correspond with each other in terms of symbiotic partnership. Estimated divergence times among Frankia and plant clades indicated that Frankia clades diverged more recently than plant clades. Taken together, actinorhizal symbioses originated more than three times after the four plant clades diverged.

Actinomycetales↗

PubMed2000

The Roles of Auxins and Cytokinins in Mycorrhizal Symbioses.

Most land plant species that have been examined exist naturally with a higher fungus living in and around their roots in a symbiotic partnership called a mycorrhiza. Several types of mycorrhizal symbiosis exist, defined by the host/partner combination and the morphology of the symbiotic structures. The arbuscular mycorrhiza (AM) is ancient and may have co-evolved with land plants. Emerging results from gene expression studies have suggested that subsets of AM genes were co-opted during the evolution of other biotrophic symbioses. Here we compare the roles of phytohormones in AM symbiosis and ectomycorrhizas (EC), a more recent symbiosis. To date, there is little evidence of physiologic overlap between the two symbioses with respect to phytohormone involvement. Research on AM has shown that cytokinin (CK) accumulation is specifically enhanced by symbiosis throughout the plant. We propose a pathway of events linking enhanced CK to development of the AM. Additional and proposed involvement of other phytohormones are also described. The role of auxin in EC symbiosis and recent research advances on the topic are reviewed. We have reflected the literature bias in reporting individual growth regulator effects. However, we consider that gradients and ratios of these molecules are more likely to be the causal agents of morphologic changes resulting from fungal associations. We expect that once the individual roles of these compounds are explained, the subtleties of their function will be more clearly addressed.

Journal Article↗

PubMed2006

Development of bioinformatic tools to support EST-sequencing, in silico- and microarray-based transcriptome profiling in mycorrhizal symbioses.

The great majority of terrestrial plants enters a beneficial arbuscular mycorrhiza (AM) or ectomycorrhiza (ECM) symbiosis with soil fungi. In the SPP 1084 "MolMyk: Molecular Basics of Mycorrhizal Symbioses", high-throughput EST-sequencing was performed to obtain snapshots of the plant and fungal transcriptome in mycorrhizal roots and in extraradical hyphae. To focus activities, the interactions between Medicago truncatula and Glomus intraradices as well as Populus tremula and Amanita muscaria were selected as models for AM and ECM symbioses, respectively. Together, almost, 20.000 expressed sequence tags (ESTs) were generated from different random and suppressive subtractive hybridization (SSH) cDNA libraries, providing a comprehensive overview of the mycorrhizal transcriptome. To automatically cluster and annotate EST-sequences, the BioMake and SAMS software tools were developed. In connection with the eNorthern software SteN, plant genes with a predicted mycorrhiza-induced expression were identified. To support experimental transcriptome profiling, macro- and microarray tools have been constructed for the two model mycorrhizae, based either on PCR-amplified cDNAs or 70mer oligonucleotides. These arrays were used to profile the transcriptome of AM and ECM roots under different conditions, and the data obtained were uploaded to the ArrayLIMS and EMMA databases that are designed to store and evaluate expression profiles from DNA arrays. Together, the EST- and transcriptome databases can be mined to identify candidate genes for targeted functional studies.

Computational Biology↗

PubMed2000

Evolutionary instability of ectomycorrhizal symbioses in basidiomycetes.

Mycorrhizae, the symbiotic associations of plant roots and fungal hyphae, are classic examples of mutualisms. In these ecologically important associations, the fungi derive photosynthetic sugars from their plant hosts, which in turn benefit from fungus-mediated uptake of mineral nutrients. Early views on the evolution of symbioses suggested that all long-term, intimate associations tend to evolve toward mutualism. Following this principle, it has been suggested that mycorrhizal symbioses are the stable derivatives of ancestral antagonistic interactions involving plant parasitic fungi. Alternatively, mutualisms have been interpreted as inherently unstable reciprocal parasitisms, which can be disrupted by conflicts of interest among the partners. To determine the number of origins of mycorrhizae, and to assess their evolutionary stability, it is necessary to understand the phylogenetic relationships of the taxa involved. Here we present a broad phylogenetic analysis of mycorrhizal and free-living homobasidiomycetes (mushroom-forming fungi). Our results indicate that mycorrhizal symbionts with diverse plant hosts have evolved repeatedly from saprotrophic precursors, but also that there have been multiple reversals to a free-living condition. These findings suggest that mycorrhizae are unstable, evolutionarily dynamic associations.

Basidiomycota↗

PubMedDate not supplied

Two C4-dicarboxylate transport systems in Rhizobium sp. NGR234: rhizobial dicarboxylate transport is essential for nitrogen fixation in tropical legume symbioses.

To investigate the role of dicarboxylate transport in nitrogen-fixing symbioses between Rhizobium and tropical legumes, we made a molecular genetic analysis of the bacterial transport system in Rhizobium sp. NGR234. This braod host range strain fixes nitrogen in association with evolutionarily divergent legumes. Two dicarboxylate transport systems were cloned from Rhizobium NGR234. One locus was chromosomally located, whereas the other was carried on the symbiotic plasmid (pSym) and contained a dctA carrier protein gene, which was analyzed in detail. Although the DNA and derived amino acid sequences of the structural gene were substantially homologous to that of R. meliloti, its promoter sequences was quite distinct, and the upstream sequence also exhibited no homology to dctB, which is found at this position in R. meliloti. A site-directed internal deletion mutant in dctA of NGR234 exhibited a (unique) exclusively symbiotic phenotype that could grow on dicarboxylates ex planta, but could not fix nitrogen in planta. This phenotype was found for tested host plants of NGR234 with either determinate- or indeterminate-type nodules, confirming for the first time that symbiosis-specific uptake of dicarboxylates is a prerequisite for nitrogen fixation in tropical legume symbioses.

Amino Acid Sequence↗

PubMed2005

Episymbiotic microbes as food and defence for marine isopods: unique symbioses in a hostile environment.

Symbioses profoundly affect the diversity of life, often through novel biochemical services that symbionts provide to their hosts. These biochemical services are typically nutritional enhancements and less commonly defensive, but rarely both simultaneously. On the coral reefs of Papua New Guinea, we discovered unique associations between marine isopod crustaceans (Santia spp.) and episymbiotic microbes. Transmission electron microscopy and pigment analyses show that episymbiont biomass is dominated by large (20-30 microm) cyanobacterial cells. The isopods consume these photosymbionts and "cultivate" them by inhabiting exposed sunlit substrates, a behaviour made possible by symbionts' production of a chemical defence that is repulsive to fishes. Molecular phylogenetic analyses demonstrated that the symbiotic microbial communities are diverse and probably dominated in terms of population size by bacteria and small unicellular Synechococcus-type cyanobacteria. Although largely unknown in the oceans, defensive symbioses probably promote marine biodiversity by allowing niche expansions into otherwise hostile environments.

Animals↗

PubMed2006

A journey through signaling in arbuscular mycorrhizal symbioses 2006.

Recent years have seen fascinating contributions to our understanding of the molecular dialogue between fungi and plants entering into arbuscular mycorrhizal (AM) symbioses. Attention has shifted from descriptions of physiological and cellular events to molecular genetics and modern chemical diagnostics. Genes, signal transduction pathways and the chemical structures of components relevant to the symbiosis have been defined. This review examines our current knowledge of signals and mechanisms involved in the establishment of AM symbioses.

Mycorrhizae↗

PubMed1993

Uptake Hydrogenase (Hup) in Common Bean (Phaseolus vulgaris) Symbioses.

Strains of Rhizobium forming nitrogen-fixing symbioses with common bean were systematically examined for the presence of the uptake hydrogenase (hup) structural genes and expression of uptake hydrogenase (Hup) activity. DNA with homology to the hup structural genes of Bradyrhizobium japonicum was present in 100 of 248 strains examined. EcoRI fragments with molecular sizes of approximately 20.0 and 2.2 kb hybridized with an internal SacI fragment, which contains part of both bradyrhizobial hup structural genes. The DNA with homology to the hup genes was located on pSym of one of the bean rhizobia. Hup activity was observed in bean symbioses with 13 of 30 strains containing DNA homologous with the hup structural genes. However, the Hup activity was not sufficient to eliminate hydrogen evolution from the nodules. Varying the host plant with two of the Hup strains indicated that expression of Hup activity was host regulated, as has been reported with soybean, pea, and cowpea strains.

Journal Article↗