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1.
According to morphologically based classification systems, actinorhizal plants, engaged in nitrogen-fixing symbioses with Frankia bacteria, are considered to be only distantly related. However, recent phylogenetic analyses of seed plants based on chloroplast rbcL gene sequences have suggested closer relationships among actinorhizal plants. A more thorough sampling of chloroplast rbcL gene sequences from actinorhizal plants and their nonsymbiotic close relatives was conducted in an effort to better understand the phylogenetic relationships of these plants, and ultimately, to assess the homology of the different actinorhizal symbioses. Sequence data from 70 taxa were analyzed using parsimony analysis. Strict consensus trees based on 24 equally parsimonious trees revealed evolutionary divergence between groups of actinorhizal species suggesting that not all symbioses are homologous. The arrangement of actinorhizal species, interspersed with nonactinorhizal taxa, is suggestive of multiple origins of the actinorhizal symbiosis. Morphological and anatomical characteristics of nodules from different actinorhizal hosts were mapped onto the rbclL-based consensus tree to further assess homology among rbcL-based actinorhizal groups. The morphological and anatomical features provide additional support for the rbcL-based groupings, and thus, together, suggest that actinorhizal symbioses have originated more than once in evolutionary history.  相似文献   

2.
Phylogenetic analyses suggest that, among the members of the Eurosid I clade, nitrogen-fixing root nodule symbioses developed multiple times independently, four times with rhizobia and four times with the genus Frankia. In order to understand the degree of similarity between symbiotic systems of different phylogenetic subgroups, gene expression patterns were analyzed in root nodules of Datisca glomerata and compared with those in nodules of another actinorhizal plant, Alnus glutinosa, and with the expression patterns of homologous genes in legumes. In parallel, the phylogeny of actinorhizal plants was examined more closely. The results suggest that, although relationships between major groups are difficult to resolve using molecular phylogenetic analysis, the comparison of gene expression patterns can be used to inform evolutionary relationships. In this case, stronger similarities were found between legumes and intracellularly infected actinorhizal plants (Alnus) than between actinorhizal plants of two different phylogenetic subgroups (Alnus/Datisca).  相似文献   

3.
Molecular analysis of actinorhizal symbiotic systems: Progress to date   总被引:1,自引:0,他引:1  
The application of molecular tools to questions related to the genetics, ecology and evolution of actinorhizal symbiotic systems has been especially fruitful during the past two years. Host plant phylogenies based on molecular data have revealed markedly different relationships among host plants than have previously been suspected and have contributed to the development of new hypotheses on the origin and evolution of actinorhizal symbiotic systems. Molecular analyses of host plant gene expression in developing nodules have confirmed the occurrence of nodulin proteins and in situ hybridization techniques have been successfully adapted to permit the study of the spatial and temporal patterns of gene expression within actinorhizal nodules. The use of heterologous probes in combination with nucleotide sequence analysis have allowed a number of nif genes to be mapped on the Frankia chromosome which will ultimately contribute to the development of hypotheses related to nif gene regulation in Frankia. The use of both 16S and 23S rDNA nucleotide sequences has allowed the construction of phylogenetic trees that can be tested for congruence with symbiotic characters. In addition the development of Frankia-specific gene probes and amplification primers have contributed to studies on the genetic diversity and distribution of Frankia in the soil.  相似文献   

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5.
Indigenous species of actinorhizal plants of Casuarinaceae, Elaeagnaceae and Rhamnaceae are found in specific regions of Australia. Most of these plants belong to Casuarinaceae, the dominant actinorhizal family in Australia. Many of them have significant environmental and economical value. The other two families with their indigenous actinorhizal plants have only a minor presence in Australia. Most Australian actinorhizal plants have their native range only in Australia, whereas two of these plants are also found indigenously elsewhere. The nitrogen-fixing ability of these plants varies between species. This ability needs to be investigated in some of these plants. Casuarinas form a distinctive but declining part of the Australian landscape. Their potential has rarely been applied in forestry in Australia despite their well-known uses, which are being judiciously exploited elsewhere. To remedy this oversight, a programme has been proposed for increasing and improving casuarinas that would aid in greening more regions of Australia, increasing the soil fertility and the area of wild life habitat (including endangered species). Whether these improved clones would be productive with local strains of Frankia or they need an external inoculum of Frankia should be determined and the influence of mycorrhizal fungi on these clones also should be investigated.  相似文献   

6.
7.
Parasites often jump to and become established in a new host species. There is much evidence that the probability of such host shifts decreases with increasing phylogenetic distance between donor and recipient hosts, but the consequences of such preferential host switching remain little explored. We develop a computational model to investigate the dynamics of parasite host shifts in the presence of this phylogenetic distance effect. In this model, a clade of parasites evolves on an evolving clade of host species where parasites can cospeciate with their hosts, switch to new hosts, speciate within hosts or become extinct. Our model predicts that host phylogenies are major determinants of parasite distributions across trees. In particular, we predict that trees consisting of few large clades of host species and those with fast species turnover should harbor more parasites than trees with many small clades and those that diversify more slowly. Within trees, large clades are predicted to exhibit a higher fraction of infected species than small clades. We discuss our results in the light of recent cophylogenetic studies in a wide range of host–parasite systems.  相似文献   

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10.
Several of the most studied actinorhizal symbioses involve associations between host plants in the subclass Hamamelidae of the dicots and actinomycetes of the genus Frankia. These actinorhizal plants comprise eight genera distributed among three families of ‘higher’ Hamamelidae, the Betulaceae, Myricaceae, and Casuarinaceae. Contrasting promiscuity towards Frankia is encountered among the different actinorhizal members of these families, and a better assessment of the evolutionary history of these actinorhizal taxa could help to understand the observed contrasts and their implications for the ecology and evolution of the actinorhizal symbiosis. Complete DNA sequences of the chloroplast gene coding for the large subunit of ribulose 1,5-bisphosphate carboxylase (rbcL) were obtained from taxa representative of these families and the Fagaceae. The phylogenetic relationships among and within these families were estimated using parsimony and distance-matrix approaches. All families appeared monophyletic. The Myricaceae appeared to derive first before the Betulaceae and the Casuarinaceae. In the Casuarinaceae, the genus Gymnostoma derived before the genera Casuarina and Allocasuarina, which were found closely related. The analysis of character-state changes in promiscuity along the consensus tree topology suggested a strong relationship between the evolutionary history of host plants and their promiscuity toward Frankia. Indeed, the actinorhizal taxa that diverged more recently in this group of plants were shown to be susceptible to a narrower spectrum of Frankia strains. The results also suggest that the ancestor of this group of plant was highly promiscuous, and that evolution has proceeded toward narrower promiscuity and greater specialization. These results imply that a tight relationship between the phytogenies of both symbiotic partners should not be expected, and that host promiscuity is likely to be a key determinant in the establishment of an effective symbiosis.  相似文献   

11.
《Plant Ecology & Diversity》2013,6(2-3):131-140
Background: Nitrogen fixation has been quantified for a range of crop legumes and actinorhizal plants under different agricultural/agroforestry conditions, but much less is known of legume and actinorhizal plant N2 fixation in natural ecosystems.

Aims: To assess the proportion of total plant N derived from the atmosphere via the process of N2 fixation (%Ndfa) by actinorhizal and legume plants in natural ecosystems and their N input into these ecosystems as indicated by their 15N natural abundance.

Methods: A comprehensive collation of published values of %Ndfa for legumes and actinorhizal plants in natural ecosystems and their N input into these ecosystems as estimated by their 15N natural abundance was carried out by searching the ISI Web of Science database using relevant key words.

Results: The %Ndfa was consistently large for actinorhizal plants but very variable for legumes in natural ecosystems, and the average value for %Ndfa was substantially greater for actinorhizal plants. High soil N, in particular, but also low soil P and water content were correlated with low legume N2 fixation. N input into ecosystems from N2 fixation was very variable for actinorhizal and legume plants and greatly dependent on their biomass within the system.

Conclusions: Measurement of 15N natural abundance has given greater understanding of where legume and actinorhizal plant N2 fixation is important in natural ecosystems. Across studies, the average value for %Ndfa was substantially greater for actinorhizal plants than for legumes, and the relative abilities of the two groups of plants to utilise mineral N requires further study.  相似文献   

12.
Summary A cloned cDNA partial copy of a soybean leghemoglobin mRNA was used to probe genomic DNA of four species of actinorhizal plants. Southern blot hybridization revealed the presence of sequences with homology to the leghemoglobin probe in DNA from Alnus glutinosa, Casuarina glauca, Ceanothus americanus and Elaeagnus pungens. The hybridization patterns of the restriction fragments revealed some fragment size conservation between the DNA of soybean and the DNA of four actinorhizal plants which are taxonomically unrelated to soybean or to each other. The results presented here indicate that globin gene sequences are much more widely distributed in the plant kingdom than has previously been thought. Furthermore, if sequence conservation is actually as high as the restriction fragment patterns suggest, the evolution of the DNA surrounding the globin sequences has been highly constrained.  相似文献   

13.
We used mitochondrial DNA data to infer phylogenies for 28 samples of gall-inducing Tamalia aphids from 12 host-plant species, and for 17 samples of Tamalia inquilinus, aphid 'inquilines' that obligately inhabit galls of the gall inducers and do not form their own galls. Our phylogenetic analyses indicate that the inquilines are monophyletic and closely related to their host aphids. Tamalia coweni aphids from different host plants were, with one exception, very closely related to one another. By contrast, the T. inquilinus aphids were strongly genetically differentiated among most of their host plants. Comparison of branch lengths between the T. coweni clade and the T. inquilinus clade indicates that the T. inquilinus lineage evolves 2.5-3 times faster for the cytochrome oxidase I gene. These results demonstrate that: (1) Tamalia inquilines originated from their gall-inducing hosts, (2) communal (multi-female) gall induction apparently facilitated the origin of inquilinism, (3) diversification of the inquilines has involved rapid speciation along host-plant lines, or the rapid evolution of host-plant races, and (4) the inquilines have undergone accelerated molecular evolution relative to their hosts, probably due to reduced effective population sizes. Our findings provide insight into the behavioural causes and evolutionary consequences of transitions from resource generation to resource exploitation.  相似文献   

14.
Abstract The term ``actinorhiza' refers both to the filamentous bacteria Frankia, an actinomycete, and to the root location of nitrogen-fixing nodules. Actinorhizal plants are classified into four subclasses, eight families, and 25 genera comprising more than 220 species. Although ontogenically related to lateral roots, actinorhizal nodules are characterized by differentially expressed genes, supporting the idea of the uniqueness of this new organ. Two pathways for root infection have been described for compatible Frankia interactions: root hair infection or intercellular penetration. Molecular phylogeny groupings of host plants correlate with morphologic and anatomic features of actinorhizal nodules. Four clades of actinorhizal plants have been defined, whereas Frankia bacteria are classified into three major phylogenetic groups. Although the phylogenies of the symbionts are not fully congruent, a close relationship exists between plant and bacterial groups. A model for actinorhizal specificity is proposed that includes different levels or degrees of specificity of host-symbiont interactions, from fully compatible to incompatible. Intermediate, compatible, but delayed or limited interactions are also discussed. Actinorhizal plants undergo feedback regulation of symbiosis involving at least two different and consecutive signals that lead to a mechanism controlling root nodulation. These signals mediate the opening or closing of the window of susceptibility for infection and inhibit infection and nodule development in the growing root, independently of infection mechanism. The requirement for at least two molecular recognition steps in the development of actinorhizal symbioses is discussed.  相似文献   

15.
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.  相似文献   

16.
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.  相似文献   

17.
Actinorhizal plants invade nitrogen-poor soils because of their ability to form root nodule symbioses with N(2)-fixing actinomycetes known as Frankia. Frankia strains are difficult to isolate, so the diversity of strains inhabiting nodules in nature is not known. To address this problem, we have used the variability in bacterial 16S rRNA gene sequences amplified from root nodules as a means to estimate molecular diversity. Nodules were collected from 96 sites primarily in northeastern North America; each site contained one of three species of the family Myricaceae. Plants in this family are considered to be promiscuous hosts because several species are effectively nodulated by most isolated strains of Frankia in the greenhouse. We found that strain evenness varies greatly between the plant species so that estimating total strain richness of Frankia within myricaceous nodules with the sample size used was problematical. Nevertheless, Myrica pensylvanica, the common bayberry, was found to have sufficient diversity to serve as a reservoir host for Frankia strains that infect plants from other actinorhizal families. Myrica gale, sweet gale, yielded a few dominant sequences, indicating either symbiont specialization or niche selection of particular ecotypes. Strains in Comptonia peregrina nodules had an intermediate level of diversity and were all from a single major group of Frankia.  相似文献   

18.
The Casuarinaceae family is a group of 96 species of trees and shrubs that are tolerant to adverse soil and climatic conditions. In the field, Casuarinaceae bears nitrogen-fixing root nodules (so called actinorhizal nodules) resulting from infection by the soil actinomycete Frankia. The association between Casuarina and Frankia is of tremendous ecological importance in tropical and subtropical areas where these trees contribute to land stabilization and soil reclamation. During differentiation of the actinorhizal nodule, a set of genes called actinorhizal nodulins is activated in the developing nodule. Understanding the molecular basis of actinorhizal nodule ontogenesis requires molecular tools such as genomics together with gene transfer technologies for functional analysis of symbiotic genes. Using the biological vectors Agrobacterium rhizogenes and A. tumefaciens, gene transfer into the two species Allocasuarina verticillata and Casuarina glauca has been successful. Transgenic Casuarinaceae plants proved to be valuable tools for exploring the molecular mechanisms resulting from the infection process of actinorhizal plants by Frankia.  相似文献   

19.
Endophyte sporulation in root nodules of actinorhizal plants   总被引:1,自引:0,他引:1  
All strains of isolated Frankia possess the genetic capacity to form sporangia since, when grown in vitro, they usually sporulate freely, depending on the physical and chemical environment in which they are cultured. Endophytic sporulation involving Frankia differentiation of sporangia within root nodules has been described in only 16 host species in 9 genera within six families of actinorhizal plants. From studies published to date, endophytic sporulation cannot be correlated with specific environmental conditions surrounding the host plants. Based on the literature and on previously unpublished observations from field and greenhouse studies, an account is given of the occurrence of sporulation in actinorhizal plants with emphasis on Alnus, Casuarina, Comptonia, Elaeagnus and Myrica . The possible role of the host plant in controlling Frankia sporulation as contrasted to the control exerted by the genetic constitution of the microbial symbiont is explored.  相似文献   

20.
Actinomycetes from the genus Frankia induce nitrogen-fixing root nodules on actinorhizal plants in the "core rosid" clade of eudicots. Reported here are nine partial Frankia 16S rRNA gene sequences including the first from host plants of the rosaceous genera Cercocarpus and Chamaebatia, 24 partial glutamine synthetase (GSI; glnA) sequences from Frankia in nodules of 17 of the 23 actinorhizal genera, and the partial glnA sequence of Acidothermus cellulolyticus. Phylogenetic analyses of combined Frankia 16S rDNA and glnA sequences indicate that infective strains belong to three major clades (I-III) and that Clade I strains consisting of unisolated symbionts from the Coriariaceae, Datiscaceae, Rosaceae, and Ceanothus of the Rhamnaceae are basal to the other clades. Clock-like mutation rates in glnA sequence alignments indicate that all three major Frankia clades diverged early during the emergence of eudicots in the Cretaceous period, and suggest that present-day symbioses are the result of an ancestral symbiosis that emerged before the divergence of extant actinorhizal plants.  相似文献   

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