Showing papers on "Frankia published in 2000"

The Actinorhizal Symbiosis.

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.

The evolution of nodulation

Abstract: In this review we will first describe the different steps leading to nodule formation, and these will be compared with processes of non-symbiotic plant development and growth. In general, aspects of both actinorhizal as well as rhizobial symbiosis are described, but in several cases, the emphasis will be on the Rhizobium-legume symbiosis because more knowledge of this system is available. Subsequently, the phylogeny of nodulating plants is described and a comparison is made between several aspects of legume and actinorhizal nodulation. At the end of this paper the relationship between nodule symbiosis and endomycorrhizal symbiosis is described, and it is discussed to what extent the development of root nodules involves unique properties, or whether processes and genes have been recruited from common plant development and the endomycorrhizal symbiosis.

Characterization of a Casuarina glauca Nodule-Specific Subtilisin-like Protease Gene, a Homolog of Alnus glutinosa ag12

Abstract: In search of plant genes expressed during early interactions between Casuarina glauca and Frankia, we have isolated and characterized a C. glauca gene that has strong homology to subtilisin-like protease gene families of several plants including the actinorhizal nodulin gene ag12 of another actinorhizal plant, Alnus glutinosa. Based on the expression pattern of cg12 in the course of nodule development, it represents an early actinorhizal nodulin gene. Our results suggest that subtilisin-like proteases may be a common element in the process of infection of plant cells by Frankia in both Betulaceae (Alnus glutinosa) and Casuarinaceae (Casuarina glauca) symbioses.

Nitrogen, Phosphorus, and the Ratio Between them Affect Nodulation in Alnus incana and Trifolium pratense

Abstract: Nodulation of Alnus incana by Frankia was studied at three levels of N (ammonium nitrate, 0.071-7.1 mM N) combined with three levels of P (0.01-1.0 mM) in a factorial design. Nodulation of Trifolium pratense by Rhizobium leguminosarum bv. trifolii was studied in a partial factorial design. Plants were in growth pouches for 10.5 weeks. In general, the degree of N inhibition depended on the P level. In A. incana, high P level stimulated nodule number and nodule dry matter per plant and per plant dry matter or per root dry matter. High P also stimulated nodule size and nitrogenase activity. Effects on nodule number seemed to be largely explained by plant growth whereas P had more of a specific effect on nodule dry matter. The N/P ratio was important, and increased N levels inhibited nodulation at N/P ratios >7 but not at N/P ratios <7. In T. pratense, high P level counteracted the inhibition of high N on nodule number and nitrogenase activity. The fact that N effects on nodulation and nitrogenase activity depend on P level should encourage more detailed work on effects of nutrient interactions on nodulation, both in actinorhizal plants and in legumes.

Characterization of the 20S proteasome from the actinomycete Frankia.

Abstract: Frankia is an actinomycete that fixes atmospheric nitrogen in symbiotic association with the root systems of a variety of non-leguminous plants, denominated actinorhizal plants. Information on the biology of proteolysis in Frankia is almost non-existent as it is extremely difficult to grow this organism. We have purified 20S proteasomes from Frankia strain ACN14a/ts-r. It is composed of one alpha-subunit and one beta-subunit, which assemble into the canonical structure of four rings of seven subunits each. The enzyme displayed a chymotrypsin-like activity against synthetic substrates and was sensitive to lactacystin, a specific proteasome inhibitor. Analysis of the structural genes and the flanking regions revealed a similar organization to Rhodococcus erythropolis, Mycobacterium tuberculosis and Streptomyces coelicolor and showed that the beta-subunit is encoded with a 52-amino-acid propeptide that is cleaved off in the course of the assembly. We report also for the first time the in vitro assembly of chimeric proteasomes composed of Frankia and Rhodococcus erythropolis subunits, which are correctly assembled and proteolytically active.

A recA gene phylogenetic analysis confirms the close proximity of Frankia to Acidothermus.

Abstract: The closer proximity of Frankia and Acidothermus cellulolyticus relative to the morphologically close Geodermatophilus found previously was confirmed by resequencing the rrs gene of Acidothermus cellulolyticus and the housekeeping gene, recA. The diagnostic sugar 2-O-methyl-D-mannose was detected only in Frankia, while hopanoid lipids were present at high levels in both Acidothermus and Frankia.

High hopanoid/total lipids ratio in Frankia mycelia is not related to the nitrogen status.

Abstract: Vesicles are specific Frankia structures which are produced under nitrogenlimiting culture conditions. Hopanoids are the most abundant lipids in these vesicles and are believed to protect the nitrogenase against oxygen. The amounts and quality of each hopanoid were estimated in different Frankia strains cultivated under nitrogen-depleted and nitrogen-replete conditions in order to detect a possible variation. Studied Frankia strains nodulating Eleagnus were phylogenetically characterized by analysis of the nifD‐K intergenic region as closely related to genomic species 4 and 5. Phylogenetically different strains belonging to three infectivity groups were cultivated in the same medium with and without nitrogen source for 10 d before hopanoid content analysis by HPLC. Four hopanoids together accounted for 23‐87% and 15‐87% of the total lipids under nitrogen-replete and nitrogen-depleted culture conditions, respectively. Two of the hopanoids found, bacteriohopanetetrols and their phenylacetic acid esters, have previously been described in Frankia. Two new hopanoids, moretan-29-ol and a bacteriohopanetetrol propionate, have also been identified. The moretan-29-ol and bacteriohopanetetrols were found to be the most abundant hopanoids whereas the bacteriohopanetetrol propionate and phenylacetates were present at a concentration close to the limit of detection. The ratio of (bacteriohopanetetrolsM moretan-29-ol)/(total lipids) varied in most of the strains between nitrogen-depleted and nitrogen-replete culture conditions. In most of the strains, the hopanoid content was found to be slightly higher under nitrogen-replete conditions than under nitrogen-depleted conditions. These results suggest that remobilization, rather than neosynthesis of hopanoids, is implicated in vesicle formation in Frankia under nitrogendepleted conditions.

Effects of symbiosis with Frankia and arbuscular mycorrhizal fungus on the natural abundance of 15N in four species of Casuarina

Abstract: were of similar dry weights at harvest. d15N values for cladodes of C. cunninghamiana, C. equisetifolia and The effect of interactions between Casuarina species, C. glauca were similar, but values for the poor growing Frankia strains and AMF on nitrogen isotope fractiona- C. junghuniana were more variable and, with the tion within the plant were determined under conditions exception of plants receiving KNO3, were lower than where changes in source nitrogen were minimized by those of the other three species. Reduced growth due growing plants in mineral nitrogen-deficient conditions to suboptimal availability of N or P had a major influand without added organic N. Casuarina cunninghami- ence on d15N and, in these conditions where plants ana, C. equisetifolia, C. glauca, and C. junghuniana could not access significant amounts of organic N, were inoculated singly with three Frankia strains or outweighed any effects on cladode d15N of colonization were dual inoculated with Frankia and Glomus fascicul- by Glomus. d15N values of nodules were higher than atum. The %N and d15N of separated parts of plants other parts of Frankia or Frankia+Glomus inoculated inoculated with the three Frankia strains or with Casuarinas, conceivably due to retention in nodules of Frankia+Glomus were not significantly different fixed N, with d15N close to zero. within Casuarina species. However, the slow-growing C. junghuniana differed in several variables from the Key words: Arbuscular mycorrhizas, Casuarina, Frankia, other three species. There was a highly significant, nitrogen fixation, nodules. linear relationship between the natural logarithms of cladode N content and d15N of plants of the four Introduction Casuarina species when inoculated with Frankia or with Frankia+Glomus, showing that nitrogen supply Casuarina equisetifolia is a tropical tree, nodulated by the and the correlated variable, plant growth rate, were nitrogen-fixing actinomycete Frankia and forming symbimajor determinants of d15N. Provision of small quantit- otic associations with both ecto- and endomycorrhizal ies of (NH 4 ) 2 SO 4 or KNO 3 increased several-fold the fungi (Cervantes and Rodriguez Barrueco, 1992). It is growth of three of the Casuarina species when inocu- used widely for the stabilization and restoration of soils, lated with Frankia alone or with Frankia+Glomus. as an amenity tree species and as a source of timber and Within species, mycorrhizal and non-mycorrhizal fuel (Diem and Dommergues, 1990). Several studies have shown that growth, nitrogen and phosphorus accumula

Natural abundance of 15N in actinorhizal plants and nodules

Abstract: Substantial enrichment of some plant parts in 15N relative to the rest of the plant is unusual, but is found in the nitrogen-fixing nodules of many legumes. A range of actinorhizal plants was surveyed to determine whether the nodules of any of them are also substantially enriched in 15N. The nonlegume Parasponia, nodulated by a rhizobium, was also included. Four of the actinorhizal genera and Parasponia were grown in N-free culture, and three actinorhizal genera were collected from the field. Nodules of Parasponia, Casuarina and Alnus were15N enriched relative to other plant parts, but only Parasponia approached the degree of enrichment found in some legume nodules. The nodules of Datisca, Myrica, Elaeagnus, Shepherdia, and Coriaria were depleted in 15N. Thus many actinorhizal nodules are depleted in 15N compared to other plant parts and enrichment is modest when it does occur. Whole plant 15N content (δ15N) in four actinorhizal plants and Parasponia showed a relatively narrow range of −1.41 to −1.90. Hence regardless of the degree of nodule enrichment or depletion, whole plant 15N content appears to vary little in plants grown in N-free culture.

Regulation of nodulation and nodule mass in relation to nitrogenase activity and nitrogen demand in Discaria trinervis (Rhamnaceae) seedlings

Abstract: A time course experiment of nodulation, N2 fixation and growth was conducted on Discaria trinervis seedlings after inoculation with Frankia isolate BCU110501, to study the regulation of nodulation in relation to nitrogenase activity. Nodulation started at 1.3 weeks after inoculation and reached a plateau at 7 weeks after inoculation. Nodules were mainly restricted to tap roots. Nitrogenase activity was first detected at 3.6 weeks after inoculation and increased throughout the 9-week experimental period. No H2 evolution could be detected, thus the symbiosis appeared to be phenotypically Hup + . Plant growth increased after onset of nitrogenase activity, except for root length growth. Nitrogenase activity expressed on either plant dry matter basis, nodule dry matter basis, or leaf area basis, did not change significantly during the study. N content of all plant parts, increased to a maximal value at 7 weeks after inoculation At this time formation of new nodules stopped and nodule dry mass relative to total plant dry mass did no longer increase. The results support the idea of a feedback regulation of nodule growth and activity through internal N level.

Isolation of infective and effective Frankia strains from root nodules of Alnus acuminata (Betulaceae).

Abstract: Two Frankia strains were isolated from root nodules of Alnus acuminata collected in the Tucumano-oranense forest, Argentina. Monosporal cultures were obtained by plating a spore suspension of each strain and isolating a single colony. The strains (named AacI and AacIII) showed branched mycelia with polymorphic sporangia and NIR-vesicles. They differed in their ability to use carbon sources: the AacI strain grew well on pyruvate, while the AacIII strain grew on mineral medium supplemented with glucose or, alternatively, with sucrose. The two strains were sensitive to oleandomycin, erythromycin, kanamycin, penicillin G, streptomycin and chloramphenicol at 5 μg/ml. The AcIII strain exhibited a moderate resistance to rifampicin, ampicillin and vancomycin. The nitrogenase activity in vitro of the strains was significantly higher in basal medium without nitrogen than that determined in the presence of ammonium chloride. Both strains were infective on seedlings of Alnus glutinosa, inducing an approximately similar percentage of nodulated plants (80%), although strain AacIII produced a higher number of nodules per plant (≤15) than strain AacI (≤6). They were also effective for nitrogen fixation in planta, determined by the acetylene reduction assay.

Hydrogenase in Frankia KB5: expression of and relation to nitrogenase.

Abstract: The localization and expression of the hydrogenase in free-living Frankia KB5 was investigated immunologically and by monitoring activity, focusing on its relationships with nitrogenase and H-2. Im ...

Interdependence of Myrica cerifera seedlings and the nodule forming actinomycete, Frankia, in a coastal environment.

Abstract: The shrub, Myrica cerifera , and the nitrogen-fixing bacterium, Frankia , form a symbiotic relationship that is important for seedling establishment on nutrient poor coastal soils. To determine potential interdependence, the spatial distribution of host plant seedlings was examined in relation to the root symbiont on a Virginia barrier island. Spatial patterns for both species were related to microtopography and soil chlorides. Myrica cerifera seedlings were more commonin the swale region than on the dune crests or slopes. Abioassay quantified the extent of Frankia distribution within a recently formed swale where the shrub seedlings were invading. Frankia occurred throughout the swale, but was absent within 20 m of the high tide line. Frankia was found in areas devoid of the host plant; M. cerifera did not occur at ~43% of the locations where Frankia was present. In contrast, the host plant seedlings were limited to areas that contained Frankia . Soil chlorides where M. cerifera seedlings occurred were lower than locations devoid of the host plant. Similarly, soil chlorides where Frankia was present were lower when compared to areas without the root symbiont. Although influenced by microtopography and soil chlorides, the successful establishment and small-scale distribution of M. cerifera seedlings in coastal soils depends on the presence of Frankia .

Effect of Freezing of Soils on Nodulation Capacities of Total and Specific Frankia Populations

Abstract: Freezing of soils from pine-, spruce-, and birch-stands that had previously been analyzed for nodulation capacities with Alnus incana as capture plant, and subsequent storage at -20°C for four years resulted in a reduction of infective frankiae. In bioassays, with A. incana, nodulation capacities of frozen soils decreased to 2, 7, and 4%, respectively, of the nodulation capacities of the fresh soils. In situ hybridization with four Frankia group-specific probes identified the Frankia populations in about 90% of the root nodules. Based on rep-PCR analysis, unidentified nodule populations were clustered into two groups outside the analyzed Frankia groups, but within frankiae of the Alnus host infection group. The analysis of specific Frankia populations in nodules on A. incana showed that the reduction in nodulation capacities of frozen soils was accompanied by shifts in nodule-forming Frankia populations. This indicates an effect of freezing and storage not only on the total Frankia population, but also on specific populations of Frankia in soil. Comparative analysis with A. glutinosa as capture plant demonstrated variable compatibilities of A. incana and A. glutinosa for infection with the total Frankia population in soil. Although statistically significant differences in nodulation capacities were not observed for soil from the spruce-stand, soils from pine- and birch-stands displayed about ten times higher nodulation capacities with A. glutinosa than with A. incana. Specific Frankia populations in root nodules on both plant species were not significantly different after inoculation with soil from the spruce- and birch-stand. Larger differences, however, were obtained for soil from the pine-stand suggesting variable compatibilities of the host plants for infection also by specific Frankia populations.

Dg93, a nodule-abundant mRNA of Datisca glomerata with homology to a soybean early nodulin gene.

Abstract: We have isolated a 590-bp full-length cDNA clone designated Dg93, an mRNA that is highly expressed in symbiotic root nodules of the actinorhizal host Datisca glomerata. Dg93 mRNA encodes a deduced polypeptide of 105 amino acids with significant identity (74%) to the soybean (Glycine max) early nodulin (ENOD) gene GmENOD93 (Kouchi and Hata, 1993). Dg93 mRNA is abundant in nodules at 4 weeks post inoculation, the earliest time assayed, and steady-state mRNA levels remain elevated 11 weeks after inoculation. Spatial patterns of Dg93 mRNA expression are complex, with transcript accumulation in the nodule lobe meristem, early infection zone, periderm, and cells of the vascular cylinder, but not in the surrounding uninfected cortical cells. Dg93 is encoded by a small gene family in D. glomerata. To our knowledge, this is the first report of a gene from an actinorhizal host that is expressed in the nodule meristem and that shares sequence homology with an early nodulin gene from a legume.

Salt tolerance of Elaeagnus macrophylla and Frankia Ema1 strain isolated from the root nodules of E. macrophylla.

Abstract: Effects of NaCl on the seed germination and growth of Elaeagnus macrophylla seedlings and multiplication of Frankia Ema1 strain isolated from the root nodules of E. macrophylla were examined. The germination rate of seeds was not reduced by N aCI at 50 mM, but was reduced with further increase of the concentration, and germination did not occur at 200 mM NaCl. Root nodules were formed in the seedlings treated with 100 mM NaCl. The fresh and dry weight of the seedlings slightly decreased by the increase of the concentration of NaCl and the rate of decrease was 10–20% at NaCl concentrations higher than 100 mM. However, Na+ concentrations in the shoot increased up to 300 mM by treatment with N aCI at a concentration above 50 mM for 30 d and in some plants the lower leaves fell. The growth of free-living Frankia was markedly suppressed and the hyphae became thick and short in the solution at 100 mM NaCl. This trend was more obvious at 200 mM NaCl. Na+ concentration in the cells in the medium with 200...

PCR-RFLP Based Screening of Frankia in Alder Nodules Having Different Levels of Nitrogenase Activity

Abstract: One hundred and thirty nodules from 13 different Alnus nepalensis trees from a site in Shillong, India, were screened for nitrogenase activity. Nodules from different trees were found to differ in nitrogenase activity estimates obtained by acetylene reduction assay. In order to analyze whether the differences in nitrogenase activities were due to different Frankia strains residing in the nodules, nodule DNA were subjected to a Polymerase Chain Reaction - Restriction Fragment Length Poly-morphism (PCR-RFLP) study. High and low activity nodules from different trees were found to contain Frankia belonging to similar PCR-RFLP groups. Therefore, the host plant appears to exert a considerable influence on the nitrogen fixation rates of Frankia nodules.

Effects of inoculation with Frankia on the growth and nutrition of alder species and interplanted Japanese larch on restored mineral workings.

Abstract: Land restored after mineral working often suffers from infertility, especially if soil materials have been lost and overburden materials have to be used for vegetation establishment. Nitrogen is the nutrient most commonly lacking because minespoils are usually deficient in organic components. A number of strategies have been tried to deal with this, including choosing lowdemanding species, using nitrogen-fixing species either pure or in mixture, or amending the spoils with organic materials such as sewage sludge. In the UK, sites lacking sufficient soil for reclamation to intensive uses such as agriculture have often been restored to forestry. For example, approximately 1300 ha of land have been planted with trees following opencast coal extraction in South Wales. Nevertheless, infertility has remained a major cause of poor forest performance on these restored lands (Bending et al., 1991; Bending and Moffat, 1999). Alders have been used for many years in woodland establishment on restored land in the UK (Moffat et al., 1989; Moffat and McNeill, 1992). Alders are actinorhizal plants which fix atmospheric nitrogen in a symbiotic relationship with the Frankia micro-organism (Akkermans and Van Dijk, 1975). In natural forest stands, the estimated contribution of alder to soil nitrogen ranges from 60–320 kg N ha–1 a–1 (Newton et al., 1968; Tarrant and Trappe, 1971). In South Effects of inoculation with Frankia on the growth and nutrition of alder species and interplanted Japanese larch on restored mineral workings

Nitrogenase activity in Alnus incana root nodules. Responses to O2 and short-term N2 deprivation.

Abstract: O 2 and host-microsymbiont interactions are key factors affecting the physiology of N 2 -fixing symbioses. To determine the relationship among nitrogenase activity of Frankia - Alnus incana root nodules, O 2 concentration, and short-term N 2 deprivation, intact nodulated roots were exposed to various O 2 pressures (pO 2 ) and Ar:O 2 in a continuous flow-through system. Nitrogenase activity (H 2 production) occurred at a maximal rate at 20% O 2 . Exposure to short-term N 2 deprivation in Ar:O 2 carried out at either 17%, 21%, or 25% O 2 caused a decline in the nitrogenase activity at 21% and 25% O 2 by 12% and 25%, respectively. At 21% O 2 , nitrogenase activity recovered to initial activity within 60 min. The decline rate was correlated with the degree of inhibition of N 2 fixation. Respiration (net CO 2 evolution) decreased in response to the N 2 deprivation at all pO 2 values and did not recover during the time in Ar:O 2 . Increasing the pO 2 from 21% to 25% and decreasing the pO 2 from 21% to 17% during the decline further decreased rather than stimulated nitrogenase activity, showing that the decline was not due to O 2 limitation. The decline was possibly due to a temporary disturbance in the supply of reductant to nitrogenase with a partial O 2 inhibition of nitrogenase at 25% O 2 . These results are consistent with a fixed O 2 diffusion barrier in A. incana root nodules, and show that A. incana nodules differ from legume nodules in the response of the nitrogenase activity to O 2 and N 2 deprivation.

Spatial patterns of root branching and actinorhizal nodulation in Discaria trinervis seedlings

Abstract: The spatial patterns of root branching (topology) and actinorhizal nodulation of Discaria trinervis seedlings under natural and controlled conditions were analysed. The link, i.e. the root segment between either two branching points, or between a meristem and a branching point, was used as a structural unit of roots. Nodulated field plants displayed a random model of root topology and experimental plants without root symbionts a herringbone model (Fitter, 1991). The occurrence of these different root topologies would suggest that root symbionts influence root model architecture. The frequency distribution of the number of nodules per link on the main roots, for field collected plants, fitted a negative binomial model. Nodules were mainly situated near the main root's proximal end. The position (number of links counted from the main root's proximal end to the root apex) of lateral nodulated roots coincided with the nodulated area of the main root. A nodulation assay showed that the spatial pattern of root nodules was not a consequence of heterogeneous distribution of infective units of Frankia in the soil. The similar pattern of nodule position in field plants and experimental plants suggested that a regulation of nodulation might be also working in plants in their natural environment.

Specificity in Discaria - Frankia Symbioses

Abstract: For some years we have been studying symbioses in native actinorhizal plants belonging to the Family Rhamnaceae, namely Discaria trinervis, Discaria chacaye and Discaria articulata. All these species are distributed in the south west of South America, at the Patagonia. We are interested in the mechanisms of regulation of the nodulation and the meaning of specificity and recognition in these symbioses, in order to look for the unknown symbiotic signals involved in the Frankia actinorhizal association.

Root Hair-Frankia Interactions in Actinorhizal Symbioses

Abstract: The term actinorhizae refers to the nitrogen-fixing nodular structures induced on roots of higher plants by the actinomycete Frankia (Tjepkema and Torrey 1979). Occurrence of actinorhizal nodules is reported for about 200 different plant species from 23 genera distributed over eight dicotyledonous families (Table 1; van Ghelue 1994). Except for the genus Datisca, all other actinorhizal hosts are woody shrubs and their geographical distribution is primarily temperate. Only some hosts of the families Casuarinaceae and Myricaceae are tropical. Actinorhizal plants possess great economic value as timber and fuel wood. They are also used extensively in land reclamation and as ornamental shrubs. Ecologically, actinorhizal plants are pioneer invaders of nitrogen poor sites (Baker and Schwintzer 1990).

Frankia and Actinorhizal Plants

Abstract: In actinorhizal symbiosis, actinomycetous soil bacteria of the genus Frankia induce the formation of nitrogen-fixing root nodules on dicotyledonous plants from eight different families (Betulaceae, Casuarinaceae, Coriariaceae, Datiscaceae, Elaeagnaceae, Myricaceae, Rhamnaceae and Rosaceae), usually woody shrubs. Phylogenetic evidence has shown that all plants able to form nitrogen-fixing root nodules, i.e. actinorhizal plants and legumes, map in the same clade and thus go back to a common ancestor (Soltis et al. 1995). More detailed studies by Swensen (1996) and Doyle (1997) have revealed that among the plants with this predisposition, both actinorhizal and rhizobial symbioses seem to have been established several times independently.