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PubMedDate not supplied

[Nitrate assimilation activity of yellow lupine root nodules ?].

Low nitrate assimilation activity of the root nodules was demonstrated by assaying the nitrate reductase, glutamate synthase, glutamate dehydrogenase, and asparagine synthase activities, as well as the kinetics of 14C-labeled saccharose incorporation in the amino acids and amides of the cortex and the bacteroid-containing root nodule zones. Irrespective of the exogenous nitrogen concentration (0, 11.2, or 25 mM NO3-), nitrate concentration in the nodules was low as compared to the plant roots, leaves, and stems. This allowed us to propose the presence of structural and/or metabolic barriers in the nodules limiting nitrate accessibility and assimilation.

Amino Acids↗

PubMedDate not supplied

Gene expression of Medicago sativa inoculated with Sinorhizobium meliloti as modulated by the xenobiotics cadmium and fluoranthene.

Alfalfa plants (Medicago sativa cv. Europe) inoculated with Sinorhizobium meliloti 2011 (formerly Rhizobium meliloti, de Lajudie et al., 1994) were cultivated for 14 days under standardized growth conditions in mineral medium with addition of the heavy metal cadmium or the polycyclic aromatic hydrocarbon fluoranthene. These xenobiotics significantly reduced the numbers of root nodules before any visible damage to the plant could be detected. EC10, EC50, and EC90 (effective concentrations reducing nodulation, shoot and root fresh weight by 10, 50, or 90% compared to the control without pollutant) were calculated. EC50 for cadmium ranged from 5.8 microM (nodulation) to more than 20 microM (root fresh weight). Testing fluoranthene resulted in an EC50 of 2.5 microg cm(-2) for nodulation, and EC50 values of more than 35 microg cm(-2) for shoot and root biomass production, indicating that the effect parameter nodulation is 10-fold more sensitive than shoot and root fresh weight. With mRNA differential display techniques the effects of both xenobiotics on gene expression in alfalfa root systems were studied. 37 differentially displayed transcripts were detected. Two of them, called DDMs1 and DDMs2, were confirmed by northern hybridization to be down-regulated in the presence of the xenobiotics. The expression of transcript DDMs1 was enhanced in alfalfa control plants inoculated with rhizobia, the transcript level was increased 2.5-3-fold compared to non-inoculated plants. This positive effect of nodulation was suppressed, partly by 35 microg cm(-2) fluoranthene and totally by 20 microM cadmium. The decrease in DDMs1 transcription was highly affected by the cadmium concentration with an EC50 of 5.9 microM. Compared to nodulation, almost identical EC10, EC50, and EC90 values were found for DDMs1 expression. Sequence analysis of DDMs1 revealed a significant overall homology (50% identity) to a hypothetical protein from Arabidopsis thaliana with high similarity to a copper transporting ATPase. High levels of transcript DDMs2 were observed in control plants with a 50% decrease in the xenobiotic-treated plants. DDMs2 gave a strong homology (82% identity) to the cytoplasmatic 60S ribosomal protein L18 from Arabidopsis thaliana.

Amino Acid Sequence↗

PubMed1990

Oligonucleotide Probes That Hybridize with rRNA as a Tool To Study Frankia Strains in Root Nodules.

Oligonucleotide probes that hybridize with specific sequences in variable regions of the 16S rRNA of the nitrogen-fixing actinomycete Frankia were used for the identification of Frankia strains in nodules. Frankia cells were released from plant tissue by grinding glutaraldehyde-fixed root nodules in guanidine hydrochloride solution. rRNA was obtained after sonication, precipitation with ethanol, and purification by phenolchloroform extraction. Degradation of rRNA, evident in Northern blots, did not affect hybridization with the oligonucleotides. Nodules of about 1 mg (fresh weight) provided sufficient rRNA for reliable detection of the Frankia strain. The utility of this rRNA extraction method was tested in a competition experiment between two effective Frankia strains on cloned Alnus glutinosa plants.

Journal Article↗

PubMed1982

Effect of changes in shoot carbon-exchange rate on soybean root nodule activity.

The effect of short- and long-term changes in shoot carbon-exchange rate (CER) on soybean (Glycine max [L.] Merr.) root nodule activity was assessed to determine whether increases in photosynthate production produce a direct enhancement of symbiotic N(2) fixation. Shoot CER, root + nodule respiration, and apparent N(2) fixation (acetylene reduction) were measured on intact soybean plants grown at 700 microeinsteins per meter per second, with constant root temperature and a 14/10-hour light/dark cycle. There was no diurnal variation of root + nodule respiration or apparent N(2) fixation in plants assayed weekly from 14 to 43 days after planting. However, if plants remained in darkness following their normal dark period, a significant decline in apparent N(2) fixation was measured within 4 hours, and decreasing CO(2) concentration from 320 to 90 microliters CO(2) per liter produced diurnal changes in root nodule activity. Increasing shoot CER by 87, 84, and 76% in 2-, 3-, and 4-week-old plants, respectively, by raising the CO(2) concentration around the shoot from 320 to 1,000 microliters CO(2) per liter, had no effect on root + nodule respiration or acetylene-reduction rates during the first 10 hours of the increased CER treatment. When the CO(2)-enrichment treatment was extended in 3-week-old plants, the only measured parameter that differed significantly after 3 days was shoot CER. After 5 days of continuous CO(2) enrichment, root + nodule respiration and acetylene reduction increased, but such changes reflected an increase in root nodule mass rather than greater specific root nodule activity. The results show that on a 24-hour basis the process of symbiotic N(2) fixation in soybean plants grown under controlled environmental conditions functioned at maximum capacity and was not limited by shoot CER. Whether N(2)-fixation capacity was limited by photosynthate movement to root nodules or by saturation of metabolic processes in root nodules is not known.

Journal Article↗

PubMed1999

A new class of plant homeobox genes is expressed in specific regions of determinate symbiotic root nodules.

A cDNA containing a homeobox sequence was isolated from a soybean nodule-specific expression library. This homeobox cDNA, Ndx (nodulin homeobox), represents a small gene family with at least two members in soybean (Glycine max) and three in Lotus japonicus. One complete 3304 bp Ndx cDNA from L. japonicus encodes a protein, NDX, of 958 amino acids. An unusual type of homeodomain that differs in two of the most conserved amino acid positions in the consensus sequence is located close to the C-terminal and appears to be the only DNA-binding domain. Weak Ndx gene expression in the root increases very shortly after infection with Rhizobium and remains throughout nodule development. In situ hybridizations show cell-specific expression patterns that suggest developmentally separate regions in maturing determinate nodules. Thus in the maturing nodule Ndx and leghemoglobin genes are expressed in a mutually exclusive fashion. The Ndx transcript is also detectable in the young nodule primordium. Ndx expression is not confined to the root nodule since Ndx is also expressed in shoot and root meristems, indicating that the Ndx gene products might also be involved in developmental processes in other plant tissues.

Amino Acid Sequence↗

PubMed1986

Primary structure and differential expression of glutamine synthetase genes in nodules, roots and leaves of Phaseolus vulgaris.

In plants, glutamine synthetase (GS) is the enzyme primarily responsible for the assimilation of ammonia into organic nitrogen. In Phaseolus vulgaris a number of isoenzymic forms of GS are found, each of which consists of eight subunits of mol. wt 41 000-45 000. The GS subunits of P. vulgaris have previously been shown to be encoded by a small multigene family and a partial cDNA clone for a nodule-specific GS subunit has been obtained. We report here the isolation and nucleotide sequencing of two essentially full-length GS cDNA clones (pR-1 and pR-2) from a root cDNA library and the deduced amino acid sequences of the corresponding GS subunits (355 amino acid residues each). The coding sequences of pR-1 and pR-2 are closely related (80% nucleotide homology, 88% amino acid homology), but their 5'- and 3'-untranslated regions have diverged almost completely. Both pR-1 and pR-2 are related to, but distinct from, the nodule GS clone, pcPvNGS-01 (or pN-1). Hybridization to genomic Southern blots showed that the three GS mRNAs are encoded by three seperate genes and indicated the existence of a fourth class of GS gene. An S1 nuclease protection assay demonstrated the presence of R-1 and R-2 mRNA in both roots and leaves and confirmed that expression of the N-1 gene is nodule-specific. Expression of the R-1 and R-2 genes in the roots did not change significantly during nodulation. However, only the R-1 gene is expressed in the nodules themselves, indicating that the R-2 gene is specifically repressed during nodule development.

Journal Article↗

PubMed2003

Description of Devosia neptuniae sp. nov. that nodulates and fixes nitrogen in symbiosis with Neptunia natans, an aquatic legume from India.

Neptunia natans is a unique aquatic legume indigenous to tropical and sub-tropical regions and is nodulated symbiotically by rhizobia using an unusual infection process unlike any previously described. Previously, isolates of neptunia-nodulating rhizobia from Senegal were characterized as Allorhizobium undicola. Here we report on a different group of neptunia-nodulating rhizobia isolated from India. Sequencing of the 16S rDNA gene from two of these Indian isolates (strains J1T and J2) show that they belong in the genus Devosia rather than Allorhizobium. Currently, the only described Devosia species is D. riboflavina (family Hyphomicrobiaceae, order Rhizobiales). The complete 16S rDNA sequences of strains J1T and J2 are 95.9% homologous to the type strain, D. riboflavina LMG 2277T, suggesting that these neptunia-nodulating strains from India belong to a new Devosia species. This hypothesis was confirmed by further studies of polyphasic taxonomy (DNA-DNA hybridisation, TP-RAPD patterns, SDS-PAGE of cellular proteins, 16S rDNA RFLP patterns, carbon source utilisation, cellular fatty acid analysis and other phenotypic characterisations), all of which support the proposal that these neptunia-nodulating strains constitute a new Devosia species, which we name Devosia neptuniae sp. nov. These gram negative, strictly aerobic short rods are motile by a subpolar flagellum, positive for catalase, oxidase, urease and beta-galactosidase, can utilise several carbohydrates (but not organic acids) as carbon sources and contain C18:0 3-OH, cis-7 C18:1 11-methyl and cis-7 C18:1 as their major cellular fatty acids. Unlike D. riboflavina, the longer-chain C24:1 3-OH and C26:1 3-OH hydroxy fatty acids are not detected. The type strain of D. neptuniae is LMG 21357T (CECT 5650T). Assignment of this new taxon represents the fourth example in the literature of a non-rhizobial genus of bacteria capable of forming a bonafide dinitrogen-fixing root-nodule symbiosis with legume plants.

Alphaproteobacteria↗

PubMed1999

Expression of a soybean gene encoding the tetrapyrrole-synthesis enzyme glutamyl-tRNA reductase in symbiotic root nodules.

Heme and chlorophyll accumulate to high levels in legume root nodules and in photosynthetic tissues, respectively, and they are both derived from the universal tetrapyrrole precursor delta-aminolevulinic acid (ALA). The first committed step in ALA and tetrapyrrole synthesis is catalyzed by glutamyl-tRNA reductase (GTR) in plants. A soybean (Glycine max) root-nodule cDNA encoding GTR was isolated by complementation of an Escherichia coli GTR-defective mutant for restoration of ALA prototrophy. Gtr mRNA was very low in uninfected roots but accumulated to high levels in root nodules. The induction of Gtr mRNA in developing nodules was subsequent to that of the gene Enod2 (early nodule) and coincided with leghemoglobin mRNA accumulation. Genomic analysis revealed two Gtr genes, Gtr1 and a 3' portion of Gtr2, which were isolated from the soybean genome. RNase-protection analysis using probes specific to Gtr1 and Gtr2 showed that both genes were expressed, but Gtr1 mRNA accumulated to significantly higher levels. In addition, the qualitative patterns of expression of Gtr1 and Gtr2 were similar to each other and to total Gtr mRNA in leaves and nodules of mature plants and etiolated plantlets. The data indicate that Gtr1 is universal for tetrapyrrole synthesis and that a Gtr gene specific for a tissue or tetrapyrrole is unlikely. We suggest that ALA synthesis in specialized root nodules involves an altered spatial expression of genes that are otherwise induced strongly only in photosynthetic tissues of uninfected plants.

Aldehyde Oxidoreductases↗

PubMed2005

Visualization of nodulation gene activity on the early stages of Rhizobium leguminosarum bv. viciae symbiosis.

A technique was optimized for the in situ detection of nodulation (nod) gene activity in Rhizobium leguminosarum bv. viciae symbiosis with compatible plant hosts Vicia tetrasperma (L.) SCHREB. and Pisum sativum L. The transcription of nodABC-lacZ fusion was visualized as beta-galactosidase (beta-Gal) activity after reaction with the chromogenic substrate X-Gal and subsequent light microscopy, while the background of the indigenous beta-Gal activity of rhizobia and the host plant was eliminated by glutaraldehyde treatment. V. tetrasperma was suggested as a suitable model plant for pea cross-inoculation group due to its advantages over the common model of V. hirsuta (L.) S.F. GRAY: compactness of the plant, extremely small seeds, fast development and stable nodulation under laboratory conditions. In the roots of both plants, a certain extent of nod gene activity was detectable in all rhizobia colonizing the rhizoplane. In pea 1 d after inoculation (d.a.i.), the maximum was localized in the region of emerging root hairs (RH) later (3 and 6 d.a.i.) shifting upwards from the root tip. Nodulation genes sustained full expression even in the infection threads inside the RH and the root cortex, independently of their association with nodule primordia. Comparison of two pea symbiotic mutant lines, Risnod25 and Risnod27, with the wild type did not reveal any differences in the RH formation, RH curling response and rhizoplane colonization. Both mutants appeared to be blocked at the infection thread initiation stage and in nodule initiation, consistent with the phenotype caused by other mutant alleles in the pea sym8 locus. Judging from the nod gene expression level and pattern in the rhizoplane, flavonoid response upon inoculation is preserved in both pea mutants, being independent of infection thread and nodule initiation.

Bacterial Proteins↗

PubMed1968

Calcium and Nodulation in Subterranean Clover (Trifolium subterraneum L.).

From a study of the effects of Ca ions on the nodulation of subterranean clover in flowing culture solutions it is concluded that root infection or nodule initiation has a higher Ca requirement than either nodule development or host plant growth in the presence of fixed nitrogen.Increasing Ca concentration from 246 to 720 mum had no effect on growth of the host plant but increased the number of nodules from 7 to 24 per plant. Decreasing Ca concentration from 246 to 4 mum progressively decreased both plant growth and nodule numbers.It is suggested that nodule infection or initiation required higher solution concentration of Ca than nodule development since transferring plants after 10 days in lower Ca treatments to 720 mum Ca for 7 days did not increase nodule numbers above those on plants treated continuously at low Ca. Similarly transferring plants from 720 mum Ca to lower Ca treatments did not decrease nodule numbers much below those on plants grown continuously at 720 mum Ca even though growth was depressed. Once initiated, nodule development proceeded at concentrations of Ca too low for plant growth.The high Ca requirement for root infection or nodule initiation was not thought to be due to effects on survival or growth of Rhizobium and could not be related to effects of Ca on a number of relevant processes:-tap root length, root hair development, or lateral root initiation.

Journal Article↗

PubMed1999

Soybean nodule sucrose synthase (nodulin-100): further analysis of its phosphorylation using recombinant and authentic root-nodule enzymes.

Sucrose synthase (SS) is a known phosphoserine-containing enzyme in legume root nodules and various other plant "sink" tissues. In order to begin to investigate the possible physiological significance of this posttranslational modification, we have cloned a full-length soybean nodule SS (nodulin-100) cDNA and overexpressed it in Escherichia coli. Authentic nodule SS and recombinant wild-type and mutant forms of the enzyme were purified and characterized. We document that a conserved serine near the N-terminus (Ser(11)) is the primary phosphorylation site for a nodule Ca(2+)-dependent protein kinase (CDPK) in vitro. Related tryptic digestion and mass spectral analyses indicated that this target residue was also phosphorylated in planta in authentic nodulin-100. In addition, a secondary phosphorylation site(s) in recombinant nodule SS was implicated given that all active mutant enzyme forms (S11A, S11D, S11C, and N-terminal truncation between Ala(2) and Arg(13)) were phosphorylated, albeit weakly, by the CDPK. This secondary site(s) likely resides between Glu(14) and Met(193) as evidenced by CNBr cleavage and phosphopeptide mapping. Phosphorylation of the recombinant and authentic nodule Ser(11) enzymes in vitro by the nodule CDPK had no major effect on the sucrose-cleavage activity and/or kinetic properties. However, phosphorylation decreased the apparent surface hydrophobicity of the recombinant wild-type enzyme, suggesting that this covalent modification could potentially play some role in the documented partitioning of nodulin-100 between the nodule symbiosome/plasma membranes and cytosol in planta.

Amino Acid Sequence↗

PubMed1983

Host Plant Cultivar Effects on Hydrogen Evolution by Rhizobium leguminosarum.

The effect of host plant cultivar on H(2) evolution by root nodules was examined in symbioses between Pisum sativum L. and selected strains of Rhizobium leguminosarum. Hydrogen evolution from root nodules containing Rhizobium represents the sum of H(2) produced by the nitrogenase enzyme complex and H(2) oxidized by any uptake hydrogenase present in those bacterial cells. Relative efficiency (RE) calculated as RE = 1 - (H(2) evolved in air/C(2) H(2) reduced) did not vary significantly among ;Feltham First,' ;Alaska,' and ;JI1205' peas inoculated with R. leguminosarum strain 300, which lacks uptake hydrogenase activity (Hup(-)). That observation suggests that the three host cultivars had no effect on H(2) production by nitrogenase. However, RE of strain 128C53 was significantly (P </= 0.05) greater in symbiosis with cultivar JI1205 than in root nodules of Feltham First. At a similar rate of C(2)H(2) reduction on a whole-plant basis, nearly 24 times more H(2) was evolved from the Feltham First/128C53 symbiosis than from the JI1205/128C53 association. Root nodules from the Alaska/128C53 symbiosis had an intermediate RE over the entire study period, which extended from 21 to 36 days after planting. Direct assays of uptake hydrogenase by two methods showed significant (P </= 0.05) host cultivar effects on H(2) uptake capacity of both strain 128C53 and the genetically related strain 3960. The (3)H(2) incorporation assay showed that strains 128C53 and 3960 in symbiosis with Feltham First had about 10% of the uptake hydrogenase activity measured in root nodules of Alaska or JI1205. These data are the first demonstration of significant host plant effects on rhizobial uptake hydrogenase in a single plant species.

Journal Article↗

PubMed2003

Host sanctions and the legume-rhizobium mutualism.

Explaining mutualistic cooperation between species remains one of the greatest problems for evolutionary biology. Why do symbionts provide costly services to a host, indirectly benefiting competitors sharing the same individual host? Host monitoring of symbiont performance and the imposition of sanctions on 'cheats' could stabilize mutualism. Here we show that soybeans penalize rhizobia that fail to fix N(2) inside their root nodules. We prevented a normally mutualistic rhizobium strain from cooperating (fixing N(2)) by replacing air with an N(2)-free atmosphere (Ar:O(2)). A series of experiments at three spatial scales (whole plants, half root systems and individual nodules) demonstrated that forcing non-cooperation (analogous to cheating) decreased the reproductive success of rhizobia by about 50%. Non-invasive monitoring implicated decreased O(2) supply as a possible mechanism for sanctions against cheating rhizobia. More generally, such sanctions by one or both partners may be important in stabilizing a wide range of mutualistic symbioses.

Argon↗

PubMed2005

Early responses to Nod factors and mycorrhizal colonization in a non-nodulating Phaseolus vulgaris mutant.

Legumes can acquire nitrogen through a symbiotic interaction with rhizobial bacteria. The initiation of this process is determined by a molecular dialogue between the two partners. Legume roots exude flavonoids that induce the expression of the bacterial nodulation genes, which encode proteins involved in the synthesis and secretion of signals called Nod factors (NFs). NFs signal back to the plant root and trigger several responses, leading to bacterial invasion and nodule formation. Here, we describe the molecular and cellular characterization of a Phaseolus vulgaris non-nodulating mutant (NN-mutant). Root hair cells of the NN-mutant plant respond with swelling and branching when inoculated with Rhizobium etli, albeit without curling induction. Furthermore, neither initiation of cell division in the outer cortex, nor entrapment of bacteria nor infection thread formation was observed. Both the bean wild-type and the NN-mutant responded with elevated intracellular calcium changes in the root hairs. Although the NN-mutant is deficient in early nodulin gene expression when inoculated with R. etli, it can be effectively colonized by arbuscular mycorrhizal fungi (Glomus intraradices). Our data indicate that the P. vulgaris NN-mutant is not blocked at the NFs early perception stage, but at later downstream stages between Ca(2+) signaling and early nodulin induction. This supports the idea that both microsymbionts are perceived and trigger different downstream pathways in the host plant.

Bacterial Proteins↗

PubMed2006

Recombination and selection shape the molecular diversity pattern of nitrogen-fixing Sinorhizobium sp. associated to Medicago.

We investigate the genetic structure and molecular selection pattern of a sympatric population of Sinorhizobium meliloti and Sinorhizobium medicae. These bacteria fix nitrogen in association with plants of the genus Medicago. A set of 116 isolates were obtained from a soil sample, from root nodules of three groups of plants representing among-species, within-species and intraline diversity in the Medicago genus. Bacteria were characterized by sequencing at seven loci evenly distributed along the genome of both Sinorhizobium species, covering the chromosome and the two megaplasmids. We first test whether the diversity of host plants influence the bacterial diversity recovered. Using the same data set, we then analyse the selective pattern at each locus. There was no relationship between the diversity of Medicago plants that were used for sampling and the diversity of their symbionts. However, we found evidence of selection within each of the two main symbiotic regions, located on the two different megaplasmids. Purifying selection or a selective sweep was found to occur in the nod genomic region, which includes genes involved in nodulation specificity, whereas balancing selection was detected in the exo region, close to genes involved in exopolysaccharide production. Such pattern likely reflects the interaction between host plants and bacterial symbionts, with a possible conflict of interest between plants and cheater bacterial genotypes. Recombination appears to occur preferentially within and among loci located on megaplasmids, rather than within the chromosome. Thus, recombination may play an important role in resolving this conflict by allowing different selection patterns at different loci.

Databases, Genetic↗

PubMed2003

Auxin distribution in Lotus japonicus during root nodule development.

For this work, Lotus japonicus transgenic plants were constructed expressing a fusion reporter gene consisting of the genes beta-glucuronidase (gus) and green fluorescent protein (gfp) under control of the soybean auxin-responsive promoter GH3. These plants expressed GUS and GFP in the vascular bundle of shoots, roots and leafs. Root sections showed that in mature parts of the roots GUS is mainly expressed in phloem and vascular parenchyma of the vascular cylinder. By detecting GUS activity, we describe the auxin distribution pattern in the root of the determinate nodulating legume L. japonicus during the development of nodulation and also after inoculation with purified Nod factors, N-naphthylphthalamic acid (NPA) and indoleacetic acid (IAA). Differently than white clover, which forms indeterminate nodules, L. japonicus presented a strong GUS activity at the dividing outer cortical cells during the first nodule cell divisions. This suggests different auxin distribution pattern between the determinate and indeterminate nodulating legumes that may be responsible of the differences in nodule development between these groups. By measuring of the GFP fluorescence expressed 21 days after treatment with Nod factors or bacteria we were able to quantify the differences in GH3 expression levels in single living roots. In order to correlate these data with auxin transport capacity we measured the auxin transport levels by a previously described radioactive method. At 48 h after inoculation with Nod factors, auxin transport showed to be increased in the middle root segment. The results obtained indicate that L. japonicus transformed lines expressing the GFP and GUS reporters under the control of the GH3 promoter are suitable for the study of auxin distribution in this legume.

Alphaproteobacteria↗

PubMed1993

Biology of Frankia strains, actinomycete symbionts of actinorhizal plants.

Frankia strains are N2-fixing actinomycetes whose isolation and cultivation were first reported in 1978. They induce N2-fixing root nodules on diverse nonleguminous (actinorhizal) plants that are important in ecological successions and in land reclamation and remediation. The genus Frankia encompasses a diverse group of soil actinomycetes that have in common the formation of multilocular sporangia, filamentous growth, and nitrogenase-containing vesicles enveloped in multilaminated lipid envelopes. The relatively constant morphology of vesicles in culture is modified by plant interactions in symbiosis to give a diverse array of vesicles shapes. Recent studies of the genetics and molecular genetics of these organisms have begun to provide new insights into higher-plant-bacterium interactions that lead to productive N2-fixing symbioses. Sufficient information about the relationship of Frankia strains to other bacteria, and to each other, is now available to warrant the creation of some species based on phenotypic and genetic criteria.

Actinomycetales↗

PubMed2005

Diverse bacteria isolated from root nodules of Phaseolus vulgaris and species within the genera Campylotropis and Cassia grown in China.

Eighty bacterial isolates from root nodules of the leguminous plants Phaseolus vulgaris, Campylotropis spp. and Cassia spp. grown in China were classified into five groups by phenotypic analyses, SDS-PAGE of whole-cell proteins, PCR-based 16S rRNA gene restriction-fragment-length-polymorphism and sequencing. Thirty-three isolates from the three plant genera were identified as Agrobacterium tumefaciens because they are closely related to the type strain of A. tumefaciens. Fourteen isolates from P. vulgaris grown in Yunnan and Inner Mongolia were classified as R. leguminosarum bv. phaseoli based on their close relationship with the type strain in numerical taxonomy and in 16S rDNA phylogeny. Twenty-seven isolates from Campylotropis delavayi, P. vulgaris and four species of Cassia grown in the central zones of China were classified into three groups within the genus Bradyrhizobium. One of these three groups could be defined as Bradyrhizobium japonicum. Our results demonstrated that P. vulgaris and the species of Campylotropis and Cassia could form nodules with diverse rhizobia in Chinese soils, including novel lineages associated with P. vulgaris. These results also offered information about the convergent evolution between rhizobia and legumes since the rhizobial populations associated with P. vulgaris in Chinese soils were completely different from those in Mexico, the original cite of this plant. Some rhizobial species could be found in all of the three leguminous genera.

Agrobacterium tumefaciens↗