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PubMed2001

DNA synthesis and fragmentation in bacteroids during Astragalus sinicus root nodule development.

Histo- and cytochemical techniques were used to study the DNA replication and fragmentation patterns in bacteroids formed by Mesorhizobium huakuii subsp. rengei in nodules of Astragalus sinicus. DNA replication was detected by the incorporation of 5-bromo deoxy-uridine. Signals denoting DNA synthesis were observed in plant nuclei within the nodule meristem and in bacteroids near the meristem. The TUNEL (TdT-mediated dUTP nick-end labeling) assay was used to measure DNA fragmentation. In nutrient-depleted 1-mpi (month(s) post inoculation) nodule sections, some bacteroids were in vacuoles, and DNA fragmentation signals were observed only in such bacteroids. In contrast, 1-mpi nodule sections without nutrient depletion showed neither bacteroid localization in vacuoles nor DNA fragmentation signals. The bacteroid translocation into vacuoles upon nutrient starvation might results from autophagy of the plant. In 2-mpi nodule sections, bacteroids with DNA fragmentation signals appeared within the cytoplasm of some nodule cells in the senescence zone.

DNA Fragmentation↗
PubMed1991

Differential expression of phenylalanine ammonia-lyase and chalcone synthase during soybean nodule development.

We have used conserved and nonconserved regions of cDNA clones for phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS) isolated from a soybean-nodule cDNA library to monitor the expression of members of the two gene families during the early stages of the soybean-Bradyrhizobium japonicum symbiosis. Our results demonstrate that subsets of the PAL and CHS gene families are specifically induced in soybean roots after infection with B. japonicum. Furthermore, by analyzing a supernodulating mutant line of soybean that differs from the wild-type parent in the number of successful infections, we show that the induction of PAL and CHS is related to postinfection events. Nodulated roots formed by a Nod+ Fix- strain of B. japonicum, resembling a pathogenic association, display induction of another distinct set of PAL and CHS genes. Our results suggest that the symbiosis-specific PAL and CHS genes in soybean are not induced by stress or pathogen interaction.

Acyltransferases↗
PubMed2006

Deregulation of a Ca2+/calmodulin-dependent kinase leads to spontaneous nodule development.

Induced development of a new plant organ in response to rhizobia is the most prominent manifestation of legume root-nodule symbiosis with nitrogen-fixing bacteria. Here we show that the complex root-nodule organogenic programme can be genetically deregulated to trigger de novo nodule formation in the absence of rhizobia or exogenous rhizobial signals. In an ethylmethane sulphonate-induced snf1 (spontaneous nodule formation) mutant of Lotus japonicus, a single amino-acid replacement in a Ca2+/calmodulin-dependent protein kinase (CCaMK) is sufficient to turn fully differentiated root cortical cells into meristematic founder cells of root nodule primordia. These spontaneous nodules are genuine nodules with an ontogeny similar to that of rhizobial-induced root nodules, corroborating previous physiological studies. Using two receptor-deficient genetic backgrounds we provide evidence for a developmentally integrated spontaneous nodulation process that is independent of lipochitin-oligosaccharide signal perception and oscillations in Ca2+ second messenger levels. Our results reveal a key regulatory position of CCaMK upstream of all components required for cell-cycle activation, and a phenotypically divergent series of mutant alleles demonstrates positive and negative regulation of the process.

Amino Acid Sequence↗
PubMed1997

A nodule-specific gene family from Alnus glutinosa encodes glycine- and histidine-rich proteins expressed in the early stages of actinorhizal nodule development.

Two cDNAs representing different members (agNt84 and ag164) of a gene family encoding glycine- and histidine-rich proteins have been isolated from cDNA libraries from Alnus glutinosa root nodules. Expression of the corresponding genes could only be detected in nodules. With in situ hybridization, the expression in nodules was found to occur in young, infected cells of the prefixation zone (zone 2). The encoded proteins contain putative signal peptides for targeting to the endomembrane system, sharing sequence similarity with signal peptides from plant glycine-rich proteins, among them nodulin 24, a nodule-specific protein from soybean. This similarity suggests that, analogous to nodulin-24, proteins encoded by agNt84/ag164 may be located at the interface between the host plant membrane and the matrix surrounding the endosymbiont. The 3' untranslated regions of the cDNAs contain unusual poly(AT)n stretches that may play a role in the regulation of RNA stability. The protein encoded by agNt84 cDNA was expressed in Escherichia coli as a fusion with maltose-binding protein, and was shown to have the ability to bind to a nickel-chelating resin, indicating that it may function as a metal-binding protein.

Actinomycetales↗
PubMed2004

A Ca2+/calmodulin-dependent protein kinase required for symbiotic nodule development: Gene identification by transcript-based cloning.

In the establishment of the legume-rhizobial symbiosis, bacterial lipochitooligosaccharide signaling molecules termed Nod factors activate the formation of a novel root organ, the nodule. Nod factors elicit several responses in plant root hair cells, including oscillations in cytoplasmic calcium levels (termed calcium spiking) and alterations in root hair growth. A number of plant mutants with defects in the Nod factor signaling pathway have been identified. One such Medicago truncatula mutant, dmi3, exhibits calcium spiking and root hair swelling in response to Nod factor, but fails to initiate symbiotic gene expression or cell divisions for nodule formation. On the basis of these data, it is thought that the dmi3 mutant perceives Nod factor but fails to transduce the signal downstream of calcium spiking. Additionally, the dmi3 mutant is defective in the symbiosis with mycorrhizal fungi, indicating the importance of the encoded protein in multiple symbioses. We report the identification of the DMI3 gene, using a gene cloning method based on transcript abundance. We show that transcript-based cloning is a valid approach for cloning genes in barley, indicating the value of this technology in crop plants. DMI3 encodes a calcium/calmodulin-dependent protein kinase. Mutants in pea sym9 have phenotypes similar to dmi3 and have alterations in this gene. The DMI3 class of proteins is well conserved among plants that interact with mycorrhizal fungi, but it is less conserved in Arabidopsis thaliana, which does not participate in the mycorrhizal symbiosis.

Amino Acid Sequence↗
PubMed1991

Onchocerca fasciata Railliet and Henry, 1910 and its nodule development in camels in Saudi Arabia.

A total of 192 male camels of three age groups (young, adult and old) from Saudi Arabia were examined for Onchocerca fasciata infection by detection of microfilariae in skin snips and nodules in the nuchal ligaments and subcutaneous tissues of the neck and shoulder. The overall prevalence rates were 10.9 and 33.3%, respectively. The prevalence rate by the skin snip technique and the number of microfilariae per gram of skin were higher in young and adult camels than in old camels. However, the prevalence rate by the detection of nodules and the number of nodules per infected camel, increased with increase in age of the camels. An increase in size and weight of nodules was reported with an increase in age of the camels. Nodules varied in diameter from 2 to 36 mm and in weight from 0.5 to 5.0 g. The overall percentage of soft viable and calcified nodules was 42.5 and 57.5%, respectively. The viability of worms decreased, but calcification increased with increased age of the camels. Four levels of degeneration and calcification of worms were described following scanning electron microscopy.

Animals↗
PubMed1996

Nodule development induced by mutants of Bradyrhizobium japonicum defective in cyclic B-glucan synthesis.

The soybean response to inoculation with B. japonicum mutants defective in cyclic beta-(1-->3), beta-(1-->6) glucan synthesis was examined by electron microscopy and by monitoring the expression of early and late nodulin genes. Two mutants were examined. Strain AB-14 is an ndvB mutant and is unable to synthesize beta-glucans. Strain AB-1 is an ndvC mutant and produces cyclic glucans containing 95 to 100% beta-(1-->3) glycosidic linkages. Nodules formed by either mutant were defective in nitrogen fixation activity. Soybean plants inoculated with strain AB-14 formed nodules roughly at the same rate as the wild-type strain USDA110, but nodulation by strain AB-1 was significantly delayed. Microscopy of nodules formed by strain AB-14 showed an overall ultrastructure similar to nodules formed by the wild type. However, in some nodules bacteroids were limited to only one part of the infected cells and in others the few bacteroids present showed signs of degradation. Nodulelike structures were formed by strain AB-1 that showed some signs of cellular differentiation. For example, clear parenchyma and sclerenchyma tissue could be seen. However, no infection threads or bacteria were evident in these structures. The expression of early (e.g., ENOD2 and ENOD55) and late (e.g., NOD26 and leghemoglobin) nodulins was examined. Nodules formed by strain AB-14 expressed all of the nodulins tested but at a reduced level. Expression of late nodulins was delayed in strain AB-14-induced nodules. Nodules formed by strain AB-1 were more strongly affected in nodulin expression. Although leghemoglobin synthesis was not detected, infection-specific nodulin transcripts of GmN93 and ENOD55 were detected. However, expression of the early nodulins ENOD2 and ENOD55 was considerably delayed and only apparent when assayed 21 days postinoculation. A low level of expression of intermediate nodulin GmN70 and late nodulin NOD26 could also be detected by 21 days postinoculation. The microscopy data show that tissue differentiation occurs in these nodules even in the absence of active bacterial invasion. These results demonstrate the importance of cyclic beta-(1-->3), beta-(1-->6) glucan synthesis to symbiotic development in soybean.

DNA Primers↗
PubMed2003

cg12 expression is specifically linked to infection of root hairs and cortical cells during Casuarina glauca and Allocasuarina verticillata actinorhizal nodule development.

cg12 is an early actinorhizal nodulin gene from Casuarina glauca encoding a subtilisin-like serine protease. Using transgenic Casuarinaceae plants carrying cg12-gus and cg12-gfp fusions, we have studied the expression pattern conferred by the cg12 promoter region after inoculation with Frankia. cg12 was found to be expressed in root hairs and in root and nodule cortical cells containing Frankia infection threads. cg12 expression was also monitored after inoculation with ineffective Frankia strains, during mycorrhizae formation, and after diverse hormonal treatments. None of these treatments was able to induce its expression, therefore suggesting that cg12 expression is linked to plant cell infection by Frankia strains. Possible roles of cg12 in actinorhizal symbiosis are discussed.

Arabidopsis↗
PubMed1996

Total Glutamine Synthetase Activity during Soybean Nodule Development Is Controlled at the Level of Transcription and Holoprotein Turnover.

Gln synthetase (GS) catalyzes the ATP-dependent condensation of ammonia with glutamate to yield Gln. In higher plants GS is an octameric enzyme and the subunits are encoded by members of a small multigene family. In soybeans (Glycine max), following the onset of N2 fixation there is a dramatic increase in GS activity in the root nodules. GS activity staining of native polyacrylamide gels containing nodule and root extracts showed a common band of activity (GSrs). The nodules also contained a slower-migrating, broad band of enzyme activity (GSns). The GSns activity band is a complex of many isozymes made up of different proportions of two kinds of GS subunits: GSr and GSn. Root nodules formed following inoculation with an Nif- strain of Bradyrhizobium japonicum showed the presence of GS isoenzymes (GSns1) with low enzyme activity, which migrated more slowly than GSns. Gsns1 is most likely made up predominantly of GSn subunits. Our data suggest that, whereas the class I GS genes encoding the GSr subunits are regulated by the availability of NH3, the class II GS genes coding for the GSn subunits are developmentally regulated. Furthermore, we have demonstrated that the GSns1 isozymes in the Nif- nodules are relatively more labile. Our overall conclusion is that GSns activity in soybean nodules is regulated by N2 fixation both at the level of transcription and at the level of holoprotein stability.

Journal Article↗
PubMed1981

Enzymes of Purine Biosynthesis and Catabolism in Glycine max: I. COMPARISON OF ACTIVITIES WITH N(2) FIXATION AND COMPOSITION OF XYLEM EXUDATE DURING NODULE DEVELOPMENT.

During the period examined from 12 to 63 days after planting, the ureides, allantoin and allantoic acid, were the predominant nitrogenous solutes in the xylem exudate of soybeans (Glycine max [L.]) growing solely on symbiotically fixed nitrogen, accounting for approximately 60% and greater than 95% of the total nitrogen in the xylem exudate before and after the onset of active nitrogen fixation, respectively. For plants between 18 and 49 days of age, the apparent rate of ureide export estimated from concentrations of ureides in xylem exudate collected over a period of one hour was closely related to the rate of nitrogen fixation estimated from measurements of C(2)H(2) reduction by nodulated root systems. After this time, the apparent rate of ureide export per plant continued to increase, reaching a maximum value at day 63 of 12 micromoles per plant per hour, even though the rate of C(2)H(2) reduction per plant declined approximately four-fold. The most probable pathway for the biosynthesis of ureides involves the catabolism of purines. The levels of phosphoribosylpyrophosphate (PRPP) synthetase, which catalyzes the formation of the PRPP required for purine synthesis, increased in parallel with the rates of nitrogen fixation (C(2)H(2)) from day 18 reaching a maximum value of 13.9 micromoles per plant per hour at day 49, and then both activities declined rapidly. During the period of active nitrogen fixation the ratio of PRPP synthesis estimated from measurements of PRPP synthetase activity in cell-free extracts to the apparent rate of ureide export was between 1 and 2. The activities of the enzymes of purine catabolism, xanthine dehydrogenase, uricase, and allantoinase, increased in parallel with the increases in nodule mass and the export of ureides with maximum activities of 13, 119, and 79 micromoles per plant per hour, corresponding with apparent rates of ureide export in the range of 9.5 to 11.9 micromoles per plant per hour. These results demonstrate that there is a close association between nitrogen fixation, PRPP synthetase activity, and ureide export in soybeans and support the proposal that recently-fixed nitrogen is utilized in the de novo synthesis of purines which are subsequently catabolized to produce the ureides.

Journal Article↗
PubMed1987

Lupin leghemoglobins during root nodule development.

Two yellow lupin leghemoglobins, Lb I and Lb II, were purified to homogeneity using the HPLC technique for final separation. Lb I and Lb II were identified by the N-terminal sequences and their reaction with antibodies against electrophoretically pure leghemoglobin. The third Lb species was detected by the combined method of isoelectrofocusing and PAGE of Lb I. It seems that Lb III represents a posttranslational modification of Lb I. Developmental changes in Lb multiple forms were examined using the Western blotting method. The content of leghemoglobin, first detectable approximately 3 weeks after infection, increased up to 6-7 weeks, and then it remained at the same level until 8-9 weeks after the infection. At the early stages of nodule formation Lb I prevailed over Lb II, while later Lb II became the predominant form. This suggests physiological role of particular forms and precise regulation of the expression of Lb genes.

Amino Acid Sequence↗
PubMed2005

An iron uptake operon required for proper nodule development in the Bradyrhizobium japonicum-soybean symbiosis.

Rhizobia live in the soil or enter into a nitrogen-fixing symbiosis with a suitable host plant. Each environment presents different challenges with respect to iron acquisition. The soybean symbiont Bradyrhizobium japonicum 61A152 can utilize a variety of siderophores (Fe[III]-specific ligands). Purification of iron-regulated outer membrane proteins had previously allowed the cloning of a gene, fegA, from B. japonicum 61A152, whose predicted protein shares significant amino acid similarity with known TonB-dependent siderophore receptors. Here, we show that fegA is in an operon with a gene, fegB, that is predicted to encode an inner membrane protein. Characterization of fegAB and fegB mutants shows that bothfegA and fegB are required for utilization of the siderophore ferrichrome. Whereas thefegB mutant forms a normal symbiosis, the fegAB mutant has a dramatic phenotype in planta. Six weeks after inoculation with a fegAB strain, soybean nodules do not contain leghemoglobin and do not fix nitrogen. Infected cells contain few symbiosomes and are filled with vesicles. As ferrichrome is a fungal siderophore not likely to be available in nodules, the symbiotic defect suggests that the fegAB operon is serving a different function in planta, possibly one involved in signaling between the two partners.

Bacterial Outer Membrane Proteins↗