Legumes form symbiotic associations with both mycorrhizal fungi and nitrogen-fixing soil bacteria called rhizobia. Several of the plant genes required for transduction of rhizobial signals, the Nod ...factors, are also necessary for mycorrhizal symbiosis. Here, we describe the cloning and characterization of one such gene from the legume Medicago truncatula. The DMI1 (does not make infections) gene encodes a novel protein with low global similarity to a ligand-gated cation channel domain of archaea. The protein is highly conserved in angiosperms and ancestral to land plants. We suggest that DMI1 represents an ancient plant-specific innovation, potentially enabling mycorrhizal associations.
Microsatellites are tandemly repeated short DNA sequences that are favored as molecular-genetic markers due to their high polymorphism index. Plant genomes characterized to date exhibit ...taxon-specific differences in frequency, genomic location, and motif structure of microsatellites, indicating that extant microsatellites originated recently and turn over quickly. With the goal of using microsatellite markers to integrate the physical and genetic maps of Medicago truncatula, we surveyed the frequency and distribution of perfect microsatellites in 77 Mbp of gene-rich BAC sequences, 27 Mbp of nonredundant transcript sequences, 20 Mbp of random whole genome shotgun sequences, and 49 Mbp of BAC-end sequences. Microsatellites are predominantly located in gene-rich regions of the genome, with a density of one long (i.e., > or = 20 nt) microsatellite every 12 kbp, while the frequency of individual motifs varied according to the genome fraction under analysis. A total of 1,236 microsatellites were analyzed for polymorphism between parents of our reference intraspecific mapping population, revealing that motifs (AT)n, (AG)n, (AC)n, and (AAT)n exhibit the highest allelic diversity. A total of 378 genetic markers could be integrated with sequenced BAC clones, anchoring 274 physical contigs that represent 174 Mbp of the genome and composing an estimated 70% of the euchromatic gene space.
The establishment of the nitrogen-fixing symbiosis between rhizobia and legumes requires an exchange of signals between the two partners. In response to flavonoids excreted by the host plant, ...rhizobia synthesize Nod factors (NFs) which elicit, at very low concentrations and in a specific manner, various symbiotic responses on the roots of the legume hosts. NFs from several rhizobial species have been characterized. They all are lipo-chitooligosaccharides, consisting of a backbone of generally four or five glucosamine residues N-acylated at the non-reducing end, and carrying various O-substituents. The N-acyl chain and the other substituents are important determinants of the rhizobial host specificity. A number of nodulation genes which specify the synthesis of NFs have been identified. All rhizobia, in spite of their diversity, possess conserved nodABC genes responsible for the synthesis of the N-acylated oligosaccharide core of NFs, which suggests that these genes are of a monophyletic origin. Other genes, the host specific nod genes, specify the substitutions of NFs. The central role of NFs and nod genes in the Rhizobium-legume symbiosis suggests that these factors could be used as molecular markers to study the evolution of this symbiosis. We have studied a number of NFs which are N-acylated by alpha,beta-unsaturated fatty acids. We found that the ability to synthesize such NFs does not correlate with taxonomic position of the rhizobia. However, all rhizobia that produce NFs such nodulate plants belonging to related tribes of legumes, the Trifolieae, Vicieae, and Galegeae, all of them being members of the so-called galegoid group. This suggests that the ability to recognize the NFs with alpha-beta-unsaturated fatty acids is limited to this group of legumes, and thus might have appeared only once in the course of legume evolution, in the galegoid phylum.
In the French-speaking part of Belgium, between march and end of may 2020, 284 patients have suffered a Covid-19 infection, 7,9% of the prevalent dialysis population. Some of them have been ...diagnosed through rt-PCT as they were symptomatic, others, asymptomatic, being diagnosed by swab viral culture. Fifty two patients died (18% of the positive patients). The vast majority of them were patients on hemodialysis, only ten cases have been observed in patients on home dialysis techniques. Primary renal disease were diabetes or renal hypertensive disease in more than 50% of the patients and the most important comorbidities were cardiac ischemic or congestive disease, autonomy problems, cancer and smoking habits.
Rhizobia nodulation (nod) genes are involved in the synthesis of symbiotic signals, the Nod factors, which are mono-N-acylated chito-oligosaccharides. Nod factors elicit, in a specific manner, ...various plant responses on legume roots. In this report we address the question of the role of nodFEG genes in the synthesis of the acyl moiety of Rhizobium meliloti Nod factors. In a Nod factor-overproducing strain with the wild-type nod region, in addition to the delta2,9-C16:2 and delta2,4,9-C16:3 acyl groups already described, delta9-C16:1 was also found, together with a series of C18 to C26 (omega-1)-hydroxylated fatty acids. A deletion of nodE resulted in the absence of C16:2 and C16:3 fatty acids, which were replaced by vaccenic acid (delta11-C18:1), but did not change the proportion of (omega-1)-hydroxylated fatty acids. A nodF deletion, non-polar with respect to nodE, resulted in the same alterations in the Nod factor N-acyl composition, showing that both nodF and nodE are required for the synthesis of the C16, polyunsaturated chains. In contrast, nodG mutations did not result in a detectable change in the Nod factor N-acyl moiety. When a plasmid carrying the nodFE genes of Rhizobium leguminosarum bv. viciae was introduced into R. meliloti nodFE- and nodFEG-deleted strains, Nod factors with polyunsaturated C18 fatty acids (C18:2, C18:3, and C18:4) could be detected. These results provide evidence that the molecular basis of allelic variation between the R. meliloti and R. leguminosarum bv. viciae host range nodFE genes lies in the fact that the two nodFE alleles specify the synthesis of unsaturated fatty acid substituents with a different carbon length.
The Medicago truncatula DMI3 gene encodes a calcium- and calmodulin-dependent protein kinase (CCaMK) that is necessary for the establishment of both rhizobial and mycorrhizal symbioses. The two ...symbiotic signaling pathways diverge downstream of DMI3; therefore, it has been proposed that legumes have evolved a particular form of CCaMK, acting like a switch able both to discriminate between rhizobial and mycorrhizal calcium signatures and to trigger the appropriate downstream signaling pathway. To test this hypothesis, we examined whether a CCaMK gene from a nonlegume species was able to restore the rhizobial symbiotic properties of a M. truncatula dmi3 mutant. Our results show that a CCaMK gene from rice can restore nodule formation, indicating that CCaMKs from nonlegumes can interpret the calcium signature elicited by rhizobial Nod factors and activate the appropriate downstream target. The nodules did not contain bacteria, which suggests that DMI3 is also involved in the control of the infection process.
Rhizobia are symbiotic bacteria that synthesize lipochitooligosaccharide Nod factors (NFs), which act as signal molecules in the nodulation of specific legume hosts. Based on the structure of their ...N‐acyl chain, NFs can be classified into two categories: (i) those that are acylated with fatty acids from the general lipid metabolism; and (ii) those (= αU‐NFs) that are acylated by specific α,β‐unsaturated fatty acids (containing carbonyl‐conjugated unsaturation(s)). Previous work has described how rhizobia that nodulate legumes of the Trifolieae and Vicieae tribes produce αU‐NFs. Here, we have studied the structure of NFs from two rhizobial species that nodulate important genera of the Galegeae tribe, related to Trifolieae and Vicieae. Three strains of Mesorhizobium huakuii, symbionts of Astragalus sinicus, produced as major NFs, pentameric lipochitooligosaccharides O‐sulphated and partially N‐glycolylated at the reducing end and N‐acylated, at the non‐reducing end, by a C18:4 fatty acid. Two strains of Rhizobium galegae, symbionts of Galega sp., produced as major NFs, tetrameric O‐carbamoylated NFs that could be O‐acetylated on the glucosamine residue next to the non‐reducing terminal glucosamine and were N‐acylated by C18 and C20 α,β‐unsaturated fatty acids. These results suggest that legumes nodulated by rhizobia synthesizing αU‐NFs constitute a phylogenetic cluster in the Galegoid phylum.
Rhizobia synthesize mono-N-acylated chitooligosaccharide signals, called Nod factors, that are required for the specific infection and nodulation of their legume hosts. The biosynthesis of Nod ...factors is under the control of nodulation (nod) genes, including the nodABC genes present in all rhizobial species. The N-acyl substitution can vary between species and can play a role in host specificity. In Rhizobium meliloti, an alfalfa symbiont, the acyl chain is a C16 unsaturated or a (omega-1) hydroxylated fatty acid, whereas in Rhizobium tropici, a bean symbiont, it is vaccenic acid (C18:1). We constructed R. meliloti derivatives having a nonpolar deletion of nods, and carrying a plasmid with either the R. meliloti or the R. tropici nodA gene. The strain with the R. tropici nodA gene produced Nod factors acylated by vaccenic acid, instead of the C16 unsaturated or hydroxylated fatty acids characteristic of R. meliloti Nod factors, and infected and nodulated alfalfa with a significant delay. These results show that NodA proteins of R. meliloti and R. tropici specify the N-acylation of Nod factors by different fatty acids, and that allelic variation of the common nodA gene can contribute to the determination of host range.
Background. Aristolochic acid (AA), the plant extract of Aristolochia species, is involved in the onset of progressive tubulointerstitial renal fibrosis in humans. Clinical and in vitro findings have ...previously suggested that the proximal tubule was the target of AA. Methods. Using a rat model of AA nephropathy, the proximal tubular lesions induced by daily subcutaneous injections of AA for 35 or 5 days were characterized biochemically and histologically. Urinary excretion of proteins, albumin, low molecular weight proteins, N-acetyl-β-d-glucosaminidase, α-glutathione S-transferase, leucine aminopeptidase and neutral endopeptidase (NEP) was determined and related to histological conventional findings and immunostainings of NEP and megalin. Results. In both protocols, an acute phase of release of urinary markers was observed within the first 3 days of AA treatment in parallel with a significant increase of specific AA-related DNA adducts reflecting early tubular intoxication. A dramatic loss of the proximal tubule brush border was histologically confirmed, while the expression of megalin decreased at the damaged apical epithelium (mainly of the S3 segment). Conclusion. Proximal tubule injury occurs early after AA intoxication in rats, with a link between specific AA–DNA adduct formation, decreased megalin expression and inhibition of receptor-mediated endocytosis of low molecular weight proteins, bringing in vivo confirmation of previous in vitro studies.
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