Structure of the Mesorhizobium huakuii and Rhizobium galegae Nod factors: a cluster of phylogenetically related legumes are nodulated by rhizobia producing Nod factors with α,β‐unsaturated N‐acyl substitutions

Yang, Guo‐Ping; Debelle, Frédéric; Savagnac, Arlette; Ferro, Myriam; Burlet‐Schiltz, Odile; Maillet, Fabienne; Promé, Danièlle; Treilhou, Michel; Vialas, Corinne; Lindström, Kristina; Denarié, Jean; Promé, Jean‐Claude

doi:10.1046/j.1365-2958.1999.01582.x

Cited by 53 publications

(35 citation statements)

References 42 publications

(60 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In addition to AcpP, S. meliloti potentially encodes four additional ACPs. One of them is the gene product of nodF, which is involved, together with NodE, in the synthesis of polyunsaturated fatty acids that are host-specific substituents of Nod factors (50). The rkpF gene product in S. meliloti 41 is a novel ACP, which presumably functions, in combination with other gene products, in the synthesis of an unusual fatty acid or ␤-ketide (14,37).…”

Section: Discussionmentioning

confidence: 99%

Characterization of theSinorhizobium meliloti sinR/sinILocus and the Production of NovelN-Acyl Homoserine Lactones

et al. 2002

View full text Add to dashboard Cite

Sinorhizobium meliloti is a soil bacterium which can establish a nitrogen-fixing symbiosis with the legume Medicago sativa. Recent work has identified a pair of genes, sinR and sinI, which represent a potential quorum-sensing system and are responsible for the production of N-acyl homoserine lactones (AHLs) in two S. meliloti strains, Rm1021 and Rm41. In this work, we characterize the sinRI locus and show that these genes are responsible for the synthesis of several long-chain AHLs ranging from 12 to 18 carbons in length. Four of these, 3-oxotetradecanoyl HL, 3-oxohexadecenoyl HL, hexadecenoyl HL, and octadecanoyl HL, have novel structures. This is the first report of AHLs having acyl chains longer than 14 carbons. We show that a disruption in sinI eliminates these AHLs and that a sinR disruption results in only basal levels of the AHLs. Moreover, the same sinI and sinR mutations also lead to a decrease in the number of pink nodules during nodulation assays, as well as a slight delay in the appearance of pink nodules, indicating a role for quorum sensing in symbiosis. We also show that sinI and sinR mutants are still capable of producing several shortchain AHLs, one of which was identified as octanoyl HL. We believe that these short-chain AHLs are evidence of a second quorum-sensing system in Rm1021, which we refer to here as the mel system, for "S. meliloti."Quorum sensing is a widespread phenomenon among gramnegative bacteria (for recent reviews see references 9, 16, and 33). This form of cell density-dependent gene regulation is mediated by sensing the concentrations of low-molecularweight compounds called autoinducers, which are produced by the bacteria. A few organisms such as Photobacterium fischeri and Pseudomonas aeruginosa serve as model systems for quorum sensing. P. fischeri, in which autoinduction was first identified, has a relatively simple quorum-sensing system. An autoinducer synthase, LuxI, produces the N-(3-oxohexanoyl)-Lhomoserine lactone (oxo-C 6 -HL), which is recognized by the LuxR regulator (11,22,25). LuxR then induces expression of the lux operon, which causes bioluminescence (47,48). This model has recently become slightly more complicated with the identification of a second autoinducer synthase, AinS, and the regulatory protein LuxO, both of which serve to modulate quorum-sensing-induced luminescence in P. fischeri (25,26,34). On the other hand, P. aeruginosa has two quorum-sensing systems (lasR/lasI and rhlR/rhlI) organized into a complex hierarchy, which together regulate numerous genes required for virulence (2, 36).The most common and well-characterized gram-negative bacterial autoinducers are N-acyl homoserine lactones (AHLs) (see above reviews). AHLs consist of a variable acyl chain attached to a conserved homoserine lactone head group. The acyl chains can vary in length from 4 to 14 carbons. They can also vary in the nature of the substituent on the third carbon, from hydrogen to a hydroxyl or oxo group. One last characteristic that can confer variability is the presence of a do...

show abstract

Section: Discussionmentioning

confidence: 99%

Characterization of theSinorhizobium meliloti sinR/sinILocus and the Production of NovelN-Acyl Homoserine Lactones

et al. 2002

View full text Add to dashboard Cite

show abstract

“…These molecules are 6-O acetylated at the glucosamine residue proximal to the nonreducing terminal glucosamine. Recently, substitution of this residue was described for Mesorhizobium loti NZP2213, where a fucose substituent was present on O-3 (23), and for R. galegae, where an acetyl substitution was found on O-3 (40). The biological importance of these substituents is currently unknown, as are the genes encoding the substitutions.…”

Section: Discussionmentioning

confidence: 99%

“…viciae, R. leguminosarum bv. trifolii, M. huakuii, R. galegae, and S. meliloti), up to three carbonyl-conjugated double bonds have been characterized (20,31,34,35,40). In addition, in the latter four species, contrary to N33, fatty acid chains are linear and generally carry a cis double bond at the 7 position.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Unusual Methyl-Branched α,β-Unsaturated Acyl Chain Substitutions in the Nod Factors of an Arctic Rhizobium, Mesorhizobium sp. Strain N33 ( Oxytropis arctobia )

et al. 2001

Self Cite

View full text Add to dashboard Cite

Mesorhizobium sp. strain N33 (Oxytropis arctobia), a rhizobial strain isolated in arctic Canada, is able to fix nitrogen at very low temperatures in association with a few arctic legume species belonging to the genera Astragalus, Onobrychis, and Oxytropis. Using mass spectrometry and nuclear magnetic resonance spectroscopy, we have determined the structure of N33 Nod factors, which are major determinants of nodulation. They are pentameric lipochito-oligosaccharides 6-O sulfated at the reducing end and exhibit other original substitutions: 6-O acetylation of the glucosamine residue next to the nonreducing terminal glucosamine and N acylation of the nonreducing terminal glucosamine by methyl-branched acyl chains of the iso series, some of which are ␣,␤ unsaturated. These unusual substitutions may contribute to the peculiar host range of N33. Analysis of N33 whole-cell fatty acids indicated that synthesis of the methyl-branched fatty acids depended on the induction of bacteria by plant flavonoids, suggesting a specific role for these fatty acids in the signaling process between the plant and the bacteria. Synthesis of the methyl-branched ␣,␤-unsaturated fatty acids required a functional nodE gene.Rhizobia are soil bacteria, now classified in several genera (e.g., Rhizobium, Sinorhizobium, Mesorhizobium, Bradyrhizobium, Azorhizobium), which form a symbiotic association with legume plants. The interaction between bacteria and plants results in the formation of nodules on the host plant roots, in which rhizobia fix atmospheric nitrogen. The association between rhizobia and legumes is specific: each rhizobial strain has a defined host range. For example, Mesorhizobium sp. strain N33, isolated from Oxytropis arctobia, also nodulates Astragalus alpinus and Onobrychis viciifolia (19,26). In contrast, Sinorhizobium meliloti efficiently nodulates alfalfa (Medicago sativa) as well as Melilotus and Trigonella species. Mesorhizobium sp. strain N33 was isolated in the Canadian high arctic and is able to grow and fix nitrogen at temperatures as low as 5°C. In addition, it was shown that arctic rhizobia promoted better growth of O. viciifolia at low temperatures than did temperate strains (27). Thus, it might be valuable to extend the host range of arctic rhizobia to agronomically important legumes, in order to improve nitrogen fixation by these plants at low temperatures. It is therefore important to understand the molecular mechanisms controlling the nodulation specificity of arctic rhizobia.Earlier work has shown that nodulation and host specificity in rhizobium-legume symbiosis are determined by signal exchanges between the bacteria and the host plant (21). Flavonoids excreted by the plant roots induce the expression of rhizobial nodulation (nod) genes. Most of these genes are involved in the biosynthesis and secretion of bacterial signals, the Nod factors, that can specifically induce symbiotic responses of the host plants. These responses include root hair deformation, division of root cortical cells and, in some instances,...

show abstract

“…Although there is a wide variability in LCO structures, two major groups can be distinguished (19,26,33). (i) Rhizobia associated with plants of the Trifolieae, Vicieae, and Galegeae tribes that form indeterminate nodules produce LCOs carrying specific polyunsaturated fatty acids and have either no substitution or a carbamoyl or an O-acetyl group on C-6 of the nonreducing terminal N-acetylglucosamine (Fig.…”

mentioning

confidence: 99%

Rhizobial NodL O -Acetyl Transferase and NodS N -Methyl Transferase Functionally Interfere in Production of Modified Nod Factors

et al. 2001

View full text Add to dashboard Cite

The products of the rhizobial nodulation genes are involved in the biosynthesis of lipochitin oligosaccharides (LCOs), which are host-specific signal molecules required for nodule formation. The presence of an O-acetyl group on C-6 of the nonreducing N-acetylglucosamine residue of LCOs is due to the enzymatic activity of NodL. Here we show that transfer of the nodL gene into four rhizobial species that all normally produce LCOs that are not modified on C-6 of the nonreducing terminal residue results in production of LCOs, the majority of which have an acetyl residue substituted on C-6. Surprisingly, in transconjugant strains of Mesorhizobium loti, Rhizobium etli, and Rhizobium tropici carrying nodL, such acetylation of LCOs prevents the endogenous nodS-dependent transfer of the N-methyl group that is found as a substituent of the acylated nitrogen atom. To study this interference between nodL and nodS, we have cloned the nodS gene of M. loti and used its product in in vitro experiments in combination with purified NodL protein. It has previously been shown that a chitooligosaccharide N deacetylated on the nonreducing terminus (the so-called NodBC metabolite) is the preferred substrate for NodS as well as for NodL. Here we show that the NodBC metabolite, acetylated by NodL, is not used by the NodS protein as a substrate while the NodL protein can acetylate the NodBC metabolite that has been methylated by NodS.Rhizobial bacteria have the unique ability to induce formation of nitrogen-fixing nodules on the roots or stems of leguminous plants. The development of legume nodules is largely controlled by reciprocal signal exchange between the symbiotic partners. Legume roots secrete specific flavonoids or isoflavonoids that induce the transcription of many bacterial genes (nod, nol, and noe genes). Most of these genes are involved in the synthesis and secretion of signal molecules that are essential to trigger nodule formation and that are known as Nod factors. Nod factors from many rhizobial species have been characterized, and their structures have been elucidated. Because their basic structure consists of a chitin oligosaccharide backbone N acylated on the nonreducing terminal residue, they are referred to as lipochitin oligosaccharides (LCOs). The nature of the fatty acid and the combination of diverse chemical substitutions provide host specificity to the LCOs produced by a given rhizobial strain (for reviews, see references 1, 7, 9, and 25).

show abstract

Structure of the Mesorhizobium huakuii and Rhizobium galegae Nod factors: a cluster of phylogenetically related legumes are nodulated by rhizobia producing Nod factors with α,β‐unsaturated N‐acyl substitutions

Cited by 53 publications

References 42 publications

Characterization of theSinorhizobium meliloti sinR/sinILocus and the Production of NovelN-Acyl Homoserine Lactones

Characterization of theSinorhizobium meliloti sinR/sinILocus and the Production of NovelN-Acyl Homoserine Lactones

Unusual Methyl-Branched α,β-Unsaturated Acyl Chain Substitutions in the Nod Factors of an Arctic Rhizobium, Mesorhizobium sp. Strain N33 ( Oxytropis arctobia )

Rhizobial NodL O -Acetyl Transferase and NodS N -Methyl Transferase Functionally Interfere in Production of Modified Nod Factors

Contact Info

Product

Resources

About