Potential for<i>Rhizobium</i>Improvement

Hodgson, A. L. M.; Stacey, Gary; Gibson, A. H.

doi:10.3109/07388558609150790

Cited by 27 publications

(8 citation statements)

References 535 publications

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“…Extracts of transformed roots (containing calystegins and mannopine) or extracts of rhizomes excised from normal plants (containing only calystegins) were partially purified prior to catabolic tests. Strains of the genera Agrobacterium, Azospirillum, Pseudomonas, and Rhizobium were chosen in the search for soil bacteria able to degrade calystegins because these bacteria are known to associate with plants and because in many cases they have been described genetically (10,15). A total of 42 strains of rhizosphere bacteria (marked with asterisks in Table 1) were tested for calystegin catabolism.…”

Section: Resultsmentioning

confidence: 99%

A plasmid of Rhizobium meliloti 41 encodes catabolism of two compounds from root exudate of Calystegium sepium

et al. 1988

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Our objectives were to identify substances produced by plant roots that might act as nutritional mediators of specific plant-bacterium relationships and to delineate the bacterial genes responsible for catabolizing these substances. We discovered new compounds, which we call calystegins, that have the characteristics of nutritional mediators. They were detected in only 3 of 105 species of higher plants examined: Calystegia sepium, Convolvulus arvensis (both of the Convolvulaceae family), and Atropa belladonna. Calystegins are abundant in organs in contact with the rhizosphere and are not found, or are observed only in small quantities, in aerial plant parts. Just as the synthesis of calystegins is infrequent in the plant kingdom, their catabolism is rare among rhizosphere bacteria that associate with plants and influence their growth. Of 42 such bacteria tested, only ohe (Rhizobium meliloti 41) was able to catabolize calystegins and use them as a sole source of carbon and nitrogen. The calystegin catabolism gene(s) (cac) in this strain is located on a self-transmissible plasmid (pRme4la), which is not essential to nitrogen-fixing symbiosis with legumes. We suggest that under natural conditions calystegins provide an exclusive carbon and nitrogen source to rhizosphere bacteria which are able to catabolize these compounds. Calystegins (and the corresponding microbial catabolic genes) might be used to analyze and possibly modify rhizosphere ecology.The factors regulating microbial growth in the rhizosphere are not completely understood but are thought to include substances released by roots (6, 33, 34) that could be species specific and act on microbial populations through negative or positive selection. In the latter case, these secondary metabolites could be responsible for nutritional selection, if they were produced in sufficient quantities and if they were refractory to catabolism by most soil microorganisms. Such substances would then provide an exclusive nutrient source to microorganisms possessing the genetic information necessary for their catabolism (26). The opines encoded by the Ti (tumor-inducing) and Ri (root-inducing) T-DNAs of Agrobacterium tumefaciens and Agrobacterium rhizogenes (see reference 40 for a review) are selective nutrients for a variety of soil bacteria under laboratory conditions (5, 32, 41), but their ability to influence bacterial growth under natural conditions has not been reported. The use of these opines as selective agents in the rhizosphere, by inserting opine synthesis genes into the plant host, would run the risk of encouraging the growth of wild opine-utilizing, pathogenic agrobacteria.We describe here the bacterial catabolism of substances produced by two species of the Convolvulaceae family and by Atropa belladonna. The synthesis of these compounds, which we call calystegins, is uncommon in the plant kingdom, as is their utilization in a sample of 42 rhizosphere bacteria, most of which were chosen for their ability to interact with plants. Under laboratory conditions these...

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Section: Resultsmentioning

confidence: 99%

A plasmid of Rhizobium meliloti 41 encodes catabolism of two compounds from root exudate of Calystegium sepium

et al. 1988

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“…Differentiated bacteria, called bacteroids, fix nitrogen within specialized structures termed root nodules. Establishment of this symbiosis requires a complex series of developmental changes involving differentiation of both plant and bacterial cells (14,17,21,22). In an early stage of this process, bacteria trapped in a curled root hair, or shepherd's crook, induce the formation of an invasion tube called an infection thread.…”

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confidence: 99%

Rhizobium meliloti mutants unable to synthesize anthranilate display a novel symbiotic phenotype

et al. 1992

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Analyses of Rhizobium meliloti trp auxotrophs suggest that anthranilate biosynthesis by the R. meliloti trpE(G) gene product is necessary during nodule development for establishment of an effective symbiosis. trpE(G) mutants, as well as mutants blocked earlier along this pathway in aromatic amino acid biosynthesis, form nodules on alfalfa that have novel defects. In contrast, R. meliloti trp mutants blocked later in the tryptophan-biosynthetic pathway form normal, pink, nitrogen-fixing nodules. trpE(G) mutants form two types of elongated, defective nodules containing unusually extended invasion zones on alfalfa. One type contains bacteroids in its base and is capable of nitrogen fixation, while the other lacks bacteroids and cannot fix nitrogen. The trpE(G) gene is expressed in normal nodules. Models are discussed to account for these observations, including one in which anthranilate is postulated to act as an in planta siderophore.

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“…B. japonicum is a member of the so-called slow-growing rhizobia (24), as opposed to the taxonomically divergent fast-growing species of Rhizobium that infect such plants as alfalfa (symbiont: Rhizobium melilotf), peas (symbiont: Rhizobium leguminosarum), and clovers (symbiont: Rhizobium trifolii). Although studies of the physiology and molecular biology of nodulation have often used soybeans (19,50), knowledge of the genetics of nodulation in B. japonicum has lagged behind that of the fast-growing rhizobia.…”

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A locus encoding host range is linked to the common nodulation genes of Bradyrhizobium japonicum

et al. 1987

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By using cloned Rhizobium meliloti, Rhizobium leguminosarum, and Rhizobium sp. strain MPIK3030 nodulation (nod) genes as hybridization probes, homologous regions were detected in the slow-growing soybean symbiont Bradyrhizobium japonicum USDA 110. These regions were found to cluster within a 25-kilobase (kb) region. Specific nod probes from R. meliloi were used to identify nodA-, nodB-, nodC-, and nodD-like sequences clustered on two adjacent HindUI restriction fragments of 3.9 and 5.6 kb. A 785-base-pair sequence was identified between nodD and nodABC. This sequence contained an open reading frame of 420 base pairs and was oriented in the same direction as nodABC. A specific nod probe from R. leguminosarum was used to identify nodIJ-like sequences which were also contained within the 5.6-kb Hindm fragment. A nod probe from Rhizobium sp. strain MPIK3030 was used to identify hsn (host specificity)-like sequences essential for the nodulation of siratro (Macroptilium atropurpureum) on a 3.3-kb Hindm fragment downstream of nodlJ. A transposon Tn5 insertion within this region prevented the nodulation of siratro, but caused little or no delay in the nodulation of soybean (Glycine mar).Soybean, an important agricultural plant, is infected (or nodulated) by and establishes a symbiosis with the nitrogenfixing soil bacterium Bradyrhizobiumjaponicum. Nodulation is a complex developmental process requiring several plant and bacterial functions. B. japonicum is a member of the so-called slow-growing rhizobia (24), as opposed to the taxonomically divergent fast-growing species of Rhizobium that infect such plants as alfalfa (symbiont: Rhizobium melilotf), peas (symbiont: Rhizobium leguminosarum), and clovers (symbiont: Rhizobium trifolii). Although studies of the physiology and molecular biology of nodulation have often used soybeans (19, 50), knowledge of the genetics of nodulation in B. japonicum has lagged behind that of the fast-growing rhizobia.The initial interactions of plant and symbiont that lead to establishment of the symbiosis require at least two sets of genes. One set (nodABCDIJ), the so-called common nodulation genes due to their ability to functionally complement nodulation-defective mutants in other rhizobial species, encodes functions important for the early steps of nodulation (20,23,40,48). A second set of genes (hsn; hsnABCD = nodEFGH) (21, 29) imposes on the plant-bacterial interaction a degree of specificity; certain plant-rhizobia combinations are favored, other combinations are excluded. Induction of these nodulation genes requires low-molecularweight compounds produced by the plant and also a functional nodD gene (22,27). Additionally, Rostas, et al. (42) have identified a 47-base-pair (bp) sequence upstream of many of the known nodulation operons in R. meliloti that are essential for nod gene induction. This sequence has been termed the Nod box.Recently, four groups have cloned the common nodulation genes from three different species ofBradyrhizobium (31,35,38,43). In each case, the common nodulat...

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Potential forRhizobiumImprovement

Cited by 27 publications

References 535 publications

A plasmid of Rhizobium meliloti 41 encodes catabolism of two compounds from root exudate of Calystegium sepium

A plasmid of Rhizobium meliloti 41 encodes catabolism of two compounds from root exudate of Calystegium sepium

Rhizobium meliloti mutants unable to synthesize anthranilate display a novel symbiotic phenotype

A locus encoding host range is linked to the common nodulation genes of Bradyrhizobium japonicum

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