Carbon and Nitrogen Metabolism in Rhizobia

Kahn, Michael L.; McDermott, Tim R.; Udvardi, Michael K.

doi:10.1007/978-94-011-5060-6_24

Cited by 22 publications

(25 citation statements)

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“…Another required plant protein is sucrose synthase (SS), which has been characterized in pea using the SS1-defective rug4 mutant 115,116 . Contrary to its name, sucrose synthase in pea nodules catabolizes sucrose to UDP-glucose and fructose, which is ultimately metabolized to malate and transported to bacteroids 101,105,115 . The L. japonicus sulphate transporter Sst1 is also required for nitrogen fixation and has been detected in symbiosome membranes 117,118 .…”

Section: Nih-pa Author Manuscriptmentioning

confidence: 98%

“…A complex amino-acid cycling system between plant cells and bacteroids might prevent the bacteroids from assimilating NH 4 + , and allow NH 4 + to be secreted for uptake by the plant 88,101,103,104 . Metabolite analysis and RNAi depletion experiments suggest that NH 4 + assimilation by plant cells occurs primarily through glutamine and asparagine synthetases [105][106][107] . In L. japonicus, RNAi depletion of the next enzyme in the nitrogen assimilation pathway, glutamate synthase, results in a reduction of nitrogenase activity and the growth of stunted plants 108 .…”

Section: Box 3 Host Invasion Parallels Between Rhizobia and Animal Pamentioning

confidence: 99%

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How rhizobial symbionts invade plants: the Sinorhizobium–Medicago model

et al. 2007

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Nitrogen-fixing rhizobial bacteria and leguminous plants have evolved complex signal exchange mechanisms that allow a specific bacterial species to induce its host plant to form invasion structures through which the bacteria can enter the plant root. Once the bacteria have been endocytosed within a host-membrane-bound compartment by root cells, the bacteria differentiate into a new form that can convert atmospheric nitrogen into ammonia. Bacterial differentiation and nitrogen fixation are dependent on the microaerobic environment and other support factors provided by the plant. In return, the plant receives nitrogen from the bacteria, which allows it to grow in the absence of an external nitrogen source. Here, we review recent discoveries about the mutual recognition process that allows the model rhizobial symbiont Sinorhizobium meliloti to invade and differentiate inside its host plant alfalfa (Medicago sativa) and the model host plant barrel medic (Medicago truncatula).The recent completion of the Sinorhizobium meliloti genome sequence, and the progress towards the completion of the Medicago truncatula genome sequence, have led to a surge in the molecular characterization of the determinants that are involved in the development of the symbiosis between rhizobial bacteria and leguminous plants. Aromatic compounds from legumes called flavonoids first signal the rhizobial bacteria to produce lipochitooligosaccharide compounds called Nod factors 1 . Nod factors that are secreted by the bacteria activate multiple responses in the host plant that prepare the plant to receive the invading bacteria. Nod factors and symbiotic exopolysaccharides induce the plant to form infection threads, which are thin tubules filled with bacteria that penetrate into the plant cortical tissue and deliver the bacteria to their target cells. Plant cells in the inner cortex internalize the invading bacteria in host-membrane-bound compartments that mature into structures known Correspondence to G.C.W. gwalker@mit.edu. Competing interests statementThe authors declare no competing financial interests. DATABASES Invasion of plant rootsAlthough plant roots are exposed to various micro-organisms in the soil, their cell walls form a strong protective barrier against most harmful species. The early steps in the invasion of barrel medic (M. truncatula) and alfalfa (Medicago sativa) roots by S. meliloti are characterized by the reciprocal exchange of signals that allow the bacteria to use the plant root hair cells as a means of entry. Initial signal exchangeFlavonoid compounds (2-phenyl-1,4-benzopyrone derivatives) produced by leguminous plants are the first signals to be exchanged by host-rhizobial symbiont pairs 1 (FIG. 1). Flavonoids bind bacterial NodD proteins, which are members of the LysR family of transcriptional regulators, and activate these proteins to induce the transcription of rhizobial genes 1,2 . For example, the M. sativa-derived flavonoid luteolin stimulates binding of an active form of NodD1 to an S. meliloti 'nod-box' p...

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Section: Nih-pa Author Manuscriptmentioning

confidence: 98%

Section: Box 3 Host Invasion Parallels Between Rhizobia and Animal Pamentioning

confidence: 99%

How rhizobial symbionts invade plants: the Sinorhizobium–Medicago model

et al. 2007

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“…Malate together with some other C4-dicarboxylic acids (succinate, fumarate) are up-taken by bacteroids via the DctA permease (Jording et al, 1994). Nearly all ATP produced in bacteroids is used to supply energy to nitrogenase en-zyme the immediate product of its which, NH 4 + is excreted into the host cytoplasm since the enzymes for its assimilation (glutamine synthethase, glutamate synthase) are repressed in bacteroids (Kahn et al, 1998;Kaminski et al, 1998).…”

Section: Nitrogen Fixation and Assimilationmentioning

confidence: 99%

Molecular Strategies and Agronomic Impacts of Plant-Microbe Symbioses

Тихонович

Проворов

2008

Ecological genetics

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The molecular mechanism of the agronomically important nutritional and defensive plantmicrobe symbioses are reviewed. These symbioses are based on the signaling interactions which result in the development of novel tissue/cellular structures and of extended metabolic capacities in the partners which improve greatly the adaptive potential of plants due to an increased tolerance to biotic or abiotic stresses. The molecular, genetic and ecological knowledge on plant-microbe interactions provide a strategy for a sustainable crop production based on substituting the agrochemicals (mineral fertilizers, pesticides) by the microbial inoculants. An improvement of plantmicrobe symbioses should involve the coordinated partners' modifications resulted in complementary combinations of their genotypes.

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“…In a free-living state, rhizobia can metabolize a wide range of carbon and nitrogen sources. This metabolic versatility allows rhizobia to adapt to the nutritional complexity of the rhizosphere, which is affected by plant root exudates (14,15,25,36).Whole genome sequences have been determined for several rhizobial species; their genomes range in size from 5.4 Mb (Azorhizobium caulinodans), 6.7 Mb (Sinorhizobium meliloti) and 7.6 Mb (M. loti) to 8.5 Mb (Bradyrhizobium sp. BTAi1) and 9.1 Mb (Bradyrhizobium japonicum) (8,10,16,17,22).…”

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confidence: 99%

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Identification of Mesorhizobium loti Genes Relevant to Symbiosis by Using Signature-Tagged Mutants

et al. 2011

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Signature-tagged mutagenesis was applied to Mesorhizobium loti, a nitrogen-fixing root-nodule symbiont of the leguminous plant Lotus japonicus. We arranged 1,887 non-redundant mutant strains of M. loti into 75 sets, each consisting of 24 to 26 strains with a different tag in each strain. These sets were each inoculated en masse onto L. japonicus plants. Comparative analysis of total DNA extracted from inoculants and resulting nodules based on quantitative PCR led to the selection of 69 strains as being reduced in relative abundance during nodulation. Plant assays conducted with individual strains confirmed that 3 were defective in nodulation (Nod − ) and that 10 were Nod + but defective in nitrogen fixation (Fix − ); in each case, the symbiosis deficiency could be attributed to the transposon insertion carried by that strain. Although the remaining 56 strains were Fix + , 33 of them showed significantly reduced competitiveness during nodulation. Among the mutants we identified are known genes that are diverse in predicted function as well as some genes of unknown function, which demonstrates the validity of this screening procedure for functional genomics in rhizobia.Key words: Mesorhizobium loti, signature-tagged mutagenesis, symbiosis, competitiveness, root nodule Rhizobia are a group of soil bacteria that establish a nitrogen-fixing symbiosis with leguminous plants. Mesorhizobium loti is an α-proteobacterial species of the group and a symbiotic partner of Lotus japonicus; this symbiotic pair is a well-documented model system for molecular genetic studies (20, 31). Some rhizobia, including M. loti, elicit root-hair curling and nodule organogenesis on roots of host plants at an early step during symbiosis. Such plant responses are triggered specifically by signaling compounds, called Nod factors, produced by compatible rhizobia. Rhizobia colonize curled root hairs and invade developing nodules via infection threads, which are formed by invagination of the root-hair cell membrane. The rhizobia are then released into the host nodule cells (33,42). These intracellular bacteria (bacteroids) reduce dinitrogen into ammonia by use of a carbon and energy source originating from photosynthates. Host plants are supplied with the fixed nitrogen and thus are able to grow under nitrogen-poor conditions. In a free-living state, rhizobia can metabolize a wide range of carbon and nitrogen sources. This metabolic versatility allows rhizobia to adapt to the nutritional complexity of the rhizosphere, which is affected by plant root exudates (14,15,25,36).Whole genome sequences have been determined for several rhizobial species; their genomes range in size from 5.4 Mb (Azorhizobium caulinodans), 6.7 Mb (Sinorhizobium meliloti) and 7.6 Mb (M. loti) to 8.5 Mb (Bradyrhizobium sp. BTAi1) and 9.1 Mb (Bradyrhizobium japonicum) (8,10,16,17,22). These large sizes can be explained by the need to accommodate the many genes responsible for symbiotic capacity and metabolic versatility. A number of genes have been assigned to functions require...

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Carbon and Nitrogen Metabolism in Rhizobia

Cited by 22 publications

References 229 publications

How rhizobial symbionts invade plants: the Sinorhizobium–Medicago model

How rhizobial symbionts invade plants: the Sinorhizobium–Medicago model

Molecular Strategies and Agronomic Impacts of Plant-Microbe Symbioses

Identification of Mesorhizobium loti Genes Relevant to Symbiosis by Using Signature-Tagged Mutants

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